Wastegate control problem

[kevin77]

I have a 1994 suburban with about 190,000 miles on it. I have no boost. I have vacuum at the vacuum pump (which I just replaced), I have vacuum to the waste gate selenoid. I checked the voltage on the connector and I have 13.97 volts.

I get no vacuum to the wastegate on the turbo. If I jumper the waste gate selenoid with a battery charger, it clicks on and I get vacuum to the wastegate on the turbo.

So it looks like I have an electrical gremlin.

I am wondering which direction to go in next -

Do I have a PCM problem?
Would a frayed or partially broken wire be the culprit?

Kevin

[Bnave95]

I had went through the very same thing your going through. Have voltage,can jump the waste gate Sol. and get boost. All my wire's from ECM checked out working, though just could not get the Elect. boost to work.Some time ago there was a good check list to trouble shout the system. Not sure what post or where it is at.May still be in the search area.
End up bypassing the Sol. with a piece of tubing to pull the wastegate closed that allowed boost. I gave up trying to get the system to work and went with Bill H. Turbo Master. This has turn out to be a life saver. I have also wondered if I were to change out the ECM if that would make a difference?
Other than the turbo not wanting to working,every thing else works fine.

[DA BIG ONE]

I had gone crazy too with boost issue, in the end I installed Heath's manual boost controller and spliced a resistor 10watts 50 ohms at the ECU to shut off the boost circuit SES light.

[JohnC]

The solenoid works on a duty cycle. The PCM switches the ground side, IIRC. Check with an electronic dwell meter. Look closely at the wiring right near the solenoid connector for breaks. Also, make sure the lines going to and from the solenoid are not cracked. The connection on the solenoid with the restriction in it goes to the pump. If everything checks out, replace the solenoid. The usual failure mode is it can't switch fast enough.

[diesel65]

I second JohnC comment about the broken wire at the connector for the solenoid.
Take a test light and connect the clip to the positive terminal of the battery and then probe the the wire opposite to the one that you got battery voltage, With the engine running the test light should be flashing. If the light is not flashing then try wiggling the wire in back of the connector.
I also try pulling the wire like I would stretch silly putty, to see if the wire is broken inside the insulation.

[kevin77]

I looked up the wiring diagrams on alldata and it does look like the selenoid is negatively switched.

The A3 terminal on the pcm goes to the 972 yellow to the selenoid (terminal B on the selenoid)

the A terminal on the selenoid is switched by the ignition.

So it looks like I am going to do some tracing once I get my little boys to bed tonight.

ALLdata also shows a barometer and the boost sensor.

Could either one of these be failing too?

Kevin

[kevin77]

I have done some additional diagnostics:

1) 1 traced the wire from the wastegate selenoid to the ecm harness. I grounded the yellow wire I traced, turned the ignition on to get +12v at the selenoid and the selenoid worked - I checked under the hood to confirm the wastegate selenoid was working, and it was. This means the connector and wiring works.

2) Just in case I got a bum vacuum pump, I pulled my electric vacuum pump out, confirmed I was getting vaccumm to the selenoid connector (29 in) and tried the electric vacuum pump with the engine running. With the vacuum gauge on the vacuum connector to the turbo, I got absolutely no vacuum.

So as I see it these are my alternatives to what the problem is:

1) bad ecm - does the ecm have a driver like the fsd on the injector pump that can fail?

2) According to alldata, I have a barometer sensor - Does this ever fail? And could it cause the selenoid to stop functioning?

3) Also, could the boost sensor be bad?

Kevin

[diesel65]

You seem to have ignored the advice I have posted, but here is more.

If you have a vacuum guage then use it to check at the solenoid for vacuum supply, you should see at least 25 inches of vacuum with engine at idle.
Reconnect vacuum line, making sure that the vacuum supply is connected to the forward port of the solenoid, connect the vacuum guage to the rear port, you should see about 15 inches of vacuum at idle, if not then check for a pulsing ground as I stated in previous post.
If you don't get a pulsing ground, reconnect the elecrical connector and go to the PCM,with the engine idling backprobe the terminal that controls the wastegate solenoid, and connect it to ground, see if you get a reading on the vacuum guage.
If you now get a reading then the PCM needs to be replaced.

I did once have a 94 Suburban that needed the PCM replaced because the boost would not work.

[Bnave95]

Kevin77
Your truck is acting just like mine. I did the same testing that you did and the same thing diesel 65 said to try. Short of R&R the ECM,I went with the Turbo Master.
I did fine at www.rockauto.com a rebuilt ECM for around/less than $100. Did not know this at the time. My loss vaccum was a couple years ago.

[Kev-o]

Just a shot in the dark, A friend of mine was working on his wifes 94' 6.5 sub and he removed the two vacuum lines from there rubber connector at the valve cover solenoid and happened to reverse them when he put it back together. And he had the same issues.

