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It just never ends. 98 Mazda 626 GF 2L. It cranks great, but there's no spark at any of the plugs and I can't connect to the ECU. Coil pack is new, I've driven it maybe five times since I replaced it. I've also been having a low voltage from the alternator for a while, about 13.75v, but can't so far find any problem with the alternator.

I'm kinda freakin out, thinking maybe the ECU has given up the ghost.

This is somewhere between a rant and wanting to have someone tell me that's it's likely not an ECU problem... arg!!!

I know I need to check the pins coming into the coil from the ecu to see if a signal is coming in or not... just afraid of what the results will be...

EDIT May 31st, 2016

So I go out today to try and make some progress on this problem, and what happens? The car starts right up and I am able to connect to the ECU / PCM with no problem.

When I connected I got a 0113 DTC. I had this error a few months ago, but I cleared it and it didn't come back. This time I cleared it, ran a KOEO test and it came back. Cleared it and ran a KOER test and it came back. This is the list of causes ( also for a few other DTCs ):

enter image description here

So I went to look at the IAT connector and found this:

enter image description here

The wire seems to be made of four strands, two of which are broken and probably making intermittent contact.

I'm going to go look for a good connector from a junk yard and splice it in, however, I'm not sure this is really the source of the problem for a few reasons. If I completely disconnect the IAT sensor the car starts up just fine, so I don't think that frayed wire would cause an intermittent ECU problem, would it? Looking at "Cranks Normally But Will Not Start" in the troubleshooting section of the WSM it does mention a few problems where a short to ground can be a cause, like with VREF and an "IG" line from the DLC, but I don't have a short to ground here, I've got a partial open.

The other thing that's making me suspicious is an aftermarket keypad immobilizer that's been installed in addition to the factory key chip immobilizer. I remember the previous owner saying he had disabled it because it had been causing him problems, however it is still physically wired into the system under the dash ( it's a nasty rat's nest of spliced wires under there ) and I'm wondering if maybe it's haunting me from the grave so to speak.

I'm still feeling like this might be related to the alternator problem since I think the voltage regulation on this model is done by the ECU.

EDIT June 2nd, 2016

So I spliced in the new IAT connector, cleared the codes, ran the KOEO and KOER self tests, and so far so good. Not sure what to make of it. I was thinking of pulling the ECU out to visually inspect it, but maybe I'll just keep an eye on things in the mean time and see what happens.

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  • I would recommend checking all the powers and groudns at the PCM. Then look at the cranks shaft position sensor.
    – vini_i
    May 29, 2016 at 20:04
  • Is there a cam shaft or crankshaft position sensor to check? How about voltage at the ECU?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 29, 2016 at 20:18
  • @Pᴀᴜʟsᴛᴇʀ2 There are both cam and crank sensors. I have to look up where to check voltage at the ECU.
    – Robert S. Barnes
    May 29, 2016 at 21:06
  • check the fuses before checking pulling down the ecu. maybe one is blown.
    – Ben
    May 29, 2016 at 21:10
  • Timing belt? What prompted you to do the initial work to the vehicle?
    – sntnmjones
    May 30, 2016 at 0:06

2 Answers 2

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So basically, the problem was shorted out wires in the Cobra alarm system which were causing the alarm system to randomly disconnect the ECU, fuel pump, etc:

enter image description here

I'm not going to copy the full answer here, you can read it over on this other question.

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The break in the wire could have possibly been causing a spike which was scrambling the ECU. I suspect that the problem won't occur anymore since you've changed that bit of loom.

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