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Old 02-20-2001, 01:26 PM   #1
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How can i test if my ecm is fried?

I think i may have fried my ecm...i sure hope not but i just want to rule it out, because if i did fry my ecm im making the switch to tpi now. My computer reads codes off, but i dont know how else to tell if its working properly. Thanks
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Old 02-20-2001, 01:55 PM   #2
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One way to tell, run the engine, and hit the ecm, if your engine skips a beat, its bad.

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Old 02-20-2001, 03:50 PM   #3
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i'd say if you can read codes it's a good sign it's working.

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Old 02-20-2001, 06:06 PM   #4
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Ok well first off, i cant run the car...thats the whole reason im trying to find out if the ecm is fried. But i can read error codes so im happy about that. Well even though i wanted to switch to tpi i dont have the money right now so its probably good its not fried Click the image to open in full size.
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Old 02-20-2001, 06:59 PM   #5
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I've seen tons of bad ECM's that were bad and would still read codes for other things.

Surprisingly enough I have also seen the ECM-beating method described above work. Smack the thing hard enough and the car would work great for a while. The story I've heard is that the circuit boards develop cracks from heat/cold and vibration.
I have never seen an ECM go bad and actually tell you (via code) that it was bad.

If I suspected one, the first thing I would do is borrow another just like it.

good luck
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Old 02-20-2001, 07:43 PM   #6
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Click the image to open in full size. Ok well if thats the case...anybody around the san fransisco bay area have a 91 305 TBI they wanna bring by my house and let me try it out?? Click the image to open in full size. cmon guys...itll be fun.
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Old 02-20-2001, 08:34 PM   #7
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Josh,

One quick check is to watch the MIL lamp before you turn the key. Insert the key and turn it to RUN, not START. The MIL lamp should turn on briefly, then off briefly, then back on continuously. This flash alerts you that the ECM has passed power up diagnostics and has a valid PROM and/or CALPK installed. If you don't get teh flash, there is something wrong with the ECM.

Another thing you can do is to insert a 3,900 ohm resistor between terminals 'A' and 'B' of the ALDL. This forces the ECM into Backup Fuel / Factory Diagnostics Mode, or Mode 1. This will force the ECM to use the lookup tables in the PROM for base fuel and spark curves.

You can try to force Mode 2, which is an I/O excersize. If the resistor is in place, and the transmission is in PARK/NEUTRAL or the clutch is depressed when teh key is turned to RUN, you should be able to force Mode 2. This will force the ECM to scan for loads and inputs, then excersize the discrete outputs at about a 32Hz rate. You shoudl hear the fuel pump realy buzzing rapidly, then teh IAC stepping, then the injectors clicking open and shut, etc. If this is working, the ECM shoudl at least be able to operate the engine in Backup Fuel (Limp Home) mode. If this doesn't work, your ECM may have an I/O problem.

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Old 02-20-2001, 08:50 PM   #8
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Josh,

If you find that the ECM is damaged, check this link from a familiar name:

http://cgi.ebay.com/ebaymotors/aw-cg...item=562535690

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Old 02-20-2001, 08:52 PM   #9
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Man I am truly impressed. Vader is the man and knows his ECM's.
much better tests than beating on the thing, though the beating is probably more fun.
The only time my ECM ever made me smile was when it hit the bottom of my trashcan.
Click the image to open in full size.

hope you find your problem.
If you can't find it and it becomes too expensive or puts you into some form of therapy, then there is always the old carburetor. Six years of it was enough for me and I admit I had to give up. Difference was I didn't have connections to knowledgable people back then like you do now with Vader and others.
(ok I feel better now... breathe)
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Old 02-21-2001, 06:20 PM   #10
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Hi, I am having a similar problem, could you explain how to put the ecm in that other mode or whatever. What is MIL, and ALDL. And where are terminals A and B. Thanks
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Old 02-21-2001, 06:20 PM
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