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Stranded 911

Hey guys... need a little help. I had to leave my 86 911 in a shopping center tonight. I had driven it 30 miles from work to the shopping center, no problems nothing different. I shopped for 30mins then hopped in it and it fired up no problem nothing different. On the way out of the parking lot, it just died. I tried to restart, but it wouldn't fire. After grinding it a few minutes, I pushed it into a parking space. After the push, I hit it again and it fired for a second and then it went dead again. My wife picked me up, we went out to eat and came back for another attempt. It fired for just a second and then went dead again. I grinded a few minutes and then gave up.

In the past week the only changes made were new ignition wires, which I have successfully driven 400 miles prior to being stranded AND I ran premium gas in it for the very first time. Again, ran 3/4 of the tank out before becoming stranded. Twice, I checked my ignition wires to see if anything was loose.. but it's all tight. It really acts like it wants to start... but won't.

I thought I get your opinions on a good plan of attack before throwing in the towel and calling for a tow. I can take some tools to the scene and check a few things. But, I'm not too comfortable doing anything major while in a parking lot. Please let me know what you think.

Thanks

-Troy
Old 12-15-2006, 05:19 PM
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head temp sensor and the DME relay are the most common things that go bad. check the 3 plugs above #3 cylinder to be sure they are snapped in tight. wack the DME relay with a screwdriver handle to see if that makes any difference. sometimes it's a quick way to diagnose the issue. it's under the left seat. small rectangle, black plastic box.
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Old 12-15-2006, 05:26 PM
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I had a similar problem that turned out to be "cold solder joints" in the Motronics box next to the DME relay. If the relay doesn't fix it you might give the Motronics box a good whack. If it starts do a search for DME SOLDER or MOTRONICS SOLDER. Good luck.
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Old 12-15-2006, 06:07 PM
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Sounds like I should definitely be looking under the seat first for the culprit. So, I'll whack the DME relay and the DME control box to see if that helps. Hopefully, that'll let me hobble it home so that I can diagnose and repair. I guess the DME and relay have a big hand in the fuel delivery... ie fuel injectors, fuel pump, etc. I guess I could also swap my red relays to see if that helps too. Seems one of these have something to do with the fuel pump.

Great advice... I knew I could count on you guys to chime in for me.

Thanks much

-Troy
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Old 12-15-2006, 07:39 PM
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Careful "whacking" the sensitive electronics in the DME. It would be wiser to remove it, and open it carefully on a bench and inspect it for cold solder joints or broken foil runs.
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Old 12-16-2006, 12:24 AM
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Just a thought... I had a '88 VW Scirocco and it once had a similar problem. I was in college and had to drive a couple hundred miles to and from home (weekends and such). One time I was going back to school and the car quit while doing 70 in the fast lane. I managed to get it restarted, but the problem persisted. Finally brought it to a dealer who drove it for a numbers of days without problem. Finally it happened again. Anyway, turns out the car had two fuel pumps and one was bad. At full tank the car ran fine. When the tank was below 1/2, it started to act up. The remaing pump could not keep the flow going.

Dave
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Last edited by slodave; 12-16-2006 at 02:21 AM..
Old 12-16-2006, 12:51 AM
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One other thought -

Wet weather and temps dropping? Sounds like it could also be water in the tank.
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Old 12-16-2006, 02:19 AM
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Quote:
Originally posted by TroyGT
Sounds like I should definitely be looking under the seat first for the culprit. So, I'll whack the DME relay and the DME control box to see if that helps. Hopefully, that'll let me hobble it home so that I can diagnose and repair. I guess the DME and relay have a big hand in the fuel delivery... ie fuel injectors, fuel pump, etc. I guess I could also swap my red relays to see if that helps too. Seems one of these have something to do with the fuel pump.

Great advice... I knew I could count on you guys to chime in for me.

Thanks much

-Troy
Please do what John Walker said to do first and check the plugs in the engine compartment.

The exact same thing happened to me and it was an old style cylinder head temp sensor. You can check this by looking at the three plugs and when you find the one that goes to the sensor, if its a single wire, then it is the old version and needs to be replaced.

I would not "whack" the DME computer but a tap or two on the DME relay (totally different animals here) may help if the relay is the issue. Please do what John said and only that, then get back to us.

Also I would carry a spare DME relay in your car at all times. They do fail and most of us buy a new one, put it in the car and put the old one in the glovebox as a spare for times like this.

Joe A
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Old 12-16-2006, 05:01 AM
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Update. Went back to the scene this morning with a few tools. Held the DME relay while turning on the ignition and I could hear it/feel it engage. So I think it was fine. Tapped it anyway. No start. Tapped lightly on the DME control box, messed with the wiring harness a little. I could hear the fuel pump hum with the key turned, so I think the pump was working fine. Went to the back and checked the three sensor plugs and wires above the #3 cyclinder... they were all nice and tight with wires in good condition. Pulled the distributor cap and rotor off, cleaned them a little, wiped out the cap and re-installed it along with all the ignition wires again. Pulled the coil cover off and checked the wiring there, all good. Pulled the plastic cover off the rear fuse panel and found one burned, the center blue fuse... which I think has to do with the heater. Replaced it. Tried to start, turns ove all day long, just won't fire up.

