Code 78 even after replaced WG solenoid, twice.

[THEFERMANATOR]

Hip hip..... Huraayy!!!

If I wouldn't have tried it, I would have been laying in bed all night thinking about it. I fixed it. Simply spliced in a wire to the negative side. Crimped a round connector on the other end of the wire and bolted it to the ground wire that is bolted in to the intake manifold. Turned the key to on position and I could hear the WG solenoid click, finally. The way it was outside of the truck. Had the wife start the engine. Bingo! WG is now pulled closed, or close to close on idle. Suction to the Waste Gate.

When I peeled away the wire loom from the that wiring harness, I could see that someone had been there before. There was electrical tape around the two wires going to that connector.

Thanks to everyone for your in put. Hopefully this thread will help someone in the future.

From your description you haven't fixed it, you have simply bypassed the ECM control and made it so it puts full vacuum to it all the time. The solonoid is powered by the ignition switch, but the ground is supplied via the ECM. By grounding the ground side to the intake, you have shorted it out to go to full boost. I have also seen doing this blow ECM in other applications as back feeding a ground from the outside can wreak havoc to the internal board. Diagnose teh sytem before you cost yourself even more money to fix it, or put a turbo master on it.

 

[carl6405]

I dont understand. I can see the Waste Gate move when I am standing out there looking at it while the wife is revving the engine. Isn't that the way it is supposed to work? Open and close? Also, I can now actually hear it spin up, very quiet, but I can hear it. Now, I know that the issue is being caused by a bad ground on the ECM, I will fix that and remove the temporary ground that I made.

 

[THEFERMANATOR]

The wastegate should stay closed until the boost gets up to a preset point that the ECM tries to regulate it at. It is controlled via the ECM according to its tables. There should be 12 volts positive to one wastegate actuator lead, and a ECM controlled on off pulse width modulated ground that it uses to control the boost on the other. This is where having a scanner omes in as it will alow you to see what the ECM is commanding according to what it is seeing via the sensor inputs. Many will also allow you to turn the wastegate off and on via a bidrectional control.

 

[L98TPI]

I have also seen doing this blow ECM in other applications as back feeding a ground from the outside can wreak havoc to the internal board. Diagnose teh sytem before you cost yourself even more money to fix it, or put a turbo master on it.

X2 On these heavily electronic vehicles never force points to 12V or gnd. Unless you really really really know what you are doing, have the factory manual and can read the schematic to make sure you are not going to blow up any thing expensive.

Ok you (as Ferm said) have by passed the control and tested the vacuum lines pump and turbo. Now (after you take off your jumper wire) put a voltmeter across the solenoid and put it where you can drive and see it (since no scanner) and see what it does. A analog meter actually will read the PWM better and give you an indication of how much the ECU is turning on the solenoid. A DVM will do though. You only need to run one wire off the solenoid to the meter, on the low terminal. Put the other lead on a handy ground. If it sit at 12V with no fluctuation downward.... well we will take it up from there.

 

[carl6405]

I do have a OBDII scanner. Wonder if there is a cable adapter out there for it?

 

[millsroger]

Carl, you said you can see the actuator move when the engine is revved??? Should not!! The vacuum source is the pump---NOT engine vacuum--isn't any!!

You probably have either a bad vacuum pump or leaky vacuum lines. The vacuum pump should produce 16-20" at idle and go up from there.

Find a cheap vacuum gauge, check at the pump, if OK check at the line going into the solenoid, if OK, check at the output of the solenoid, may be a couple " lower but close, if OK check at the actuator.

The waste gate on the GM turbo is a flapper that is held closed by the actuator to allow the turbo to spin up. When it is released and allowed to open the exhaust bypasses the turbine wheel so no spin fizzy.

The acuator is supposed to be held HARD closed by the vacuum until the ECM tells it different. It does that by pulsing the solenoid off. Those pulses start out narrow and get wider, like a blinking lite. That gradually lowers the vacuum getting to the actuator and the exhaust pressure opens it.

