CEL Light on and off

[green_grenade]

Guys.
Here is my question. I can be driving along and the CEL light will come on. It usually does it when I am at a constant speed for a while. Nothing changes in the way it is running. Then it will go off. I can not figure out what the heck would be causing it. It usually will shut off before I can take it and have it read. Here is a list of the new parts that it all has.

New TPS
New IAC
New 02 sensor
New fuel filter
New Engine Coolant sensor


Like I said it does not change the way it runs at all. Just the light comes on for some reason. Two things I cant stand. Lights on and leaks and I am fighting both. LOL

[Kudzupatch]

Have the codes checked anyway, the computer stores some (all?) codes. Throwing parts at it in hopes of finding it is just wasting money.

[95 S_Trucker]

What's the year make and model? OBD II will store codes when the light is not illuminated. You can flash the codes yourself on an OBD I system. No need to wait to plug in a scanner.

[green_grenade]

Originally Posted by Kudzupatch

Have the codes checked anyway, the computer stores some (all?) codes. Throwing parts at it in hopes of finding it is just wasting money.

No No, these are all the parts that have had to be replaced along the way in the last month.

Originally Posted by 95 S_Trucker

What's the year make and model? OBD II will store codes when the light is not illuminated. You can flash the codes yourself on an OBD I system. No need to wait to plug in a scanner.

It is a 89 Chevy 2500. 5.7L. I will have to mess with flash the codes myself then. It is so off and on when it decides to do it. That is the weird thing.

[95 S_Trucker]

As soon as the light comes on, pull over. Don't shut the truck off. Grab a paper clip or jumper and get the code.

[Boog]

Egr related ill bet.

[green_grenade]

Originally Posted by Boog

Egr related ill bet.

So I am seeing that the EGR valves are very picky and you need to get the same one to match the numbers on the one you have, Is that true?

[ChevyTech]

The ECM in a 1989 has memory. It can store multiple codes at the same time.

The light does not need to be illuminated to read the trouble code/codes that are stored in the system.

Because your truck is a 2500, it may have a different EGR system then most the 1500 trucks.

There are multiple types of EGR valves. You need to know which kind of EGR it has.

TBI trucks are generally Negative back pressure EGR or Port EGR systems, except California emission 4.3 TBI trucks had Linear EGR valves.

The negative back-pressure EGR systems are very about the EGR valve you use.

I have posted many times on these topics and you can find those posts with a search.

[green_grenade]

Originally Posted by ChevyTech

The ECM in a 1989 has memory. It can store multiple codes at the same time.

The light does not need to be illuminated to read the trouble code/codes that are stored in the system.

Because your truck is a 2500, it may have a different EGR system then most the 1500 trucks.

There are multiple types of EGR valves. You need to know which kind of EGR it has.

TBI trucks are generally Negative back pressure EGR or Port EGR systems, except California emission 4.3 TBI trucks had Linear EGR valves.

The negative back-pressure EGR systems are very about the EGR valve you use.

I have posted many times on these topics and you can find those posts with a search.

Thank you sir. I will start doing some digging on this item now.