73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: bnoggle on June 08, 2017, 12:09:37 AM
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Can someone please tell me where the throttle position sensor is located on a 1983 chevy 250 integral head. The truck has a very rough idle, poor shifting, and feels like it wants to stall every time you go near the gas. Any other suggestions would also be appreciated. A brief list of what has been recently (past three months) replaced/rebuilt are
Head gasket
Exhaust gasket
Thermostat
Plugs/wires/cap/rotor
All vacuum hoses
Carb rebuild
Tv cable
Electronic ignition
All Vacuum fittings
Transmission filter
EGR
Water pump
Belts
Alternator rebuild
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Shouldn't be a tps. As far as I know
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Verify the firing order 1-5-3-6-2-4. Did you spray for vacuum leaks using B12 or other aerosol carburetor cleaner, including all around the integral intake manifold, carburetor, etc? What procedure did you use when adjusting the valves? Did you verify valve motion on all cylinders? Did you have the cylinder head Magnafluxed (checked for cracks) and rebuilt while it was off the engine or simply replaced the head gasket? Did you run a dry/wet compression check beforehand and after? What were the pressures? Have you checked engine vacuum? What carburetor float level setting did you use to adjust the float?
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Verify the firing order 1-5-3-6-2-4. Did you spray for vacuum leaks using B12 or other aerosol carburetor cleaner, including all around the integral intake manifold, carburetor, etc? What procedure did you use when adjusting the valves? Did you verify valve motion on all cylinders? Did you have the cylinder head Magnafluxed (checked for cracks) and rebuilt while it was off the engine or simply replaced the head gasket? Did you run a dry/wet compression check beforehand and after? What were the pressures? Have you checked engine vacuum? What carburetor float level setting did you use to adjust the float?
I used the float level setting included in the kit I purchased from mikes carb parts
Engine vacuum levels all read normal around 17 ft lbs at the intake manifold
Ran a dry compression test when lashing the valves. From 1-6 the values were 135, 145, 140, 145, 150, 140
Cylinder head was checked for cracks, and milled flat
I used the propane torch method but never found any leaks except at the vapor canister. It has since been replaced.
Just verified, firing order is correct and TDC is at firing positions 1&6
When lashing valves I found tdc and then tightened valves on cylinder 1 until there was no more up and down motion. I then tightened them 1/2 turn more. Next I turned the engine 1/3 a turn to get to cylinder 2 and repeated the process. Once I finished tightening valves I ran the engine with the valve cover off to check that everything was ok. It ran smooth for about 5 minutes and then the problem described above began again. I shut it down and replaced vacuum lines. It ran smoothly for about 5 minutes again and then the problem came back. Etc.
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Would there a a cam position sensor?
Do you think it could be an ignition control module?
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It's been a while since I done a inline six, but I thought there was supposed to be some lash? I am pretty sure when I did my brothers 292(same basic motor) it had a lash setting of .004"
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Did that motor have hydraulic lifters?
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The 250 L6 uses zero lash hydraulic lifters. Greater than zero lash adjustment is for solid lifters. In 1983, Federal emissions vehicles didn't use feedback emissions systems, so there are no sensors linked to an ECM for fuel and ignition control.
Vacuum isn't measured in "ft-lbs." Did you mean "in Hg?" Was the vacuum gauge needle steady, floating, bouncy, or _________?
Although safe, the propane method is not as reliable for discovering difficult vacuum leaks. Check again for vacuum leaks using Berryman's B12 spray, but be careful since it's very flammable. Spray all around the Varajet carburetor and intake, especially where the fuel bowl attaches to the throttle plate and around the throttle shafts. With the engine off, open the throttle about 1/4 and move the throttle shaft side-to-side to determine the amount of side play between the shaft and plate. There should be no more than ~0.005".
