Are you getting 12V at pin 27 of the DME. This is fed from the alarm module "Code Lock 1". Not sure, but I think the alarm prevents voltage going to pin 27 of the DME.

If this is OK and the DME is getting power, but no spark, then it can only be a DME issue, CPS fault, wiring break, incorrectly jumped airbag wiring or faulty coil.

The '92 968 has no ignition control unit right? The S2 has one of these between the DME and coil and if faulty there will be no spark.

 

Eric,

I'm following most of what you're saying, but not all, as I've never worked on an engine management system before, and my understanding of how all the components interact is rudimentary at best.

Yes, I'm getting +12V at terminal 27 of the DME when the key is in the start position. I'm also getting +12V at pin #7 of the 14-pin connector, which Joel Frahm told me indicates the alarm is not shutting off power to the DME. According to the wiring diagram, pin #7 goes to something called C64 - no clue what that is. And of course I'm getting +12V at terminal 18 of the DME connector whenever the battery is connected.

As far as the other possible causes you've listed:

- I've ruled out the CPS, because the tach needle bounces ryhtmically when I crank the engine
- It can't be the DME itself, because I've tried it with a different DME (only after making 100% certain I had straightened out the wiring at the 14-pin DME passenger footwell connector). Plus, I don't see how the DME could have gone bad just sitting for two years.
- I've checked the resistance across the various terminals of the coil per Clark's Garage's instructions, and everything checks out. I know someone who has a spare coil, so I could try installing it. However, a bad coil wouldn't explain why the blink test isn't working (would it...?). Plus, from what I've gathered, they fail pretty rarely, and again, it's just been sitting unused for two years.
- It still could somehow be related to the fact that I removed the air bag control module, but I've jumpered connectors 3 and 4 of the T41 connector, and across terminals 11 and 12 of connector #1 going into the ABCM (which seems redundant, since both connectors use exactly the same wires). I have a spare ABCM on the way, so I should be able to rule this in or out in the next few days.
- As far as a faulty wire somewhere, that of course is my worst nightmare. But I have inspected the condition of the wires in the harness when I had the engine out, and I didn't see any signs of trouble, like worn insulation.

Let me ask you this. Based on all the information I've posted on this problem over the past 2+ weeks (which I've summarized in this post), if this were your car, what would you do next? Thanks.

Edit: I said above that I don't quite understand everything you've said, but forgot to state what. You said earlier that terminal 1 at the coil gets its signal from the DME, yet you later stated "If you crank the engine and there is no spark to the plug when grounded then the issue is likely to be the DME terminal 1 is not firing a signal." These two statements seem to be contradictory (but of course this is surely because of my ignorance). Could you please clarify? Thanks.

 

OK, a major (if unexplained) breakthrough. I talked to Pete Fitzpatrick of RS Barn, and he told me that actually, the fuel pump doesn't energize when the key is in the start position. I'd been taking the lack of fuel pump hum, and my non-functional blink test, as indications that my DME isn't sending out a signal. But after talking to Pete, I decided to go back and check just for spark, and sure enough, there's spark! It's fainter than I had expected, especially looking through a dusty windshield, and I didn't even notice it after the first couple of cranks, but sure enough, it's there. Unfortunately, I have no idea what I may have done to fix the spark (getting the wiring to the 14-pin passenger footwell DME connector correct is the most probable thing), or maybe I didn't have the plug well enough grounded in my earlier attempts, so maybe I've had it for awhile (it's been awhile since I've tested for it). But anyway, this is a major step forward.

So, my next question is, when is the fuel pump supposed to turn on? At the DME relay terminals, with the key in the start position, I'm getting +12V at terminal 30 (labeled "battery" in the DME relay's diagram), and +12V at terminal 86 (ignition switch). But I'm getting 0V at terminal 87 (power to DME & injectors) and 87b (power to fuel pump). Is this normal? Would somebody mind checking - it's very simple - you just have to pull your DME relay and stick the leads of a voltmeter into these labeled terminals. Thanks.

 

OK - I probably wasn't clear. The DME terminal 1 provides a "signal" to coil terminal 1. This signal in terms of a voltage pulse effectively activates/turns on the coil so it will produce a high voltage spark.

I'll have a look at the wiring diagram.

PS - where there is something like "C64" in the wiring diagram, that refers to the coordinates on another wiring drawing where this line connects to. Simply find the grid C64 (on another drawing) and look for the coordinates of where you were. This effectively is the link between the two wires.

Are you sure the DME relay is good. I once got a new one that was faulty (Uro Parts rubbish)

I would look for voltage for you, but at the moment I'm in the middle of sump and belt jobs, hence batteries and wires are disconnected.

Have you also tried jumping 87b and 30 to see if the fuel pump is working?

