1998 v6 3.8 PCM/ECU issue need help

4833 Views 7 Replies 3 Participants Last post by wmburns, Apr 2, 2015

prtlock

Discussion Starter · Mar 29, 2015

Hi everyone, recently had trouble with my readiness test on my v6 for a CA smog and have narrowed down my problem to my PCM/ECU. I was hoping that someone would be kind enough to post a PCM pinout for a 1998 v6 3.8 or know of where I can find one, so I can tell which pins are continuously active and which ones are which. Any help would be appreciated! Thanks!

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Cem Sengul

· #2 · Mar 29, 2015

I'd love to help you out with this, but I do not know much about mechanics, are you saying your v6 mustang failed a smog test?

Are you running an offroad x pipe because I heard a lot of people in Cali who run offroad pipes just remove them and install factory pipes during emissions testing and re-install afterwards

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prtlock

Discussion Starter · #3 · Mar 30, 2015

No the issue was that my actual readiness tests were being erased after being set once i turned my car off. I got some advice that power to my PCM is being interrupted, so i checked my battery and its terminals and they are fine. So the problem has to be in my PCM. But the problem is that i do not know which pins are which on my PCM harness which is why ive been looking for a diagram that shows me.

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wmburns

· #4 · Mar 30, 2015 (Edited)

PCM C294 pin #55 wire color "Y" Feed from fuse PCM in the Battery Junction box.

http://www.allfordmustangs.com/forums/v6-tech/305656-96-mustang-fuse-help.html#2664116

FWWIW, are you aware that the fault could be in the battery itself? What is the condition of the grounds around the radiator core support? Are they clean and tight?

If this were my car, I would get an "add a fuse" and monitor voltage with a VOM to see if it ever drops below 9 Volts. It's very unusual for this to be a bad PCM.

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prtlock

Discussion Starter · #5 · Mar 31, 2015

Thanks for the info! I checked wire 55 (Y) but there was no power going to it when the engine was off. The only wire with constant power when the car was off was wire 70 (White/Red), so i was wondering if that is the only wire that feeds power to the PCM to keep the readiness tests alive or if there are others too?

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wmburns

· #6 · Mar 31, 2015

prtlock said:
The only wire with constant power when the car was off was wire 70 (White/Red), so i was wondering if that is the only wire that feeds power to the PCM to keep the readiness tests alive or if there are others too?

There are 104 pins on C294! Some are used and some not. There are "several" power leads for various reasons. In addition there are multiple grounds.

Pin #55 is labeled as "keep alive" power.

I also have doubts that you are counting the pins correctly. Because on the Ford service wiring diagrams C294 pin#70 is wire color W/O for the "Electronic air management".

To best answer your detailed question recommend getting a copy of the Ford service manual and wiring diagrams. If interested in getting a copy for yourself I maybe able to help. PM if interested.

Does this car run and drive generally well? Are there any other DTC codes? Do the readiness tests EVER complete?

I'm not certain this problem is a bad PCM. Seems more likely to me to be a loose connection or a bad battery. Why? Because if the keep alive power were totally out, the idle would be total crap because the PCM could never "learn" anything. This tells me that the power interruption is intermittent.

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prtlock

Discussion Starter · #7 · Apr 1, 2015

wmburns said:
There are 104 pins on C294! Some are used and some not. There are "several" power leads for various reasons. In addition there are multiple grounds.

Pin #55 is labeled as "keep alive" power.

I also have doubts that you are counting the pins correctly. Because on the Ford service wiring diagrams C294 pin#70 is wire color W/O for the "Electronic air management".

To best answer your detailed question recommend getting a copy of the Ford service manual and wiring diagrams. If interested in getting a copy for yourself I maybe able to help. PM if interested.

Does this car run and drive generally well? Are there any other DTC codes? Do the readiness tests EVER complete?

I'm not certain this problem is a bad PCM. Seems more likely to me to be a loose connection or a bad battery. Why? Because if the keep alive power were totally out, the idle would be total crap because the PCM could never "learn" anything. This tells me that the power interruption is intermittent.

The car actually runs great and some of the readiness tests do set after 20 miles or so but still when the engine is shut off they are erased. After i scan it when I attempt to set them though The codes P1132 & P1131 show up, which says "lack of HO2S11 switch, Sensor indicates Lean/rich" (depending on the code). I thought maybe this could have something to do with this issue, such as the initial problem that caused a short in the wiring or vice-versa. Any thoughts?

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wmburns

· #8 · Apr 2, 2015

prtlock said:
The car actually runs great and some of the readiness tests do set after 20 miles or so but still when the engine is shut off they are erased. After i scan it when I attempt to set them though The codes P1132 & P1131 show up, which says "lack of HO2S11 switch, Sensor indicates Lean/rich" (depending on the code). I thought maybe this could have something to do with this issue, such as the initial problem that caused a short in the wiring or vice-versa. Any thoughts?

FWIIW, the readiness test will NEVER complete IF there's an outstanding DTC. This is by design.

Fix the outstanding DTC codes and try again.

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