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Can Stock Computer Chips Go Bad

Discussion in 'The Garage' started by blazerguy 90, Oct 23, 2005.

  1. blazerguy 90

    blazerguy 90 1/2 ton status

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    On 87 to 90 350 TBI trucks are the stock chips in the computer the same ?, I have a miss im trying to track down, the miss only seems happens after my Blazer goes into closed loop, so im thinking its something in the computer. my fuel pump is new, the 02 sensor is new, the coil and ignition module is new, the egr valve is good. on some of the other forums I frequent ive read that this can happen and has happened to some other people ive talked to. I have a stock computer chip from an 87 chevy truck (350 TBI) that I can try, will it work in my 90 Blazer ?. :confused:
     
  2. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    If it's electrical, it can go bad. The ECM would actually be the thing to replace. Check all sensors, make sure they're getting base voltage from the ECM. Should be around 5 volts.
     
  3. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    You sure the EGR is good? How did you test it? BTW, ECM's are different on some of the trucks for emissions and other factors. Make sure you get one that has the same setup...if that's the problem.
     
  4. blazerguy 90

    blazerguy 90 1/2 ton status

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    I pulled the egr and cleaned it, then used a vacuum pump to draw some vacuum on it and it would hold vacuum, no leaks.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    99% of all problems blamed on the ECM/PROM, are not.

    That should be the very last component to look at when diagnosing the system. If the check engine light comes on in run/engine off, and it flashes a code 12 when you pull them, the ECM is more than likely good. But in any case, that is still an unlikely problem.

    The system is using the PROM to run open loop as well as closed loop, so the problem would be the ECM/PROM why? :)
     
  6. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    If anything, the prom is the part that is used the most during open loop. Once it goes into closed loop, it uses sensory information to deviate from the defined prom values, to get the engine running its best. I'd be checking all my sensors / actuators that come into play after the truck enters closed loop :)
     
  7. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    Not sure if this was meant for me??

    If so, best to replace both for the reason that if the actual failure is on the board and the PROM fried, you really want to buy a new PROM...to have it fry again? Hell, we have to replace ECM's because the fan hub won't engage.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    No, not directed at you, but my question to you then is, if you have an intermittent problem, (or miss) is your first thought to blame the ECM or PROM? You say "fry", if something goes bad (such as the injector drivers) the problem is not going to be intermittent or sporadic. Agreed?

    What I'm saying is that statistically speaking, the ECM and PROM are nowhere near likely as a culprit, and money and time is better spent diagnosing problems than guessing and throwing money at them.
     
  9. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    If it totally blows, more than likely.....but that's also why I said to check base voltage. If an ECM took a dump, it more than likely won't be sending that to every sensor it looks at.

    It wouldn't be my first place to look, but I've seen stranger things happen. I've seen them crap out without any codes, even better, when they still light the CEL on start up check.
     
  10. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    My truck did that to me too -- turned the ses on, and even flashed code 12, but my prom was junk.
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    Did it run with a miss and that was the only problem?
     
  12. blazerguy 90

    blazerguy 90 1/2 ton status

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    dyeager535

    when I start my Blazer up when its cold it runs great, but you can tell when it goes into closed loop because it starts to miss and the idle will go up and down a little, ive checked everthing I can think of, am I missing something ?, is there something I need to check that I havn`t ?, on another website that I go to there was a guy having the same problem, when he finally got it fixed it turned out to be a bad maf circuit in the prom, thats why im asking if the computer could be my problem.
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    As a for instance...every possible indicator there was told me that my ECM was bad at one point. I checked the connector at the ECM on a whim, and the MAF wire connector was loose and not making contact consistently.

    One of the major sensors brought into play by closed loop is the O2 sensor. Go to autozone, have them throw their scanner on it, and see what the O2 is doing. At the same time you can probably look at all the other sensors and perhaps see whats going on. Do research on what kind of values you should see for all of the sensors with a scanner, and you should be way ahead. :)
     
  14. blazerguy 90

    blazerguy 90 1/2 ton status

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    I don`t know if this makes a difference or not, but when I got my Blazer I changed the stock 02 sensor to a 3 wire heated 02 sensor.
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    it might, what brand? :)

    On the same note, can you trace the problem to before or after you swapped the O2 sensor? I'm guessing after.
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    Yes, I made that up. Every time an ECM is blamed and replaced, it's the real cause. Just like carburetors. When a vehicle that is carbureted doesn't run right, it's the carb.

    After ruling everything else out, replace the ECM. Boy that doesn't sound like "blame the ECM last" or anything of that sort.

    Odd that someone that just joined takes their two first posts to *try* and make me look like an ass. Nice try Fierospeeder, you think you will actually ever grow up? How long has it been, 6 months? Not like you have any boards you can go to anymore though I guess. You obviously don't have enough work to keep your mind focused on something other than another male.
     
  17. blazerguy 90

    blazerguy 90 1/2 ton status

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    Am I missing something here ?, who is Fierospeeder ???.
     
  18. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    :confused: Ditto..missing something here...
     
  19. dyeager535

    dyeager535 1 ton status Premium Member

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    Guy that does nothing but attempt to harass me. Already banned, comes back on at various times under new lusernames (this time "joemillionaire") and gets promptly booted again. Mods went in and deleted his posts to this and another thread, but left my sole response in this one.
     
  20. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    Ahhh, ok. Wow, some people really have no lives....
     

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