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Carrera no start

'88 Carrera -- drive to work, runs beautifully, park. Return 2 hours later, starts right up. But as I'm adjusting my seat belt, she dies. Cranks fine, but no sign of life, as if someone suddenly pulled the fuse on the fuel pump.

I know it could be a bunch of things, but I'm thinking -- hoping -- that it's something very simple. I'm hoping there's an easy answer to try before waiting an hour in the cold for the AAA tow.

Any suggestions?

Thanks!

P.S. My apologies for posting what i'm sure is a common question, but at the moment I don't have the luxury of going through the archives.
Old 02-27-2017, 01:41 PM
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Hello There:

In view of the fact that your car was running fine until now, my best guess is DME RELAY, SENSORS or LOW/DEAD battery.

Reference sensor, speed sensor could have died which would explain why it worked just fine earlier. Does your Tac bounce when you are cranking the engine?

Of course, I am no expert, but in view of the symptoms described, I would check those items first.

When was the last time the car was serviced?

Hope this helps.
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Last edited by TibetanT; 02-27-2017 at 05:26 PM.. Reason: spelling
Old 02-27-2017, 01:51 PM
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Thanks, that does help. The obvious thing to do first swap the DME relay, then call the tow truck if that doesn't work (duh -- why didn't I do that before taking the bus home??).
Battery's fine. I think I would have noticed if the tach were bouncing around, but I'll pay attention to that tomorrow when I'm back at the car.
Old 02-27-2017, 02:17 PM
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check the speed and ref sensors resistance per the Bentley manual, your symptom is representative of one of those failing. They fail like a fuse and the car wont run at all
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Old 02-27-2017, 02:30 PM
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I would check dme sensor, cylinder head temp sensor... Of course assuming the electrical system checks ok
Old 02-27-2017, 02:41 PM
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As everyone says, the DME relay is the first thing to swap. You should always carry a spare. Do not buy a cheap Uro relay. Get a German one or better yet the solid state one made by a fellow Pelican. If that solves it, great. If not the flywheel sensors are next to check. Call a local PCA friend with a Carrera and put your DME in his car and see it it runs. If not the DME itself has issues. Don't put his DME in your car. There are conditions that your car can damage a good DME. Put your DME in his car.

If you don't know how old the sensors are or if you suspect they are original, replace them anyway.

Good luck.
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Last edited by GH85Carrera; 02-28-2017 at 05:40 AM..
Old 02-28-2017, 05:33 AM
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Swapped the DME relay -- I had a spare in the car -- but no luck. That would have been too easy.

Now the 911 is in the garage after a ride on the flatbed -- first time she's let me down. Anyway, the next step will be to check the speed and ref sensors, per Crude Rudy's advice.

This will be my initiation into motronic troubleshooting after casually reading countless threads on the topic, thinking my car would somehow be exempt. Looking forward to learning something ...
Old 02-28-2017, 02:19 PM
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Same thing happened to me. Swapped DME relay but still no start. Search and use the no start list to check. I checked resistance on my sensors and they were fine but after PMing with Ingo on this forum he said that isn't a definitive way to check them. I replaced mine and she fired right up. It's fairly easy to do
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Old 02-28-2017, 05:46 PM
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Let us know. Had the same thing happen, but the DME swap out worked fine. Very interested to know what happened.
Old 02-28-2017, 06:02 PM
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Nearly the same thing happened to me about 2 years ago. Ran fine, started fine, died and wouldn't restart. Took a while to work through the list but it ended up being a reference sensor, replaced BOTH (using the BMW part trick at less than 1/2 the Pcar part price $). It wasn't an easy replacement involving complete removal of the bracket and resetting the air gap on the car (yes there is a trick fix). Its been 100%ever since.

I did buy an extra sensor so I have one on the shelf thereby guaranteeing it will NEVER fail!
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Old 02-28-2017, 06:21 PM
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For whatever reason no one ever seems to suggest in these no-start threads that it could be the fuel pump. That's what it was when this happened to me. I pointlessly replaced the speed and reference sensors after incorrectly diagnosing them as bad. A simple test of the fuel pump would have clearly shown me that it was bad. So now I always advise people to check that as well before they start replacing parts

See my thread here, I got lots of great detailed troubleshooting help:

Broken down near Pt. Reyes, CA
Old 02-28-2017, 09:16 PM
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Maybe because the symptoms are pretty different. In my case the car just died completely at 55MPH. Would crank over but would not start.