Unplug the EGR valve and plug the vacuum hose while the engine is running rough to determine whether there is noticeable improvement. With the engine at operating temperature and the air cleaner removed, while idling rough hoover the carburetor using a clean shop rag to enrichen idle fuel mixture to determine whether there is any improvement.
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why did you have head work done? did you have this problem before the head work?
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why did you have head work done? did you have this problem before the head work?
Three reasons, first I was trying to solve this problem. Secondly the head gasket was 34 years old and had 88,000 miles on it. Third, I had an exhaust leak between the manifold and the head.
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Checked for leaks again with spray, and found none. Spraryed all around the carburator, adn the integrated head intake. Also sprayed aroud vacuum lines, egr, pcv, and any other vacuum component I could find. Next i tried enrichining the fuel air mixture, the engine bogged down and smoke came out of the tailpipe. I suspect it has become an electrical problem, since my last post I have noticed a constant static in the radio. I checked wirng and there are no problems there. Multiple antennas have the same problem. I also noticed the noise gets worse with the hood up, so I am convinced there is an electrical component malfuinctioning somewhere. I checked the alterator boot, distrubutor cap, spark plug torque, and spark plug wires. All are installed correctly. Could it be the ignicion control module? I have heard they go out fairly often.
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i dont know. what your saying is your issue reminds me of my mud truck when i first got it and was learning about everything. i want to say it was an issue between timing and carb adjustment. first thing i had to do was adjust the timing (mind you this was on a sbc) and hook the vacuum advance to manifold vacuum instead of ported. then adjust the carb till it ran great.
but i didnt have any smog stuff on mine, do you have any? or a cat?
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The truck has all the exhaust equipment that came standard in 1983, including a CAT. I was told by someone today to start replacing sensors until I find the one that is causing the truck to run rough. I also picked up a new condenser unit today thinking that could possibly be part of the problem. I have not gotten time to go install it yet but will post again tomorrow after I do. Please keep the ideas coming.
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the sensors on your truck should be very limited and none should effect the truck due to not having an ecm. a condenser for the ac? have you tried to remove the exhaust? before you replace anything you should try to eliminate what you can and if that can be done cheap or free then thats even better. unless you have spare cash just to be tossing at the truck
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the sensors on your truck should be very limited and none should effect the truck due to not having an ecm. a condenser for the ac? have you tried to remove the exhaust? before you replace anything you should try to eliminate what you can and if that can be done cheap or free then thats even better. unless you have spare cash just to be tossing at the truck
It's a condenser like in the traditional sense of points and condenser. I'm not sure what it is actually called, but the package calls it a radio condenser. It sits in the distributor next to the ignition control module. I did remove the exhaust, well actually it rusted through, it still ran rough though. Originally I thought it was running poorly because of no back pressure from the exhaust, but that apparently isn't the case. Unfortunately under the current laws in Pennsylvania I must have all emissions equipment connected, and present to pass inspection otherwise I would disconnect all of it. They don't really care if it works or not so I guess I could make it look like the emissions equipment is connected. I will try disconnecting what few sensors I have tomorrow.
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None of the "sensors" on your truck affect drivability. The "primary condenser" in HEI systems suppresses electrical interference that otherwise could propagate through the vehicle wiring. The change in radio noise between the hood open and closed suggests that RFI in your truck is actually emanating from the ignition secondary and being received through the radio antenna.
Collectively, the symptoms you've described imply a failing ignition coil, although the ICM and pick-up coil can mimic similar effects. Replace the complete distributor replete with cap, coil and vacuum advance - replacing individual distributor components, one-at-a-time, can cost >150% of a complete assembly. You should be able to find a complete assembly for about $100.
Edit:
Make sure the hood is suitably grounded to the body by installing a 1/4" wide, flexible braided strap or 12-gauge wire between the hood and firewall sheetmetal. Allow sufficient length for hood closing and opening without binding.
