3.2 cranking but no spark

[gremlin]

Cool thanks, I just OHM'd out the sensors, and they're good. I ordered the light from Amazon it'll be here in a few days, and we'll see what we have then, beginning to suspect computer, as everything else seems good. It's that or fuel pressure, as I've not validated that, I would think that if I let the pump build though (Since it runs with the key in run, and not just when the DME tells it to, have to fix that one day) it would at least sputter or cough.

Also I noticed the tach doesn't move when it's cranked, is that important.

[ischmitz]

Electronically all three (tach, injectors, coil ) will work once the sensors see flywheel motion. The tach isn't always good enough to show the ~200 RPM during cranking though. So I'm not sure I'd put too much into that observation. Let's see what the NOID light will tell us.

[gremlin]

Noid light shows injectors not firing, next up trying to check grounds


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[ischmitz]

Injectors don't need GND. They get +12V from DME relay and GND pulses from the DME. If the coil works your GND to the DME is fine.

You start to narrow issues to the DME. Send me a PM if you need it checked/repaired.

Ingo

[gremlin]

I'm going to try my dme in another car first, I have a spare but don't want to blow that up, what can kill a dme?

[ischmitz]

DME killers would be shorts in the harness (injectors, coil) or a miss-wired tachometer

[gremlin]

Hmm, seems unlikely those would have cropped up in a car that's been running for 20 years but that's where I'll look. I'm going to try my ECU in a friends car this weekend, and go from there. Is it more likely it just failed or that something killed it? I'm also thinking I should trace the harness for the injectors back and make sure it didn't just come unplugged, the engine was out earlier this year, it's seen 2 tracks days and maybe 200 miles of street driving since then but we could've screwed something up when it went back together.

[mysocal911]

Originally Posted by gremlin

Hmm, seems unlikely those would have cropped up in a car that's been running for 20 years but that's where I'll look. I'm going to try my ECU in a friends car this weekend, and go from there. Is it more likely it just failed or that something killed it? I'm also thinking I should trace the harness for the injectors back and make sure it didn't just come unplugged, the engine was out earlier this year, it's seen 2 tracks days and maybe 200 miles of street driving since then but we could've screwed something up when it went back together.

Besides the injector harness coming loose, an over-voltaging alternator (bad regulator)
can damage the DME control unit's injector output resulting in no injector signal.

[gamin]

Has anyone mentioned to check for tightness the ground connections on the intake manifold above #1 cylinder? A number of them come together there. Saw this happen before. Wasted a lot of time doing a lot of checks. Problem solved by simply tightening the ground connection. Duh.

[patz]

When mine exhibited those symptoms, it turned out to be the 12v power to the DME fuse. It had worn thru the metal on the top. Replaced the old fuse and haven't looked back.

[gremlin]

Where can I measure for 12v to the DME At the relay or pull the power on DME? Would this be the case if I have spark and it cranks?

For grounding I attached some jumper cables to that bolt on the runner and ran it tot he front of the car where the batteries - terminal are attached to the chassis, no difference so I doubt it's a poor ground.

I'd check alternator but how do I do that when the engine won't run? It won't be measurable while cranking!

[scarceller]

One shorted injector will take out the other 5 because all 6 are wired in parallel. I suggest you unplug the injectors on the LHS cyl1-3 and see if it attempts to start. Basically you are eliminating the 3 LHS injectors to see if she starts. Then do the opposite RHS the same way. If you find that disconnecting the LHS injectors now allows the engine to start then one of those 3 are shorted, continue plugging them in one at a time till you find the shorted injector.

I mention the above because you already said you can't detect injector pulses with a noid light. You can also try the noid light test again but unplug all injectors except just 1, and test at that 1 injector to see if you now have pulses.

I don't see this as a common problem but I have seen it a few times.

[mysocal911]

Originally Posted by gremlin

I'd check alternator but how do I do that when the engine won't run? It won't be measurable while cranking!

Right, you can't until the engine runs and you still might not determine over-voltaging
if the alternator is intermittent. But if the DME ECU's injector output turns out to be
your injector problem, an intermittent alternator can cause that. As mentioned, a shorted
injector/injectors or wiring can cause the same problem, but it's rare.

[gremlin]

Thanks I'll check these things next. Seems like all I've got left are rare failures, as I've already found the common ones are good.

[mysocal911]

Originally Posted by gremlin

Thanks I'll check these things next. Seems like all I've got left are rare failures, as I've already found the common ones are good.

Hopefully it's a simple wiring problem and not your control unit.
Make sure the up-shift wire from the control unit (pin 11) is not being used
nor connected incorrectly as this will also damage the injector output.

[Stutzdriver]

Has anyone checked the flywheel sensors. I had one of mine fail so I put in both new to head off any future issues as they were a fita to replace....Put them in and it fired right up! These are either good or bad no in betwen...If there is no signal to the DME from these sensors the DME will do NOTHING, frustratinf when it happens suddenly.

[gremlin]

Yup above in thread plus if either of those fail you won't get spark. I haven't checked CHT sensor just yet, so I'll also do that but next up is looking for a shorted injector. I doubt that the upshift wire is the issue as the car's run in this configuration for 23 years now...

[cabmandone]

Originally Posted by gremlin

Yup above in thread plus if either of those fail you won't get spark. I haven't checked CHT sensor just yet, so I'll also do that but next up is looking for a shorted injector. I doubt that the upshift wire is the issue as the car's run in this configuration for 23 years now...

CHT shouldn't effect spark, it will effect fuel mixture. Car will run REALLY rough with a bad CHT or one that looks connected but isn't (as was my case when my car started running like crap)

[scarceller]

You need to be very clear on what works and what does not. If you have spark then both crank sensors are working. So if you have spark but no injection pulses we know it's something in the injector drive circuit or the injectors. I test for coil and injector pulses with a simple LED test light, you can get one at Walmart for about $5.00 but it MUST be the LED type. Just unplug an injector and put the light across the 2 pins in the injector harness and have someone crank the starter, the LED must flicker if you see no LED activity you have no inj pulses. You can use the same test light across the coil's '-' and '+' posts and it will also flicker if you have coil pulses. The LED test light can even be used to test both crank sensors, unplug each sensor and put the light across the pins that go to the sensor, then crank motor and again the test light must flicker.

Where are you located?

[patz]