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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: SkidRo on September 26, 2016, 01:42:10 pm
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All,
Sorry for the long read but I want to give as much info as possible. I have this weird issue that I can't narrow down. My truck has about 87000 original miles and it is all stock. It has A/C (still works), automatic, power brakes and steering.
Up until my battery died a few months back the carb ran (acted) fine except for a slight dead spot right off of idle. Then the original battery, which was about 9 years, old died. After I replaced the battery the carb started to act up to a point where I could drive it but only if I keep the throttle open/rpms higher (like cruising around in second gear). However, once at a stop light etc. it might idle but I typically have to put it in neutral and press the accelerator fast enough to get it past the dead spot. It also has a hard time idling once the choke opens. I know this generally means the idle circuit is dirty/bad BUT the other day I started the truck and it ran fantastic. Like so good that I decided not to buy a new carb. I drove it around for a while to charge the new battery. It was acting very weak which I attributed to not driving it that much and having to start it over and over when it died on me. I also had the battery and charging system checked by my local FLAPs a few weeks prior and they claimed that everything was good. I will take that assessment with a grain of salt though.
On my drive when it was running like a champ, I stopped at the local Home Depot. I went to start the truck and the battery barely manage to turn the engine over and start. Immediately the carb went back to the same issue. it has a flat/continuous dead spot off of idle and a rough idle. Once through the dead spot the truck runs great. I didn't think I would make it home due to the stop and go traffic.
Once home I put the battery on my charger. The next morning it was fine and cranked like new. However the carb was acting the same. But once it clears that flat spot it runs great. The only thing that I have done in regard to the carb is add some Techron in the tank on the last fill up and shoot some carb cleaner into it. Again, except for the other day that treatment didn't appear to have helped. I have almost ran through that tank of gas and I was thinking of doing the same treatment.
So, am I looking at an electrical and carb issue or just an old Quadrajet that is dirty and doesn't like the gas in the DC/Maryland area.
Many thanks,
Rory
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When was the last time the carb was rebuilt
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I have owned the truck for three years. It should be presumed the carb had never been rebuilt by the previous owners (2). If these can be rebuilt with success I have the means to do so once I buy the proper rebuild kit. I have rebuilt several motorcycle carbs in the recent past. I also have no issue with buying a rebuilt one from National if that is the end suggestion.
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What year is this truck?
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Please include Year, Make, Model etc.. when posting (http://forum.73-87chevytrucks.com/smforum/index.php?topic=5220.0)
...Up until my battery died a few months back the carb ran (acted) fine except for a slight dead spot right off of idle. The original battery was about 9 years old and dead. I got a new battery, which seemed to take care of that issue....
What do you mean by this? What issue was resolved by replacing the battery ...the 'dead spot' off of idle or the 'dead battery' won't crank?
...It also has a hard time idling once the choke opens....
Does it run and idle correctly with the choke closed? If you hover the carburetor with a shop rag or mist carb cleaner down the carburetor throat, will it idle? Have you sprayed around the base of the carburetor, intake manifold and vacuum lines for vacuum leaks?
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What year is this truck?
X2
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Sure sounds like a lean miss to me, cracked vacuum lines.
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Sorry all, I thought the year and make was in my avatar. The answers to your questions are as follows.
It's a 1986 C10 Scottsdale.
"What do you mean by this? What issue was resolved by replacing the battery ...the 'dead spot' off of idle or the 'dead battery' won't crank?"
That was a terribly stated sentence on my part. The cranking caused by the dead battery. The dead spot is still present in the carb off of idle just magnified. I was trying to ask can a weak battery cause this type of carb issue. I have reworded my original post to make more sense - hopefully.
"Does it run and idle correctly with the choke closed? If you hover the carburetor with a shop rag or mist carb cleaner down the carburetor throat, will it idle? Have you sprayed around the base of the carburetor, intake manifold and vacuum lines for vacuum leaks?"
When the choke is set the engine will fast idle fine. However, when the choke opens it tends to stall out. I have sprayed carb cleaner in the carb and it will stall if I do not give it gas. I have not tried spraying around the base or any vacuum lines yet. I will do this when I get home tonight.
