Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
You may be right with the injectors. GM makes a cleaner that you run through the system, best out there. I would want to see what the o2 sensors are doing, with those miles you cannot rule them out. If you have the 3.8L You may have an issue with the intake or plenum. The plastic around the egr melts and coolant enters the intake where only the egr should.
I would check for a sticking egr valve, cleaning the egr usually helps with performance along with the fuel service and throttle cleaning. I will continue to check out other causes for you.
File In Section: 06 - Engine/Propulsion System
Bulletin No.: 99-06-04-005B
Date: September, 2001
This bulletin is being revised to update labor time allowance for labor operation J5645.
Please discard Corporate Bulletin Number 99-06-04-005A (Section 6 - Engine).
Some owners may comment on driveability symptoms of long or hard starts, chuggle, rough idle and light or intermittent misfire. The malfunction indicator lamp (MIL) may also illuminate.
Due to various factors, the fuel injectors may become restricted. At this point, no specific fuel, fuel constituent, or engine condition has been identified as causing the restriction. The restriction causes the engine to operate at a lean air fuel ratio. This may either trigger the MIL to illuminate or the engine to develop various driveability symptoms.
Fuel injector restrictions, deposits, can be cleaned on the vehicle, using the following procedure. Under NO circumstances should this procedure be modified, changed or shortened.
Pre-measured containers eliminate the need to measure the amount of GM Top-Engine Cleaner being added to the J 35800-A, injector cleaning tool. In Canada, use P/N 992872. It will be necessary to measure and dispense Top Engine Cleaner into the J 35800-A, injector cleaning tool.
Parts are currently available from GMSPO.
I know with the older GM transaxles they used to have o/d problems and stick in overdrive. We would just unplug the trans connector. With some vehicles the torque converter gets dirt and worn bushing/clutch material stuck in the torque converter and at cruising the converter locks up for o/d but stays in o/d. This could cause stalling and no power. Take a look at the fluid color and smell ( dark and burnt) if it's dirty I would try a flush. If it's really bad a flush might cause the trans to stop shifting(no clutch material)
I would love to see on a scanner what it is doing when the loss of power is felt. It happens at 20 mph , which makes be believe it's less trans and more air/fuel issue.DESCRIPTION The Mass Air Flow (MAF) sensor measures the amount of air which passes through the throttle body. The PCM uses this information to determine the operating condition of the engine, to control fuel delivery. A large quantity of air indicates acceleration, while a small quantity indicates deceleration or idle.The scan tool reads the MAF value and displays it in grams per second (gm/s). At idle, it should read between 4 gm/s-7 gm/s on a fully warmed up engine. Values should change rather quickly on acceleration, but values should remain fairly stable at any given RPM. A failure in the MAF sensor or circuit should set DTC P0101, DTC P0102, or DTC P0103.
I would pull some spark plugs and tell me what color are they, black or white.
According to alldata your fuel pressure should be 48-55. That is enough to cause a issue, you said you have 36-39. Try disconnecting the fuel pressure regulator vacuum hose, it should boost the pressure.
I have worked for independant shops and have seen aftermarket parts e bad new. I also saw how guys at the dealership would think unless the part was GM it won't work. I'll keep searching, this is a tough one. I know when you have problems like this you can never go over the basics enough or rule out parts that were replaced.
As I was looking through alldata I worked with a guy at a Chevrolet dealer. He worked at Cadillac before this, he told me about a car he worked on with etch assistance. I forget the model and make but it was GM. It was under warranty and had a stalling issue on turns. The GM tech line told him to replace several parts. The last was the fuel rail, that is what caused the stalling. Maybe you could get from a junk yark the fuel rail,regulator, injectors(the whole assembly) and see what happens. If it feels like fuel you may be right. Just a thought.
I just has a problem with my car, very unusual. I was driving down the road and all of a sudden it started smoking, pinging and no power. I barely made it home. After I shut the car off, I tried to restart and it soumded like it locked up. I thought it didn't overheat, no oil light. I checked the coolant, fine. I let it sit and tried to start it again later, a few more rotations but the same thing. Now I am thinking it has to be an injector. I pull the spark plugs and crank over to see which one. Cylinder #1 fuel come pouring out, disconnect the plug and still coming out but as a mist. I pull the rail and check for cracks, plugs on the even side are lean and rich wet on the odd. I call the dealer and he has one injector and I get the plugs. Pop it back together and thank GOD it runs and after a few days pretty good. I have never seen a injector let loose like that. My car is a 1994 concorde 3.5L.
that would make sense since this seems to be an intermittent problem.
I don't know if I will see that guy again. He used to work with me at the Chevrolet dealer. If it makes you feel better they replaced many parts under TAC hotline advice. They even missed with the engineer, the rail was a last guess.
I remember once replacing a MAP sensor on one with an aftermarket brand. It was wrong and caused some performance issues. I have also seen(chrysler) some MAP sensros be bad and not set any codes. How is the map. The more I read the past posts I see what looks like an issue that might be hid by the extra fuel given on cold running. I am still looking
Not sure about disconnecting the map electrically. I would think if you pull the vacuum and plug the line it should simulate low vacuum and cause it to run rich.
There is a common thread with the tps and the map, the 5 volt ref feed. It could be a bad connection at the pcm or map or just a bad map.
Knock sensor would make sense for loss of power and being electrical it could get worse with heat. With the scanner you will see the timing retard when the hesitation happens. Usually they set the light, haven't seen one cause a hesitation. But you learn stuff all the time with cars, I will remember this one.
I hope this is it.