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73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: zieg85 on June 13, 2021, 02:40:39 PM
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I am trying to troubleshoot a truck I just bought as a daily driver...
It is a 1990 C1500 with a 5.0L 700R4. It runs great until the engine is completely warm then it misses especially under load (climbing a slight hill). I just replaced the cap and rotor. A couple days ago I replaced the O2 sensor (rusted out and hanging by the wire) then the coolant temp sensor, code 14 check engine light which now I have no light. What else could cause this? TPS/MAP/EGR? Again it runs great until fully warm, about 15-20 minutes, temps have been high 80's
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How are the plugs and wires? Check the exhaust back pressure.
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How are the plugs and wires? Check the exhaust back pressure.
Plugs look great, beige colored nothing fouled. Plug wires OK, no burn marks. No back pressure, original cat, turbo muffler right after. I don't understand the TBI and how the sensors start working once operating temps are met. It runs like a scalded dog and when the operating temp gauge hit the mark it is like a switch turns on and it starts to miss. It doesn't set a code. What sensors would be inactive until that time?
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Truck only has 102,300 and no blow by or signs of wear. It doesn't leak anything either
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Unplug the o2 sensor and drive it,if it runs good after it gets warm you have a closed loop issue with the system.
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Do you have datastream on a scan tool? What's the fuel integrator & block learn at? Have you checked for vacuum leaks?
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using the chart pictured I measured 286 ohms at 184 degrees water temp. I will unplug the O2 sensor and take it for a spin next.
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Unplug the o2 sensor and drive it,if it runs good after it gets warm you have a closed loop issue with the system.
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Runs the same as it did plugged in when at operating temp
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Do you have datastream on a scan tool? What's the fuel integrator & block learn at? Have you checked for vacuum leaks?
I only have the mid level OBD2 Craftsman 87702 scanner. No vacuum leaks that I can detect. Nice and quiet at idle and guessing 600 rpm, 90's didn't have Tach's
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Do you have datastream on a scan tool? What's the fuel integrator & block learn at? Have you checked for vacuum leaks?
Do these cables actually work?
https://www.ebay.com/itm/GM-12-Pin-OBD1-to-16-Pin-OBD2-Convertor-Adapter-Cable-for-Diagnostic-Scanner-New-/401533946179
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Look at the main shaft in the distributor. Does it have any side to side movement. Also check the magnets at the top for cracks. If you find you need to replace the distributor get a new one not a rebuilt.
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May be the ignition coil? It gets hot and starts layering short?
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Do you have datastream on a scan tool? What's the fuel integrator & block learn at? Have you checked for vacuum leaks?
Do these cables actually work?
https://www.ebay.com/itm/GM-12-Pin-OBD1-to-16-Pin-OBD2-Convertor-Adapter-Cable-for-Diagnostic-Scanner-New-/401533946179
For $8 I'm sure it's worth a try but if oyu are going to own an OBDI vehicle, you need to have a scan tool for it.
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I had a slight bit of play in the distributor so I changed that and returned the new ignition module I didn't use. That wasn't it. I put a new coil on it, no dice either. Next logical thing was to just replace the spark plugs. That was it. No visible cracks, all looked great, proper gap but obviously were failing. Thanks so much for the suggestions.
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How are the plugs and wires? Check the exhaust back pressure.
Always start with the basics. Definitely get yourself and OBDI scan tool
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How are the plugs and wires? Check the exhaust back pressure.
Always start with the basics. Definitely get yourself and OBDI scan tool
Thanks again Vile. I ordered a cable, hopefully my mid level scanner can work seeing run time data.
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I use WINALDL on TBI trucks (as long as it is covered. The 1991 with 4L80E wasnt at one time.
http://www.winaldl.joby.se/ (http://www.winaldl.joby.se/)
I made my own cable with some electrical probes and a Ethernet jack.
You can see it here (you have to have a 9 pin output though. http://forum.73-87chevytrucks.com/smforum/index.php?topic=7711.msg47384#msg47384 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=7711.msg47384#msg47384)
Used it to diagnose the Suburban I had.. http://forum.73-87chevytrucks.com/smforum/index.php?topic=3984.0 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=3984.0)
What about the IAC?
Pull the distributor and check the mag pickup the burb I worked on had them rusty and bad..
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I use WINALDL on TBI trucks (as long as it is covered. The 1991 with 4L80E wasnt at one time.
http://www.winaldl.joby.se/ (http://www.winaldl.joby.se/)
I made my own cable with some electrical probes and a Ethernet jack.
You can see it here (you have to have a 9 pin output though. http://forum.73-87chevytrucks.com/smforum/index.php?topic=7711.msg47384#msg47384 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=7711.msg47384#msg47384)
Used it to diagnose the Suburban I had.. http://forum.73-87chevytrucks.com/smforum/index.php?topic=3984.0 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=3984.0)
What about the IAC?
Pull the distributor and check the mag pickup the burb I worked on had them rusty and bad..
The inside of the distributor was rusty and crusty, I couldn't ever recognize the screws that held the ignition module on so I just decided to replace the entire unit and return the ignition module. That was not the issue either. The IAC tested within the voltage parameters in the testing procedure. Even though the Platinum plugs looked great I changed them and that was the problem all along
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... Even though the Platinum plugs looked great I changed them and that was the problem all along
Wow that is both sad and encouraging.. All came down to plugs
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Did you change the gap on the platinum plugs? You can't run a gapper between the electrodes on a platinum or iridium plug. Even the slightest amount of drag will disturb the platinum and could have caused your problem.
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Even though the Platinum plugs looked great
Please don't say you used Bosch Platinum's :o
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Even though the Platinum plugs looked great
Please don't say you used Bosch Platinum's :o
no but that was what was in it. Put some AC non platinum
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no but that was what was in it.
They are absolute garbage
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no but that was what was in it.
They are absolute garbage
Good to know... I got about 150 miles down the road and my service engine light came on and went off. Truck started bogging real bad and barely made it safely to a parking lot where my son came and got me with a uhaul dolly. Anyway my brother in law came with an OBD1 scanner. All tests pointed to the MAP sensor. Changed it and that wasn't it. I really don't know where to turn. He is going to do some checking tomorrow and see if he can come up with something else.
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Have you checked the fuel filter?
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Have you checked the fuel filter?
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New fuel filter less than 250 miles ago
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Before drifting too far afield, verify the fuel pressure.
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Before drifting too far afield, verify the fuel pressure.
Some run time data, weird voltage reading and re-ac curing code 42 and 44 with the known history of the truck are pointing to wiring based on a very similar situation reported on a mechanics resource my brother in law sent me to try.
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This is the Diagnostic for 42:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=36657.msg308237#msg308237
44 means lean so I too say check fuel pressure. What does the TBI regulator look like. I had one with a broken spring...
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Before drifting too far afield, verify the fuel pressure.
Put the parts cannon away. Check the basics, fuel pressure, proper timing set, and preliminary checks before you buy parts.
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I had a 90 tbi did the same thing, change the filter again and see if it runs better.
Might have trash in the tank.
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After all that, do you have a Dirty Harry Magnum 44?