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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Pearlmoto on May 11, 2017, 04:51:11 pm
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Hello everyone. Have a curious problem and was wondering if anyone has any insight.
Truck is an 86 K30 4spd, all original and bone stock w 22K miles, LT9 350. Since this truck is my daily driver, I have replaced the following items with all AC delco parts:
fuel pump
water pump
all belts
fan clutch
TVS switches
Intake manifold gaskets
Cap/rotor/plug wires/plugs
hydroboost pressure lines
both oil pressure switches
temp switch
tstat and water neck
upper/lower radiator hoses
clutch slave cylinder
When I bought the truck my fuel pump went out and I replaced it and all was well. Today, after a long cruise on the highway, I park the truck and return to it noticing an odor akin to locktite, and the truck was hard to start. In traffic a mile later it dies. I manage to restart to a huge cloud of white smoke, park and pop the hood, and notice the fuel evap canister is overflowing with gas (hence the odor I was noticing). I remove the air cleaner assembly and manage to limp the truck home, but it will only limp in first gear, any additional load and the motor will quit. The oil pressure is good and the temp is good. It revs fine out of gear if not a little weak.
These are the same symptoms I experienced when my fuel pump initially went out, but seeing as the replacement only has about 500 miles, and given the evap canister was overflowing, I'm concerned it may be something else.
I have the factory service manual and will test the fuel pump per chevy instructions. But the overflowing evap canister is obviously dangerous and I'd like to figure out why that is happening too.
Does anyone have any experience or suggestions?
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Update:
I pulled the vapor canister and it was indeed filled to the brim with fuel. Obviously, this probably will have an impact on driveability....
I did fill up yesterday. I have read that overfilling can cause this problem. Any merit to that with our year trucks?
Why would the canister just fill up like that?
I did find this. Looks like I may have figured out my problem:
"Should it become saturated, the tank will be unable to breath in, the pump will struggle, the car may stall, and you might experience premature pump failure."
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How full did you fill the tank? With the engine idling, does fuel visibly drip from the carburetor main nozzles? With the engine idling, is there strong continuous vacuum reaching the vapor canister through the 1/4" hose from the engine? If you draw a vacuum on the 3/32" vacuum hose ports on the vapor canister, will they maintain vacuum or do they bleed off? Be careful that you don't get a mouthful of fuel.... Is the canister "vent port" obstructed?
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Possible fuel tank pressurized and forcing fuel in to can.
Fuel has to go uphill to get in the can.
The gas cap should vent into the tank.
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It's unusual bc I did nothing different than I normally do when filling up. I didn't spend any extra time trying to squeeze in every drop.
The vapor canister was filled to the brim. When I removed it I managed to pour out a full quart or so. There is strong continuous vacuum going to the canister w the engine idling. Fuel is not visibly dripping from the carb main nozzles.
I have ordered both new canisters for my truck, the main vapor canister and the smaller secondary canister that is connected to the port labeled "air cleaner" off the main canister.
When I was broken down and pulled the gas cap it did hiss as pressure was relieved.
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Fuel tank(s) plumbed to a vapor canister employ sealed fuel fill caps, forcing the tanks to "vent" through the canister. Did you check whether the small ports on the purge and bowl vent valves will maintain vacuum that is applied to them? Does the truck have single or dual fuel tanks?
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I have not tested the vent valves on the canister as I have purchased new ones. However, I can go and hook up the mightyvac to the old canister and check to see if theyll hold vacuum. My understanding is that once saturated with gas, the charcoal is ruined and the canisters must be replaced, so I didn't do any testing on the old unit.
The truck has dual tanks. I only use the driver side bc I am unsure of the condition of the passenger and do not want to risk sucking gunk into the fuel system until I drop that tank to clean it. I have never attempted to swap over to the passenger tank.
I wonder if the accumulation has been happening over time - yesterday I did notice evidence of gas leaking out the canister before I saw it actually happening as I limped home. The raw fuel leaking out the canister did not smell fresh, as I mentioned before, but more similarly to locktite? Perhaps simply running through the charcoal made it smell that way.
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You stated...There is strong continuous vacuum going to the canister w the engine idling. IIRC should only have higher vacuum with higher RPM's. At least that is how my 74 is working. Don't think high vacuum at idle is normal. I could be wrong.