One pin on the solenoid has +12 in run and start. The other pin goes to the ECM. If you were to connect an oscilloscope to that pin you would see it jump from +12 to ground as the pulses are sent. The amount of time it is grounded and the number of times in a second determine how much vacuum gets thru the solenoid. In operation it is actually vibrating faster or slower.

Hope this helps the brain get around what is actually an upside down circuit.


Oh yea, hook that solenoid back up to the harness wires and then solder and tape them up. After you get good vacuum you can tell if the turbo is working because it stops smoking when you stick your foot in it. A boost gauge is the only way to know exactly how much boost you have. Scanner may read the sensor but a gauge is IMHO, more user friendly and more accurate.

 

[millsroger]

According to my diagrams, the +12 is Light Blue/Black, also goes to EGR valves if you got em. ECM wire is Yellow and goes to pin A3.

More than about 2" vacuum loss at output of the solenoid at idle says it's probably bad.

 

[Turbine Doc]

Some pretty good reference material in our TRL on vac/turbo WG system http://www.thetruckstop.us/forum/sh...al-Turbo-Wastegate-System&p=421715#post421715 I updated it this morning to include some info on a problem I once had where the vac actuator had a hole in it that was not allowing the vac supplied to the actuator to stay open due to a leak in the diaphragm in the actuator.

It looks like you are narrowing in on your problem poor connectivity in the gnd side of the actuator guys here will help you through it, I'm sort of out of a good real time help loop tending to my wife in hospital following hip surgery.

 

[carl6405]

Turbine..I am sorry to hear about your wife. Actually, you helped more than you realize. You were the first to respond and mentioned a possible ground issue. It is definitely a ground issue or a PCM issue, I am convinced of that.

 

[millsroger]

Hey Turbine, here is some input for your 'howzit wurk' post: The GM pressure chart shows 7psi from idle to about 1200 at any "throttle" setting. (TPS or eq). Holds that 7psi at half throttle to about 1500. From those points it ramps up as TPS and load increase to max of 11.5 at wot, max load, 1800 RPM. Holding wot it then ramps back down to 7psi at 3400 RPM. At 3400 RPM it holds 1psi up to about half throttle then ramps up to 7. Chart is a 3D map, don't recall where I found it, called "Targeted Boost Pressures, RPM vs Fuel flow.

At this point my boost gauge is 'on order', but I kind of doubt that at idle it is gonna make 7psi, be lucky to make 0psia.

It does show what GM should have programmed into the ECM for intended pressures.

 

[THEFERMANATOR]

View attachment 34911
Hey Turbine, here is some input for your 'howzit wurk' post: The GM pressure chart shows 7psi from idle to about 1200 at any "throttle" setting. (TPS or eq). Holds that 7psi at half throttle to about 1500. From those points it ramps up as TPS and load increase to max of 11.5 at wot, max load, 1800 RPM. Holding wot it then ramps back down to 7psi at 3400 RPM. At 3400 RPM it holds 1psi up to about half throttle then ramps up to 7. Chart is a 3D map, don't recall where I found it, called "Targeted Boost Pressures, RPM vs Fuel flow.

At this point my boost gauge is 'on order', but I kind of doubt that at idle it is gonna make 7psi, be lucky to make 0psia.

It does show what GM should have programmed into the ECM for intended pressures.

This 3D chart is a screen shot from tunerpro using the aforemenetioned copyrighted definition files. This chart is not correct in many accounts, and mislabled we have found from playing with slim's truck(one of the many reasons we need a GOOD definition file before tuning proceeds) so don't go by it. GM spiked the boost up to about 11 and then drops it back to 7 at sea level after a second or 2.

 

[millsroger]

Thanks for clarifying Ferm, as I said, couldn't 'member where I got it zactly, but the text said it was the stock GM chart.

Would have to believe that any spike is intentional by GM tho. ECM should be fast enough to dump the waste gate pretty quickly and the MAP is certainly gonna be quick. A 'slight' overshoot maybe, but anything more is not an accident.