pettybird

So I got stupid and decided to change my engine wiring harness in the middle of winter. I was having a bunch of weird electrical problems, so I posted a wanted ad for a harness. Lart came through with one that looked a lot nicer than mine. I have no doubt he'd stand behind it, but (1) it's a PITA to install a harness, especially in freezing temperatures and (2) I tore up my old one enough when I took it out I kinda need to fix this one. And hey--who doesn't like diagnosing an electrical problem?


The car ran Saturday immediately before I removed the old harness, and it's my daily driver.

There is no tach bounce, no injector pulse and no spark.

Things I've checked:

DME relay--installed another known good AND jumpered the board. Fuel pump turns on, etc.

Reference sensor--the one in the car is only a year old, but I swapped it out for a brand new one.

There is power to the DME at terminals 3-4? with the ignition on.

There is continuity at pins 47-48 for the reference sensor.

No change when I pulled the harness plugs off of injectors 1&2, meaning (I hope) that the injector driver is not somehow shorting out.

There is no change when I disconnect the TPS, AFM, O2, oil pressure switch or cam sensor.

Connected jumper cables to a running car to increase cranking voltage



The gauges read--all warning lights work, and the tach does move initially, and then comes to a rest just above bottom when the ignition is switched back off.

It was suggested that the wiring for the two-prong temp sensor in the head, if shorted, would cause a no start. Also, the harness I just installed had two wires coming from the plug by the fuse box that were not on my harness...looks like a black and a black/yellow, and the wires were at least 4 feet long. I have no idea where this would even go.

What else am I missing? I have to press the 951 into service until I get this squared away and I'd really rather not drive it through the rest of an Ohio winter, especially on Z rated directionals...


Thanks

Doug

pettybird

anyone?


I'm not complaining too much about driving a chipped '89 turbo with M030, 10 speaker sound and sport seats, but it's going to snow some more soon!

flightline

Ideas: Check good ground at pins 16,19,5 and 28. Did you also check the speed sensor resistance (pins 8,27)?

Is there battery voltage at the injector plugs (pin 2, red/blue wire)?

My understanding is that the fact that the fuel pump runs (with the DME relay, not neccesarily with a jumper) means that the DME is turning on, and registering that the crank is turning at some minimum speed (200 rpm?).

gtroth

i'd go through the 944S/S2 DME Diagnosis and Troubleshooting Guide in the FSM and measure all the signals at the DME connector. You'll need an oscilloscope for the ref+speed sensor measurement which with your symptoms I would definately do.
And this is what the Guide says should happen for shorted NTC II engine temp sensor (sounds like it might have some trouble staying running when cold):

pettybird

thanks guys. Now I need to duck out of work early enough to check this stuff in the daylight!

aj986s

I'm not a expert on this, but you may also want to check on the year of the harness versus the year of the car and ECU. We've had to do some engine swaps over the years, and ran into some compatability issues with the ECU. The shop that worked on mine had to do some tedious analysis to confirm that signals from engine sensors were getting to the right inputs for the ECU. If the wiring harness is from a different year car, you may want to consider sourcing/borrowing an ECU equal to the harness year, and try starting with it plugged in.