 

Well, it's a miracle. Once I saw that I had spark, and Pete Fitzpatrick from RS Barn straightened me out on the fact that the fuel pump actually does no turn on when the key is in the start positions (I had been assuming the lack of fuel pump hum, along with a non-functioning blink test, was an indication that my DME wasn't sending out a signal), I went ahead and jumpered the DME connectors, turned the key, and voila! It fired right up!

Unfortunately, since I'd been operating under a pair of faulty assumptions, I'm not sure what exactly is responsible for bringing my engine back to life. I think it was probably getting the wiring on the 14-pin DME connector in the passenger footwell correct, although it might also have been the extra jumpering of the ABCM. But in any event, my ordeal is behind me. And not only does it run, but there are no Horrible Noises, the idle oil pressure is much higher than before the rebuild (north of 3 bars, where it was below 2 bars before), and, wonder of wonders, there are no leaks! So I went ahead and installed the DME relay, fired it up again, and it ran fine, confirming that my DME relay is good. And, most amazing of all, my blink test magically works now! I need to run out and buy a lottery ticket...

I really appreciate all the help and advice from folks like Eric_Oz_S2 (thanks to whom I now understand what those boxed designations in the wiring diagram mean), DocMirror, and Vinnie.

And a special thanks to Pete from RS Barn (with whom I have no affiliation) for his help not only with troubleshooting my no-start problem, but for the great products he sold me for the build. In particular, the dual oil coolers appear to be doing an amazing job. Per the instructions with my break-in oil, I heated the oil in the sump with a pair of space heaters prior to starting the engine, to about 120 degrees F. After firing it up , the oil temp quickly dropped to 92 degrees, and stayed there for quite awhile, before finally starting to climb. After about 15 minutes of a fast idle, long after the coolant temp gauge settled in at a steady 8:00 o'clock reading, the oil temp finally reached a reading of 119 degrees. I attribute this to the dual coolers. I can only imagine how great of a job they'll do with the car actually moving! Should be great at the track in the middle of the central Texas summer. I also bought a cat back exhaust from Pete (sounds great), as well as a host of other items, and he's always been great about answering my questions.

 

^^Glad you got everything sort out & from now on you can sleep well at nigth without waking up sweating from those nigthmars you had lately.

 

When I removed mine, I just snipped the one wire to turn off the light. Do you have the rest of your dash/instrument cluster in? When I rebuilt mine it wouldn't want to start until I put the instrument cluster back in. I also heard that the alarm can stop if from starting. You getting spark?

Sorry late, just replied to the front page, just seen you figured it out.

 

Thanks, Ernie. I forgot to acknowledge you for your contribution of posting the pins on the T41 connector to jumper. I think you were right about that all along.

 

I'm glad you got it going. Now get out there and drive it!

 

Glad to here it didn't get the best of you. Wow what a battle. Now.......... when is the test drive???

 

The test drive is still a ways off. I still have to (deep breath here...)

- Put the DME unit and glove box back
- Perform a blink test, now that it's working, and address any issues it might turn up
- Call the machine shop and beg them to finish drilling out the spindles to accomodate the larger diameter ball joint pins in my Racers Edge A-arms
- Install the suspension
- Buy tires
- Find a drivers seat. Ideally, I'd like to find one used to cut down on cost - something like a Sparco Evo or Sport 2000
- Test the fit of the used fiberglass hood I bought (likely to be awful), then have it, the splitter, and the brake duct scoops painted
- Install a roll cage
- Buy a harness

So, many weeks left to go before it's track-worthy. But if I can get the suspension on soon, and of course get the tires, I could install the Corbeau seat I'm planning to use as the passenger seat and take it for a spin as soon as a week or so. Why do I think this is wildly optimistic?...

 

I think you may have said this wrong. The fuel pump does run when in the start position, after the DME confirms that you have a valid CPS signal. Reread the first line of post 27 where I mentioned than a while back.

Also; DME relay ( you can jumper this once you get spark going)

 

Doc,

I wish I had paid better attention to the first two lines of your post 27 (to make matters worse, you weren't the only one who pointed this out to me). Somehow, I got it stuck in my head that the fuel pump comes on, and makes an audible hum, when the key is in the start position (the one right before the crank position), and I was interpreting the combination of the absence of this hum, the fact that my blink test wasn't working, and the lack of any voltage at pins 87 and 87b at the DME relay terminals, as indications that my DME wasn't sending any signals out to to the fuel and ignition systems. Had I checked for the presence of spark on the 21st, which was when I finished getting the wiring of the 14-pin DME connector in the passenger compartment correct, I'm sure the car would have started. So, all this time I (and the participants of this thread) spent chasing down how to "properly" jumper the air bag control module connectors was a complete waste of time.

 

We all get sidetracked sometimes. I see it on the 928 board all the time. We give advice on a troubleshooting step and the OP goes on his own way. I do it too. Just glad you're back to running. Hope you took the pax airbag out.

 

Yes, the passenger side air bag is out.