Help Needed Starting my 86 911 Carrera

[polewog]

Hello All,

I am relatively new to trying to troubleshoot car problems with my 86 911 Carrera and would really appreciate some help with my starting problem.

I found the following article on the forums and went through most of it:

Pelican Technical Article: 911 Carrera Engine Starting Troubleshooting

A little background:
Last July (2010), I drove my car to work and it was running great. It was around 95 degrees that day and when I went out to my car at the end of the day it would not start. I did not have time to deal with it then so I went home and left it in the parking lot overnight. When I returned the next morning, I tried to start it and it started and ran well again. I drove it home and parked it in the garage. That is the last time that it has started.

The engine will crank all day long but the engine will not even think about turning over. We went through the guide at the link attached above (did not check for spark or try the air cleaner piece (steps 1 and 2)) as well as the Bentley service manual troubleshooting for the DME relay and fuel system. We eventually tried replacing the DME relay because we found that the fuel pump does not "whir" when you turn the ignition key but it will when you jumper relays 5 and 7 to get the 12 volts to the pump. Putting 12volts at the pump and then turning the key did not help the car start either.

All the other tests, up through the DME relay, seem to pass except the one in the Bentley service manual that says to check for ground at pin 85b while cranking the engine. Rather than reading zero this reads about 1.5 - 2volts. When we saw this we starting measuring a few more places and found that we were only getting about 10 volts out of the DME to the fuel pump. This lead us to believe that the DME relay may have too much resistance across it and is causing the problem but this was not the case. The new DME relay only has 10 volts as well and once we jumper 12 volts to the fuel pump it works.

Any ideas for me? I am not sure it is leading to a grounding issue, an issue with the computer, or something else.

Any help would be greatly appreciated.

Thank you,

Paul Lindsay

[gregwils]

I am not an electrical guru, but there were a few things that weren't clear to me from your post. Does you car not run at all or only intermittently? You said you went through most of the troubleshooting guide, but you think you may have a grounding issue. Did you go through the car and clean all the grounding points? You really need to eliminate bad grounds as a possibility and it sounds like you have a leak somewhere.

[darrin]

making things as simple as possible, your problem stems from one of two deficiencies: 1) no spark, 2) no fuel. I'd start by backing up in the testing process and doing the first two tests specified in the link you provided -- confirming whether you're getting a spark and then confirming whether the car will start if starting fluid, etc. is introduced into the air intake.

This will enable you to more effectively troubleshoot forward.

[Crude Rudy]

pul #1 plug wire, insert an old plug into it, ground the case to the engine, have someone start the car and look for the blue spark. If u have no spark check for correct speed and crank position sensor resistance at the 3 connector bracket/location right side of engine per Bentley. Check for proper terminal resistance, if out of speck replace both sensors with the BMW parts. Cheaper than the P parts

[Flat Six]

Originally Posted by polewog

Hello All,

I am relatively new to trying to troubleshoot car problems with my 86 911 Carrera and would really appreciate some help with my starting problem.

I found the following article on the forums and went through most of it:

Pelican Technical Article: 911 Carrera Engine Starting Troubleshooting

A little background:
Last July (2010), I drove my car to work and it was running great. It was around 95 degrees that day and when I went out to my car at the end of the day it would not start. I did not have time to deal with it then so I went home and left it in the parking lot overnight. When I returned the next morning, I tried to start it and it started and ran well again. I drove it home and parked it in the garage. That is the last time that it has started.

The engine will crank all day long but the engine will not even think about turning over. We went through the guide at the link attached above (did not check for spark or try the air cleaner piece (steps 1 and 2)) as well as the Bentley service manual troubleshooting for the DME relay and fuel system. We eventually tried replacing the DME relay because we found that the fuel pump does not "whir" when you turn the ignition key but it will when you jumper relays 5 and 7 to get the 12 volts to the pump. Putting 12volts at the pump and then turning the key did not help the car start either.

