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88' Turbo S - Runs great, except...

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Old 02-06-2018, 08:55 PM
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arains44
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Default 88' Turbo S - Runs great, except...

Hey everyone, I've been a member of the Rennlist community for a while but have not posted a lot. I have a 1988 944 Turbo S in Ocean Blue with 160k miles on the clock.

It runs really well, the car's entirely stock except for a stainless exhaust. However, recently I'm an an issue where the car will stumble (almost like a fuel cut, but seems more likely to be ignition), and sometimes shutoff all together. All I have to do is cycle the ignition and she fires right back up. I've replaced the DME relay, which certainly made the car run a little better but didn't fix the issue, and just did spark plugs.

I recently had the head gasket replaced, and did the timing belt, water pump, turbo/ little water pump, and a assorted belts and hoses. The issue has only cropped up since doing the head gasket, although that doesn't necessarily mean it's related. It's almost certainly not mechanical, as cycling the ignition cures it. There's no ryhme or reason as to why it cuts out, and it actually seems to run better under more load at high rpm. It's very intermittent, although happens more often after going over bumps, and at highway speeds. I usually don't have it happen on surface roads. The vehicle is currently my daily driver, so I'm really trying to get it sorted asap.

I have some ideas as to what to look for next, but have tried enough that at this point I just want another perspective. Any input or advice is helpful!
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Old 02-06-2018, 09:37 PM
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There's a couple plugs on the back against the firewall that read the crank/flywheel. Are they in good shape? I know mine are completely crumbled and need rebuilt. Loss of signal from intermittent electrical connection could be the issue. And if they were messed with during the work they could not be connected well. BTDT
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Old 02-06-2018, 09:58 PM
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Agree, make sure the speed and reference sensors are properly grounded and also not frayed.
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Old 02-06-2018, 10:26 PM
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is the ignition switch original?
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Old 02-06-2018, 10:29 PM
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When you say "shutoff" does it mean full power loss as if you switched the ignition off (no lights on the dash or do you have the lights) or you lose power as in engine running but not revving?
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Old 02-07-2018, 07:52 PM
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When I say shutoff, I mean lose power. The lights stay on on the dash, and everything still has power, the engine just stops running. The engine shuts off, but everything else keeps working. I just have to cycle the ignition and it fires right up!

@audisport very possible. I'll check those.

Speed and reference sensors look very good.

To my knowledge the ignition switch is original. I've only had the car for 4 months or so, and the previous owner kept records, but they're not as good as you would hope..
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Old 02-07-2018, 10:05 PM
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The speed/ref sensors can "look" great, because the wires that fray (and it's purely a matter of time) hide under the rubber boots. If you AmorAll those boots they will look brand new, even though the wires inside are frayed to smithereens. Peel the boots back and take a look before ruling them out, because you have the classic symptoms. It runs better at higher rpm because the amplitude (voltage peaks) of the sensors increase with speed. Removing the head means moving those wires around, which can make brittle, soon-to-fail wires finally fail. If it ever gets to the point where the car won't start, check for tach bounce/twitch when you crank it. The fact that it has always started right back up is the only part that might suggest it's something else -- like the ignition switch or relay or DME/KLR -- so no guarantees But if you play the odds, I bet speed/ref sensor connectors fail at ten times the rate of the other likely culprits (other then the DME relay...).

See where to look here:

https://rennlist.com/forums/944-turb...onnectors.html

p.s., the connectors audisport is referring to 'are' the speed/ref connectors...
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Old 02-08-2018, 01:09 AM
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This may be a silly question- what does your key ring look like? Do you have a lot of keys on the ring, or a heavy item on the ring like a framed picture of Lucile Ball (don't judge) or something? That can sometimes put stress on the ignition switch as well.

Agree that the speed and ref sensors should be your first place to check.

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Old 02-08-2018, 09:25 AM
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Funny enough I do actually have a pretty heavy key ring... Should I try driving it without the other keys on there? I'll definitely look into speed and reference sensors.

My key chain isn't abnormally large, but it is pretty heavy. If that's the case, would you suggest replacing the ignition switch (I'll obviously keep the other keys on a separate key chain...).
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Old 02-08-2018, 11:46 AM
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Took off all of the other keys from my key chain on the way to work this morning. Still experienced the same symptoms. I tried moving around the key while in the ignition, both idling and driving and it didn't cause the car to stutter or turn off.

