How to diagnose a 87 starting problem?
 

I have an 87 Carrera with 75,000 miles. It has run flawlessly since buying it 10,000 miles ago. Today, I tried to start it and it just turns over but wont start. I am familiar with older carbed 2.0's, but I am a little lost on this model. Here is what I have done so far.
1. Removed air cleaner and sprayed starting fluid. Still wouldn't start
2. Tried to get a spark from the coil to the center of the distributor. No spark visible.
3. Checked all fuses

What should my next step be?

Thanks,
John

Tap on the DME relay under your drivers seat and see if it starts.

Okay, second attempt - not sure where the first reply went...

Do you have a Bentley service manual - if not, you should get one asap.

A no spark condition could be caused by problems with one or more of the following:

1 - Cap, rotor.
2 - Coil.
3 - DME/Fuel pump relay. (Under drivers seat between altitude sensor and DME ECU).
4 - DME ECU itself.
5 - Speed and/or reference sensor/s.

Good luck.

Do you smell any fuel out the exhaust when you try cranking it over? If not, replace your DME relay first. After, possible, but not typical causes would be the TDC or RPM sensor.

If you do smell fuel, then check your coil and wires, or your head temp sensor is bad if it barely starts. Otherwise your DME box may need repair.

+1 on DME Relay, you should have a spare anyways.

Before that, check to see if the fuel pump is pumping, if not it is the relay.

Thanks all for the replies. I have tried several things that where mentioned. My son has a good running 87 and I have been stealing parts from his.
1. I exchanged the coil
2. I exchanged the two metal relays that are rearward of the coil.
3. I exchanged the relay under the seat.
Prior to replacing the relay, I pulled a plug and checked for spark. I was only getting a single spark that would not continue as I cranked the engine. I was only able to see the spark again if I turned off the ignition completely and then tried to start again. Then I would get the single spark. Is there any other parts I should try and swap?
Thanks again for all the help.
John

REPLACE the DME module......banging on it only pizsses it off.

Exchange Motronic units and see if his 87 starts with yours or vice versa. That'll answer that question.

Hi Mikez and all. I swapped a good DME module for mine and it still is not working. I also tried swapping the rotor.

John,
There is a good tech article on this problem in the technical articles section of this site.

Hi Ned,
I didn't find anything in the tech articles, but I am glad you reminded me to check there first. Thanks,
John

Cmon John,

Its 3rd from the end in the Fuel Injection section, thats 3 up from Suspension.

Hi Ned,
I found that article. Thanks for pointing me in the right direction. Don't know how I missed it the first time.

It has been a long day and I still don't have it running. So far I have swapped almost everything that the article and others have suggested.
Rotor
Coil
DME Relay
DME ECU
I am not smelling fuel and I am not getting a spark. It turns over, but wont start even when I use starting fluid.
Is there something else that can be tested?
Thanks.
John

Hmmm,

Have you checked the OHMs on the speed/reference sensor?

When I screwed up my reference sensor, it did nto turn over either. replaced it and Voila!

Just to confirm, you swapped both the DME relay (small black box) and the DME (large silver box) under the drivers seat with known good ones?

If yes it might be one of the sensors. Disconnect them and measure resistance across the two pins. It should be around 1 kOhm. If you find them in spec you need an oscilloscope to see if they produce the respective output while cranking the engine. You are looking for a 2V p-p sine signal on the speed sensor and single pulses with 2V p-p on the reference sensor.

Ingo

Ingo

Just chiming in with a relatively cheap suggestion - one of the first steps in diagnosing a starting problem should be checking + cleaning your grounds, in case you haven't tried it yet.

reference sensor
 

Hi Draco,
I have not checked the speed/reference sensor but to clarify, the car turns over fine. It just will not start. Would the sensor still be a suspect?
Thanks,
John

Hi Ingo,
I did swap both parts. The relay and the Motronics box. I will try and locate the speed sensor and the reference sensor. I can swap them off another car to test.
Thanks,
John

Connectors for the two sensors and the CHT are to the left of the electric fan on top of the engine. On the vertical metal clip. Don't recall which is which but you should be able trace them down and to check the signals there. They would be a pain to change out so I'd check them first. Ken

Mysterious car starts for no apparent reason!

I went to start diagnosing the speed sensor and the reference sensor and for no apparent reason the car fired right up. I haven't done anything since last night, and it certainly didn't work then. I did have the battery charger connected all night, but it was turning over fine before charging. Is there any logical reason for it to start working, or am I destined to be revisited by electrical gremlins at the most inconvenient time possible.
Thanks,
John