968to986

Hi everyone,

I've been chasing what seems to be an elusive no-start problem. I got some good suggestions on the Facebook group, but still haven't been able to solve it. I'll try to be as detailed as possible. 87 951 with Tial wastegate, LR chips, manual boost controller, 3 bar FPR, rebuilt K-26 turbo. Ran fine for the past couple of years, but would occasionally have a no-start issue, but would always start later. Several weeks ago, I was driving it when it just died. Got it off the road and within five minutes was able to get it started. Died again pulling into my driveway and I haven't been able to restart it since.

What I've tried so far, somewhat in order:
Replaced fuel filter, no change
Tested for spark, no spark at plugs
Replaced both reference sensors (crumbling connectors)
Installed LR ref. sensor harness (previous rodent damage, but car still ran), no change
Tach bounces during cranking, suggesting reference sensors are working?
Battery was showing just under 12V, so had it charged just to be sure, no change
Pulled DME relay, jumpered as per Clark's Garage, fuel pump running, but no start
Pulled apart DME relay, soldering look fine, reinstalled relay
Still no spark at plugs, but I get spark from coil lead
Replaced cap and rotor with a used one from a running 924S, still no spark at plugs

So that's where I'm at. I'll admit to being fairly mediocre at systematic troubleshooting, so any suggestions would be most appreciated. Thanks!

divil

To answer your question about the sensors, yes the bouncing tach should rule out the sensors and harness. A common enough issue after that is the KLR, but since you're getting a spark form the coil lead, that rules that out too. How did you test that? One possible explanation is that the way you're testing for a spark at the plugs is flawed, and you really do have a spark. Then the problem is most likely going to be fuel. It sounds like the pump is running, but there's still the injectors, harness, DME. One way to check all this is to pull the rail with the injectors attached, and use a container to catch any fuel while you crank the engine. If you're seeing fuel being injected then you can rule out a lot of stuff.

fast951

Since you are getting spark at the coil lead, then Speed/Ref sensors + DME relay + DME + KLR are working.

It may be needed to check injectors spraying, if you figure out ignition issues and still no fire. For now, let's assume you have fuel. But to eliminate the chance of flooding the engine, remove the fuel pump fuse while dealing with the ignition issues.

How did you verify you have spark at the coil lead? Did you actually use a spark plug connected to the distributor center lead? If your answer is yes, then there isn't much left to test. You have distributor cap and rotor then plug wires.
Do you know the history/condition of the used cap & rotor?
Did you use multiple plug wires to verify if there is spark?
Did you verify that the timing belt is operational and engine is turning?

It' s properly something simple.

​​

968to986

Thanks for the reply. I have an inline spark tester (just a cheap one) that I plugged into the lead from the coil. I could see spark in the tester. Did the same for the plug leads, though I did not actually plug the tester onto the spark plug, just on the lead going to the plug. Maybe it has to complete the path?

I will check for fuel at the rail later today (going fly fishing in a bit!). One thing that is weird is that I don't hear the fuel pump when I try to start it unless I have the DME relay jumpered. Will the DME relay from the 924S work as a test relay?

Tom M'Guinn

Not entirely sure I follow your post, but you won't get spark without a path to ground. I'd double check for spark at the plugs... I'm guessing you have it and your problem is elsewhere...

968to986

I'm finally getting back to this issue after being out of town. To answer some of these questions:
To check spark at coil lead, I didn't use a spark plug, just plugged my spark tester into the lead. It showed spark.
I swapped out the cap and rotor from a running 924S, but it is used. Still no spark at plug.
I have not yet checked for spark at all four plug leads (though I did check at cylinder 1 and 2), but I will tonight or tomorrow.
Timing belt is intact, presumably rotating. I'll also confirm that.

Just to rule out the DME relay, I installed a new one yesterday, no change.
I also did the the three wire emergency start jumper as per Clark's Garage (87, 87a, 30). Fuel pump runs, no start.
During this, I had the battery jumped to my truck to give plenty of cranking power.

A couple of questions of my own:
Should I try testing for spark with the jumper wires in place of the DME?
Should I be testing ignition switch?
Should I be testing the actual DME?

Any more suggestions would most appreciated! I just finished my front Koni coilover conversion and I'm dying to try it out.

Chris Prack

Coil wire spark but no spark at plug wire? This should be pretty straight forward. Is the rotor spinning while the engine cranks? If the cap and rotor are known good then you have mechanical issue with the rotor drive or cam belt etc.. The only other issue I can recall is a failing coil. It wouldn't produce enough spark to fire the plugs but had enough to produce spark at the coil wire.

Tom M'Guinn

I'd use a spark plug to check for spark from the coil wire, and then at the end of the plug wires. Put the lead on the plug as normal, and use a jumper cable to ground the body of the plug to the grounded chassis. If you still have spark at the coil and not at the plugs, then Chris (welcome back) pretty much sums it up, although I'd toss in the theoretic possibility of very bad spark plug wires that are letting the spark out before getting to the plugs... (And, no point in messing with the DME relay if you really have a good spark pulse at the coil.)

968to986

Thanks, I'll try to confirm that the rotor is spinning. Though I do see spark from the coil wire, it seems a little weak, so maybe the coil is weak.

Also thanks, I'll try using a plug to test for spark. It's true I don't trust my cheap spark tester. I feel like one question I have to answer is whether the spark coming from the coil good spark or weak spark.

968to986

Okay, so I'm continuing to test for the answer to this problem. Today I used a spark plug in the coil lead to test for spark from the coil. I used jumpers cables (one side) to ground the threaded area of the plug to the negative terminal on the battery (adequate ground, correct?). There was no spark. I put cheap spark tester on the lead, and there is spark. WTF? I also used Clark's recommendation of grounding the plug and running a lead from the negative side of the coil (green wire removed) and touching that to ground at the negative terminal. I was able to get a couple of weak sparks at the plug but very inconsistent.

But I decided to go with the results from the grounded spark plug, so let's call it no spark from the coil. Checked for voltage across the positive and negative terminals with the ignition on, no voltage. Okay, so bad coil? Installed coil from running 924S and got the same results, no spark, no voltage. BTW, resistance checks out the same on both coils, within spec as per Clark's Garage. So why would I not be getting voltage to the coil?

Tom M'Guinn

Follow the full test clark set out here:

http://www.clarks-garage.com/shop-manual/ign-04.htm

You can't test for voltage across the coil, so that test doesn't tell you anything. Test for 12v between the black wire and chassis ground. If you have 12v there, then see if the tach bounces when you crank it (to check for speed/ref signals and DME ignition pulse), and confirm the boost gauge shows 1 (or close) when the ignition is on and engine is off (to check for power at the DME/KLR).

968to986

Thanks again, Tom, not only for your help here but for the many other suggestions you've made in various threads I read related to no-start problems. You're right of course, I misread Clark's coil voltage test. I got voltage on both coils by testing at coil terminal to ground. Tach does bounce, and boost gauge shows a little under 1 bar with ignition on. I got hopeful for a moment when I discovered the coil lead could be pushed a little tighter into one of the boots. Alas, no change. Though all the plug wires and coil wires look in great shape (seems like good quality, pliable, no cracks), I suppose my coil wire is defective. Feel like I'm grasping at straws now.

Dan Martinic

Dan Martinic