I have serched the forum to no avail.. So here goes.. My 94 suburban is on the 3rd computer in less than a year.. I have triple checked all the grounds and added new ones. I have tried computers from the dealership and parts stores. They last for couple of months and then they go wacko.. and each time the problems it causes are different. I have had the wiring harness tested and it was ok. Im at a total loss.

 

define, "wacko"

 

I didnt replace the first computer.. It had a reman deal computer when i got it but it was only a couple months old.. When it went bad the tranny stopped shifting correctly and replace the tranny and it still did it and put a new computer in it and that fixed it.. then bout 3 months later it started running sloppy no power kinda stuff.. warranty the computer and it ran fine for for 4 or 5 months.. now its mesing with the emisions system and put it on a scanner last nite and it says that i have 230* of timing, the CTS was reading -30 (im in TX and it wasnt that cold last nite) knock sensor was on the entired time detecting knocks..the tps was getting a signal into the computer but not out and read a steady 1.4 V no matter where the throttle was. and after driving for awhile then restarting it goes into "limp mode" ..

 

ok, are you getting a true 5v signal to your map and tps?

 

i am to the tps.. dont remember bout the map

 

Well I swapped out the computer and presto my truck runs good again.. But for how long?????

 

I would check the charging system & see if it is overcharging. Do you have any extra electrical accessorys that might cause a high voltage spike when they are switched off. Offroad lights, big amp, ect ect ect ......

 

take the computer apart and look for fried out parts, that will narrow it down if so.

 

Its stock inside and out.. still has the working cassette player in it.. only thing it has thats not stock is a vortec cam and roller tip rockers..and i dont hardlly thing thats the cause of my problems.. and i just almost litterally replace everthing when i did the motor 30k ago.. i replaced ALL the sensors cept the charcoal canister solenoid sensor..beats me I am clueless on this one. But its running really good once again.

 

A noisy alternator might putting ac spikes on12V bus which may be causing unexplained ECM failures. Missing ground straps could also be contributing to increased failure rates.

//RF

 

Next time the computer fries, take it out and pull the case apart and check the inside. There are large TVSS as well as reverse-input protection diodes that can be cooked after a while if they are forced to dissipate an excess ammount of power (ie, bad alternator, starter generating large spikes, etc.). The ground straps are also important. Check them all at the rear of the engine and the body, especially the large one from the battery. If one has come off, or is heavily corroded, it will need to be replaced. The same also goes for all the 12V leads from and to the main power block and starter. Anything that causes intermittent losses of power will cause spikes, which can kill the PCM.

There are other things that can kill teh computer as well, such as sensors pulling too much power, which can force the voltage regulator to dissipate an excess ammount of heat. One suspect would be the TV solenoid in the transmission. IIRC, thats fed with +12 V modulated by the PCM, and can pull quite a bit of current if it develops and internal short.

Pull the PCM down, but leave it hooked up, and run the truck. The PCMs case should get warm, but not hot. If the case is hot to the touch, then there is something pulling too much current thru the PCM.