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You stated...There is strong continuous vacuum going to the canister w the engine idling. IIRC should only have higher vacuum with higher RPM's. At least that is how my 74 is working. Don't think high vacuum at idle is normal. I could be wrong.
The canister receives both manifold and ported vacuum.
I have not tested the vent valves on the canister as I have purchased new ones. However, I can go and hook up the mightyvac to the old canister and check to see if theyll hold vacuum. My understanding is that once saturated with gas, the charcoal is ruined and the canisters must be replaced, so I didn't do any testing on the old unit.
The truck has dual tanks. I only use the driver side bc I am unsure of the condition of the passenger and do not want to risk sucking gunk into the fuel system until I drop that tank to clean it. I have never attempted to swap over to the passenger tank.
I wonder if the accumulation has been happening over time - yesterday I did notice evidence of gas leaking out the canister before I saw it actually happening as I limped home. The raw fuel leaking out the canister did not smell fresh, as I mentioned before, but more similarly to locktite? Perhaps simply running through the charcoal made it smell that way.
My thought is to discover the cause to avoid a recurrence of symptoms with the new canisters. The reason for testing the purge and bowl vent valves on the old canister is to determine whether the valve diaphragms are perforated. And, again, make sure the canister vent ports are not obstructed. In addition, without running the engine, switch tanks and check the fuel level in the tank you do not use. Is it FULL? How many lines connect to the fuel pump?
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Thank you everyone for your feedback, BD thank you for your suggestions.
I checked the canister, and both purge and bowl vent valves hold vacuum.
The fuel pump has three lines - the threaded hardline to the carb, and large and small 90* nipples for inlet and vent. It's the delco 41378.
The passenger tank fuel sender is grounding out when I hit the fuel selector button and pegging to past full, but the tank selector is humming when I hit the button. But I don't believe there's any fuel in that tank given it makes no sloshing noises at all when I rock the truck back and forth.
Something I just discovered....I removed the passenger filler cap and there is gas sitting right inside the neck! I rocked the truck a bit and it drained back....
Perhaps I need to drop the gas tank sooner than later?
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The third (1/4" ID) line connecting to the fuel pump is a fuel return line to the fuel tank. The return line's purpose is to help cool the fuel pump and prevent vapor lock. It is not a vent line.
Although, both fuel tanks are plumbed directly to the vapor canisters for tank venting and evaporative emissions control, the fuel return line is supposed to be plumbed through the tank selector valve so that fuel returns to the same tank from which it is drawn. The tank selector valve on your truck is a motorized valve (hence the "humming" sound) as opposed to the older solenoid type valves that "click" when energized. Motorized valves sometimes bind mid-travel and/or leak internally, resulting in various symptoms, which can include drawing and/or returning fuel to both tanks simultaneously, or returning fuel to the opposite tank from which fuel is drawn. The fact that the fuel gauge pins past full when selecting the passenger tank (an indication of an "open" fuel sender electrical circuit) suggests the selector valve is binding mid-travel. Consequently, I suspect that fuel has gradually transferred into the passenger tank through the malfunctioning selector valve, causing the tank to overfill, flooding the vapor canisters.
Assuming this scenario is correct, you will need to restore proper operation of the tank selector valve or suffer a recurrence of symptoms with the new canisters. Likely, you will need to replace the motorized selector valve and verify proper operation of the dash mounted selector switch. Keep us apprised.
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I replaced the fuel selector valve yesterday upon receiving my parts - I used ac delco U7000. I also ordered a new switch, ac delco d7003, but I have yet to install it. I will get to that this evening.
The fuel reading on the passenger tank is still way past full. I did start the truck and run it for a few minutes on each tank, so perhaps the passenger tank is simply brimming with fuel? Before I changed the valve the needle would peg out to nearly 6 oclock:
(http://i.imgur.com/K4SbJVGh.jpg)
This selector also doesn't hum like the last one, it just kinda clicks.
I have also replaced the vapor canisters with new delco units. I have not connected the fuel tank vent and would like to drive the truck a few miles to ensure it won't overflow and foul another canister - aside from the obvious, would it be otherwise inadvisable to vent to tank to atmosphere and cap the fitting at the canister while I test drive?
My plan is to run the passenger tank until it's empty and see if the needle does anything. I purchased a spare fuel filter to replace after I've run it through just in case that gasoline is old.