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im with bd about it being in the distributor. you can get the icm and coil tested at a parts store but theres no way to test the pick-up coil. i know you already replaced the cap and rotor. so at this point i would take the icm and coil off to get them tested. since it happens all the time when the engine is cold or hot one of them should test bad. if you do as bd suggested you could also keep the old distributor for backup
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Had the icm and coil both tested, both were bad. Replaced the distributor, and now I don't have any power. It runs well but does not shift or speed up properly. The radio static is gone, and the timing was reset properly. I'm not sure what's wrong with it. Also when it shuts down there is pre-ignition. I turned the idle down to 450 rpm.
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New or reman distributor?
By "pre-ignition," do you mean the engine knocks and keeps running when shut off (aka, dieseling, after-run)? Is there an idle solenoid on the throttle linkage side of the carburetor? Is it connected and adjusted to positively extend when the ignition is switched on and then fully and immediately retract when the ignition is switched off? What are the curb and base engine idle RPM settings that you used?
With the engine running and while using a timing light, if you apply vacuum to the distributor vacuum advance does the timing advance? How much? Does the can hold vacuum? Then, with the vacuum advance disconnected, does the timing advance if you rev the engine? How much? At what engine RPM does it stop advancing?
With the engine off and the distributor cap removed, can you rotate the rotor ~10° CW against spring tension? Will it return to its original position when released? Is the rotor rotation consistently repeatable by hand or does it stick/hang up?
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New or reman distributor?
By "pre-ignition," do you mean the engine knocks and keeps running when shut off (aka, dieseling, after-run)? Is there an idle solenoid on the throttle linkage side of the carburetor? Is it connected and adjusted to positively extend when the ignition is switched on and then fully and immediately retract when the ignition is switched off? What are the curb and base engine idle RPM settings that you used?
With the engine running and while using a timing light, if you apply vacuum to the distributor vacuum advance does the timing advance? How much? Does the can hold vacuum? Then, with the vacuum advance disconnected, does the timing advance if you rev the engine? How much? At what engine RPM does it stop advancing?
With the engine off and the distributor cap removed, can you rotate the rotor ~10° CW against spring tension? Will it return to its original position when released? Is the rotor rotation consistently repeatable by hand or does it stick/hang up?
By pre ignition I do mean diesel ink. I managed to fix that by turning idle way down. Apparently when I replaced the distributor it somehow changed my idle speed. There is no idle solenoid on the carburetor. Curb is ~450, base is set from factory (aka I forgot to check). The timing does not advance much, maybe 2 degrees when vacuum is applied. The can holds vacuum, and was new with the distributor. Timing does advance about 2 degrees when vacuum is disconnected and engine is revved. I cannot tell what rpm it stops advancing as the interference in my engine bay is too much for my tachometer to give a good reading with engine revved, but I would guess it is about 4,000 rpm based on sound alone. The spring tension in mechanical advance seems good. It is the same as in the old distributor. Rotor seems to advance and return freely.
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By preignition I do mean dieseling. I managed to fix that by turning idle way down. Apparently when I replaced the distributor it somehow changed my idle speed. There is no idle solenoid on the carburetor. Curb is ~450, base is set from factory (aka I forgot to check). The timing does not advance much, maybe 2 degrees when vacuum is applied. The can holds vacuum, and was new with the distributor. Timing does advance about 2 degrees when vacuum is disconnected and engine is revved. I cannot tell what rpm it stops advancing as the interference in my engine bay is too much for my tachometer to give a good reading with engine revved, but I would guess it is about 4,000 rpm based on sound alone. The spring tension in mechanical advance seems good. It is the same as in the old distributor. Rotor seems to advance and return freely.
If there is no idle solenoid, then curb idle and base idle are the same. Dieseling results from too much air entering the engine and/or improper ignition timing. Poor engine power can result from insufficient or poorly implemented ignition timing. W/o an accurate tachometer or timing advance light, diagnosis of the distributor timing curve can be difficult. However, two degrees vacuum advance is insufficient. Manufacturer references are available that accurately describe timing curves by distributor number and application. Unfortunately, I don't have them at my disposal. Strictly as a guess without any reference materials, I expect vacuum advance should be in the range of 8° - 16°. Mechanical advance probably should be in the range of 20° - 30°. Where is the base timing set?