Kev-o

[redmanf18]

Hi Everyone,

I'm new to the forum and 6.5 world, having just purchased a 95 2dr 4wd Tahoe. I have a DTC 78 - Turbo Wastegate Solenoid Fault code that comes up and the check engine light comes on above 2100 going up hill or accelerating. Am I heading in the same direction for problems as mentioned above or is this something different. Thanks for your help.

Michael

[JohnC]

Have you confirmed that the vacuum lines are connected to the correct ports on the solenoid?

How did you confirm the solenoid works if you can't get it to pass vacuum to the wastegate?

[Bnave95]

Hi Everyone,

I'm new to the forum and 6.5 world, having just purchased a 95 2dr 4wd Tahoe. I have a DTC 78 - Turbo Wastegate Solenoid Fault code that comes up and the check engine light comes on above 2100 going up hill or accelerating. Am I heading in the same direction for problems as mentioned above or is this something different. Thanks for your help.

Michael
Can You move the waste gate rod while Eng. is running? With Eng. off the rod should move back and forth eazy. If there is any leaks,just small enough that the waste gate can hold open at idle but under boost at the RPM'S,A load like going up a hill the vaccum won't hold under the Ex. presure and SES will set.
Reason I say this,to check your line's for small leak's is I had a Long Block installed several years back and the Mec. split the rubber connector at the waste gate. Leaked just enough to not be able to hold the waste gate open under loads.

[Bnave95]

Just a shot in the dark, A friend of mine was working on his wifes 94' 6.5 sub and he removed the two vacuum lines from there rubber connector at the valve cover solenoid and happened to reverse them when he put it back together. And he had the same issues.

Kev-o
This is possable,other than the rubber ear tab should go over the nipple on the solenoid. If back words the rubber ear on the boost will be bent flat against the solenoid.

[Bnave95]

You seem to have ignored the advice I have posted, but here is more.

If you have a vacuum guage then use it to check at the solenoid for vacuum supply, you should see at least 25 inches of vacuum with engine at idle.
Reconnect vacuum line, making sure that the vacuum supply is connected to the forward port of the solenoid, connect the vacuum guage to the rear port, you should see about 15 inches of vacuum at idle, if not then check for a pulsing ground as I stated in previous post.
If you don't get a pulsing ground, reconnect the elecrical connector and go to the PCM,with the engine idling backprobe the terminal that controls the wastegate solenoid, and connect it to ground, see if you get a reading on the vacuum guage.
If you now get a reading then the PCM needs to be replaced.

I did once have a 94 Suburban that needed the PCM replaced because the boost would not work.
Hear some what I found on my system, at solenoid.
#1 When test light is to the Pos. of battery there is no flashing.
#2 When test light is to the Neg. of battery there is a bright light to the + side of the solenoid.
#3 Still on Neg. of battery,test light to wire from PCM and the test light glows dim and stays steady.

[kevin77]

Flipping the vacuum connector has worked. I now have boost to the wastegate on the turbo.

I had replaced the selenoid with a new OEM - but the tab on the vacuum connector is currently backwards from where the sidetab fits over the side.

What side of the selenoid should the little brass hole be on? I threw my old one out and I am wondering if they changed the oem around to confuse me. The Orange vacuum line is the supply and goes on in the middle of the selenoid and the port that goes to the wastegate is on the side - the opposite of the way the vacuum connector is designed.

And now that I got boost, I hammered it and got...

DTC 62 - Turbo Boost Sensor Circuit Low

Also the power of the truck dropped (safe mode?) After It gave me this code.

Does this mean I need a new boost sensor?

Kevin
Living in a state of confusion.

[BobND]

Here's a (poor) photo of the 3 solenoids on my '94 K1500 pickup. You can (almost) make out the connections to the plastic lines. Is your's HD emissions, with only the boost control solenoid?

http://ndtc3500.stellarnet.com/~blweltin/Bob/Sole.jpg

[kevin77]

Yes, I have an 'F' engine with no egr - just the boost selenoid.

Kevin

[kevin77]

This is what my selenoid looks like:

http://www.kkissman.com/wastegate.jpg

[JohnC]

The pump connects to the port with the restrictor.

The lines can be pulled from the rubber connector and may have gotten switched.

Drive it for a while. Sometimes when the system is not working it can get gummed up. After working for a while it settles down. (At least that's my theory...)

[jimcreek]

my 1994 6.5 had the turbo boost senser bad

[kevin77]

For my peace of mind making sure everything was working with the vacuum pump and wastegate selenoid, I double checked the vacuum.

at the selenoid connector, the vacuum pump was pulling 29in

at the connector for the wastegate on the turbo, I was pulling 15in

I did not have the engine all the way warmed up (I wanted to stay in a nice warm garage)


Kevin

[Rodney Walker]

I to was having trouble with my 94 6.5. It would blow black smoke and no power. I put a new pmd and cooler,glow plugs and injectors in it helped a little but still smoked and no power. I checked all the vacuums had 15" at wastegate actuator. I found I had a plugged cat. Cut it out Goes like crazy now.:)