Dead Computer?

1988 Chevy C1500
4.3L V-6

I'm experiencing the same bogging down and stalling out stated in many other threads. However, I have done my research and after replacing nearly every component under the hood, it's come down to this fact. My coolant temperature switch, normally should be at 5 volts, is only at a mere 1 volt !! This is clearly the cause of my computer wanting to modify the air-gas mixture and starves the engine into setting off a Code 44 (Oxygen Sensor). Once the Service Engine Light comes on, she will sputter and die at the next traffic light. The sensor is new and there is a proper ground.

Has my computer decided to up and die or is there a way to restore the 5 volts back into the coolant temperature switch?

UPDATE:

Today I almost couldn't drive my truck to work, so I decided enough was enough, and I unplugged the temperature switch....low and behold the engine jumped to life and ran like a champ again! I tested the voltage going thru the wires again and found it to be at 5 volts solid!

Could my entire problem be a faulty temperature switch that was brand new out of the box???

you could use an ohm meter to check the switch. Check the resistance reading when cold and then check it as it warms up and make sure it changes

1988 Chevy C1500
4.3L V-6

I'm experiencing the same bogging down and stalling out stated in many other threads. However, I have done my research and after replacing nearly every component under the hood, it's come down to this fact. My coolant temperature switch, normally should be at 5 volts, is only at a mere 1 volt !! This is clearly the cause of my computer wanting to modify the air-gas mixture and starves the engine into setting off a Code 44 (Oxygen Sensor). Once the Service Engine Light comes on, she will sputter and die at the next traffic light. The sensor is new and there is a proper ground.

Has my computer decided to up and die or is there a way to restore the 5 volts back into the coolant temperature switch?

UPDATE:

Today I almost couldn't drive my truck to work, so I decided enough was enough, and I unplugged the temperature switch....low and behold the engine jumped to life and ran like a champ again! I tested the voltage going thru the wires again and found it to be at 5 volts solid!

Could my entire problem be a faulty temperature switch that was brand new out of the box???


UPDATE 2:

I took a voltage/ohms meter and checked the resistance on the coolant temperature switch, both cold and hot and wasn't satisfied with the readings, so I returned the switch to the store for a new one. Ran good for a while and now it's back to running like "poop-on-a-stick".

So I bought a new computer/ECM and PROM for my truck and I am going to switch them out and see if that works. (Wish me luck)

However, someone told me that it's the distributor! He said the magnets in it are shot and the computer cannot advance the timing approprietly.

Does this sound like it "holds-water" for anyone???

Hey,
I am having the exact same problem as you with the exact same engine. I was wondering where you found the temperature switch on your truck. I figure it is worth a try since I cant find anything else that seems to work. Detailed instructions and or pictures would be greatly appreciated.
Thanks,
Jimmy Dager

Hey,
I am having the exact same problem as you with the exact same engine. I was wondering where you found the temperature switch on your truck. I figure it is worth a try since I cant find anything else that seems to work. Detailed instructions and or pictures would be greatly appreciated.
Thanks,
Jimmy Dager

Right on top of the manifold next to the thermostat. Check out your Haynes or Chilton's manual for your truck. It's fully illustrated.

Good luck.

yes you can get a bad sencer strate from the maker. worse news is thay pop them out by the thousands so you can repeat the same effect a few times. check the codes on the box if thay are from the same lot there could be a manufactor problem in the sencer.

it could also be a probem with the voltage feeding the sencer. there could be a grounding problem in the system. when you unplug the sencer you will get the 5 volts back. but the system will try to ground thru the sencer when pluged in. if its a ground problem you will get all kinds of strange stuff happing.

the only way to realy be shure is to get a diagram and check all the grounds. add a few if needed. i have found a lot of companys will try to save a penny by not running enuff ground wires. big problems will start showing up latter when thay get durty.

The coolant temp sensor electrical connections cause a problem on GMs when they wear. Try using another plug the male end that plugs into the sensor. It will cause the same problem you discribe.

Hey,
It ended up being a fried ignition module. If anyone else is having a problem similar to mine, I would deffnitly suggest taking this off and taking it to an auto store and having it tested. It is free and really easy for you to do and could save you hundreds in parts if you just guess and replace parts or take it to a shop. On my truck and similar years, it is located right under the distributer cap. It is held down with two little bolts and has three wire harnesses going to it. just take this piece off and have it tested, might save you lots of time and headache. Thanks for everyones help.
Jimmy Dager

Good to hear it Jimmy!

One down and one to go.....

UPDATE: 3

I'm still at it and I'm making progress.
I've replaced EVERY component under the hood, including coil and distributor.
I've checked for vacuum leaks and found none.
I've checked for shorts and found none.

