GM 6.5 turbo diesel problems..

[chilliwak]

I have a 94 Yukon with a 6.5 turbo diesel. The motor is high mileage (400k) The truck strts fine cold but is a ***** to get running warm. At higway speeds at a constant throttle position the motor will get a surge that feels kie I have given the truck full throttle. Then it will almost die as if there is no throttle. I have asked some guys and they think its a injector pump problem. Weird because the motor has lots of power and otherwise runs fine. Any help would be apreciated... Cheers, Chilli..

 

[Woofwagon]

Look for fuel leaks on and around the fuel pump. Also there is a fuel control module that can get over heated. This module is usually moved away from the engine by modders. This is the PMD.

 

[chilliwak]

Look for fuel leaks on and around the fuel pump. Also there is a fuel control module that can get over heated. This module is usually moved away from the engine by modders. This is the PMD.

Thank you Woof. The pmd is replaced and moved away from the engine. New fuel filter installed. The battle goes on...

 

[Woofwagon]

Check the fuel injector return lines, they may not be weeping but may be letting air in, getting air bubbles in the system causing the hard starts. Also check the glow plugs themselves along with the glow plug controller. Also, put a bottle of Stanadyne or Diesel 911 in the fuel tank and see if the situation improves. Sounds like to me that the injection pump is having it's timing thrown off by air bubbles in the system.

 

[1stDeuce]

Make sure you're lift pump is working too. The IP can kinda work with cold fuel when it's cold, but as it warms up, leakage gets the best of it and it'll start starving for fuel intermittently...

 

[REDROVER]

I have a 94 Yukon with a 6.5 turbo diesel. The motor is high mileage (400k) The truck strts fine cold but is a ***** to get running warm. At higway speeds at a constant throttle position the motor will get a surge that feels kie I have given the truck full throttle. Then it will almost die as if there is no throttle. I have asked some guys and they think its a injector pump problem. Weird because the motor has lots of power and otherwise runs fine. Any help would be apreciated... Cheers, Chilli..

Those Motors are very simple ,

U have 2 possible suspects here

Lift pump going out ,
Or injection pump going out,

When lift pump also known as fuel pump is about to expire , it looses its suction power witch in ur case is 14psi only , and you have injection pump that constantly needs fuel under engine load
What happens is in between fuel pump and injection pump now you have air
Because fuel pump can't keep up with the demand ,
That air going true your injection pump is what's causing sudden drop in power or opposite sudden full power feeling ,
And this happens more when your engine is warm because components inside the fuel pump expend allowing more air to go true than fuel ,


Next case is your injection pump
That is getting old and not pumping enough fuel to injectors and that will give you the same effect creating vacuum between injection pump and injectors

Fuel pump is around 60 bucks on those
And injection pump is DB2 if I am not mistaken,

You can buy very low mileage military take off from eBay around 400 bucks that will last u another 400 k miles



Glow plugs have noting to do with your case they are only for starting a cold engine

 

[bfdiesel]

94 6.5 should have the DS4. Not as cheap as the old DB2. I would check the lift pump and the filter first, but it sounds like a flakey injection pump.

 

[toylandcruiser]

How reliable are these engines? I found a couple on Craigslist and know little about them.

 

[bfdiesel]

Reliable and gutless.

 

[Rot Box]

Lightly crack open the fuel filter bleeder (it will get a little messy) while the engine is running. The bleeder is on top of the fuel filter.. If fuel comes out the lift pump is working. If fuel does not come out and the engine stumbles or stalls the lift pump or more likely the oil pressure switch (OPS) is bad. The OPS is on the rear driver side of the intake manifold. Not hard to change you'll just need a large deep socket.

I hate to say it but good cold starts/poor hot starts are a good sign the IP is on its way out. I agree with everyone above rule out everything else if you can before buying a new pump. There are a lot of crappy 'rebuilt' pumps out there I would take the time to find a reputable builder that specializes in Stanadyne pumps. It's money well spent in the long run.

Hope you get it sorted!


Edit: From what I've seen over the years I would cary a spare OPS (and socket to change it) for safe measure. Kinda like crank sensors on power strokes... They work for a long time until they don't and then you're dead in the water. Although a 6.5 will start without a lift pump eventually it is very hard on the starter and injector pump.

 

[Woofwagon]

+1 Rot Box

 

[chilliwak]

I had the old diesel diagnosed. Injector pump is bad. $2500 repair!:Wow1: OUCH!:exclaim:unk03::yikes:

 

[PlethoraOfGuns]

I think your year was the first year they started using electronic DS4 pumps. I just had my DB2 pump rebuilt on my 2007 6.5L. Ran me about $1400. Don't complain too much, imagine rebuilding an injection pump on a Duramax...

If you got 400k miles on your original pump, tip your hat to that little pump. Get the truck back on the road and do another 400k...

 

[chilliwak]

I think your year was the first year they started using electronic DS4 pumps. I just had my DB2 pump rebuilt on my 2007 6.5L. Ran me about $1400. Don't complain too much, imagine rebuilding an injection pump on a Duramax...

If you got 400k miles on your original pump, tip your hat to that little pump. Get the truck back on the road and do another 400k...

You are probably right Plethora, but even still for that money I could have picked up a good used motor. Welcome to the world of diesels. The only plus is that I got the truck cheap. Time to fix er up....:Wow1:

 

[Bushcoat]

Seems a bit steep chilli, last pump I had rebuilt (actually was an exchange service) was $400 and change. I believe a brand new stanadyne pump from your GM dealer is under $2000. I think my price was around $1400 CDN with discount. Your diesel shop may be able to get a new pump cheaper than the GM dealer. I cant recall if that includes fuel driver module. And iirc, its around 6 or 7 hours labor by the book.
400k out of a pump sounds amazing, GM used to warranty the pumps up to 200k km because of their problems.
I guess $$$ involved depends if you are doing any other work at the time, obviously need gaskets.
I'd have a real good close look at everything engine related before investing in the pump. Last time I had a pump that was on its way out, I was evading it then popped a head gasket. So now, I couldn't evade the pump issue any longer, so attacked the head gasket issue, sent heads to my local shop for a refresh and found them to be full of cracks. So ordered new heads, gaskets, might as well do injectors, return lines, glow plugs, etc, and the pump. Once it was running great again, the turbo took a dive. So I bought the a team turbo. Then got another couple years no trouble, then I guess we outgrew the truck and needed a back seat.
I guess I am trying to say, a drop in "improved" motor would have been cheaper and easier.
Now that I have no more 6.5, I keep my fingers crossed with my duramax. I'm in way over my head on any sort of repairs it ever might need, I miss the simplicity and economy factor of the 6.5 motor.

Hopefully this hasn't gotten the best of you, and you are still enjoying your summer vacation here in the great white!