Is my ecm bad? or not wired correctly - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums
 
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post #1 of 6 (permalink) Old 07-01-2019, 08:04 PM Thread Starter
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Is my ecm bad? or not wired correctly

I Have a 94 Pontiac formula LT1 and computer that I put into a 94 S10 truck. I made my own harness from the firebird harness and melded it into the truck harness. I'm not new to doing it this way I have done a few before. Hence my user name AstroIROC My first swap was 20 years ago when I put an IROC tuned port into my Astro van. The LT1 will fire and run. Has no power and wont rev unless you rev slowly. The computer shows no codes using my laptop and Scan9495. It does show info from the ECM, such as vin and vehicle information that is in the ECM. I have rechecked the pinouts from the ALDL to the ECM and they seem correct. Using the flash method of grounding the ALDL connector does not give me code 12 or any codes. could this possibly be a bad ECM? Thanks in advance for the help Astro IROC
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post #2 of 6 (permalink) Old 07-01-2019, 10:16 PM
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If you are judging whether the PCM is bad or not by whether it flashes codes, don't, because 94 and up PCMs don't do that. A 1993 and earlier ECM would. Scanning (which you are already doing with Scan9495) is how you retrieve codes. Could be something else you have overlooked.
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post #3 of 6 (permalink) Old 07-02-2019, 05:07 AM Thread Starter
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Thank you shoebox. Yes, I was basing that opinion on the PCM flashing codes. I'll unplug something and see if I can get it to set a code. Could be that the injectors are not flowing properly. They were clogged from setting a few years. I used a can of carb cleaner to pressure clean them as I triggered them with a battery. Is there a way to test them for correct flow?
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post #4 of 6 (permalink) Old 07-02-2019, 07:12 AM
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I suggest using scan9495 to do a running sensor scan. See what the sensor data is telling you. If you can't actually drive car, do the scan with it sitting. You should be able to run engine at various rpm to check data. You can still get good data which can lead you in the direction to fix problems.

Look for fuel trims that are not normal On a 94 pcm 128 fuel trim is what pcm is aiming for. Short term trims should go above and below the 128 mark regularly. But long term should be close to 128 mark if engine is fueled correctly. Clogged injectors, which will spray a stream instead of a well atomized spray pattern, will usually show up as rich mixture. But can show as lean mixture, if injectors are clogged enough.

If you haven't a clue as to what the sensor data is saying, PM me with your email address. I'll send you the pdf file of "scanner readings and what they mean". A note however; the fuel trims listed in the pdf are for a 96 & later obd2 car. Instead of 128 with trims going above & below, obd 2 uses 0 as the center line. Trims read + or - from 0 in obd 2 scans.

Just remember to use the 128 mark as perfect fuel trim. Anything above 128 is pcm adding fuel because of lean O2 reading. Anything below 128 is pcm subtracting fuel because of rich O2 reading.

Now to the O2 sensors. Bank 1 is driver side. Bank 2 is passenger side. O2 reading of 450 is the center mark. O2 reading above 450 indicates a rich mixture. Pcm will subtract fuel. O2 reading below 450 indicates a lean mixture. Pcm will add fuel. The O2 readings should be constantly changing. Jumping above and below the 450 mark.

If they don't move or change readings really slowly, O2 problem exists. Could be a problem with O2 itself, it's heater, wiring, grounds, or connectors. Other sensor data is important also. We will continue after you test for fuel trims and O2 data.

94 service manual has Pcm pin outs & wiring diagrams. If you don't have it, get @ www.mediafire.com/?40mfgeoe4ctti

Last edited by cocobolo95; 07-02-2019 at 07:21 AM.
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post #5 of 6 (permalink) Old 07-02-2019, 07:27 AM Thread Starter
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TY coco. I do have a 94 service manual, I used it extensively to wire the PCM and LT1 to the truck. The o2 sensors are new. I will take running sensor scan readings this weekend. Thank you for that valuable information. I shall learn!! I will also PM you
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post #6 of 6 (permalink) Old 07-05-2019, 07:31 AM Thread Starter
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UPDATE! after unplugging everything and replugging, the PCM is now showing codes. I tracked it down to a bad coil, it will now rev and has power, but is misfiring. its setting codes 16,41,42 intermittingly. So it looks like its an Opti or wiring issue. So Thanks for the help guys, looks like the PCM is ok. I will post new threads as I work through the codes. Thanks again
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