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No Start, No spark, No coil pulse

 
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ViktorTsoi  



Joined: 31 Dec 2013
Posts: 80
Location: Idaho

PostPosted: Wed Sep 27, 2017 2:08 am    Post subject: No Start, No spark, No coil pulse Reply with quote

A friend of mine recently acquired a 84 944 from his dad that had not been driven for some time. He did the FOES, replaced the reference and speed sensors, rotor, cap, and plugs. He said it would start, idle poorly, and die if the accelerator was pressed quickly, but would keep running if the accelerator was pressed slowly. Occasionally would backfire through the intake lightly and die.

He asked me to look at it for him the next day. Wouldn't start, tried starter fluid didn't fire. No tach bounce so suspected DME. Replaced with good one out of my car, no difference. Checked reference and speed sensor with oscilloscope at ECU connector and both have a strong clean signal. Checked power and grounds at the ECU connector with DVOM and then a test light, everything looked good. Checked for coil pulse backprobing at the ecu connector, nothing. Replaced ECU with a good one from my car, no change.

Did not check the injectors, never smelled any fuel so I suspect they are not being fired as well.

Don't know what to check next. Any input would be appreciated.


Thanks
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1978 924 -parts car
1982 924 -sold
1985 944
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toast54  



Joined: 08 Sep 2014
Posts: 78
Location: Oklahoma City OK

PostPosted: Wed Sep 27, 2017 2:56 am    Post subject: Reply with quote

Something I ran into was a detached DME ground wire (brown) from the fuel pump relay socket. It was well-hidden and there isn't a lot of slack to the wire itself Fixed that and it started, still wouldn't stay running. I had somehow mucked up the potentiometer "arms" in the AFM. It runs, but I still have an issue with the DME and it will die suddenly, but that's another issue to address. Just my .02
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Grenadiers  



Joined: 20 Feb 2007
Posts: 3223
Location: Nelson, WI & Prescott, AZ

PostPosted: Thu Sep 28, 2017 10:58 am    Post subject: Reply with quote

Check the rotor, that small little @#$Q^$#^ screw that holds it in place, might be missing.
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'88 924S Track car.
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ViktorTsoi  



Joined: 31 Dec 2013
Posts: 80
Location: Idaho

PostPosted: Thu Sep 28, 2017 5:02 pm    Post subject: Reply with quote

I looked at it again tonight. Took the cap off, rotor is attached properly.

The owner mentioned the car may have had ignition switch issues in the past so I rechecked the power and grounds to the ecu in the run and start positions.

I pulled the DME relay back out to test power and ground at the socket, all the connectors are present and everything checked out, but there is a 500 ohm resistance on the pin that the ecu grounds (85b I think). The resistance is the same measured at the ecu end.

I stuck the DME relay back in and pulled a plug to check for spark again. I cranked it and could see spark, and the car started and ran on 3 cylinders for a few seconds. I shut it off, put the spark plug back in, restarted it and it idled rough. Revved it up and it ran perfect, revved freely. Let it back down to idle and it died after ten seconds of rough idling.

Would not restart, no spark, no injector pulse, no coil pulse, no tach bounce. It does have fuel pressure.

Unplugged the DME relay, plugged back in. No change. Wiggled it no change. Swapped in different DME relay no change. Swapped the ecu no change.

Seems like an ecu issue to me, but my ecu starts my car just fine. I scoped the reference and speed sensors in my car and they look the same as his.

Does anyone know exactly what inputs the ecu requires to provide the coil pules? I thought it just needed power, ground, reference and speed signals.
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1978 924 -parts car
1982 924 -sold
1985 944
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Grenadiers  



Joined: 20 Feb 2007
Posts: 3223
Location: Nelson, WI & Prescott, AZ

PostPosted: Fri Sep 29, 2017 1:28 am    Post subject: Reply with quote

Did you check the TPS? Seems the car runs at WOT but nothing else.
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'83 944 Track car.
'88 924S Track car.
'89 944 Turbo
2004 Winnebago Vectra monster RV
2012 Jeep Wrangler
2014 Kia Soul
2001 Ford F350 powerstroke
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