I called in a rollback and paid $85 bucks to have it hauled back to my house. Got it where I wanted it in my driveway, paid the man, and went inside for a drink. Because I'm a glutton for punishment, I went back outside with my drink in hand and hit it once more... it fired right up. NO PROBLEMS AT ALL. I let it run for awhile, revved it, never could get it to fail again. I'm thinking possible water in the gas tank or line. The car is parked on a slight incline now with a 1/4 tank of gas. The parking angle plus the jostling of the tow may have any water in the tank move out of the fuel intake from the gas tank and that's why it runs like a top now. I'm gonna pick up a de-ice additive and that to the tank, but I still don't feel too confident about driving it again. It has been a daily driver car for over a year now. I drive it about 90 miles a day and in a year have never had a minutes trouble out of it, except for a few minor oil leaks, etc. It's never left me stranded before. Where should I start looking or replacing parts? I'm not sure where to begin.

Appreciate everyone's help on this.

-Troy
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Old 12-16-2006, 12:04 PM
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replace the head temp sensor if it's the old single wire type, (check the white plug above #3, on the engine side of the plug, for one or two terminals). and replace the DME relay. it doesn't hurt to go over the computer circuit board with a powerful magnifying glass, looking for cracked solder joints. they often show up as a tiny circle in the solder blob.
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Old 12-16-2006, 12:25 PM
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Quote:
Originally posted by Joeaksa
Please do what John Walker said to do first
Joe A
I laughed out loud when I read this. I've wrenched on plenty of cars, chased down problems like this many many times. You want to know what my advice is? My advice is to listen carefully to what JW suggest, and follow those suggestions faithfully. I notice he has offered some new suggestions. I've listened to JW's advice many times and followed it with great success. I've ignored his advice too. Twice. It was a mistake both times. Now I listen more carefully.
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Old 12-16-2006, 12:56 PM
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Supe,

I posted this because other posters suggested whacking on the DME computer and John did not say to do this, yet the gent with the broken car was going to give it a try. Tap on the relay, not the computer, they are not the same thing!

John's right on the money and he is recommending exactly what I would do and Troy is having exactly the same symptons that I had when my CHT sensor was tits up. Found it to be the old single wire version and once replaced the engine fired right up.

Joe
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Old 12-16-2006, 01:07 PM
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John, I'll do exactly what you suggested. Sounds like you have quite a fan following who trust what you say. I'll do the same.

It's next day now, continues to start just fine, I've move it around a little see if jostling it about makes any difference. It's all good now. I've added a water remover to the gas tank, will check the head temp sensor wiring and replace if single wire type, and I'll replace my DME relay and check the solder joints on the DME control unit. After that, I guess I'll just have to drive it and see if it happens again.

Thanks John, and everyone for all the great advice and support. You guys are a great resource.

-Troy
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Old 12-17-2006, 10:08 AM
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I'm back again... yes, since I had the car towed home it has been starting up just fine through the holiday. I didn't drive the car anymore and I went ahead and ordered a new CHT sensor and a new DME relay before xmas. Today, the car wouldn't start again. All the same symptons as before. I went outside, spent a couple of hours replacing the single wire CHT sensor with a new two wire CHT, no dice. I then pulled the DME relay (circa 1989) and replaced it with a new one... again, no dice. It turns over all day long, but won't fire. Fuel moisture eliminator was added to the gas tank, so I don't thinks it's that now.

At least it's at home and currently in a failed state. Hopefully I'll be able to track it down and eliminate the problem this time around. I still have some time to work on it before heading back to work next week. What should I check next?

Thanks

-Troy
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Old 12-29-2006, 08:50 PM
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Did you ever check the solder joints in your DME box? Here's a link with trouble shooting. Good luck.

'87 Carrera has intermittent no start problem
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Old 12-29-2006, 08:57 PM
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I haven't pulled the DME box yet... only because I've heard that you shouldn't pull it unless you really know that's where the problem lies. I was thinking that maybe the speed sensor would be a good place to check next... after determining if I'm getting fire and/or fuel.

-Troy
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Old 12-29-2006, 09:19 PM
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You know, before you get too crazy disasembling stuff, no matter what the technology, engines require air, fuel, spark and compression to run.

Do you smell fuel at the tail pipe after you cranked it for a bit?

Did you grab an old spark plug, connect it to one of the leads and see if you are getting a spark?

These simple tests will help you narrow down where to look.
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Old 12-29-2006, 10:50 PM
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I can understand not wanting to pull the DME box. Being an electronics engineer by trade I am far more comfortable opening a box and checking a P.C. board for cold solder joints than pulling a spark plug. That is why I chose to check the box first. I am a newbie here and a hobby mechanic. I have tremendous respect for Master Mechanics like John Walker who share their vast experience and time for free. Do what they say. Do what you are comfortable with. If your not comfortable get some help.
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Old 12-30-2006, 09:05 AM
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I agree with Harryd, keep it simple. Its either spark or fuel. Probably spark because it seems to be intermittent. Do the spark plug test first to see if you are getting spark at the plug while cranking. On my 3.2 I can hear the DME clicking while I am cranking it over. Additionally check and clean "all 'grounds, (battery, manifold, underbody to gearbox) These are very important with the motronix system.
Old 12-30-2006, 09:16 AM
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All the things listed above but how much fuel do have in the tank. If it says 1/4 maybe it is actually out of gas. Depending on how you park it may run then not run. Just a thought. Also no need to waste money on fuel additive to remove water. Just run some ethenol every now and them. It is 10% alchohol same stuff you just paid $1.50 for a pint. Remember to alway check the simple stuff first. Not simple but how about a bad impulse sensor.
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Old 12-30-2006, 10:33 AM
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