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Wanted to update this thread. I'm still having a bit of a headache!
The selector repair worked, and both tanks and gauges are functional. Yesterday I drove 60 miles to pick up some motorcycles and the truck did great.
This morning I filled the opposite tank w gas, switched over, and drove off. About a quarter mile down the road the truck sputters and dies. If I try to restart it'll run if I hold the gas and immediately die. I figure it's the new valve malfunctioning, so I attempt to switch back to the other tank, but the truck operated the same and left me stranded. Remember, the selector valve, switch, and fuel pump are new. The valve was still reading the fuel levels accurately when I'd switch the tanks after the truck stalled.
So far I have:
checked fuel flow - it filled a 16oz bottle overflowing after 20 seconds of cranking
replaced fuel filter - it looked ok
loosened gas caps to check for any pressure but tanks are vented to atmosphere right now anyway
checked all fuses - OK
I haven't done pressure or vacuum checks on the fuel pump as the truck is sitting in a parking lot a ways from my house. Since flow was adequate and it's new, I'm trusting it's ok.
I was convinced I had a fuel issue, but pump flow is there and that has me wondering if this new problem and the tank switching are unrelated.
I'm headed back over there now to try a good coil and ignition control module next to round out those items. Any ideas would be helpful.
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Does the engine start and run once it cools down?
Try to determine whether the problem is fuel delivery or ignition related. When the engine stalls, remove the air cleaner and look down the carburetor throat while opening the throttle a couple of times; is there a strong flow of fuel from both accelerator pump nozzles? Remove the wire from the most accessible spark plug and hold it near a bare ground while an assistant cranks the engine; is there a spark? What color is it?
FYI - The fuel pump should deliver about one quart (32 fl oz) of fuel in 30 seconds of cranking using a fully charged battery (1 qt in 20 sec is common). So, 16 fl oz in 20 sec is slightly low, although still workable if draw and pressure are suitable.
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Thank you for your reply BD.
The motor will not run on its own at all. It will fire up and struggle if I pump the pedal but it will not idle - it immediately dies if I don't nurse the pedal. If I hold the pedal down to achieve any kind of RPMs, it will surge and fall to near stall, then surge again.
I am seeing the accelerator pump function, and fuel is draining the bowl whenever I disconnected the line to check on the new filter.
My distributor has a new coil, cap, rotor, and ignition control module, and plug wires are new. That just leaves the pickup coil as suspect. However, I will do a spark test this evening to verify.
After I verify 12v at the coil and proper spark, I will test the fuel pump using a gas can for feed and see if the engine fires from there. If it does, I can assume I have a fuel line or selector valve failure. If it doesn't start, I will pull the carb and see if there's junk in the needle and seat.
I have been using the right side tank since I repaired the valve and have filled up about 3 times. Perhaps there's some gunk in the carb, but the old filter did not have a bunch of crap in it. Perhaps the new fuel pump ate it all up...
I'll report back after my tests. It really does feel like a fuel delivery issue in my experience and not an ignition issue.
Frustrating issue considering I spent the dime on all new AC Delco parts!
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Remove both ends of the 3/8" hose connecting the carburetor fuel bowl to the vapor canister and nestle the low end of the hose in a clean rag. Rinse the hose out with aerosol carburetor cleaner and inspect the rag for black carbon granules.
Count the number of turns to lightly seat the idle mixture screws then remove the screws from the carburetor. Were both screws adjusted the same number of turns? Thoroughly blow out the idle mixture passages using carburetor spray and compressed air, alternately, then reinstall the screws and adjust them the same number of turns out from seated as originally counted. Is there any improvement?
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Update:
Running the fuel pump from a can did not change anything. Motor fires like it should, and immediately dies. It'll will only run if I make it using tons of throttle.
EDIT: I have checked spark, it is big and fat and yellow during cranking
BD - just saw your message will proceed that way next
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Today I dug into the carb and found 2 hiccups....
I rebuilt this carb ab 1000 miles ago and it has run well up until the trouble I've recently run into.
I went ahead and pulled the carb down again and found a bit of sediment in the bowl, which I wasn't terribly surprised to see given the recent fuel tank service, It was a super fine powder:
(http://i.imgur.com/YF9GF3Z.jpg)
A thorough cleaning of all orifices is obviously in order.
