I just bought a 1994 K2500 w/ 5.7. The engine runs fine when cold but as it warms up it starts to "surge" at idle and when you come to a stop it acts like it wants to stall then it grabs. If you sit at a light for more than a few moments it will start to idle lower and lower until it stalls. I have replaced the TPS , tuned it up , replaced fuel filter, and cleaned out the EGR. I have no codes or lights. BUT If I unplug the MAP sensor the idle is fine but it still feels like it looses power if you are going down the road and try to hold a steady pedal. I feels almost like it is running out of gas. Weak fuel pump? weak pressure reg? I drove this truck home 110 miles with no problems. I put a new exhaust on it and the problems started. O2 sensor? I have a 92 truck with 5.7 that runs great that I have been swapping parts to see if I can find the problem. swapped MAP, Idle control, temp sensor. all dont help the 94 and dont effect the 92.
BAFFLED & FRUSTRATED. PLEASE HELP
THANKS
JOHN
2007-08-22 00:56:25 · 7 answers · asked by z28guyjd 1 in Cars & Transportation ➔ Car Makes ➔ Chevrolet
Check for a vacuum leak
2007-08-22 01:04:03 · answer #1 · answered by startrektosnewenterpriselovethem 6 · 1⤊ 0⤋
If you don't have any codes set, you should be fairly certain that your electrical part of the fuel and emission systems are good. The first thing to do is to check all the spark plug wire connectors at the dist cap, coil, and all of the spark plugs. You have to check each one and do it one by one to be sure you don't cross wires. You are looking for signs of corrosion or carbon tracking. This can be rust, black, white, or streaked black colors. Any sign of this and you should replace all wires, dist cap and rotor, and even the coil as if the tower is corroded you cannot clean it enough and the corrosion will return. If you are sure that is okay, use a spray cleaner type stuff and spray it around the intake and TBI area. You are looking for a vacuum leak and the motor will react if you hit one. If that's okay, I would lift the TBI unit up and inspect the gasket and ultimately replace the gasket. These had a tendency to split and leak vacuum, but maybe yours has split and covered the IAC bore underneath it. If all that is okay, I would have an in-line fuel pressure gauge installed to see what the pressure is when running. You need around 12-15 psi to be good. It doesn't happen very often, but you could have a plugged strainer inside the tank that is restricting fuel flow as well. Good luck.
2007-08-22 07:46:49 · answer #2 · answered by Deano 7 · 0⤊ 0⤋
This could be any of a number of items. With modern fuel injected engines, there is much more to go wrong with the old carburetor engines.
First, the idle speed is controlled by an idle air control valve that is regulated by the engine management computer based on information provided from several sensors. The idle speed can not be manually adjusted.
From your description, the first thing I would look at is the Mass Airflow Sensor (MAF). This sensor can get dirty and send bad data to the computer. This can be easily and cheaply cleaned. Look for a product called CRC Mass Airflow Sensor Cleaner. This can be found at NAPA. It can most likely be found at other auto parts stores also. Follow the instructions on the can exactly or you could destroy the sensor making a cheap repair an expensive one. This problem is difficult to diagnose, but easy to fix. See the link below for the product description.
Don't throw any more parts at it until you are convinced you found the problem. There are way too many parts to change and way too much money to spend to just randomly throw parts at it, hoping to find the problem.
If this is what your mechanic is doing, maybe it's time to find a new mechanic. If you are doing this yourself, sometimes it's OK to admit that you are in over your head. Find a good reputable mechanic to assist you.
It appears these other items have already been looked at, but I would revisit them.
The problem could be with the fuel system. The fuel pressure regulator, dirty fuel injector(s), of dirty fuel pump.
It could be a bad oxygen sensor. This device is located in the exhaust near the engine. It reads the exhaust temperature. The information from this sensor is used to calculate the air / fuel mixture.
It could be a leaking vacuum line or bad vacuum diaphragm in a sensor. It could be a leaking intake manifold gasket.
The engine could simply be due a tune-up. If it is way overdue a tune-up, it will run poorly.
2007-08-22 01:27:29 · answer #3 · answered by Mad Jack 7 · 3⤊ 1⤋
Happened with our 2000 4.3L vortec blazer. If it almost feels like its flooding its probably the Mass Air Flow sensor (MAF) Took it to a few different mechanics and couldn't figure it out, tried lookin for anything spark or fuel untill we hit the MAF so try that and hopefully you'll save yourself the time and Money of everything else
2007-08-22 14:51:37 · answer #4 · answered by Anonymous · 1⤊ 0⤋
since you replaced the exaust you mentioned the O2 sensors. they usually throw a check engine light but they will cause poor running conditions. you only have one i believe on the 92 but you may have more on the 94. you dont hear any exaust leaks right? that would cause loss of power. i would replace the O2 sensors and if that dont work have a compression test done, as well as check the fuel pressure at the throttle body. good luck
2007-08-22 06:13:00 · answer #5 · answered by jonste415 2 · 0⤊ 0⤋
>I had the same type of trouble with my 1988 Silverado 305 V8...
LONG STORY short. Fuel pump was failing intermittently.
We to checked everything under the hood!!! seriously we checked everything. and come to find the FUEL PUMP was the problem.
We tested Fuel pressure and Fuel volume and both read fine...
Fuel Pump is most likely the problem.
BEST WISHES,
"/JOe
2007-08-22 22:29:08 · answer #6 · answered by "/ J()€ 5 · 0⤊ 0⤋
Cam timing sensor.
2015-08-23 08:26:25 · answer #7 · answered by Don 1 · 0⤊ 0⤋