Remove the #1 spark plug and bring the piston to TDCC. Peer through the spark plug hole with a bright penlight or substitute a long straw touching the top of the piston to verify that the piston is at the very top of its stroke. Once you confirm that the piston is all the way up, look at the timing marks on the balancer and see whether they align to zero. This will determine whether the outer ring of the balancer has slipped, throwing the timing mark out of compliance.
Did you ever check for side-play in the throttle shaft of the carburetor (see prior post)? Do you still have the original distributor?
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By preignition I do mean dieseling. I managed to fix that by turning idle way down. Apparently when I replaced the distributor it somehow changed my idle speed. There is no idle solenoid on the carburetor. Curb is ~450, base is set from factory (aka I forgot to check). The timing does not advance much, maybe 2 degrees when vacuum is applied. The can holds vacuum, and was new with the distributor. Timing does advance about 2 degrees when vacuum is disconnected and engine is revved. I cannot tell what rpm it stops advancing as the interference in my engine bay is too much for my tachometer to give a good reading with engine revved, but I would guess it is about 4,000 rpm based on sound alone. The spring tension in mechanical advance seems good. It is the same as in the old distributor. Rotor seems to advance and return freely.
If there is no idle solenoid, then curb idle and base idle are the same. Dieseling results from too much air entering the engine and/or improper ignition timing. Poor engine power can result from insufficient or poorly implemented ignition timing. W/o an accurate tachometer or timing advance light, diagnosis of the distributor timing curve can be difficult. However, two degrees vacuum advance is insufficient. Manufacturer references are available that accurately describe timing curves by distributor number and application. Unfortunately, I don't have them at my disposal. Strictly as a guess without any reference materials, I expect vacuum advance should be in the range of 8° - 16°. Mechanical advance probably should be in the range of 20° - 30°. Where is the base timing set?
Remove the #1 spark plug and bring the piston to TDCC. Peer through the spark plug hole with a bright penlight or substitute a long straw touching the top of the piston to verify that the piston is at the very top of its stroke. Once you confirm that the piston is all the way up, look at the timing marks on the balancer and see whether they align to zero. This will determine whether the outer ring of the balancer has slipped, throwing the timing mark out of compliance.
Did you ever check for side-play in the throttle shaft of the carburetor (see prior post)? Do you still have the original distributor?
No play in the throttle shaft. I checked the marks yesterday when I re lashed the valves, they appear to be between 2 and 3 degrees off. I timed it that way and it runs better, but there is still a significant engine miss when the engine gets warm. At cold idle it is smooth. I do still have the original distributor.
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I have also noticed in the past few days that I have an unburned gas smell coming out of the tailpipe when cold, but once it warms up and starts to shake the gas smell goes away. Jos could the two be connected?
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So, when the engine runs rich the symptoms disappear. Try adjusting the base timing to 12° to see what happens.
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So, when the engine runs rich the symptoms disappear. Try adjusting the base timing to 12° to see what happens.
Engine has been adjusted to 12 degrees before TDC. It runs better, but there is still a significant gas smell coming from the tailpipe when after the engine warms up. It also begins to shake a bit still when this happens. I tried timing to several different points and 12 degrees is definitely the best. Could it need to be an mixture screw adjustment?
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I have also noticed in the past few days that I have an unburned gas smell coming out of the tailpipe when cold, but once it warms up and starts to shake the gas smell goes away.
Engine has been adjusted to 12 degrees before TDC. It runs better, but there is still a significant gas smell coming from the tailpipe when after the engine warms up. It also begins to shake a bit still when this happens. I tried timing to several different points and 12 degrees is definitely the best. Could it need to be an mixture screw adjustment?
