Mr4btTahoe
New Member
- Joined
- Aug 14, 2018
- Messages
- 22
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- Transmission
- Automatic
Hey alls,
So just put a fresh long block in my 1990. Everything is sealed up... fresh plugs.. coils and wires are only a year or so old and in good shape... same for the ICM. I replaced the CPS while the engine was out. Has a new o2 sensor... new intake temp sensor (looked nasty). Other than that, everything is the same.
It starts right up... runs glass smooth. Blip the throttle hard and it'll start misfiring... then it will smooth back out. Its much worse when cold. Once warm, it drives great... runs smooth... but if sitting at an idle and snap the throttle open hard.. it drops cylinders and smells pig rich... then it will clean up and run smooth again. When the engine is warm and the throttle is snapped hard... say 4k+rpm, it'll start running rough as it returns to idle... stumbling for a few seconds... then it cleans up and runs glass smooth again. Bring the idle up slow when its warm or during normal driving conditions, its fine as well.
When cold and it does this, it will stall at times... and the only way to get it to start back up is to hold the throttle wide open. Its flooding. Also when cold, it does it with barely any throttle at all until it warms up.
I'm assuming its a rich condition causing the misfire. I've checked all of the sensors... everything seems to respond when unplugged as it should. Unplug the CPS and it stalls instantly. Unplug each coil pack and it makes a noticeable difference but not the misfire that is happening. TPS causes an instant high idle... IAC will cause a stall when unplugged and warm (seems to be working fine... higher idle when cold... gradually drops as it warms up... etc.) No vacuum leaks that I can find... EGR seems to be fine... coolant temp sensor doesn't make much of a difference.
The truck has had a bad exhaust leak where the manifold meets the exhaust system. The bolts wont budge and the connection is loose. Could the new o2 sensor be responding faster than the old one... picking up the exhaust leak and causing a rich condition when the throttle is snapped?
I can't pull codes on this truck for some reason. It's always been that way though. Check engine light is dimly lit always... and if you jumper the diagnostic connector, it does nothing but cycle the fuel pump a few times. Its been that way for years though so it's not the cause of the issue.
Sorry for the long winded post but I'm really at a loss on whats causing this. Never had an issue like this one.
Engine was replaced due to massive oil leaks.... well sorta. Pulled the engine for a full re-seal and clutch job. Head ended up being cracked... couldn't find a good head and a fresh one was stupid expensive. The long block came with a 4 year warranty so figured it was the best option. This doesn't seem like a mechanical issue at all.
Appreciate any input.
So just put a fresh long block in my 1990. Everything is sealed up... fresh plugs.. coils and wires are only a year or so old and in good shape... same for the ICM. I replaced the CPS while the engine was out. Has a new o2 sensor... new intake temp sensor (looked nasty). Other than that, everything is the same.
It starts right up... runs glass smooth. Blip the throttle hard and it'll start misfiring... then it will smooth back out. Its much worse when cold. Once warm, it drives great... runs smooth... but if sitting at an idle and snap the throttle open hard.. it drops cylinders and smells pig rich... then it will clean up and run smooth again. When the engine is warm and the throttle is snapped hard... say 4k+rpm, it'll start running rough as it returns to idle... stumbling for a few seconds... then it cleans up and runs glass smooth again. Bring the idle up slow when its warm or during normal driving conditions, its fine as well.
When cold and it does this, it will stall at times... and the only way to get it to start back up is to hold the throttle wide open. Its flooding. Also when cold, it does it with barely any throttle at all until it warms up.
I'm assuming its a rich condition causing the misfire. I've checked all of the sensors... everything seems to respond when unplugged as it should. Unplug the CPS and it stalls instantly. Unplug each coil pack and it makes a noticeable difference but not the misfire that is happening. TPS causes an instant high idle... IAC will cause a stall when unplugged and warm (seems to be working fine... higher idle when cold... gradually drops as it warms up... etc.) No vacuum leaks that I can find... EGR seems to be fine... coolant temp sensor doesn't make much of a difference.
The truck has had a bad exhaust leak where the manifold meets the exhaust system. The bolts wont budge and the connection is loose. Could the new o2 sensor be responding faster than the old one... picking up the exhaust leak and causing a rich condition when the throttle is snapped?
I can't pull codes on this truck for some reason. It's always been that way though. Check engine light is dimly lit always... and if you jumper the diagnostic connector, it does nothing but cycle the fuel pump a few times. Its been that way for years though so it's not the cause of the issue.
Sorry for the long winded post but I'm really at a loss on whats causing this. Never had an issue like this one.
Engine was replaced due to massive oil leaks.... well sorta. Pulled the engine for a full re-seal and clutch job. Head ended up being cracked... couldn't find a good head and a fresh one was stupid expensive. The long block came with a 4 year warranty so figured it was the best option. This doesn't seem like a mechanical issue at all.
Appreciate any input.