All the other tests, up through the DME relay, seem to pass except the one in the Bentley service manual that says to check for ground at pin 85b while cranking the engine. Rather than reading zero this reads about 1.5 - 2volts. When we saw this we starting measuring a few more places and found that we were only getting about 10 volts out of the DME to the fuel pump. This lead us to believe that the DME relay may have too much resistance across it and is causing the problem but this was not the case. The new DME relay only has 10 volts as well and once we jumper 12 volts to the fuel pump it works.

Any ideas for me? I am not sure it is leading to a grounding issue, an issue with the computer, or something else.

Any help would be greatly appreciated.

Thank you,

Paul Lindsay

Paul: First, welcome.

If I understand your post correctly, you went through the troubleshooting diagnostics posted above, and the troubleshooting diagnostics listed in the Bentley, correct?

If so, you may also want to check the speed reference and crank position sensors as I don't think they're specifically listed in either diagnostic list. Plenty of good threads here re: testing, diagnosis, and repair/replacement of these sensors. Here are a couple:

911 3.2 No-Start Troubleshooting

speed/ref. sensor wire covers crumbling

Inexpensive Carrera Speed & Reference Sensor alternative?

'84 - '88 Carrera cheap(er) DME speed and reference sensors available


But as Darrin and Crude Rudy point out, it's fuel and/or ignition. Crank position & speed reference sensors affect spark and timing.

Good luck, hope this helps. And how about posting a few pictures of your car?

[polewog]

First, thank you all for your suggestions. I have went through the trouble shooting in both the link and the bentley manual but I did not do steps 1 and 2 that refer to checking for spark and fuel. So per everyone's suggestion, I will try these two things next and see what results I get. I was going to start there but we noticed that the fuel pump was not running when the ignition was turned so we started trying to figure that out and got side tracked.

This may take me a few days to get to but I will let you know what I find out from these two things.

Flat six: I have uploaded a picture of my Porsche for you. It still needs some work but I am trying to slowly keep working on it. I have had it for about two years and I think I have worked on it more that I have had it on the road. I really want to get it started so that I can enjoy it this spring.

Thanks again for your suggestions and I will let you all know what I find.

Paul

[Flat Six]

Nice . . . keep at it!

[Socbum]

+1 on cleaning the grounds. I had an ignition coil and ignition coil wire fail on me and went though the same steps. After replacing the coil and wire I discovered that the root cause was a short on the ground point in the engine bay. After cleaning the ground points she has been running strong.

I did not find the issue until I went through the diagnostic steps without skipping around.

Hope that helps, good luck.

Originally Posted by gregwils

I am not an electrical guru, but there were a few things that weren't clear to me from your post. Does you car not run at all or only intermittently? You said you went through most of the troubleshooting guide, but you think you may have a grounding issue. Did you go through the car and clean all the grounding points? You really need to eliminate bad grounds as a possibility and it sounds like you have a leak somewhere.

[polewog]

Well, it has been a while but I was finally able to get the car started. I traced it down to a spark issue so I was then able to go through the no spark troubleshooting guides in the Bentley book. It turned out that the speed sensor plug had come loose and was causing a problem. I found this because I went to ohm it out and thought that it seemed a little loose when I disconnected it. It ohmed out fine and I plugged it back in and just to be sure I tried to start the car and it started up just fine.

I am glad it was easy but a little disappointed that the car was down for almost a year due to a loose connector.

Thank you all for you help.

[Flat Six]

Paul: Glad you got it fixed, and thanks so much for letting us know. So many times advice is offered but we never find out how well (if) it worked out or not.

[Hydrocket]

Originally Posted by polewog

Well, it has been a while but I was finally able to get the car started. I traced it down to a spark issue so I was then able to go through the no spark troubleshooting guides in the Bentley book. It turned out that the speed sensor plug had come loose and was causing a problem. I found this because I went to ohm it out and thought that it seemed a little loose when I disconnected it. It ohmed out fine and I plugged it back in and just to be sure I tried to start the car and it started up just fine.

I am glad it was easy but a little disappointed that the car was down for almost a year due to a loose connector.

Thank you all for you help.

Yea that sure is a bummer. But you would have found it quickly had you not skipped the check for spark and/or fuel troubleshooting.