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#1
05-20-2007, 09:31 PM
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ecm or not
1991 grand prix 3.4 duel o/h cam ecm code 33 (not reading IAC), won't idle down 2500 warm or cold changed IAC , no change suspected ecm changed with one from local salv yd, got new problems, code 35 (not reading map sensor), but IAC responding ok,idles good 900 but runs rich no power, tried changing eproms between ecms, problem codes follow eproms. I am at loss as to what the problem really is, put original ecm with org eprom runs good but won't idle down. ecm serv #16149396
Last edited by gtodale; 05-21-2007 at 09:00 AM. 
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#2
05-21-2007, 08:56 AM
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Re: ecm or not
First, your code definitions are not correct
Code 33: MAP sensor signal voltage was too high (low vacuum) for 5 seconds when throttle opening was under 6%. Code 35: Idle speed was over 200 RPM outside the desired engine speed commanded by the ECM for 50 second second: the ecm service# you gave (16149363) doesn't show as a good number I would bet your issues are an intake gasket vacuum leak. A vacuum leak will cause both a low vacuum reading and a high idle, so both codes you're getting could be tripped by the leak. Since you've used different e-proms with different calibraitons, each could come up with different codes depending on how they are programmed. Also, if the ECM you installed is not from a 3.4X, it will not work, as the 3.4X and 3.1's use different ECM's as well as e-proms. It appears 91-93's with the 3.4X all use the same ECM.
__________________
 Still waiting for the "good old days" I'll get to bore my future grandchildren with!
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#4
05-21-2007, 09:32 AM
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Re: ecm or not
The problem with using a used ECM from these cars is the fact that they are mounted under the hood, and exposed to the elements. The chances of getting a good one is slim at best.
Another thing that can cause low intake vacuum is a timing belt. If the belt is stretched, it can retard the timing to the point of low vacuum. These belts are a @%$# to change, and are supposed to be done every 60k miles or so. It's not impossible that the new gasket is leaking due to pits in the castings, or if you didn't use loc-tite on the bolts, they may have loosened back up. You need to start the engine and spray WD-40 (or something similar) along the seam of the intake and block/heads and see if the idle changes. If it does, you have a gasket vacuum leak.
__________________
Still waiting for the "good old days" I'll get to bore my future grandchildren with!
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#5
05-21-2007, 11:43 AM
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Re: ecm or not
I have sprayed wd-40 everyware around motor no changes, timing belt changed recently, all timing marks line up like the book says. all mating serfaces on intake looked good (no pits ect.) have checked wiring harness looks good metered IAC at grey connector by ECM got readings Chilton book says it should have. Replaced MAP sensor, throttle pos. sensor. Stil no luck motor will not idle below 2500. My first thought was vacum leak found one hose split so I changed it and several others I didn't like the looks of. thanks for the replys and any help you can offer...
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#6
05-23-2007, 07:50 PM
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Re: ecm or not
to richtazz;
You were correct on it being vacum leak, intake gasket & pcv hose(where it connects to block under intake)WD-40 never made a difference, but when I placed unlit accelitine torch by intake it became real obvious, car idles smooth and like it is supposed to. Thanks again for the feedback it did help..... gtodale Last edited by gtodale; 05-23-2007 at 08:29 PM.
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