"Sure sounds like a lean miss to me, cracked vacuum lines."
I am leaning toward this as a potential cause. Now it's a matter of figuring out which line/what's generating the leak .
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I am leaning toward this as a potential cause. Now it's a matter of figuring out which line/what's generating the leak .
One by one disconnect the vacuum lines to the carb and plug them, see if any makes and improvement. If the ESC connection on the distributor is still there that also may make the timing go whacky off of idle.
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1) Was this a California truck? i'm trying to determine if the carb is a CCC carb.
2) If not, then being an 86 it probably has that dual accelerator pump thing and this could be contributing to the problem.
3)......Or the regular accelerator pump may need to be checked.....
4) Please DO NOT buy a carb from national.
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1) It is not a California truck. It was bought new in Damascus, MD and it has lived its life here.
2&3) Now that you mentioned it, this issue has some commonality on an issue I had with the carbs on my Corvair. The two primary carbs had bad/incorrect accelerator pumps. They had a dead spot off of idle and then when cruising the car would jerk. They also had many more issues that have since been resolved. I agree that the pumps could be an issue on my truck. This ties into an earlier post about when the carb was last rebuilt, which was never.
4) Please let me know the issue with National. Or, if you prefer, PM me.
I did not get to the truck last night to do any troubleshooting. I will work on it on Saturday and report back any finding in regard to vacuum leaks, etc.
Thanks for all the suggestions so far.
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When the choke is set the engine will fast idle fine. However, when the choke opens it tends to stall out. I have sprayed carb cleaner in the carb and it will stall if I do not give it gas. I have not tried spraying around the base or any vacuum lines yet.
An accelerator pump failure will only cause a 'flat spot' when opening the throttle quickly. It will not affect idle with constant throttle. You need to figure out the idle issue first.
Count the exact number of turns in to lightly seat the idle mixture screws, record and post the counts. Remove the screws and thoroughly spray the idle passages with Berrymans B12 carburetor cleaner followed by compressed air. Reinstall the screws, adjusting to the same number of counts, out. Spray and check for vacuum leaks as previously recommended. Have you made any changes to the timing?
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BD, I will perform the tests and procedures as suggested and post the results. The timing has not been adjusted since I gave it a tune up 2 years ago.
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Good! For now, leave the timing as is so a new complication isn't introduced into your diagnosis.
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agreed, start with what you know is likely wrong, dont add to the mix
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Rory, in addition to the repair steps already outlined, lift the distributor cap to inspect the rotor and carbon button inside the cap. Look for any chalky discoloration on the plastic, carbon tracking or excessive burn-back of the button.
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This is what I managed to do this past weekend. Despite my best effort and using images of the carb I unfortunately could not locate the idle mixture screws. They may/must have a cap over them. So any work on the carb was minimal. I did find one vacuum hose that was broken and someone had wrapped it in electrical tape. It is a thin hard plastic line that runs to the back of the carb. After removing the tape I managed to slip some shrink wrap over the two ends, and then slip another piece of tubing over that so make sure the line did not collapse or separate. I also removed the distributor cap and noticed that the metal contacts on the cap and rotor button had arc marks on them. I cleaned them with 1000 grit sand paper and electrical cleaning spray. The two front nuts holding the carb onto the manifold were loose. I tightened them and checked the rears and they were fine. The only other thing that I was able to do with the carb was spray the Berrymans into the primary and secondary sides and around the outside. I also made sure all of the electrical connections were properly seated. Spraying clean cleaner around the base of the carb, the carb itself and the vacuum lines did not have any affect on the way the truck ran.
I started the truck without the air cleaner and gave it gas. It still had a dead spot, backfired out of the carb (nice flame), and then idled fine. I turned it off and installed the air cleaner, etc. Then I took it for a drive. It started and idled fine. It still had the dead spot off of idle and it wanted to cut out unless I accelerated though it. While driving about 25 mph it backfired one more time and then it ran perfect. No issues at all. I took it out on a main road and was able to cruise, open it up, and then come to an idle and repeat numerous times. I drove back home and turned it off and on a few times without issue.