Your statements are contradictory. Why? The residual symptoms sound like an engine misfire caused by a carburetor issue (wrong or improperly installed gasket, plugged passage, incorrect adjustment, etc) or bad fuel. What brand & number spark plugs did you install?
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I have also noticed in the past few days that I have an unburned gas smell coming out of the tailpipe when cold, but once it warms up and starts to shake the gas smell goes away.
Engine has been adjusted to 12 degrees before TDC. It runs better, but there is still a significant gas smell coming from the tailpipe when after the engine warms up. It also begins to shake a bit still when this happens. I tried timing to several different points and 12 degrees is definitely the best. Could it need to be an mixture screw adjustment?
Your statements are contradictory. Why? The residual symptoms sound like an engine misfire caused by a carburetor issue (wrong or improperly installed gasket, plugged passage, incorrect adjustment, etc) or bad fuel. What brand & number spark plugs did you install?
Autozone brand spark plugs are what I installed. Sorry for the contradictory statements, to clarify at 12 degrees before TDC is where the engine runs best. By best I mean least rough. Though it runs best there it still has a significant gas smell when the engine is warm as well as a noticeable roughness when you stop at a stop sign. Otherwise the roughness is not noticeable. I played with the idle speed a bit and it didn't seem to make any difference.
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This is a long shot, but replace the spark plugs using ACDelco R45TS gapped at 0.035". Be sure to check the spark plug gaps with a gauge before you install them - never assume gaps are correct out of the box. And, don't substitute with another brand or part number.
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and triple check the firing order
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New spark plugs gapped at .035 did not make a difference. Also checked firing order again and it is still 1, 5, 3, 6, 2, 4. I have noticed over the past few days a ticking sound coming from the engine when it gets warm. The ticking sound starts around the same time as the rough idle, so I'm fairly sure the two are connected. Around the same time the ticking sound started I also started having trouble getting the engine to start when it is hot. It cranks for longer than it used to before firing up. Any ideas?
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Is the tick from the distributor?
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Is the tick from the distributor?
It may be from the distributor, or it may be from a valve. It only is noticeable when the engine is warm and at a higher rpm than idle. It gets louder the higher you rev the engine. It's hard to tell exactly where it comes from because of the engine noise.
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I did a valve lash, set the timing, and set the idle speed again today. The tick is still present, so my guess is it is the distributor. The good news is the truck now idles better than it ever has before. There is still just a hint of a misfire when warm but the engine is smooth enough that it doesn't rattle the passengers too much when sitting at a red light. Do you think the little misfire is a distributor problem, or just an adjustment problem. If so what should I adjust again?
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Many excellent suggestions have already been made, and I will not attempt to re-invent the wheel. I had a similar situation with my '85 Silverado. After a complete engine swap with a fresh engine, the truck would not start at all. I tinkered with the timing and then the idle mixture to get it to run, but my performance was terrible - lackluster power, shuddering, unburned fuel smell in the exhaust. One day, sufficiently tired of this, I began spraying carb cleaner around the top of the engine. Aiming at the back of the carb seemed to make the engine speed up. Upon removing the carb, I discovered that I had cracked the throttle plate by over-tightening the brake booster line. Replacing the throttle plate, re-timing, re-setting idle mixture, and now it drives like I had hoped for.
In my situation, I had retarded the timing and enriched the idle mixture far from what would normally be correct, just to get the truck to run at all. Because it ran, I thought my adjustments had helped, when in reality they were just masking the real problem - a massive vacuum leak from my own carelessness.
I am not necessarily suggesting that you have a vacuum leak. You have already checked for that. My point is that sometimes the erratic problems are caused by something that is not on our regular checklist. By your statements, you have had most of your engine apart at some point in this endeavor. Go back to the beginning. Check everything from step one, even if it seems preposterous. Persist and you will find the problem. Good luck !