Seems like the speed/ref sensors are more likely. The only thing I can correlate the issue to is bumpy roads. Additionally, it shut off right after start-up this morning. I fired it back up and it ran fine. I'm having the speed and reference sensors replaced while I'm at work today.

This issue is so intermittent it's very hard to show or explain to anyone... I drove 30 minutes yesterday without it happening, and then it shut off on me twice on my 10 minute drive to work today!

Thanks for the responses, super helpful!
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Old 02-08-2018, 01:37 PM
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Originally Posted by arains44 View Post
Took off all of the other keys from my key chain on the way to work this morning. Still experienced the same symptoms. I tried moving around the key while in the ignition, both idling and driving and it didn't cause the car to stutter or turn off.

Seems like the speed/ref sensors are more likely. The only thing I can correlate the issue to is bumpy roads. Additionally, it shut off right after start-up this morning. I fired it back up and it ran fine. I'm having the speed and reference sensors replaced while I'm at work today.

This issue is so intermittent it's very hard to show or explain to anyone... I drove 30 minutes yesterday without it happening, and then it shut off on me twice on my 10 minute drive to work today!

Thanks for the responses, super helpful!
Just try unplugging the reference sensors and plugging them back in. Had that same thing happen to a friends car, cleaned the pins and no more issue. Recent work on the car leads me to the possibility of the 30 year old injector harness possibly having an issue. The insulation gets brittle and once disturbed falls apart leaving the possibility of the two wires to touch, when this happens the car shuts off. Good luck!
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Old 02-08-2018, 02:53 PM
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If you are uncomfortable peeling back the rubber boots to look for frayed wires, just wiggle the connectors/wires while the motor is running and see if you can induce the problem. As for replacing the sensors, be aware that these sensors plug into connectors on the engine harness, and it is the engine harness side that goes bad at least as often (probably more often since the sensors tend to get replaced and the design under the boot is less susceptible in the first place). So, while it can't hurt anything but your wallet to replace the sensors, if the problem persists, you'll want to test the harness side and, if needed, replace those connectors or install a patch harness like this one from Lindsey Racing:

https://www.lindseyracing.com/LR/Por...4-HAR-REF.html
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Old 02-09-2018, 08:29 PM
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Originally Posted by Tom M'Guinn View Post
The speed/ref sensors can "look" great, because the wires that fray (and it's purely a matter of time) hide under the rubber boots. If you AmorAll those boots they will look brand new, even though the wires inside are frayed to smithereens. Peel the boots back and take a look before ruling them out, because you have the classic symptoms. It runs better at higher rpm because the amplitude (voltage peaks) of the sensors increase with speed. Removing the head means moving those wires around, which can make brittle, soon-to-fail wires finally fail. If it ever gets to the point where the car won't start, check for tach bounce/twitch when you crank it. The fact that it has always started right back up is the only part that might suggest it's something else -- like the ignition switch or relay or DME/KLR -- so no guarantees But if you play the odds, I bet speed/ref sensor connectors fail at ten times the rate of the other likely culprits (other then the DME relay...).

See where to look here:

https://rennlist.com/forums/944-turb...onnectors.html

p.s., the connectors audisport is referring to 'are' the speed/ref connectors...
Best answer here.
[Followed up by another great answer re: the engine harness]

Originally Posted by arains44 View Post
I have a 1988 944 Turbo S in Ocean Blue with 160k miles on the clock.
You mean, you have THE 1988 Turbo S in Ocean Blue, right? There's only one.

Did you buy it from the guy in FL? Or are you the guy in FL, and you moved to AL?
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Old 02-12-2018, 09:16 AM
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I bought it from the guy in FL. Properly represented car, it's in amazing shape for 160,000 miles. Only issues that have cropped up have been from it sitting for too long. The old coolant was probably never changed, sat for 5-10 years, turned acidic and started eating the HG..

Okay, update: I replaced both speed and reference sensors, AND swapped out the DME with one from another Turbo S. The issue is resolved. Now all I need to do is swap back to my DME to see if the speed and reference sensors were the fix, or if my DME has an issue.

Thanks for all the ideas!
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Old 02-12-2018, 11:49 AM
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Glad you solved it.
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