8 cylinder front engine iconic vehicle
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By Geza-aka-Zombo
#118813
Engine started oddly, as it took 5 or 6 seconds of cranking before it finally fired up (normally takes 1 or 2 sec.) Last driven a week ago. Drove normally for about 15 minutes, then stalled while driving. Started, but wouldn't idle or stay alive without slight throttle. Wouldn't rev much or stay running under any load. Engine got rougher as I continues to try to start it and keep it running. I noticed some black smoke coming out the exhaust while I was fiddling with the throttle trying to keep it alive. Flat bedded it back home.

I believe the LH and EZ modules are original (135K miles), as are the coils and MAF, though I added a new connector/wiring to the MAF a few years ago. My first thought is it's ignition related?? Any advice on what I should start troubleshooting would be appreciated. Thanks.
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By worf
#118987
Geza-aka-Zombo wrote: Sat Nov 27, 2021 5:56 pm I believe the LH and EZ modules are original (135K miles), as are the coils and MAF, though I added a new connector/wiring to the MAF a few years ago. My first thought is ...
... that it is a wonder it runs. Seriously.

At this point in its life cycle it should just be starting it's 3rd Mass-Air Sensor.
LH is due to die at any moment due to the well-known materials defect.
EZK module doesn't have a common failure but, EZKs are beginning to fail simply due to various on-board components reaching end-of-life.
Coils... original coils last a long time. I have yet to diagnose a bad coil.
The coil final ignition stages are however entering end-of-lifetime stage. This is especially true if you already have replacement amps (due to either poorer quality of replacements and/or previous technician not cleaning-off the old heat sink paste and applying new heat sink paste.) I've replaced several sets of these in the last year or two.

Based upon your symptoms your mass-air sensor has finally degraded to the point that it is so far out of spec that the adaptive engine management code can't deal with it. It is also possible that one or both of the coil final stage amplifiers are dying.

Contact Rich at Electronik Repair (https://electronikrepair.com/home-page) and send him your Mass-Air Sensor for testing.

If Rich says it's out-of-spec or almost-out-of-spec have him rebuild it.

You might think about sending him your LH for testing too.
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By Mrmerlin
#119011
To expand on Daves advice i would send in the the computers and the MAF and have all of it tested and refurbished,
get a new factory 02 sensor as well,
test the temp 2 sensor and replace it and its connector if there is any variance,

sniff the vacuum lines to the dampers and FPR for fuel if you smell any fuel replace all three of these parts
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By worf
#119047
What Stan wrote -^

It would be a good idea to go through my inspection guide and in particular the electrical tests.

The implication here - and what I intended to post above but didn't - is that it is highly likely that you have more than one component that's not doing what it supposed to do.
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By byrdman454
#119120
Rich is a great guy for the rebuild. I used him for my LH long ago and haven't had any issues. The only thing I would caution is that his rebuilds will not work with the Sharktuner or any of the John Speake (JDS) designed items. Maybe that has changed recently, but was not the case when I had mine rebuilt. If you use the Sharktuner or Spanner, I would verify it will still work after his rebuild or just go with the JDS rebuild. I think Roger is a US agent for JDS.
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By worf
#119121
byrdman454 wrote: Mon Nov 29, 2021 11:53 am Rich is a great guy for the rebuild. I used him for my LH long ago and haven't had any issues. The only thing I would caution is that his rebuilds will not work with the Sharktuner or any of the John Speake (JDS) designed items.
Incorrect.

Rich’s rebuilds have worked with the Sharktuner for almost 10 years.

The JDS Spanner only worked on ‘89s. So, rebuild compatibility with it is irrelevant.
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By byrdman454
#119294
Good to know on the Sharktuner (I have never owned one), but I will have to disagree on the Spanner (at least over 10 years ago). I bought the Spanner when it first came out (probably 2005) and still have it. They sold a different plug for the '88 since it changed in '89. It worked fine on my '88 until I had my LH rebuilt. The spanner was even sent to Rich to see what the issue was and there was something disabled in their rebuild that didn't allow the Spanner to work any longer. I will have to say my LH rebuilt is older than 10 years and pre-Sharktuner so they must have changed something with their rebuilds to make it all work.
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By worf
#119453
byrdman454 wrote: Tue Nov 30, 2021 5:08 am Good to know on the Sharktuner (I have never owned one), but I will have to disagree on the Spanner (at least over 10 years ago). I bought the Spanner when it first came out (probably 2005) and still have it. They sold a different plug for the '88 since it changed in '89. It worked fine on my '88 until I had my LH rebuilt. The spanner was even sent to Rich to see what the issue was and there was something disabled in their rebuild that didn't allow the Spanner to work any longer. I will have to say my LH rebuilt is older than 10 years and pre-Sharktuner so they must have changed something with their rebuilds to make it all work.
Ok. I stand corrected.

When I got the Spanner in '04/'05 (I too don't remember) I tested it on my '89, '91, and '94. It only worked on my '89. Subsequently I tested it on two '89s that rolled through the shop and it worked. I took it to SITM and tested it on a bunch (8-12-ish IIRC) of '89s to '95s and it only worked on '89s. I also tested it on an '87 at SITM and it didn't work, but at that point I wasn't being thorough. I talked with another multiple 928 owner at SITM who confirmed that my findings were consistent with his.
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By Geza-aka-Zombo
#122526
Quick update. I sent to LH, AZ-K and MAF out to Rich at Electronik Repair for test. The LH was bad and the MAF was well out of calibration; AZ-K tested OK. Looking forward to getting the repaired units back and installed, and will provide another update.

BTW I asked Rich if the modules looked like they were fiddled with and he said they appeared to be original, so, 35 years and 135K miles - not bad! I'm hoping the car runs better with the repaired parts, as I always felt it wasn't running as it should - seemed to have sluggish throttle response. Since I never drove another 928, I didn't know for sure, but hope to feel the difference with the proper operating parts.
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By Geza-aka-Zombo
#123366
Received and installed my modules yesterday. Started right up, idled well and seemed to be more responsive and smoother on the brief test drive I did. I think the emissions were better, too. Looking forward to putting more miles on to get a real sense of the improvements.
SeanR, linderpat, worf and 1 others liked this

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