Your car sputtered and even restarted a bit so I would immediately suspect a fuel delivery problem (filter or pump). Definitely there is a decent list of quick checks and the pump should be pretty high up on the list since it is fairly easy to check.
Old 03-01-2017, 03:46 AM
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What next?

Latest update:
(DME relay swap had no effect)
No spark (removed one of the plug cables and tested with a spare plug grounded to the engine)

Checked resistances for reference and speed sensors per Bentley instructions:
Upper connection::
919 ohms across #1 and 2 terminals, "1" (infinite resistance?) at all settings across #1 and 3, and across #2 and 3.
Lower connection:
917 across #1 and 2, "1" across #1 and 3, #2 and 3.

I assume those results are normal (?). By the way, which one is the speed sensor connection, and which the reference sensor? The cables lack the identification tags mentioned in the Bentley manual.

So assuming that the fuel delivery system is OK, and the two sensors as well, what next?
Old 03-04-2017, 02:36 PM
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Could be ignition switch? check the multi plug behind the ignition barrel, ensure it's secure.( Look up from footwell ). Normally no lights turn on dash when keys turned to on, if ignition switch plug loose

Or the multi plug in the engine compartment, left hand side, behind the plastic cover / had similar symptoms caused by this before
Old 03-04-2017, 03:04 PM
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Turn the key on and see if the ICV is vibrating. If it is, the DME is probably okay and the problem could be a failed sensor. They can ohm out okay but still be defective. Your car is an 88 so they are now 29 years old and I would change them anyway. The BMW versions are about 1/2 the cost. Report back on the ICV.
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Old 03-04-2017, 03:22 PM
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ICV vibrates with key on. A positive sign.

I don't mind replacing the sensors, but I'd like to come up with a good hypothesis re: my no start condition before I start throwing parts at the problem. Would a failed sensor explain a sudden change from smooth running to no-spark (that is, not preceded by poor running conditions or intermittent starting problems)? And does anyone have a good sense of how likely it is for sensors to ohm out OK and still fail?

Is there any other easy explanation for my no spark condition that's easy to check before I order new sensors?

One final question: are the two sensors, speed and reference, the same item? (So I would order BMW part # 12-14-1-708-619, 2x.

Thanks for all the helpful advice so far ...
Old 03-05-2017, 07:31 AM
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There are a few guys on this forum who can explain the hypothesis to you in great detail, scarceller is one of them. He knows everything there is to know about the Motronic system and he's walked me through extensive troubleshooting a few times on my Motronic based car. Based on this experience I can tell you that sensors can sometimes ohm within specs but still be defective. Being that your's are pushing 30 years old it only makes sense to replace them anyway because at that age they can fail at any time. If I bought a 30 year old Carrera, the first thing I would do is change them even if it was running fine because I dont want to be stranded. If you're not getting spark to the plugs, and the ICV is vibrating, the DME is powering. If the relay is working, the most likely culprit would be a speed/reference sensor. Having said that, there is a very systematic method to troubleshooting these systems and this has been covered many times before. I would search the old threads under "motronic /no start". It may be something else but in order to find out you'll need to go through the entire process. Both sensors are the same BTW. I believe the BMW part just has a slightly longer cable as opposed to the Porsche one. Dont know the part number but search will tell you that as well. Good luck. Make sure you dont get the sensors crossed if you end up replacing them, that will certainly cause a no start.
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Last edited by Rodsrsr; 03-05-2017 at 09:25 AM..
Old 03-05-2017, 09:22 AM
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Have you checked the DME computer for cracked solder joints? On mine it caused symptoms exactly like yours - would run until warm and then wham, no spark. Cool it down and it would start up again.

The coil transistor is standing upright from the board on a heat sink, that's the one that cracked on mine.

If you have it in the no-start condition, you could try tapping gently on the DME to see if it starts.

HTH,
Chuck.H
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Old 03-06-2017, 06:00 AM
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^ What Chuck said. Mine quit while driving down the road. I hemmed and hawed forever, trying to find the cause. My tech lent me his spare DME and the car fired right up. So I sent my box to Ingo(on this board), and had it back within a week. Car has run perfectly ever since. Since our cars are over thirty years old now, it would not hurt to have the DME checked by a professional. Everyone seems to point to the relay. If only it was that easy, LOL.
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Old 03-06-2017, 06:29 AM
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Did you check the ohms on the CHT sensor?
Old 03-06-2017, 06:35 AM
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