1995 Tahoe questions

[jrsavoie]

1995 Tahoe questions

I have 2 what is it questions.

There is a 2 wire plug I believe they were green and black that was hanging down by the fuse box. I did not see where to plug it into. I have no idea how long it's been off or where it goes. I will post a couple pics.

On the firewall above the fuse box there is something that is vacuum operated. I'll show pics of that also.

When you start the Tahoe the rod that activates the turbo still moves. I have very good vacuum.

If you plug in directly to the turbo, it holds tight.

I am sealing the valve covers, changing injectors, testing glow plugs, changing to F intakes and servicing. Don't let the under hood PMD bother you. It's the spare and when I am done, it will be in the bumper also.

Any ideas would be appreciated.

Thanks

 

[THEFERMANATOR]

The firewall mounted sensor is the barometric pressure sensor, and on S engines it also provides feedback for the EGR valve. As to the 2 wire plug, I'm not sure.

 

[jrsavoie]

My thought is that the turbo solenoid is either not working or is not being told to work.

I was under the impression that you could move the rod on the waste gate when the vehicle was not running and when you started the vehicle the rod would be held one direction or the other.

When I start the vehicle there is no change in the rod unless I loop the vacuum line to the waste gate.

So I think that tells me there is something wrong at the vacuum solenoid or could it be the sensor?

 

[WarWagon]

2 wire plug - Front or rear windshield washer pump motor?
Are the PS lines leaking or being dripped on?

Any codes? Any other symptoms like black smoke and no power? (Well relative to a stock 6.5 no power... )

 

[jrsavoie]

All of that will have to be found out later. I just got it in to do the maintenance work on it.

From talking to others my guesstimate is an unused plug for rear window washer

 

[ak diesel driver]

your vac lines could be leaking also

 

[jrsavoie]

They do not seem to be. When I bypassed turbo solenoid, and had vacuum direct to the turbo, the turbo rod was very hard to move, like what I would have expected on vehicle start up. Unless I am remembering that wrong.

I thought I remembered that when the vehicle was NOT running you could move the waste gate rod back and forth rather easily. But as soon as yopu started the vehicle the rod became hard to move because it was being controlled.

The rod on mine only becomes hard to move if I hook the vacuum line direct to the turbo

 

[ak diesel driver]

sounds like the solenoid then

 

[THEFERMANATOR]

Solenoid or boost pressure sensor.

 

[jrsavoie]

12569240 is the EGR Baro sensor - verified

The waste gate solenoid for the 95 Tahoe is GM 1997255 - verified

The EGR solenoids - vacuum regulator valves EGR SOL VLV (vent) & EGR SOL VLV (PWM) have 2 different numbers, but I do not know which is which.

1997225 & 1997226

Where is the EGR delete thread / instructions? I am switching from S to F intakes

 

[jrsavoie]

Solenoid or boost pressure sensor.

Ok where is the boost pressure sensor on the 95 Tahoe and the 96 Suburban - F engine?

The turbo is not working on the 1996 Suburban now. I have a new wastegate solenoid - not installed yet. AC Delco part# 214-1073 GM part number 1997227

I realize I can just plug this solenoid in and if it works I am good to go, But I would like to know how to diagnose this properly.

How do I test for voltage at the plug for the wastegate solenoid to tell if my issue is the solenoid or the boost pressure sensor?

 

[Husker6.5]

It's not an issue of voltage to the Wastegate Solenoid, it is an issue of the electromagnetic motor inside the solenoid failing so that vacuum from the pump vents to the atmosphere all the time (even if the computer commands it to close and supply vacuum to the wastegate) therefore allowing the wastegate to blow open from exhaust pressure and not allowing the turbo to spool up and create boost. This results in massive black smoke upon acceleration from a stop if you use any go-pedal or if you try to accelerate to pass, etc. I reiterate, your Wastegate Solenoid is shot, it's not the computer (unless the diagnostic code gives the dreaded "dead ECM code 55"). Replace the solenoid with a new one and your problems will disappear. If they don't, I will pay for the solenoid.

 

[Husker6.5]

Or, you can just ditch the vacuum pump, wastegate solenoid and vacuum actuator and go with a Turbo Master mechanical actuator.

 

[WarWagon]

Or, you can just ditch the vacuum pump, wastegate solenoid and vacuum actuator and go with A Team Turbo.

Fixed it for you.

Reference for the stock WG system:
http://www.thetruckstop.us/forum/threads/reference-material-turbo-wastegate-system.2648/

 

[Husker6.5]

Fixed it for you.

Reference for the stock WG system:
http://www.thetruckstop.us/forum/threads/reference-material-turbo-wastegate-system.2648/

I thought we were keeping this on a low budget for him! Under $10 at the hardware store and he can build his own mechanical wastegate actuator!

 

[jrsavoie]

I was surprised to see the Part numbers of the waste gate solenoids for the 95 Tahoe - GM 1997255 / ACD# 214-637

And the 1996 Suburban AC Delco part# 214-1073 GM part number 1997227 were different.

Does the wastegate solenoid need to be grounded?

The base on the 96 was broken, so it was not grounded. Don't know if that makes any difference. Got the new solenoid on. Now back out to mount the spare PMD. The old spare was toast. Would not even start the Suburban. Glad we never had an issue while on the road.

 

[Husker6.5]

No, it does not need to be grounded, per se. The bracket is just a convenient place to mount the two EGR and wastegate vacuum solenoids, if Light Duty, or just the wastegate solenoid if Heavy Duty. The current path grounds through the electrical connector. The solenoid is spring loaded so that the vent port is always open - the vacuum pump is sucking in air - until the ECM signals the application of voltage to the solenoid, which then closes and routes the vacuum from the pump to the wastegate actuator which then closes the wastegate, spools the turbine which causes the compressor to produce boost. The solenoid is either ON or OFF, so boost is regulated by either closing or opening the wastegate.

 

[Husker6.5]

That's the simple explanation. I'm sure that the @THEFERMANATOR would be more than happy to elucidate further on the subject of PWM circuits and how varying ON-OFF cycles can produce varying amounts of boost pressure, or the Pros vs. Cons of trying to get a 1st Gen Duramax and Allison to interface with the wiring harnesses of a 400 platform Suburban and have everything talk to each other, years before stand-alone engine/transmission controlers came onto the market for the Duramax/Allison.

 

[Husker6.5]

In other words, @THEFERMANATOR would be the source expert around here and would be glad to explain how the ECM interfaces with the various sensors to turn the solenoid on-off to vary the boost pressure, and how he got the DMax/Allison and its ECM to interface with his Burb's wiring harness and happily motor him down the road before there were stand-alone controllers for the DMax and Allison that enabled swaps into other vehicles.

 

[THEFERMANATOR]

The difference in the solenoid as I was told when I did m8ne WAY back when I was still 6.5l powered was the old solenoid had no filter, new style had a filter. I actually ran the new style waste gate solenoid on my 95 with no problems. It's a very basic system. The vacuum pump pulls vacuum of at least 15", then the ecm sends a pulsed signal to the solenoid to cause the solenoid to alternate between the vacuum source and vent. At 100% duty cycle it is sending full vacuum to the wadte gate actuator, and at 0% it is venting the waste gate actuator circuit to atmosphere so no vacuum reaches the waste gate actuator. Iirc it should be around 60% idling, and vary beyond that while driving to hit the desired boost table(with the exception of GM's goofy logic of having it overshoot boost initially to try and reduce snap enissions).