I am not stating that the issue is resolved until I test it further and can get into the carb itself.
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Replace the spark plugs, check the plug wires and install a new fuel filter. Inspect for arcing between the wires and ground (this is most easily accomplished at night in the dark) and measure the wire resistance with an ohmmeter (should measure anywhere in the range of 1,000 - 3,000 ohms per foot of individual wire length). Look inside each of the plug wire boots for traces of black soot and/or any greenish discoloration.
With the engine off and choke held open, look down the primary throats of the carb using a bright flashlight and open the throttle. There should be two strong streams of fuel exiting the accelerator pump nozzles each time the throttle opens. There should be zero lag between throttle opening and accelerator pump squirt. In order to remove the idle mixture screw caps for adjustment, the carburetor will need to be removed. I would postpone that step for the time being.
Does the engine pop-pop-pop-pop back through the carburetor whenever the throttle is open rapidly?
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As a side note, 85-86 trucks had a dual capacity accelerator pump (both 4.3 v-6 and 305,350 v-8s). i'm not sure why only 85-86 trucks had this? But just pointing it out.
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I will check the wires and boots (and fix if needed) and replace the plugs. I use the same technique for the Corvair to check for arcing. Ditto for the checking of the carb for immediate squirts of fuel. I'll do these tonight.
If I recall correctly, if the throttle is opened rapidly it acts fine. No popping or backfiring at all. But I will check this too. It's when it comes off idle slowly that the dead spot is felt. Then it seems like the too much fuel is being delivered, it bogs down and it will get a back fire. Also, if I am at cruising speed whether 35 or 60 it has that flutter or dead spot. When I give it more gas to get past that point it appears that it is loaded up with too much fuel, will back fire and then run okay until I get back to a steady cruise again.
I have not driven since the last troubleshooting so I do not know how it is running right now. When I parked it it was running good.
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Popping thru the carb would indicate lean. Along with the rough idle could have picked up some blockage in the idle tubes
When you get on it hard your accelerator pump shot covers up your lean spot and your into your off idle and main circuit.
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...It's when it comes off idle slowly that the dead spot is felt. Then it seems like too much fuel is being delivered, it bogs down and it will get a back fire. Also, if I am at cruising speed whether 35 or 60 it has that flutter or dead spot. When I give it more gas to get past that point it appears that it is loaded up with too much fuel, will back fire and then run okay until I get back to a steady cruise again.
Rory, your write-ups hint at a few possible causes, but lean fuel delivery seems to dominate. Perform the actions recommended to date to eliminate them as variables. Adding to your list of things to check, disconnect at both ends the 3/8" fuel bowl vent hose that runs between the carburetor fuel bowl and the vapor canister. Wash it out with carb cleaner into a clean rag. Inspect the rag for any trace of black carbon granules washed out of the hose.
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I didn't get the opportunity to work on the truck this weekend. I will fire the truck up when the sun drops to check for any arcing or grounding of the wires. I also bought a new fuel filter which I will replace as soon as possible as well as check the canister line. I did move the truck and it acted the same with that dead spot off idle. It was also back firing out of the carb quite a bit. Once I got past the dead spot and moving it appeared to run fine. However, if I was cruising at a moderate speed (in that dead spot zone) the truck, at times, would cut off or just sputter.
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I managed to put some time into the truck this weekend. I did not spot any grounding of the spark plug wires when tested while it was dark outside. I was able to replace the fuel filter in the carb. The old one did not look dirty or clogged but it may have been. I could not get the line that runs from the carb to the canister disconnected. I was concerned that I would break it so i did not force it off. Starting the engine produced several results all random. It may start and everything works perfect - idles, very minimal flat spot (like it always had), and accelerates fine. Or it may sputter, backfire out of the carb and have a huge flat spot off of idle. These happen while in park and/or driving.
