Chevy Turbo Diesel - Engine Troubles

I think the 1998 models may have had a drive by wire throttle control system. (I may be wrong about what year they actualy started using that system though) Its entirely possible it has a bad throttle sensor or a bad engine speed sensor.

Take it to your local dealership and they can tell you in a few minutes whats wrong with it. Just be prepared to put it in neutral and shut off the engine if necessary when driving over there.

Thanks tcmtech but this thing need a few new nuckles on the front end and the brakes/brake fluid needs to be replaced. Also a new power steering pump and pressure hoses. This thing is not going on the road yet. I am starting with the engine, if it not worth fixing then I might pull the motor and tranny and make a cargo trailer.

How does this thing make vacum? Just on a down rev?

there is a vacuum pump located on the top of the engine, mounted at the front. it should look similar to an old style distributor, with multiple hoses attached.

Like Charlie said, most diesels have a vacuum pump. They have an open air inlet (no throttle plate like a carb or gas fuel injection), and the engine speed is controlled by regulating the fuel via injector pump (newer common rail motors have electronic injectors, but same idea). Therefore the inlet manifold has very little or no vacuum. Add a turbo & you actually have positive pressure in the manifold. So they add a vacuum pump either driven off the cam or perhaps the fanbelt system. This provides vacuum for your power assisted brakes, and on some vehicles the internal heater controls.

Perhaps check that the throttle lever on the injector pump is correctly returning to the idle position. Or that someone has not wound up a throttle stop screw etc. Coming from an impound, who knows what the previous cowboys have done to it! :)

Good Luck

Tony

I was chasing vacum lines and a few have holes, that could very well be "part" of the problem. I also bought a OBD 2 code reader/ clearer. Nothing is coming up on the code reader. Frig that is a tight spot to work!

Thanks

the "gas pedal" is electronic, sends a signal to the ECM, which commands the injection pump.

there is no vacuum signal in a diesel. its efficiency results partially from lower pumping losses from no throttle plate.

you're probably best having the codes read, before spending more money.

Thanks, I am going to look into finding a "shop" manual . I did pick up a OBD 2 code reader. Looks like a fairly good one. paid 250. Will have to turn the phone off in order to get something done.

Thanks, you are quite familiar with these trucks or this diesels engines.

Hello Wood I, Here some links on runaways throttle symptoms and repairs.

The truck stop.

Diesel Place.

Also you may want to check all the electrical grounds and battery terminals it appears that can cause problems with some of the different engine moduals. Also check for after market high idle kits. If battery voltage is under "I think 12.5vdc" it can cause the engine to rev higher but not to what you described though. There seems to be some good reasons to relocate the vacumm pump to a cooler location than on the engine. And to relocate one of the moduals that is located on the intake system and relocate to a better place so it can run cooler and have a good grounding point.

I would check out the throttle position sensor for any problems with a multi-meter for sure.

Hope this helps it was about all I could find on the Chevys I'm more a Ford 7.3 type.

After you get running good I would look in to running a bio-diesel mix it will run better than on the ultra-low sulfur fuel that out there now. One warring keep a fresh fuel filter and check/change any rubber hoses and gaskets/o-rings out to something better that is bio-safe Viton hoses and gaskets. The bio-diesel is a good solvent and can clean out the garage in the fuel system that why to keep a fresh filter handy.

Charles

I can almost feel your pain :) From the description of your engine runability problem, I would be looking at the operation of the injection pump. That 6.5 engine will produce almost no boost without the engine being under a load. The maximum boost is only 7 to 8 Psi with the engine at full load, and boost will not make the engine rpm change with the engine running like you have it. The only thing a diesel needs to make power is fuel and air, and turbo boost is a product of fuel being burned in the engine. This 6.5 turbo has a waste gate, which is controlled by vacuum. On the left rear of the engine is the wastegate solenoid, which is controlled by the PCM. You can watch the command value of this solenoid with a scan tool. Since the engine is surging, I would recommend using a Tech 2 scan tool, (GM factory tool, which is the only scan tool that is capable of accessing the injection pump data) and watch the commanded and actual pump timing, the pump fuel rate, the TDC offset, and injector closure time and missed cam and crank pulses. The actual and commanded timing should never be more than 3 degrees apart. If more, that is an indication of the timing ring being worn that is on the inside of the pump. The fuel rate should be flat line steady with steady engine rpm. If it is changing, that is also an indication of the injection pump being worn out. The big piece of data is the injector closure time, and the missed cam and crank sensor pulses. The closure time should be between 1.3 ms & 1.6 ms, and should not vary by more than .1 ms at all engine loads and engine speeds. Once the closure time gets over 1.7 ms, the load on the pump driver module transistor gets too high, and the transistor fails. Many times the pump driver module will be replaced to fix this problem, but that is only a patch on the real problem. The only way to fix the real problem is with a new injection pump. There are several things that cause these pumps to fail. Dirty fuel and low quality fuel filters are right at the top of the list. The frame rail transfer pump is also right up there too, since the pump gets weak, although the engine still starts and runs great. When the transfer pump gets weak, the fuel volume delivered to the injection pump goes down, which causes the injection pump to overhead, and run without proper lubrication. This heat causes the pump driver module to overheat, thus causing it to fail. Poor grade of fuel will also cause optical sensor failures, which causes pump failures.

My advice is to take this pickup to a qualified diesel shop that has the proper tooling, training and experience and let them properly test & repair the system. This vehicle has the 16 pin DLC, but it is not OBD2 compliant, and hooking a code reader to the DLC will not get any information that will be of any help for this problem. Also, the Tech2 is needed to properly set the injection pump timing.