samcknig

I have run into an issue with my beloved 86 951 that leaves me very nervous to drive it anywhere. For the last few months, sometimes the car will just crank and crank and not turn over. The car will start and run fine for weeks, then all of a sudden the crank-and-not-start problem will come back. It will continue to not start for a few days or more, then all of a sudden one day I will try again and it fires right up.

I took it to a supposedly knowledgable shop in Cincinnati and in the middle of their testing, the car decided to start for them. So they charged me the testing fee and sent me on my way. The problem has happened twice since then as well.

The car is currently in one of its no-start funks. I tried jumpering the alarm module as shown on Clark’s Garage thinking that might be causing the issue, but that did not help.

Any suggestions on what to check next would be appreciated. I can’t really drive the car anywhere for fear of being stranded again by it.

Thanks in advance.

joker2cv

You should check in order:

DME relais
RPM and REF sensors

I'm assuming that the spark plugs, wires, cap and rotor are in good shape.
Did you check fuel delivery?

Paul Waterloo

I have a similar issue with my 87....on my car it's the RPM and REF sensor wiring that goes along the top of the engine. It will run, but every once it a while it will stall coming up to a stop light. Sometimes it restarts, other times not....open the hood, jiggle the wiring at the connectors at the top of the engine (mine are not mounted in the mounts for the connectors), turn the key and she starts right back up.

Has also happened a few times when cold in the garage.

samcknig

Thank you both for the suggestions.

Spark plugs and wires are new within a year, so I am hoping they aren't the issue.

I have replaced the DME relay a couple times now (mainly because that's the first thing shops like to do and charge for).

Is there a write up on how to check the RPM and REF sensors? I will visually inspect today, but I don't really know what I am looking for. EDIT: I FOUND A WRITE-UP FOR THIS ON CLARK'S AND WILL ATTEMPT TONIGHT

As for the fuel, I have not checked fuel delivery (mainly because I don't have equipment to or know how).

Thanks again.

mtnman82

http://www.roguetuning.com/crank_angle_sensors
something to look at/think about...

Tom M'Guinn

Check to see if the tach is bouncing (twitching) when it won't start. If not, try wiggling the speed/ref sensor wires. The wires tend to fray under the rubber boot, so even when they look good they can be bad. Could be many things, but this is a common symptom of a common problem...

samcknig

Thanks, guys. So I went to crank it and see if the tach twitched, and of course the car fired right up. I guess I need to wait for the next no-start to see if the tach is twitching.

I never thought I would be bummed that my car started...

944Phil

Have you changed your starter or notched the bellhousing for the speed and ref sensors?

My car has a lot of trouble starting too. I put a rebuilt starter in and notched the bellhousing. The starter has electrical noise which throws off the speed and reference sensors, it's even more pronounced since I notched the bellhousing which removes some sheilding. There is an updated bracket (check paragon). The updated bracket helped for me, but it's not cured.

My car always starts, it's just embarassing sometimes when I have to crank it a few times

User 52121

Easily the #1 most common no-start reason has to do with the reference sensors, reference sensor wiring, or both.

Next time it doesn't start, if you notice the tach doesn't wiggle a little as you crank it, pop the hood and wiggle the connectors (two similar connectors, usually mounted to a bracket on the backside of the intake manifold), then try cranking again. The wiring tends to degrade over time and start to lose connection, preventing the DME from seeing the crank position signal.

Dash01

Could be a solder joint in the Motronic has gone bad. Simple reflow of the solder joints for the ignition transistor will fix it. Ign. transistor is a Bosch 1012 mounted to an aluminum heat sink on the side of the printed circuit board. It's drum-shaped, about the size of 4 stacked nickles. If the transistor itself is toast, can be replaced with BU941 transistor from DigiKey, about $3.50 each.

Google for info on Motronic resolder.

Simple test is to spank the Motronic while cranking the car: If the engine is cranking but no start, spank (slap not too hard) the Motronic to jar any hairline solder cracks for continuity. Also, when the car is running, spank the Motronic and see if that kills or stumbles the engine. Since the Motronic is mounted on the passenger side footwell, get an assistant to help, or use a broomstick, etc.

Prime suspects on crank but no start situations are main and fuel relays, speed and posistion sensors, ignition switch, and Motronic.

Start with the cheapest and easiest, such as swapping relays. I don't know about your car, but for example on BMW E36 there are 3 interchangeable relays--fuel, horn, and rear window defroster. It's handy to know to swap them if your car won't start some stormy night. Alternatively, plug the fuel relay in the horn socket, see if the horn still honks as a test. That's on a BMW E36, but perhaps your car has similar. Find out.

Most experienced 944 guys carry some spare relays in the glove box.

mdj577

Timely post for me.

My 86 failed to start for the first time today. I have noticed a couple of things:

1) dead cold the car starts immediately every time without a problem
2) hot, meaning after driving for a good 10 miles +, will re-start quickly if the time it has been off is not long (less than 5 min or so), but
3) if it has been driven then turned off and sitting for a moderately long period (over 10min but less than 45min) starter will crank the engine for a prolonged time before starting.

This 3rd condition happened to me today only the engine would NOT fire. After letting it sit for 30min + it started!!!

Any thoughts? I would like to nip this problem in the bud.

ehall

Okay, before you worry about any of the DME this or that or fuel yada yada, go back to Ton McGuinn's post. Until you can determine if the tach bounces, or not, during the no-start phase, don't chase anything else. There is about a 90% probability that it is frayed sensor wires. Lindsey Racing sells a replacement harness and sensors. Turn the car over and watch the tach. If it doesn't move, it's the ref sensor wiring. The sensors themselves just sit there, so it isn't the actual sensors, but the wiring. The car wouldn't run at all if the sensors were out of adjustment.
As jobs go, this one isn't that hard, even for a novice. This is one of the very most common problems with these cars, due to age. Once changed, you're good for another 20ish years.

ehall

Yours is likely more DME related, as some suggested above. You can replace the relay, but it's likely a problem in the actual DME. I'm sure one of these guys has a link to the previous discussion thread on DME resistor issues.

Tom M'Guinn

These symptoms might be from injectors leaking fuel into the cylinders after shut off, effectively flooding the engine until the gas evaporates away. Try flooring it when cranking -- opening the throttle will get extra air in there and may help. Worth a try anyway... Might also be worth checking the DME temp sensor.

mdj577

Thank you ehall, and all the rest, for the ideas and advice. In about a week I am installing DME and KLR chips (along with couple other goodies) from Lindsey. Hopefully this will solve the problem and I will not get stranded before then.

I will post with updates on status either way.