'88 911 decides to not start :(

[Socbum]

Back story, '88 911 coupe purchased earlier this year. Car was converted by PO to pure track car but kept most of the replacement bits. PO got bored with the track scene and parked the car in the garage for 7 years.

Purchased car and converted it back to street legal, mechanic did all of the engine work and she was running strong until last week. For winter I took her to a friends house that has extra garage space. In December I was driving it about once or twice a week than one day it decided not to start. It cranks strong but won't start. I have a Bentleys manual and have searched here for diagnostics.

Today I'm going to go through the following diagnostics to find the root cause.
Spark test
Coil power test
Coil fuse check
Distributor, cap & rotor test
Spark plug wires (replaced earlier this year)
Reference sensor
Dme relay test (I smell fuel and hear the fuel pump which is new this year too)

Question, Bentleys shows a picture of the fuse box and points to the fuse in the 8th position in panel 1 as the ignition coil fuse. Looking at the fuse box table in the back of the book it doesn't mention the ignition coil at all. Can someone confirm?

Also, do I have to remove driver seat to get to the dme relay?

Any other ideas?

Thanks for the help

[Tippy]

You test the cylinder head temp sensor? If mine is unplugged, it won't start at all.

It is the 2-pin plug on intake #3.

[Crude Rudy]

If it has spark and fuel and the DME relay swap does not fix it, check the crank position and speed sensors. U can measure the proper resistance at the set of 3, 3 pin connectors on the left side of the engine below the fan blower per the Bently manual. These sensors were my problem and were described to me by Draco as "light bulb" sensors, they either work fine or dont work at all. I bought mine from a BMW parts supplier online and they were way less than 1/2 of the Porsche part. The sensor and connector were the same but the cable was about 1 in longer. Remove the wheel and shock and only took 30 min to replace and get the car running. Only PIA was reinstalling the firewall gasket that insulates the 2 wires.

[shbop]

Originally Posted by Crude Rudy

If it has spark and fuel and the DME relay swap does not fix it, check the crank position and speed sensors. U can measure the proper resistance at the set of 3, 3 pin connectors on the left side of the engine below the fan blower per the Bently manual. These sensors were my problem and were described to me by Draco as "light bulb" sensors, they either work fine or dont work at all. I bought mine from a BMW parts supplier online and they were way less than 1/2 of the Porsche part. The sensor and connector were the same but the cable was about 1 in longer. Remove the wheel and shock and only took 30 min to replace and get the car running. Only PIA was reinstalling the firewall gasket that insulates the 2 wires.

+1 on what Crude Rudy says.

[rusnak]

First make sure the battery has a full charge, around 13v, check the voltage at the icv. Make sure that the icv is humming with the key in "run". Feel for two clicks in the dme relay while turning the key to start. If so, then spray some starting fluid into the throttle as someone turns the key. Should start.

[azasadny]

Do you have an old alarm system still wired into the harness somewhere?

[DonMo]

factory alarm or motronic darlington transistor finally dies. Both have given me a no start with fuel. If you were near west palm beach , florida I would offer to let you swap my box and see if that works but I can't tell where you are from your signature.

[Dave Colangelo]

Check your fuse panel for corrosion on the tabs. I once had what I though was a big electrical issue but turned out to be a corroded fuse. To they eye it just looks a bit worn, the solution was to sand all the fuse tabs down to clean copper and replace all the fuses, total cost 5$ for fuses.

Always carry a spare DME relay with you, when i was DDing by 924s I always had one in the glove compartment.

Regards
Dave

[wildcat077]

Originally Posted by Crude Rudy

If it has spark and fuel and the DME relay swap does not fix it, check the crank position and speed sensors. U can measure the proper resistance at the set of 3, 3 pin connectors on the left side of the engine below the fan blower per the Bently manual. These sensors were my problem and were described to me by Draco as "light bulb" sensors, they either work fine or dont work at all. I bought mine from a BMW parts supplier online and they were way less than 1/2 of the Porsche part. The sensor and connector were the same but the cable was about 1 in longer. Remove the wheel and shock and only took 30 min to replace and get the car running. Only PIA was reinstalling the firewall gasket that insulates the 2 wires.

Does anybody have the P/N and the source for the BMW replacement parts ?
This is good to know ...

Cheers !
Phil

[Socbum]

Thanks for all the tips. Here are the results of the testing.

No spark at the plug
low voltage at the ignition coil terminals -- 6 or below volts on each terminal
Fuse box in front compartment all are fine (need to investigate for corrision)
voltage at fuse is 12 volts

Does this mean the ignition coil is bad or the wires to the coil have a problem?

