1994 6.5 Waste Gate Issue

[t_c_r_]

I totally rebuild my 1994 (electronic) 2500 GMC 6.5, VIN 2GTFK29S2RXXXXXXX, as per thedieselpage.com suggestions. (New injector pump, ceramic pistons, liquid dampener, new heads, starter and on and on.) I did not replace all of the electronic solenoids, bells and whistles as there were no codes to deal with at the time of the rebuild.

After 2,000 miles of working out minor vacuum issues etc, I launched out to Texas pulling a 3 ton trailer. At Lost Trail pass a "service engine" light came on, the turbo boost dropped from 15 psi to 5 psi at 3,000 RPM. I pulled over, idled the engine to cool (it was not over heated) and shut it off, re-setting the computer and resolving the service engine light. At the GMC dealership in Idaho, the waste gate solenoid was replaced. All was well until pulling the grade into Aspen CO. and the same issue occurred again. The Denver CO. dealership troubleshooter said the turbo checked out and replaced the waste gate vacuum assembly. Pulling a 6% grade into New Mexico resulted in the now familiar service engine light and turbo boost drop. In texas, I checked the vacuum - 20 lbs from the pump. Each hard vacuum line from the vacuum pump to the EGR and solenoids to the waste gate were tested and held pressure.

As long as I keep the turbo boost below 10 psi under a pull, regardless of RPM, the service engine light stays off and I can limp up hills. Anything in the 12 - 15 psi range under a pull or passing causes the drop in boost.

What next?
Joyfully,

TC Richardson

[DmaxMaverick]

Welcome aboard!

Overboost. In the absence of aftermarket programming (the "chip"), more than about 12 PSI will cause PCM fits, and limp mode, as you've experienced. Either reduce your max boost to below 12, or install an aftermarket program that will accommodate the overboost. You could use a "boost fooler", but I don't recommend it (it's a trade-off for other potential issues).

[Robyn]

Since you have spent the $$$$$ to build a really good engine here is what I would do if it were mine.

If the truck does not have a 3-1/2" or larger exhaust, get one.

Add a power chip from Heath or Kennedy
Get rid of the vacuum controlled wastegate and add the tubo master device from Heath diesel.

Install a Pyro and boost gauge set.

Adjust your boost to allow about 12 PSI max and your set.

Use the gauges religously and dont run the Exhaust temp past 900 Post turbo or 1000-1100 preturbo.


The chip will clean up all the nasty gremlins that are bothering the ECM (computer) and you wont see the ses light any more. (At least not for the same reasons)

The power will be great and the thing wont defuel.

The vacuum system is a Joke and a contant source of agravation.

Just remember, with the chip and the Turbo master, you are now in charge and not the computer. The only thing between your boot and melting the little six and a half is your watchful eye when running hard.

Around town and just loafing things will be fine. You start horsing things and you need to watch the gauges.

No more than 12 PSI and keep the temps in the ranges I mentioned.


Good luck, have fun




Best

Robyn

[t_c_r_]

I totally rebuild my 1994 (electronic) 2500 GMC 6.5, VIN 2GTFK29S2RXXXXXXX, as per thedieselpage.com suggestions. (New injector pump, ceramic pistons, liquid dampener, new heads, starter and on and on.) I did not replace all of the electronic solenoids, bells and whistles as there were no codes to deal with at the time of the rebuild.
>
>After 2,000 miles of working out minor vacuum issues etc, I launched out to Texas pulling a 3 ton trailer. At Lost Trail pass a "service engine" light came on, the turbo boost dropped from 15 psi to 5 psi at 3,000 RPM. I pulled over, idled the engine to cool (it was not over heated) and shut it off, re-setting the computer and resolving the service engine light. At the GMC dealership in Idaho, the waste gate solenoid was replaced. All was well until pulling the grade into Aspen CO. and the same issue occurred again. The Denver CO. dealership troubleshooter said the turbo checked out and replaced the waste gate vacuum assembly. Pulling a 6% grade into New Mexico resulted in the now familiar service engine light and turbo boost drop. In texas, I checked the vacuum - 20 lbs from the pump. Each hard vacuum line from the vacuum pump to the EGR and solenoids to the waste gate were tested and held pressure.
>
>As long as I keep the turbo boost below 10 psi under a pull, regardless of RPM, the service engine light stays off and I can limp up hills. Anything in the 12 - 15 psi range under a pull or passing causes the drop in boost.
>
>
>
>What next?

[john8662]

That's the computer pulling fuel, completly normal. You need to do one of two things to resolve this.

#1 Boost Fooler, as produced by Kennedy Diesel, plugs into the MAP sensor plug and fools the computer to what boost it's actually seeing.

#1 Flashsed E-Prom for the computer, perfer a performance eprom from Kennedy or Heath (these are the only two to trust) that gives you more fuel and eliminates the defuling due to setting codes for overboost.

You're overboosting the engine right now, according to the computer.

Are you intercooled? I wouldn't run anything more than 12psi w/o one.

I'm also a little curious why your stock engine with stock wastegate is giving you this much boost, you also need to check the wastegate arm on the turbo for smooth operation, it's possibly it's hanging (or something is hanging it up).

J

[93GMCSierra]

You must have gauges to know what your boost is right?
If you don't have an intercooler you should not go so high as mentioned.

[Robyn]

YESSSSSS Gauges are a necessary item to know whats going on.

Not real sure why a stock programed engine would be overboosting with the vacuum system still in place.

Has anything been done such as adding a power chip ???

I have never seen a stocker run over 8 PSI.

Boost and pyro are available from many sources.
Banks, Heath, Kennedy and there are several instrument companies that offer such items. Isspro, VDO and a host of other outfits offer gauges of all sorts.

Check the waste gate to be sure that the linkage is not fouled up in any way. The lever on the side should move freely back and forth with the engine off.

If the thing is still overboosting with all the stock stuff then either there is a glitch in the vacuum/electronic systems or the wastegate has an internal problem.

To find out if its internal to the wastegate, unhook the vacuum hose at the wastegate actuator and drive the truck, if you still get the overboost then the wastegate is either plugged or ????

Now what exact code is the ECM giving you??? Pull the codes.

12 PSI max without an aftercooler or water alcohol injection.

Pyro at preturbo no more than 1000F or 900F post turbo

If you run a cooler then 15 would be a good place to stop on a six and a half.

Let us know
Robyn