The battery continues to perplex me too. It was low on the charge so I put it on the charger. Remember, I bought this battery new in June 2016. When fully charged and cranking the engine turns over slow/sluggish. The volt meter also reads around 8 volts. Once it starts the volt meter goes to around 14 volts - like it is charging. What I think I have observed is that when the battery is fully charged the carb works better. There are a few electrical connections on the carb - a two prong connector right above where the float bowl is (and the fuel filter) and the choke. I removed the two prong connector and it was filthy inside like a gummy substance. I cleaned the connections and plugged it back in. As for the battery, why isn't holding a charge? I have turned off all of the electrical components - radio, heater/A/C, etc. so there is no drain on the battery. When I take readings when it's running or not it reads 12-13 volts. I have not taken a reading when the engine is turning over but I suspect it will read low volts. I noticed the two prong connector at the alternator was dirty so I unplugged it and determined it was not making good contact with the two prongs in the alternator. Maybe this is why the battery is not charging. I can't describe what was in the plug except that it was hard to remove. It looked and felt like tar although I doubt it was. Carb and brake cleaner would not remove it. I manage to get the connector and the prongs clean and plugged it back into the alternator. I don't know if this was contributing to the battery issue or if the battery is bad out of the box. But the original battery was dead as a door nail suggesting it was not being charged by the alternator.
At this point I had to stop work. However, I am beginning to think that a low charge on the battery MAY have an effect on the engine and carb. It seems when I charged the battery the issue goes away until the battery gets to low to even start the truck. This is speculation but sometimes fuel and carb issues are really electrical issues.
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...The battery continues to perplex me too. It was low on the charge so I put it on the charger. Remember, I bought this battery new in June 2016. When fully charged and cranking the engine turns over slow/sluggish. The volt meter also reads around 8 volts. Once it starts the volt meter goes to around 14 volts - like it is charging. What I think I have observed is that when the battery is fully charged the carb works better. There are a few electrical connections on the carb - a two prong connector right above where the float bowl is (and the fuel filter) and the choke. I removed the two prong connector and it was filthy inside like a gummy substance. I cleaned the connections and plugged it back in. As for the battery, why isn't [it] holding a charge? I have turned off all of the electrical components - radio, heater/A/C, etc. so there is no drain on the battery. When I take readings when it's running or not it reads 12-13 volts. I have not taken a reading when the engine is turning over but I suspect it will read low volts. I noticed the two prong connector at the alternator was dirty so I unplugged it and determined it was not making good contact with the two prongs in the alternator. Maybe this is why the battery is not charging. I can't describe what was in the plug except that it was hard to remove. It looked and felt like tar although I doubt it was. Carb and brake cleaner would not remove it. I manage to get the connector and the prongs clean and plugged it back into the alternator. I don't know if this was contributing to the battery issue or if the battery is bad out of the box. But the original battery was dead as a door nail suggesting it was not being charged by the alternator.
At this point I had to stop work. However, I am beginning to think that a low charge on the battery MAY have an effect on the engine and carb. It seems when I charged the battery the issue goes away until the battery gets to low to even start the truck. This is speculation but sometimes fuel and carb issues are really electrical issues.
The sticky brown accumulation in the gray plastic tower protruding from the top of the fuel bowl is condensed solids from fuel that has wicked up out of the bowl along the two wire leads from the dual capacity fuel pump solenoid. It is recurring maintenance to clean periodically. The brown-black crud in the alternator connector is desiccated antioxidant used to control corrosion of the electrical connections to the regulator. It is not detrimental and should be replenished with fresh antioxidant compound, such as Truck-Lite NYK-77 Anti-Corrosion Compound (http://www.truck-lite.com/webapp/wcs/stores/servlet/ProductDisplay?urlRequestType=Base&catalogId=10002&categoryId=13124&productId=50965&errorViewName=ProductDisplayErrorView&urlLangId=-1&langId=-1&top_category=15555&parent_category_rn=15555&storeId=10001) available from many commercial truck dealerships and truck stops. Alternatively, you can use Gardner Bender Ox-Gard (https://www.delcity.net/store/Anti!Oxidant-Compound/p_6994.h_148563.t_1.r_IF3003&mkwid=AxI4Y6hS&crid=11472933143) or similar compounds available from the electrical departments of most hardware stores.
