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Old 06-05-2008, 10:24 PM   #1 (permalink)
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No Ground Signal To Waste Gate Solenoid

I would like to start my first post by thanking everyone for this very informative forum. I am almost happy to facing a problem with my truck because it lead me here.

I have done several searches and a few hours of reading before posting this. Although I have learned much from my reading I still have the same problem.

I have a 1994 K2500 with 6.5L Turbo non EGR with 490000KM. Over the last 14 years I have become very familiar with this truck. It has had two replacement injection pumps (blue tag and then green tag) 2 new PMD's not including the new ones on the new pumps. Injectors and glow plugs at 300,000 and glow plugs again at 300,000 and a new glow plug harness (defective glow plugs that burnt up several peoples trucks. I was lucky to just burn up the wires. The glow plug manufacture paid for the repair) I installed the FSD Cooler kit with the last PMD. I have replaced the oil pressure switch about 5 times due to the lift pump contacts failing and replaced the lift pump twice.

That brings me to the waste gate solenoid. I have experienced on two previous occasions a service engine soon light and black smoke while climbing hills. Both the light and smoke disappear when I let off the throttle. Both of those occasions produced a code 78 and was fixed with a new solenoid. This time it didn't work! I replaced the solenoid out of habit but still no boost and code 78. I have since checked and verified the operation of the vacuum pump, the vacuum hoses, the waste gate and actuator, and the new solenoid. I have replaced the MAP sensor with a known good one but not checked the atmospheric pressure sensor on the firewall.

The electrical connector at the waste gate solenoid shows 13.6VDC with a meter but will not allow enough current to flow to activate the solenoid. The meter reads 13.6VDC from the positive wire to engine ground but the ground wire shows high resistance to ground with the meter. After reading another very informative post about a similar problem that ended up being a poor connection at the connector I replaced the connector with a new one but still no go. If I connect the positive wire from the connector to the solenoid and ground the other leg of the solenoid to the block it operates and the waste gate actuator advances.

I guess that brings me to my actual question. Does the yellow wire from the solenoid connector go straight to the ecu and if so what connector and pin is it located in? Also is it possible that the ecu would be getting a false reading from the atmospheric pressure sensor (the only part that I have not verified) and not producing a long enough pulse to activate the solenoid. Is it possible that my ecu may have gone bad? I am confused by the fact that my meter shows 13.6VDC at the connector but I assume it has to do with the fact that it is producing a narrow pulse width and my meter refresh rate does not show it???

Sorry about the long wordy post but I wanted to supply as much info as possible.

Thanks!

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Old 06-05-2008, 11:46 PM   #2 (permalink)
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you could get a turbomaster that will eliminate the vac setup but if you've got a bad ground wire i'd say just replace the ground wire. i've got a wiring diagram from a 1997 truck. i'll see if it tells me what pin it is. maybe it'll be the same on your truck.

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Old 06-06-2008, 08:14 AM   #3 (permalink)
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Thanks for your help! If the diagram is just for 97 it will likely be different because the 97 is ODB 2 but it still doesn't hurt to check.
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Old 06-06-2008, 08:21 AM   #4 (permalink)
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The PCM should be controlling the ground.
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Old 06-06-2008, 11:04 AM   #5 (permalink)
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Quote:
Originally Posted by corolla View Post
The PCM should be controlling the ground.
Sorry about my terminology, I was referring to the PCM as the ECU. Anyway, Yes the PCM should be controlling the ground. Do you know what Pin or connector the wire is located in in the PCM and does the yellow ground wire from the solenoid run directly to the PCM? I have got three connectors in my PCM all of which have got solid yellow wires and have been checked for general loose connection by the yank-pull test.

Thanks
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Old 06-06-2008, 11:28 AM   #6 (permalink)
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i would check that affected ground wire for a break inside the insulation at the plugin [ weak point when flexing the wire]and where there could be a flex point going into the main harness. check your main grounds pass side rear of head for clean,tight and same condition as above mentioned.
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Old 06-06-2008, 11:35 AM   #7 (permalink)
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Quote:
Originally Posted by Bison View Post
i would check that affected ground wire for a break inside the insulation at the plugin [ weak point when flexing the wire]and where there could be a flex point going into the main harness. check your main grounds pass side rear of head for clean,tight and same condition as above mentioned.
I actually replaced the plug connector to eliminate the chance of a break at the solenoid. I have been unable to locate the other end of the wire at the PCM but I will check it also and then ohm out the wire at that time. Would a bad main ground at the head not affect more than one circuit?

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Old 06-06-2008, 11:55 AM   #8 (permalink)
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The yellow wire from the wastegate solenoid runs direct to the PCM, to a 24 pin pink connector.
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Old 06-06-2008, 12:07 PM   #9 (permalink)
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Quote:
Originally Posted by chickenhunterbob View Post
The yellow wire from the wastegate solenoid runs direct to the PCM, to a 24 pin pink connector.
Thanks for the info! I will check the connection at the PCM and ohm the wire. Is it possible that something would be telling the PCM not to pulse the WG solenoid at idle?

Thanks Again
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Old 06-06-2008, 10:50 PM   #10 (permalink)
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Update...I have located the waste gate ground wire at the PCM and checked continuity. The wire is good! I have checked and cleaned all (I think all) grounds under the hood.

Is it possible that the PCM is not telling the solenoid to energize at idle? I don't have a scan tool for OBD1 to check. Is there a sensor in the circuit that I have not tested that could be sending a false reading? Failing that I guess I need a new PCM but I find it strange that this would be the only circuit in it to fail

Please help!

Thanks

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