Injectors Not Firing / No Spark

McClintock16 · 05-24-2005, 09:48 PM

Went to the bank, and came out, wouldnt start. Waited a few minutes cranked again and finally it started and ran fine. Started fine for a couple hours of running around. Then in Lawrence, wouldnt start. Waited, let it cool down, started up again. Got home to see WTF was goin on, and it wouldnt start again. Checked plugs for oil thinking that sneaked up on me again, clean, a little glazed, but clean. Figured Eh, it'll start later... nope! So I dug into it AGAIN! Im gettin REAL good at this! No tach bouncy! Jumpered the DME Relay, no start. Pulled fuel rail, NO PULSING! So no fuel, I thought great! I found a problem! Figured crap why no pulsing? So eventually I pulled a plug again, NO SPARK! I figured HELL I'm on a roll! So I ran some ohm testing on the speed and ref sensors. Could not for the life of me get an ohm reading on the speed sensor, ref checked out fine. So I go into my hand dandy personal Porsche Parts Dealer (aka A plastic box) and pulled out a brand new speed/ref sensor, that god knows why is in there... And slapped it on, still no bouncy tach and of course still no start. So here are a few q's:

Which sensor controls the bouncy tach? Speed, or Ref?

I was told that only the ref sensor is essential to startup, this true?

What else would cause the DME to NOT pulse the injectors?

Zero10 · 05-24-2005, 11:02 PM

I would stand behind your initial diagnosis of speed and/or reference sensor(s). Changing the one sensor makes perfect sense. They seem to be the first place to start looking.

Here's one thing I did for s***s and giggles.
Unplug the speed sensor (the back one), and put an ac voltmeter on the 2 output pins (the ones that you can actually measure a resistance on), then watch the AC voltage as you crank it. Sounds like they might be gapped wrong. It's a relatively simple check. For comparison, my freshly-gapped snesors gave me about 5 VAC when I was cranking the engine. Any less than 2.5VAC or so and the DME will not see the signal, since the pulses will still be a logic low.

I previously printed off a big troubleshooting guide, since once I finished my engine rebuild, I had no fuel injector pulse, and no spark, but I have since lost it, but I grabbed it from Clark's garage, under ignition troubleshooting.

McClintock16 · 05-25-2005, 04:14 AM

I hope thats it, but I dont see why all of sudden they would be gapped wrong... Is it possible for it too just move like that? Cause I havent touched it...

McClintock16 · 05-25-2005, 06:20 AM

GOT IT! I put the very brand new sensor up as the ref. and was just NOT getting the voltage out of it that I wanted, well it turns out that the sensors HAVE to be tightened WAY down! Do they ground through the bolt or something? Well anyways, I was getting the proper resistance readings at the DME plug so I knew the wiring had to be pretty good and I decided to go ahead and tighten the ref WAY tight and boom she bounced and fired! Thanks for all the late night help! I sure didnt get any sleep! So Im thinking the speed sensor was what went bad...

Thanks Again! Im goin for a drive!

Zero10 · 05-25-2005, 09:09 PM

Good to hear you got it going!!
If they're not tightened down properly, they don't push all the way in, and will act just like they're gapped wrong

I guess it was kind of late at night when I posted, lol.
It shows, since I called then snesors

Drive it! Enjoy it! I wish I could do the same.

McClintock16 · 05-25-2005, 11:07 PM

What all is left to do on the turbo Zero?