Charge the battery then disconnect the charger. The engine should remain off for the following checks. Connect an analog (filament type) test light between the battery terminals and notice how bright the test light illuminates; this in "normally bright" illumination. With every electrical appliance in the truck shut off and the doors closed, disconnect the negative battery cable and insert the test light between the battery negative post and the ground cable. How brightly does the test light illuminate - 'normally bright' or less than normally bright? When you open the door or pull the headlamp switch, does the test light get brighter?
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BD,
I will run these tests in the next day or so. To be clear, you want me to test between the negative post and the ground cable (negative battery cable) while it is disconnected. Is this correct?
Rory
Charge the battery then disconnect the charger. The engine should remain off for the following checks. Connect an analog (filament type) test light between the battery terminals and notice how bright the test light illuminates; this in "normally bright" illumination. With every electrical appliance in the truck shut off and the doors closed, disconnect the negative battery cable and insert the test light between the battery negative post and the ground cable. How brightly does the test light illuminate - 'normally bright' or less than normally bright? When you open the door or pull the headlamp switch, does the test light get brighter?
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Correct. The test light should be inserted between B- and the ground cable, such that the only connection to the battery's negative terminal is the test light. Inserting the test light in series between the battery and cable will tell you whether there is sufficient parasitic draw on the battery to discharge it. Analog test lights illuminate "normally bright" at ~40ma of current flow, depending on the bulb used in the test light. If the test light is dim when connected in series with all appliances switched off (including engine compartment lamp, dome lamp, glovebox light, etc), parasitic draw isn't an issue. If the test light illuminates 'normally bright,' further diagnosis is indicated.
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That is exactly what I thought you were getting at. Thanks.
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Update - I charged the battery. I disconnected the positive cable while charging so I could get a good charge. The battery reading is 12.85 volts. Next with my test light I connected it between the positive and negative posts. It was bright. I connected the positive cable to the battery and ran the same test with the same results. Next I disconnected the negative cable and place the test light between the negative post and the ground cable. The light did not come on ( I will do this test again). However, when I connected the light between the negative post and frame (or a bolt) the light came on. It appeared to be the same brightness. That was all I could do last night. I did disconnect the positive cable again and I will take a volt reading tonight to see if the battery dropped significantly from the 12.85 volt reading.
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...when I connected the light between the negative post and frame (or a bolt) the light came on. It appeared to be the same brightness....
Which did you use - a filament type test light or an LED test light? Was everything shut off, all doors closed, underhood light disconnected, etc? Do you have a sound system installed that uses a direct connection to the battery? Does the truck have a factory clock?
Start removing fuses one-at-a-time until the test light dims or extinguishes.
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LED type. It's a cheap one from a local flaps. Everything was off, doors closed, no hood lights or clock. There is an aftermarket radio installed ( by the previous owner) that must have a direct connection to the battery for the clock. I'll start with that fuse and the lead to the direct connection and then keep working through fuses etc if the radio isn't the issue.
Thanks for your help. I appreciate it.
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Unfortunately an LED test light isn't workable for this grass roots method, because its current flow is too limited. It can return a false indication of a problem that may not exist. With regard to square body trucks, a battery can be expected to support a continuous current draw of ~35 - 45 ma, up to as high as 60 ma, imposed by ECM, radio memory, etc, depending on year and accessory configuration. The simplest LED test light will illuminate at full brightness with only ~20 ma of current flow. LED logic probes can illuminate with microamps of current flow. Unless you are troubleshooting low voltage logic circuits that are sensitive to over-current, an LED test light should be avoided. In general, use a filament type of test light to troubleshoot power related problems.
Based on your LED test light you maybe chasing a ghost. Do you have an ammeter? If so, what is its maximum scale?
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No worries on the LED tester. Apparently I bought one a year ago so I just need to find it. I do have a ammeter - a Harbor Freight special. I will check the scale on it tonight.
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I was able to run some tests today with an analog test light. With the negative cable disconnected from the battery I ran the test light between the negative post and the negative cable. It glowed very dim. When I turned on the headlights it went to normal bright. The same results when I opened the door. If I understand your instructions correctly, this is a normal condition.
