zogster

Maybe an ignition coil problem?

I tried the crude coil test as per Clark's Garage, disconnecting the lead to the distributor, connecting a grounded spark plug, and then touching a ground wire to the (temporarily disconnected from green wire) ground terminal on the coil. No spark at plug.

divil

Did you check the resistance of the coil (described in Clark's Garage)?

Also, I think I left something important out earlier...I said you should see 12v on the positive coil terminal with the key on. You should see 12v on *both* primary terminals.

zogster

No, didn't check the resistance. I'll try that, and check for +12V on both terminals.

Can a coil problem be intermittent like this? The issue has the feel of a bad connection somewhere, in that while the engine is running it's running smoothly, and it either starts and runs cleanly, or doesn't start at all. Kinda binary, all very on/off…

zogster

So I have +12V at both terminals when ignition is on.

Resistance measured at around 6K Ohms for the secondary coil, and 2 Ohms for the primary. Clark's Garage says 0.4-0.6 Ohms for primary, so it appears well out of spec

divil

Yeah that does sound bad. I honestly don't know how that could be intermittent, but with the coil failing to produce a spark, and showing at least 3 times the proper resistance, I think I'd replace it. Since it sometimes works, it might be worth repeating the coil tests next time the car actually starts - i.e. before it cuts out by itself, stop it and do the resistance check and the spark test.

jeffro951

I suggest you test the speed an reference sensors as thoroughly first and watch this video on how to do it.
if the sensors pass those tests then test for fuel and spark you will need a noid light to test for power to the injectors.
My guess is you have a faulty sensor or wiring to them. Lindsey racing sells a nice replacement harness for the sensors, I would suggest the harness for the injectors as well.

zogster

Thanks! Tested as per video, and I think both sensors check out.

Speed sensor gave about 800 Ohms and 2V

Ref sensor about 1100 Ohms and 0.1V

The ref sensor output seems low at 0.1V, but it's a voltage and it's below 1V, so I guess that's OK...

I'm going to try and pick up a coil today and see where that gets me.

zogster

ps. and, duh, the video actually shows about 0.1V for the ref sensor voltage... not low at all

Alpine951

The wiring in these cars is old. I experienced similar problems of no start and jiggling wires. Here is a pic of the injector wiring in my car. This condition also existed with the reference sensor connectors on my car as well. it gets worse when you move stuff around like doing turbo work, removing the intake manifold, etc.. I had to put new ref sensors , plus a new harness wire going from the ref sensor connector down to the dme, plus I cut out the injector pig clips and spliced in new bosch connectors. I would bet if you cut open the rubber boots on the reference sensor connectors you would probably find this condition. Maybe the same for the injector clips as well.

jeffro951

I agree with Alpine 951, I have 2 turbos and I have rebuilt the harness in both cars and installed new grounds and wow what a difference it makes. I had problems with intermittent injectors that's were a noid light is worth its weight in gold. Also the last one I did the coolant sensor connector was shorting out causing all kinds of issues. The wire harness has been disturbed were the coil has not. if the coil was functioning before the rebuild/refresh is should still be good now but it is not a bad idea to replace it with a MSD blaster.

zogster

I replaced the coil as planned, and it didn't make a difference. Same routine: couple of no-starts, a bit of staring and swearing, and then it started, and shut down after a minute or two.

The wiring in my engine bay is original so is showing alot of the same signs of age that you're describing. The boots on the TPS and AFM connectors are split, the injector connectors are in various stages of deterioration, the speed and reference sensor connectors are starting to fall apart (had starting trouble caused by those before.)

So an intermittent problem due to bad wiring somewhere in all that mess now looks pretty likely.

I was planning on replacing injector pigtails, and the 3-pin speed and reference sensor connectors... maybe I should go ahead and replace at least the rest of the speed and ref wiring, and maybe other sensor wiring where it's easy enough to get to

jeffro951

I just made a photo album of my current cars and there is a few pics of my harness after rebuild. 944online sells a complete connector kit for around 150 bucks. I highly suggest you get a noid light to test for power at the injectors because after I rebuilt my second harness I still had one bad injector lead so I replaced the injector harness with one from Lindsey and problem solved. would have been a pain to find this without the noid light. Also I suggest the reference sensor harness from Lindsey because the wire used is shielded and yours will be brittle and hard to work with when you go to put a new end on it, it can be done as I did it but if I have any problem there again the first thing I will do is install the replacement harness.

jeffro951

Okay I just read through the whole thread again and I have a few questions for you.
What year is the car?
Does it have a factory alarm? after market alarm?

If it is an early car then I would replace the electrical portion of the ignition switch since it is a common failure. You can bypass this to test by pulling the connector and with a 3 wire jumper like what you would use to bypass the DME. plug one in terminal 15 and one in 30 and touch 50 to start the car.

Did I just teach everyone how to hotwire a car? I thnk so lol

zogster

Looks like I can replace the speed and reference sensors without pulling the turbo out again so I may go ahead and do that... though I'm a bit reluctant to replace things that are working. I'm seeing tach bounce and the sensors check out according to the video test procedures so it does look as if they're OK.

The Noid lights look worth getting - I haven't looked at possible injector trouble, though the plugs smell of petrol after cranking, so I think that side's good

zogster

Jefro: it's an '87, RHD. No alarm any more (pulled the old one out last year) but it has an Autowatch immobiliser. I don't think that's causing trouble, partly because when I suspected it a while back I learned how to bypass it, and I've tried the bypass trick while troubleshooting this stuff.