Engine Died While Drive - Will Not Start
 

Hi All,

I have an 88 911 3.2; The other day while driving home from work the engine cut out (tach dropped straight to zero). The car will crank, but not start. I had it towed home - but it will not start.

I was driving at 55MPH on the highway. Everything was normal. The car has never done this before and never had any kind of starting issues.

I did search around the forum,but this seemed pretty different from other issues/threads I could find.

Any suggestions would be appreciated.

beren

High percentage chance the DME relay. Buy and replace, avoid URO products.

Assume you have checked for spark, fuel and air?

Fuel pump buzz'ing (or not) is an easy check.

+1

Is the idle air control vibrating?

Had this happen twice with my SC...it was a bad coil each time.

Check the obvious first. DME relay as others have said.

Thats not an easy check on a motronic car, because the fuel pump only turns on while the engine is cranking. You have to jumper the fuse (#3 I think) to see if the pump comes on with key in run.

Thanks guys - appreciate the help. I'm decent with the basics, but by no means an expert. I'll order a DME replacement.

It does seem like the fuel is not getting to the engine. After 30 seconds of cranking away I would think you would smell something at the tail if fuel was flowing. I would think if the pump failed I would have had some sputtering or something. In this case I was driving for about 30 miles and it just went dead.

I'll check for a spark tomorrow - I guess I'll just yank a plug from the right hand bank and get the wife to turn the engine over and see if there's a spark. Battery looks good on a voltmeter and I don't see anything wrong with fuses.

DME relay is the quick obvious choice

Also check that the DME is getting over 12V and that it is grounded well (check the engine ground strap also). I can't remember the specific voltage but if it's even slightly deficient, it shuts the fuel injectors down.

Careful on excessive cranking in case you are getting gas, don't want to hydro lock. Tim

How do I do that? pull it off and check the terminals? What position do I need the key in to do this?

Give the intake a shot of ether/quick start when cranking. No start, it's the DME. If it tries to start it's the fuel pump.

I really don't think a cylinder ever actually tries to fire. The engine is cranking away, but it never really sounds like it is trying to start. In all the years the car has started right off - 2-3 seconds and vroom, even after a few weeks of no driving in the winter. I never drive in bad weather or terribly cold stuff.

Before you do anything turn the key on and put your hand on the IAC

+ 1, fastest way to find out if you got sparks.

Do this.^^^ Turn key on and see if the Idle control valve is vibrating. If it is then jumper fuel pump fuse to see if it comes on with key in run. (I believe it is jumping fuse 3 to 4) If car starts the relay is bad. Or you can just wait the 2 days until your new relay arrives and see if it starts. ;)

If you are a novice, wait for the new DME relay, plug it in and let us know.

This just happened to me tonight - pulled the distributor cap, scuffed up the points, and voila - she started right up! Time for a new cap and rotor.

The DME controls the fuel injectors and the spark. So if the DME relay fails, the DME doesn't get its 12-13VDC supply, and you won't get either a spark or fuel because no signal is sent from the DME to the injectors to open, or to the spark coil to fire.

The cylinder head temperature sensor can fail, but that usually means really hard starting, and I think generally the engine will run, albeit not very well. If you are getting spark (easy to check) and fuel (not quite so easy), then I'd look at CHT replacement. The ether squirt will be diagnostic here. Your '88 should have the two wire CHT sensor, which is said to fail less frequently than the single wire ones the '84s had.

Put your hand on the relay and turn the ignition to run. You should hear or feel a click. If not, it's not getting power or it is defective. Check the fuse that supplies power, pull the relay and re-install or replace it.

While I keep a spare just in case, my no start on my 3.6 was caused by a defective fuse.

Thanks everyone! It was the DME relay. I replaced with with one from the host and she started right up and runs normally again! :D

The DME relay in the car looked original. The hardest part was getting the nut off without shearing the bolt off. Little WD40 and 15 minutes loosened it up.

Definitely something to keep in an "oh sh--" bag - should maybe have a sticky thread for suggestions on what to keep in that.

I pulled apart the old one and didn't see any obvious issues. A pretty delicate device with those little switches.

It's good you've ordered a new dme to try, you need a spare for the glove box anyway if that's not it.

I had no start issues on my 85 a while back and ended up replacing the speed sensor for a couple of weeks of running then repeated the no start yielding a bad reference sensor. Replaced it too, running fine since then (many months, now).

The No. 1 "no start" troublehooting item I gleaned from lots of pp forum searching and reading:

Check for spark before you start buying parts or checking fuel.

Didn't see your last post before I sent mine in, glad you found it. Get another for a spare!

You meant the DME relay not the DME.

Yes the relay - updated my post above.

Great, now you need to re-order as one should always have a working spare in the glove box.

Small price to pay for those DME car.

When you get the spare relay pop it in and check it so you know it works before you put it in the glovebox. get some fuses while you are ordering, its also handy to have a window switch.

Carry a full set of fuses already. I'll have to add some more tools like a 10 mm box wrench that you need to change out the DME relay.

The usual failure mode of these DME relays is a cracked solder joint. The circuit board, with its heavy relay coil, is held to the board into which the wire connector plugs by various pins soldered in. The vibrations of the car, and the up and down motion of the coil board, can eventually crack one of these soldered connections which carries current or ground or the like. You can test with a multi-meter to see which one is bad. You can just reflow/resolder all of them just to be sure. Then test it - it should work. If you put a piece of foam between the bottom of the relay board and the case, it should support it and might prevent this happening again. Then it can be your spare. Of course, if the contacts are all pitted and burned, or one of the tiny wires which energizes the solenoid coil is broken, maybe it is for the dust bin.