One thing that I did find, but resolved, prior to the test was a wire connected to one of the rear lights. It looks like there was a cap on the truck and I think the PO tapped the wire to operate a dome light. The metal spade end MAY have been touching the bed of the truck. It was jammed inside one of the "post" holes without being wrapped in tape. I remove the wire prior to the testing. Basically I don't know if this was the issue or not.
The radio has a always on power line and I disconnected that while testing. It made no difference in the test light - it stayed dim.
The battery stayed charged during this past week. I did have the positive cable removed during this time. I am going to leave the cable connected and see how the battery is holding its charge tomorrow and report back.
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My last post was premature. I went to start the truck and the battery barely turned the engine over. It eventually started but it died immediately. I managed to get it started but it barely cranked over. The battery, while reading 12.66 when I took an initial reading is now at 12.62v. When cranking the in-dash volt meter dropped to around 8 volts. I took the battery out and had it tested at the FLAPs where purchased. It was 12.62 volts and had 549 CCA. It is a 550 CCA battery. They said that the battery is fine. I reinstalled it and started the truck - slow cranking. Once running the voltage at the battery was a over 13 volts but I can't remember exactly what the reading was. It appears the battery is charging while the engine is running.
What I did discover is that the wire that I thought was the radio power is actually a wire that operates the overhead light when the doors are open. The PO must have spliced the wire for whatever reason instead of fixing the issue. I unplugged it.
I am wondering if the starter or solenoid may be related to the problem. I have read some posts whereas the comments suggested the starter.
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...With the negative cable disconnected from the battery I ran the test light between the negative post and the negative cable. It glowed very dim. When I turned on the headlights it went to normal bright. The same results when I opened the door. If I understand your instructions correctly, this is a normal condition....
Correct. Although, you shouldn't have disconnected any wiring before the test - just made sure that all appliances were switched off.
Check for voltage losses across the starter cabling: Without disturbing the battery cable connections, connect your voltmeter positive lead to the battery positive post and the voltmeter negative lead to the 3/8" battery cable stud on the starter. Record the voltage reading while cranking. Repeat the procedure with the voltmeter negative lead connected to the battery negative post and the positive lead connected to shiny bare metal on the starter frame. Post the results.
Did your local parts house actually load test the battery or just perform a conductance test?
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Rich, I don't know the exact test they conducted. The dude connected a digital device to the battery (it was out of the truck) and ran a test. A piece of paper came out and said it was fine. I explained the load issue but he insisted that the battery was fine. I am not convinced that he did what I wanted or the battery is working properly under load.
I will run the new tests as soon as I can. It's dark when I get home from work now so it may be this weekend.
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Take whatever time you need.
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I was able to do a few quick tests today. I measured the battery and it was 12.75 volts. I had the positive and negative cables connected to the battery since Tuesday. I will take that as a good sign. I then attempted to start the truck. It cranked real slow but eventually started. Unfortunately it cut off. The next attempt to start it produced nothing. The engine would not even turn over. I took another voltage reading on the battery and it was 12.57 volts. I am charging the battery now to run the suggested tests above. I will also verify the ground to the engine block is good.
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The starter was bad. It sounded like a jar of grinding ball bearings when I got under the truck. I have the new one installed and it starts fine. I am in the process of shimming the starter - the old one did not have any.
It took two shims. The starter sounds fine when cranking now.
I took it for a spin and it appears to be running fine. There is a slight hesitation coming off of idle very similar to how the truck ran since I have owned it. I will be happy with this if it continues to run like this. However, I need to drive it some more to see if the big dead spot returns.
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Yeah, it started to look that way back on the 8th. Glad you got the cranking problem resolved.
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I drove the truck all day today. It runs great. The carb issue went away. It starts, idles, accelerates, runs on cruise control, everything. This was the strangest issue that appears to be non-carb related. But I have heard most carb issues are electrical.
Thanks to everyone and especially Rich for providing troubleshooting tips and suggestions.