Second, and I believe more critically, was that this brass tube next to the idle pickup tubes had fallen out the airhorn and was sitting in the carb body:
(http://i.imgur.com/8F7UQVFh.jpg)
In fact, I hadn't even noticed until I flipped the body upside down to drop out the choke rod lever. I carefully tapped it back into the airhorn.
I'll reassemble the carb when my rebuild kit arrives this week and see if this fixes the issues.
If problems persist, I think it could be safe to assume that tank sediment may have fouled the new fuel pump.
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Reinstalled carb - truck has been sitting now about 2 weeks. It wouldn't crank over at all.
Going to put in another fuel pump. The pressure was not great enough to fill the bowl, and I'm concerned ab the color of the gas coming out of it. It's as if the same gunk in the carb has fouled the pump.
I'm also going to add a second in line filter after the fuel selector valve to try and prevent this from happening in the meantime.
I suppose It's time to drop and flush the tanks.
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With that much silt in the tank(s) the fuel tank pickup sock(s) may be plugged. Test the fuel pump before you replace it - there may not be anything wrong with it. I would also look for a different fuel station - their storage tanks could be the source of all that silt.
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I was worried about that, but since the truck behaved the same when I set the pump up on a remote tank, I figured I could eliminate all of the tank components as suspect for now.
I replaced the pump yesterday but need to get a filter before I start it.
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I went to start the truck today and lo and behold - SAME TROUBLE. Starts up, runs a second, farts out.
I know these trucks are easy to work on, but dang if this one isn't stumping me.
I took a video of the behavior. To me this sounds like a fuel issue. I can get the truck to fire off after a few squirts of the accelerator pump, but it won't run:
https://www.youtube.com/watch?v=Z6xijtumkls
I may take the carb back off so I can take a close look at the idle screw circuits. I was thorough with my cleaning using compressed air and solvent, but perhaps I missed something.
I'm running out of ideas here.
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Run the truck off of a fuel can directly to the pump. Prime the hose first so you have fuel in it before you drop the hose in the can and keep it somewhere safe where it won't spill or ignite fuel vapors.
Any chance someone poured something in your gas tank? Are you 100% positive the fuel lines are properly routed? I've seen the vent hose and return hose mixed up many times and would make sense with your overflowing canister.
You mentioned yellow spark, you should have a bright blue spark across a .060" gap. Don't spark test it with the fuel system open. How old is the pick up coil and module? are you sure you aren't losing spark? Is it consistent or intermittent spark? Have you pulled the distributor cap and inspected?
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I have done a remote can test on the first fuel pump. It did not change anything. The fuel I was using was also from a different service station than the gas currently in the tanks.
I can set up a remote test for the pump I just replaced just to check for good measure. The lines are correct - kind of a tough to mix them up given the hose size and routing, as well as the fact that the selector valve only takes feed and return lines. I also had the truck running perfectly for a good while before it farted out.
The overflowing canister was a result of the selector valve stuck in a half open position - I believe it caused the tanks to bleed over and overfill, thus backing out the vent. This problem was solved with the new selector valve.
The pick up coil is the only part of the distributor that has not been replaced. The module is new. I am not sure I'm not losing spark - I did the test visually by holding a spark plug to ground and cranking, but it seems to be consistent. I pulled the distributor cap to replace the module, the cap and rotor are only a few hundred miles old.
The gas tanks have locking gas caps, so unlikely someone has sabotaged anything.
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Do this: start the engine and run it until it quits. Shut the ignition off and without moving the throttle, remove the fuel bowl cover and check the fuel level. If the bowl is dry or nearly so, there's a fuel delivery issue. If fuel is at the normal operating level, the problem is caused by something else. While the bowl cover is off, verify the float setting @ 13/32" (10 mm).
(http://i.imgur.com/8F7UQVFh.jpg)
Referring to the image above, lay a straightedge across the "flat" underside of the cover from side-to-side across the main air bleeds and measure the net amount of arch. Some arch is normal, caused from tightening the forward two carburetor mounting bolts. Excessive arch will cause late tip-in of the main circuit. Post your findings.
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Any chance you have the little filter in the inlet of the carb with the rubber check valve backwards. Some have it.
Don't recall if you checked or replaced that filter.
Did you try to keep it running by carefully pouring a small amount of fuel in the primary bowls after it starts to eliminate the ignition system?
