eric 87
Full Access Member
- Joined
- Aug 3, 2021
- Posts
- 89
- Reaction score
- 26
- Location
- Kentucky
- First Name
- Eric
- Truck Year
- 1987
- Truck Model
- GMC Sierra Shortbed
- Engine Size
- 305 tbi
Emergency. If I can't figure this out I will let shop have one more crack at it. Then I will put a ford engine in it just to spite the truck!
Here is the issue. I had a missing engine when I had to accelerate and it got worse. Like a pack of lady finger firecrackers going off. It is a 87 stock 305 TBI.
Replaced and also TESTED each sensor with appropriate tools.
TPS, Map, IAC and Temp sensor. None of it worked.
Rebuilt the Throttle body and replaced the computer using the Prom chip in the old computer. Didn't totally fix issue but helped it a bit
Took to the shop to have him go over what was done. This fellow and his shop know GM products....well most if not all products but they race GM cars as well.
He replaced the distributor. The pickup coil was shot the magnets were off etc. He also checked the throttle body again and pressure.
AH at last it was fixed.....but wait. The drive home...it seemed to cough as in nose dive and then take off and that was at a steady speed maybe light accel.
As I continued home with wife following me in my old farm truck (FORD) it did this more often randomly. As we neared home it was pronounced as if the truck was being shut off with the key or as if I was totally out of gas. Had half tank. I drove to the neighborhood gas station with flashers on since I was on back road. Nope I was half tank.
When I restarted it the RPMs went HIGH. Shut off and restarted and they went LOW barely idling. Next day wife thought she would attempt to drive it to grocery since it otherwise had driven great on the way home.
It quit on her a mile from home at stop sign. Idle was so low. She had no steering and got it to a driveway and restarted it to have it rev probably over 2500 rpm. She turned around and brought it home and took old betsy the farm truck.
I drove it later about 10 mile circle and NOTHING HAPPENED until right before getting home. It did a quick cough again as if a split second power off. No backfire.
Next morning I called shop and he was going to go back through everything that had been done. He had it on a laptop doing the tune and took it out and it never acted up before we picked it up. But he said he would rather I be happy than to lose business.
I left to take back to shop and this time it shut down a mile from home. Driving steady speed. About 40mph. First the engine off but the radio stayed on. But then all of a sudden I lost the radio. Coasted to a driveway. While coasting I put in neutral and tried to start it. Nothing. I got to a driveway put in park and cranked....nothing. Then doing what you are not supposed to do....I pumped the THROTTLE BODY a few times and it started. IT of course ran rough initially but only a few seconds and it smoothed out. I took it home though since she was at work and could not follow me the 20 miles to the shop. IT is going back next week by driving or by rollback.
If someone can help me in a direction to search I would appreciate. If I or he can't find it I will either do a carb swap and ditch the TBI OR SELL IT AS IS and let the person know as it might quit on a test drive. SO far this has cost about 550 from the parts and labor gun. Much of it done myself. I may toss all the new stuff and do the intake carb distributor etc. Cut my losses.
I like it but I do not like being on the side of the road.
I love my classics as my other is a 69 firebird. But I will not keep what I can't drive. My 69 is local show quality but I drive and do not have historic tags on it. If it doesn't get driven it gets sold.
So Pleading for help as I rather like this truck. But when a round nosed ford with 276k miles is more dependable...
Sorry to be long winded. But an update. It also dropped voltage when I hit the brake pedal. Down to 8 on the gauge! I tested the alternator and battery. I turned every accessory on I could and tested as well. Alt checks out. But could it be going bad and it cause the power failure randomly?
Even though it started with the pumping of throttle body I think this is electrical. That had been rebuilt and it wouldn't explain why I am losing all power even to radio with key still in the run position.
Here is the issue. I had a missing engine when I had to accelerate and it got worse. Like a pack of lady finger firecrackers going off. It is a 87 stock 305 TBI.
Replaced and also TESTED each sensor with appropriate tools.
TPS, Map, IAC and Temp sensor. None of it worked.
Rebuilt the Throttle body and replaced the computer using the Prom chip in the old computer. Didn't totally fix issue but helped it a bit
Took to the shop to have him go over what was done. This fellow and his shop know GM products....well most if not all products but they race GM cars as well.
He replaced the distributor. The pickup coil was shot the magnets were off etc. He also checked the throttle body again and pressure.
AH at last it was fixed.....but wait. The drive home...it seemed to cough as in nose dive and then take off and that was at a steady speed maybe light accel.
As I continued home with wife following me in my old farm truck (FORD) it did this more often randomly. As we neared home it was pronounced as if the truck was being shut off with the key or as if I was totally out of gas. Had half tank. I drove to the neighborhood gas station with flashers on since I was on back road. Nope I was half tank.
When I restarted it the RPMs went HIGH. Shut off and restarted and they went LOW barely idling. Next day wife thought she would attempt to drive it to grocery since it otherwise had driven great on the way home.
It quit on her a mile from home at stop sign. Idle was so low. She had no steering and got it to a driveway and restarted it to have it rev probably over 2500 rpm. She turned around and brought it home and took old betsy the farm truck.
I drove it later about 10 mile circle and NOTHING HAPPENED until right before getting home. It did a quick cough again as if a split second power off. No backfire.
Next morning I called shop and he was going to go back through everything that had been done. He had it on a laptop doing the tune and took it out and it never acted up before we picked it up. But he said he would rather I be happy than to lose business.
I left to take back to shop and this time it shut down a mile from home. Driving steady speed. About 40mph. First the engine off but the radio stayed on. But then all of a sudden I lost the radio. Coasted to a driveway. While coasting I put in neutral and tried to start it. Nothing. I got to a driveway put in park and cranked....nothing. Then doing what you are not supposed to do....I pumped the THROTTLE BODY a few times and it started. IT of course ran rough initially but only a few seconds and it smoothed out. I took it home though since she was at work and could not follow me the 20 miles to the shop. IT is going back next week by driving or by rollback.
If someone can help me in a direction to search I would appreciate. If I or he can't find it I will either do a carb swap and ditch the TBI OR SELL IT AS IS and let the person know as it might quit on a test drive. SO far this has cost about 550 from the parts and labor gun. Much of it done myself. I may toss all the new stuff and do the intake carb distributor etc. Cut my losses.
I like it but I do not like being on the side of the road.
I love my classics as my other is a 69 firebird. But I will not keep what I can't drive. My 69 is local show quality but I drive and do not have historic tags on it. If it doesn't get driven it gets sold.
So Pleading for help as I rather like this truck. But when a round nosed ford with 276k miles is more dependable...
Sorry to be long winded. But an update. It also dropped voltage when I hit the brake pedal. Down to 8 on the gauge! I tested the alternator and battery. I turned every accessory on I could and tested as well. Alt checks out. But could it be going bad and it cause the power failure randomly?
Even though it started with the pumping of throttle body I think this is electrical. That had been rebuilt and it wouldn't explain why I am losing all power even to radio with key still in the run position.
Last edited:
)...anyhow I digressed there!