I did not go any further on my list because of the problem seems to be at the coil.

I did order a DME relay just in case based on all of the comments.
Yes, the anti theft device is still in the car and thanks for the offer to switch but I'm in Columbus OH.


Thanks again for the help

[Dave Colangelo]

I had a similar issue on my 88 924S which has a similar ignition system. I however was not getting any voltage at the coil, it turned out that there was a problem with the ECU. The transistor that controls the coil had fried.

You can test the coil with a DMM, I forget how to do it but I think you test from center to one of the pins a google search should give you want you want.

Regards
Dave

[rick-l]

Originally Posted by Socbum

No spark at the plug
low voltage at the ignition coil terminals -- 6 or below volts on each terminal
Fuse box in front compartment all are fine (need to investigate for corrision)
voltage at fuse is 12 volts

The Bentley shows the coil directly connected to the battery with no fuse. Is this correct? All I have is page 5 of the FSM but it show a single (continuous) 2.5 mm^2 black wire from the jumper bus (15 - on and start) on fuse 7 and 8 going to the coil.

[rick-l]

Originally Posted by Dave Colangelo

I had a similar issue on my 88 924S which has a similar ignition system. I however was not getting any voltage at the coil, it turned out that there was a problem with the ECU. The transistor that controls the coil had fried.

You can test the coil with a DMM, I forget how to do it but I think you test from center to one of the pins a google search should give you want you want.

Regards
Dave

disconnect the black wire and see if it reads battery voltage (on the wire that is).
ignition on of course

The factory manual says---
Primary resistance between ter. 1 and 15: 0.4 to 0.7 ohms.
Secondary resistance between ter. 1 and 4: 5.0 to 8 .7 kohms.

[rick-l]

To save you some time here is all I can glean from the manual:

The wire to the coil comes from the unfused side of fuses 7 and 8 (the junction between) in the luggage compartment.

The wire is solid black and it says it is 2.5 mm^2 which if I assume correctly this number is indeed the size that would be a wire between the size of 14 and 12 awg.

The other wire on that node should be black with a red tracer (the same size).

This wire goes to the ignition switch.
It should be the only wire on the ignition switch with those markings.

[Crude Rudy]

If there is no spark the DME is not sending a signal to fire the plugs, a weak coil would cause a weak spark bur u should be able to see it in the dark with a spare plug in one of the plug wires.

I got the sensors from Bavarian Autosport, www.************, they were $57 each their p/n was 0 261 210 002 flywheel pickup-533, 535

[Socbum]

thanks for all of the help.
I'm waiting on the DME relay and I'm retesting the coil.

I did not get a spark at the spark plug wire but I am getting fuel.

If the DME relay doesnt fix the problem I will move on to the speed and crank sensor and the cylinder hear temp sensor.

I will post results after the swap

[rick-l]

You realize the DME relay will not effect the voltage you see at the coil?

Why not wonder out and look at the condition of the terminals around those fuses or even better bring your meter.

[dshepp806]

Originally Posted by Dave Colangelo

Check your fuse panel for corrosion on the tabs. I once had what I though was a big electrical issue but turned out to be a corroded fuse. To they eye it just looks a bit worn, the solution was to sand all the fuse tabs down to clean copper and replace all the fuses, total cost 5$ for fuses.

Always carry a spare DME relay with you, when i was DDing by 924s I always had one in the glove compartment.

Regards
Dave

THAT'S one of the FIRST things I did (on the fuse box) when I bought my 89 several years ago.....sanding down to fresh shiny copper (everywhere),..nice cleaning,.....retension,..all new fuses throughout...I watch it like a hawk (still)..certainly NOT the best design.

Best!

Doyle

[rusnak]

Yup. Logical starting point is to clean all contacts for the battery, grounds including dme, and the fuses with a small brass brush until shiny. Battery should be tested as well. Does the dme relay click twice ehile turning the key to start?

[Socbum]

Originally Posted by rick-l

You realize the DME relay will not effect the voltage you see at the coil?

Why not wonder out and look at the condition of the terminals around those fuses or even better bring your meter.

Followed your advise and checked the volts at each fuse with the key in the start position. I got a strong 13.6 v on the fuses (except for the fuses for lights which) and there is no corrosion on the tabs. I plan on removing each fuse and sanding the contact points in the fuse box so the look like a shiny penny.

The battery is new and the clamps are clean.

I put my finger on the dme relay and turned the key to start and I felt a single click. When I turned the key to off I felt a single click. Relay should arrive tomorrow and i will swap that out. Fingers are crossed.