You can also slightly crack the secondary's open by hand at the lower linkage. This will add a little fuel from the secondary system to see if it will run.
May sound unorthodox but...
If it does run better, fuel supply or primary carb circuit problem.
Have you plumbed in a pressure gauge between the pump and carb?
Also there should be residual pressure in the fuel line to the carb after it quits. Take a straw or similar and through the vent towards the center of the carb above the float bowl and push gently down on the float a bit and it should flood if the bowl is full of fuel.
As far as spark, an inline spark tester works nice also for checking that.
Best of luck, sure can be frustrating.
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The tube that fell out is for the POE (pull over enrichment) in the secondary system. Comes in to play when the upper secondary flaps first start to open adding fuel as the secondary's begin deliver fuel preventing a hesitation.
They are not a primary or idle circuit function.
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Thanks for the replies fellas.
I'm about to go outside and do the suggested steps.
blazer74 - the filter is new and oriented correctly, with the opening towards fuel flow.
I have not tried to keep it running by pouring gas in - I can try that when I have a second hand.
I have not put a pressure gauge between the pump and carb since I replaced the unit altogether anyway.
My neighbor is experienced with these old trucks - he sauntered over and told me my condition sounds like timing, and that it could have jumped time. I was skeptical of this as it is a completely out of left field suggestion. I went ahead and pegged the distributor in either direction to see if it offered an improvement. All it did was make the truck sound really advanced or really retarded. I don't think this is a timing issue.
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Here's a few pics of what I found when I pulled the air horn:
(http://i.imgur.com/CaP4ROW.jpg)
(http://i.imgur.com/sx9I79bh.jpg)
Fuel pump is working as it should. I'll measure the airhorn deflection when I check the float.
I have the carb on my bench now. My top gasket tore when I pulled the lid so I may have to wait and order another one.
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If that image was taken immediately after it died out, unless there is fuel contamination, the symptoms are not fuel related. Are you certain the tanks are not contaminated with diesel?
Your neighbor hinted at "timing," referring to valve timing. Valve timing problems can produce various symptoms, but generally cause decreased engine vacuum and power output. To check for a valve timing issue, read through Re: 86 C10 Loping (http://forum.73-87chevytrucks.com/smforum/index.php?topic=27593.msg229607#msg229607). Then to verify correct harmonic balancer registration, which can impact the relative position of the ignition timing marks on the balancer, read through Re: Not 100% what's wrong here (http://forum.73-87chevytrucks.com/smforum/index.php?topic=26872.msg223842#msg223842). Replacing a timing chain and sprockets, if you determine they are the cause, involves removing the water pump, the crankshaft harmonic balancer and the timing cover. Some people also remove the engine oil pan. You can anticipate that a timing chain replacement will consume an entire weekend the first time you perform the repair.
Once valve and ignition timing are verified, move on to ignition system diagnosis.
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hey i recognize these pictures from imgur. theyre very liberal on there and will let you know if you make a mistake. i commented "i got you fam" with a link to here. thought i recognized that quad off of one of our trucks.
btw hi blackbetty
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I am seriously starting to consider a bad fuel scenario, despite having done a remote gas can test. It's entirely possible the truck was running of the remnant fuel in the pump and carb line and I quit testing before it had a chance to get to the fresh gas. I should have purged the lines first. Look at this, it hardly even smells like gas:
(http://i.imgur.com/rrETY2B.jpg)
I need to try and run it off fresh gas again before I move forward.
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I agree, that's the prudent next step.
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Well, after all of this headache I found the issue, and it is indeed contaminated fuel. I didn't prep the lines effectively the first time I did a remote gas can test and wasted lots of time.
Here's an image of the fuel, fresh gas on right for comparison. About an inch of water is sitting on top of whatever else is in there:
(http://i.imgur.com/dwiQ1lE.jpg)
In all my years working with trucks and motorcycles, I've never personally experienced a bad gas situation. Nice to learn something new but I have wasted 3 weeks chasing a very obvious problem.
I suppose it's time to drop and purge the tanks....and figure out what to do with 30 gallons of trashgas
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Don't beat yourself up. You know what they say about hindsight being 20/20. Nothing is obvious until you actually observe it. Plenty of professional technicians have been stung by contaminated/poor quality fuel. So, look at it this way, you just earned a stripe! 8)
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End Game, Fixed!!
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thank you everyone for your time and suggestions.