This condition was progressive. At 1st it just developed a major loss of power and would stumble if given gas, then shortly after it would recover. I had just replaced my transmission and it ran for about 3 days and then this problem started. I was getting EGR and MAF sensor trouble codes but cleaned those and now the codes are gone. I have 55-60lbs of fuel pressure with no bleed-off. I cleaned the throttle body and replaced the gasket. The TPS sensor had sketchy readings so I cleaned it and it's working properly now with correct voltage readings. I cleaned the IAC solinoid but am unclear on how to confirm it's opperation. I checked for vacuum leaks but only found 1 small accessory leak and repaired it. I cleaned up all electrical ground connections I could find. I disconnected the battery and let it drain then sprayed contact cleaner on all ECM connections. I confirmed the battery was fully charged and then reconnected it. I inspected the entire engine wiring harness for chaffing or exposed wires and found nothing notable. I Replaced: - Fuel filter - MAP sensor - Distributor cap, rotor, and spark plug wires
Do a back pressure test for the exhaust system. It might have it plugged up catalytic converter
Testimonial: "Success!!! I decided to start out yesterday by loosening the exhaust pipes from the manifolds as it was easier than trying to pull out one of the O2 sensors and she fired right up! I can't believe that a clogged Catalytic converter could stop a vehicle dead in it's tracks like that to the point where it wouldn't even move."
Check/replace spark plugs. My 97 Accord recently would sputter when I got on the gas too much but would idle fine and under light throttle. Started getting a little worse. Checked the plugs and the gap was way too big. $10 for new plugs and it runs perfect again.
Testimonial: "Thanks for the advise Scott. Admittedly I have neglected to look at the spark plugs because they're hard to get at and the van was running fine and idles smoothly, it just won't move under any load now."
You've taken care of some really good things to check. A sensor would be my bet too. However, you could be dealing with a set of loose connectors, most likely a wiring harness when they changed out your transmission; I'd look where the engine-transmission join, or anyplace they would have had to disconnect wires to get to the transmission. They could have been loosely connected, and have come further apart. Perhaps if you find some loose connections, zip tie it or rubber band it together if the connector is cracked or broken.
Testimonial: "Thanks for your advise Washed! I installed the transmission myself and have had a good look all around that area for anything I may have missed but everything looks secure. Could my problem have anything to do with the connector on the side of the transmission?"
How did you clean the throttle position sensor ?
Testimonial: "I dismantled it and cleaned the contact surfaces with contact cleaner. It was quite easy and resembles a volume pot on a piece of stereo equipment. I confirmed it's operation with a multi-meter afterwards and it's working flawlessly now."
Check the fuel pressure
SOURCE: 1989 GMC 2500 5.7L - engine surges and stalls at idle. Loses power at cruising speed.
Wow you have replaced a lot of stuff. Lets go back to the Fuel pump. When you replaced it did you replace the hose between the pump and the sending unit. These are common for splitting. Have you hooked up a fuel pressure gauge to check what pressure you have? It should be real close to 13 psi and should raise to at least 18 or 19 when you pinch off the return line.
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Double check the MAP sensor and it's vacuum connection . Have you tested for exhaust restriction ? Fuel volume test ?
May need to try making a temporary block off plate for the EGR as it may be being commanded on too quickly causing the stumble .
On the idle air control when you first crank it up, even a warm restart it should flare high for a few seconds . That is one way to know it functions and the computer can activate it .
Thanks for the advice Robert. I did suspect the EGR valve originally and it did generate a trouble code so I cleaned it. It seemed to be moving fine and wasn't very dirty. Afterwards the code disappeared but I'll try the block-off plate and see what happens and get back to you.
As for the IAC. The RPMs don't flare high when I start it up so I'll investigate that as well.
I've replaced the MAP sensor (original was pretty dirty) and did some DVM tests on it. Vacuum seal and DVM readings seem good. However, I noticed that sometimes it won't start at all and if I unplug the MAP it fires right up although it still won't accelerate.
Fuel pressure seems good but I'll have to try a fuel volume test. I've never done that before although it seems easy enough.
Re Exhaust flow: I will attempt to pull one of the O2 sensors out (LOL) and see if there is any change.
Fuel volume should flow about an ounce per second or a quart in half a minute . The EGR block off can be cut from an aluminum soda can .
2 good tips thank you. I'll try all these things on Sunday.
Do be extremely cautious when doing the fuel volume test . Keep a fire extinguisher nearby .
All good, thanks. I have the proper equipment for the test, just never had to perform it til now.
Success!!! I decided to start out yesterday by loosening the exhaust pipes from the manifolds as it was easier than trying to pull out one of the O2 sensors and she fired right up! I can't believe that a clogged Catalytic converter could stop a vehicle dead in it's tracks like that to the point where it wouldn't even move.
I reconnected the exhaust and drilled a hole in the CAT and was able to drive it last night! The CAT is fully welded to the "Y" pipe and extension pipe to the muffler so it will have to go to the muffler shop to be replaced but at least I can drive it there now instead of paying $100 for a tow truck. After 2 months of scratching my head I was starting to doubt my mechanical skills. Thanks for all your advise during this ordeal Robert. You're the man!
You the man my brother . You did the process of elimination very well . Takes time and patience on these computer controlled vehicles . Never know if it's mechanical or electronic now. Congrats
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