Question-------------------------
Followup To the one thing that i have done last week was put new plugs.cables.distributor and o2 sensor.one thing that i noticed is that the truck always seems to idle high,never drops no matter how warm the motor is.egr solenoid was replaced and the egr was checked for freezing and its not.occasionaly the egr code will flash at h'wy speeds,but once you shut the motor off the light stays off.if its the map or throttle sensor why dont i get a trouble code?
Thanks again
Question -
Hi'
I have a question regarding my 1988 Chevy S-10 2*4 with a 2.8 litre motor.The car also is an ex California emission vehicle and has a 700r4 O.T. transmission.The problem is that anytime i go up hill the truck slows down to 20 mph will shift pick up 5 more miles and right away shift down and go 20 mph.This happens over and over until i reach the top of the incline and than the car shifts to its regular speeds.No matter how fast i approach the incline the truck wont let me keep the speed and will drop me to 20 mph.What i noticed that if the temp. gauge reads below 210 degrees the truck will keep me in any speed until the temp. reaches 210 and the truck will drop to only 20 mph. What do you think the problem is? thank you.
Answer -
Hello Tom,
You did a good job by noticing that bit of info.
That means that it is running in Open Loop while cold, and therefore not using sensor readings to make adjustments to the fuel mix.
When it reaches operating temperature, it switches to closed loop, and uses O2 sensor, throttle position sensor, MAP(vacuum) sensor, mass airflow sensor, etc.
You have eliminated fuel pump, fuel filter, plugs, plug wires, coil pack, distributor, and plugged exhaust system, since those would be problems when cold also.
The EGR valve is not stuck open, and vacuum leaks are not the problem for the same reason.
Now, the computer(ECM) could be opening the EGR valve, but I doubt it.
I would check,(Now don't just run out and buy one...check them with a manual and ohm meter), first the throttle position sensor, then the MAP sensor(vacuum, ie manifold absolute pressure),then oxygen sensor.
The injectors are fine, they are just not being told to inject when it warms up.
I doubt the ECM itself is the problem, but that is a possibility also.
The temperature sensor is probably fine, since it is causing the change at the correct time.
Seems like you could disconnect the temp sensor, and keep it in open loop forever, doesn't it? Hmmmm. Wonder how often that is done.
It is a different temp sensor than the temp gauge sender if you have a gauge.
Van
AnswerHi Tom,
A dirty fuel filter or low fuel pressure could explain the power loss, and there is no code for that, at least back in that model.
But that wouldn't explain why it runs good when cold. That possible problem should have been eliminated just by that fact.
It is possible for the throttle position sensor to be returning a signal, which would prevent a code from being set, and yet the signal could be incorrect, which could cause the lack of power.
Van
