94 base model will crank but not start - 3000GT/Stealth International Message Center
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Old 11-12-2012, 12:32 PM   #1 (permalink)
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Default 94 base model will crank but not start

I recently got this car from my brother.
The engine was rebuilt about a year or so ago (maybe20k miles or so.) not sure exactly. It overheated recently so I replaced the water pump, the thermostat. Car ran good in driveway for about 20 min without overheating. Got stuck in a traffic jam and started to overheat. I got it off the road and found a busted lower rad hose so i let it cool down and changed it. The split in the hose was aimed at the Area where the PTU and coils are and sprayed them pretty good with hot coolant. Then it wouldn't start so I towed it back to my house. I have fuel delivery ( fuel on the plugs) when I checked the spark I found that the middle coil is giving spar but the 2 outer coils are not giving spark. I met a guy who has multiple 3k's near me and he brought over some working ignition parts out of his 94. Swapped plugs and wires, all coils, swapped PTU, swapped ECU, swapped the fuel relay. With all the working parts it still does the same exact thing. He thinks that it is the etacs box that is behind the dash of the left side of the steering wheel. I looked it up and that looks like it controls accessories only. What does that box do exactly? And could that bow being bad cause the car not to start. If it is not this then what could it be? Could that coolant Have shorted out a plug or something to the PTU or coils. Should I check the timing again? Pease help this car is my daily driver I have a motorcycle that I have been driving but it's getting cold lol.
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Old 11-12-2012, 03:32 PM   #2 (permalink)
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Default Re: 94 base model will crank but not start

Anyone? Come on guys
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Old 11-12-2012, 07:12 PM   #3 (permalink)
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Default Re: 94 base model will crank but not start

So i thought maybe a crank sensor would be out but im pretty sure you wouldnt get spark on any of them.
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Old 11-12-2012, 10:24 PM   #4 (permalink)
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Default Re: 94 base model will crank but not start

yep, the cam and crank sensors will prevent any ignition event if one or both is bad. I still think it's the PTU. Or harness connections leading to or from it. It's too coincidental to not consider that possibility considering it ran fine before getting doused with coolant.
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Old 11-13-2012, 01:58 AM   #5 (permalink)
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Default Re: 94 base model will crank but not start

I thought it was the PTU also but it does the same thing when a working PTU was installed. I guess I will have to check the wiring and connectors. Can anyone tell me or point me in the direction of how to test the plug to the PTU. and what voltages it should produce at the certain pins.
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Old 11-13-2012, 02:04 AM   #6 (permalink)
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Default Re: 94 base model will crank but not start

And yea I had a strong feeling that the coolant had a negative effect...
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Old 11-13-2012, 05:13 AM   #7 (permalink)
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Default Re: 94 base model will crank but not start

If you shorted out and killed the the transistors in the PTU it is possible that it killed the output transistors in the ECU to two of the coils. Test your ECU in another persons car.

Another possibility is connectors to and from PTU still have moisture inside and are shorting out. Clean them out with a water displacing electrical solvent like CRC electrical cleaner, cable clean, or even brake cleaner.

good luck.
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Old 11-13-2012, 08:47 AM   #8 (permalink)
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Default Re: 94 base model will crank but not start

a 94 base is DOHC, correct?

Here is the ignition circuit schematic for a 94 DOHC and the operation explained for cam/crank sensors to ECU to PTU.

By reading the operation of the system and studying the diagram, you can troubleshoot the ECU (without the need to look for a loaner), PTU, and coils.

You'll need a voltmeter, leads with clips, and a straight pin or sewing needle (attached to the positive lead). Jam the straight pin (sewing needles are stronger) into the appropriate pin # from the backside of each connector. This allows you to check signals while keeping the wiring harness intact.

The ECU drives components by switching on and off 5V signals.

But yeah...check for moisture inducing a short in the connectors first
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File Type: jpg ignition operation.JPG (87.1 KB, 11 views)
File Type: jpg dohc ignition system.JPG (83.9 KB, 14 views)
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Old 11-13-2012, 02:35 PM   #9 (permalink)
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Default Re: 94 base model will crank but not start

Jester,
I have already tried another ECU that is good and another PTU that is good and another set of coils that are good. Still does the same thing. I have been using crc connector cleaner on all of the connectors and still no luck. I still think it is something to do with wiring though.

Black94tt
Thanks for the link I will look into it and get back to y'all.
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Old 11-13-2012, 02:58 PM   #10 (permalink)
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Default Re: 94 base model will crank but not start

And yes it Is DOHC
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