However, I just learned today that the Throttle Body injectors have a final filter screen inside each one!!!
That makes a fuel filter under the truck on the frame, a second at the inlet of the Throttle Body and a final one inside each injector, for a total of 3 inline filters!!!

I'm going in! Wish me luck!

UPDATE: 3

I'm still at it and I'm making progress.
I've replaced EVERY component under the hood, including coil and distributor.
I've checked for vacuum leaks and found none.
I've checked for shorts and found none.

However, I just learned today that the Throttle Body injectors have a final filter screen inside each one!!!
That makes a fuel filter under the truck on the frame, a second at the inlet of the Throttle Body and a final one inside each injector, for a total of 3 inline filters!!!

I'm going in! Wish me luck!

A word of advice. Don't start doing micro surgery on the injectors, the chance of that inline screen being a problem on the individual is very slim. If there clogged, high pressure purge will do the job. And the issue of the solid state ignition module metioned by Jimmy, I never had one or heard of one that went bad gradually. They usally stop you dead in the water when they fail.

The chevy computer is designed to have a limp home mode when the ignition module fails. The truck will run like crap (richer) but will get you home. Ford and Dodge will leave you on the side of the road when they fail.

Perhaps I wasn't very clear about the distributor....I bought a remanufactured one from Advanced Auto Parts. The ignition module, along with the rest of the distributor is new.

Thank you for your input, though. :-)

Dude
when you unpluged the coolant temp sensor and the engine ran good that would seem to lead you to a ground or wiring problem. Lots of waisted money on parts you dont need

Well.....today I replaced the filters in the injectors and WOW! What a difference! Although the injector filter screens both looked reasonably good, a new set made a world of difference. Now I can see the injectors spraying fuel not just dribbling a mist like earlier.

I hope this is the solution....Check Engine light came on once, probably due to habit(heheh), but the light quickly turned itself off and has stayed off for the rest of the day. Starts and take offs are not a problem anymore.

I hope it stays this way. Thanks to everyone for thier input.

The Bad: It's back to running like CRAP!

The Good: The shop foreman at the Chevy dealer is running out of ideas!
Basically, he's narrowed it down for me to one of two issues.

A. The fuel pressure regulator is sticking and needs to be replaced.

B. Unbelievably, inside the gas tank, the little cotton sock on the end of the pick up tube on the fuel pump is being partially sucked up into the pick up tube.

The Ugly: I'm beginning to believe it's choice B. Sigh. I'm going to start another thread in order to explore this option futher.

The Bad: It's back to running like CRAP!

The Good: The shop foreman at the Chevy dealer is running out of ideas!
Basically, he's narrowed it down for me to one of two issues.

A. The fuel pressure regulator is sticking and needs to be replaced.

B. Unbelievably, inside the gas tank, the little cotton sock on the end of the pick up tube on the fuel pump is being partially sucked up into the pick up tube.

The Ugly: I'm beginning to believe it's choice B. Sigh. I'm going to start another thread in order to explore this option futher.

There's no cotton sock on the fuel pump suction tube, Its a mesh plastic of some type (maybe mylar). It's fine wooven like the screens you find in replaceable filter element type fuel filters.

i have k1500 with a 5.7 tbi the truck will start run for a bit then shutdown at first i thought it was a fuel problem replaced filter and pump put a more psi pump thinking this may work it still dies after a few minutes of runnin whaty else can it be im going and check the dist see what happens then im going to try the filter in the injector

Grim0404-your problem is usually the ignition module and pickup coil in the distributer--usually good idea to relace entire distributer when this happens and you have over 100,000 miles on the vehicle- or you could just replace the pickup coil and module.

hey thanx you where right i ran diagnostic and ur right order one came diffective turned back in put the new one in perfect thanx for ur help

I'm glad it worked out for you. I've owned and worked on enough chevy's that about everything that could happen has happened to me.

Sorry for the delay(years).
Thanks for all your help.
I forgot to post the solution.
It was the wires leading to the fuel injectors.
They were crushed by the air filter housing and limited the amount of current.
There were only 2 thin strands of copper wire left in tact on one wire!
The other wasn't much better.
Cut the wires and spliced them back together.
Ran like a champ again.

Unfortunately, she died in the summer of 2010 at the ripe old age of 22.
The engine went the same time the tranny went.
Perfect timing.

Long live my "new" 1997 Chevy K-1500 4x4 !!!

Well.....today I replaced the filters in the injectors and WOW! What a difference! Although the injector filter screens both looked reasonably good, a new set made a world of difference. Now I can see the injectors spraying fuel not just dribbling a mist like earlier.
Where did you get the new screens?

Part number?