93 chev k2500 suburb 7.4 tbi

new motor ,map,tps,o2,speed sensor,shift solinoids, new dist.cold start engine, no cold loop,(idle only about 750)engine light on,(code 42)holds on to shift points,no misses, go for a drive, stop, turn off, restart
engine, idles normal but begines to miss with tach spike not neccasarily corrisponding to spike,(like voltage spike, from 750 to 2000 on tach)no engine light,miss is severe enough to almost kill engine (very sharp misses,like voltage from distributor dropping off),turn off, restart after ten minutes engine light back on, spike gone, smooth idle,no misses. this has to be the ecm dosnt it. my gm mechanic doesnt even know what it is.
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superbee wrote:

    Start with going to someone that has a OBD1 Scan Tool. The scan tool will show sensor readings not just the trouble codes. Charles
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i have a mechanic that works at a dealer with the scanner, hes comming over on saturday but last time we scanned it ther were questions on exactly what all the different dc voltages(.6 to 5)should or should not be. trying to find someone who can actually troubleshoot these readings is like finding a needle in a haystack. i dont think the tool tells you what the different voltages should be.i guess ill try to write the readings down and post them so i can get one of you F1 mechanics out there to tell me what they mean. SUPERBEE
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while most guys who do this for a living most likely know most of the acceptable ranges for the various sensors.... the shop manual for that specific truck lists all that type of information. Most of the time if the sensor is out of range it will set some type of code in the ECM.
wrote:

Elbert snipped-for-privacy@me.com
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its is storing the code 42,shouldnt the check engine light stay on. A code is a code why does the light go off on the very next start and start missing and getting a volt spike in the tach. You would think this could possibly be loose or pinched wiring, but the same day engine will run fine with the light on, it just holds on to shifts,(shifts at 600 to 1000 rpm over normal shift points). When i here you say most of the time it stores some kind of code that sounds like chevrolet purposful engineering like when you by 70k mile warranty and the trans goes by-by at60k. i really like the truck and im a chevy guy,but im ready to yank all this tbi crap and go carburated,somthing i can service. SUPERBEE
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wrote:

A TBI setup is very dependable....I have a 92 K1500 5.7 TBI. Find someone that knows what they are doing and can work on a computer controlled vehicle.
Even though I played mechanic many years ago... in the past you had both hard and soft codes. A hard code is set in the ECM memory and will continually display through a scanner or by checking the codes manually with something like a paper clip and watching the check engine light flash (on certain year model GM vehicles). A soft code will "trigger" the check engine light but will not be saved in the memory of the ECM.
Trust me... A TBI runs very well compared to a carb setup. You need to bite the bullet and carry it to a shop of your choice that does this type of work. If all the electronic sensors and so forth are "new" to you...then its really not worth messing with the truck at home.
I've had very few things go wrong with my truck that were "electronic" or related to the ECM / sensors.
If the check engine light comes on and for that matter comes on and stays on you need to get it fixed. It still may run or perform adequately, but something is wrong that needs to be most likely replaced.
Often times you need to rule out other issues before you blame the electronics. Vaccum leaks, gasket failure....the basic stuff.
I think Code 42 is EST (Electronic Spark Timing).
To work on these type trucks you need some type of shop manual and a basic understanding of how the sensors work and the acceptable ranges. The shop manual will walk you through a troubleshooting tree diagram for many of the codes, that will assist you in determing the problem.
I know on some of these trucks when they get a lot of miles on them the distributor needs to be replaced....but once again I would carry the truck to a shop that is knowledgeable on this type of work (which would be your local GM shop or any mainstream auto repair shop).
While TBI engines are not great about performance mods, they are very dependable and for the most part perform adequately. Of course I wish mine had about 150 more HP... ----------- Elbert snipped-for-privacy@me.com
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