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94 GMC Yukon 6.5L diesel, looking for advice/info on rebuilds, etc.

C

Chefhusker

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Hello all, looking to learn more about my truck. I'm looking into performing a complete engine rebuild, never done a diesel but I've done a few Chevy 350s. Not sure what knowledge carries over and what to let go. I see a lot of threads worth looking into here, and I thank anyone who drops a line wishing to point me in a good direction. Thank you!
 
Welcome.
My thoughts are depends on goals and budget. Is the truck worth it? 350 is dirt cheap in comparison! Why rebuild? Hi milage, blowby, low oil pressure? Loss of power? Want to tow better? Any current mods or upgrades? Injection pump?

Should get at least the better water pump later model iirc 99+ gm spin on fan. Might be 2000 - the balanced flow water pump. The rest depends on above?
 
Welcome! Yes, why rebuild? You will find these are a throwaway engine and it's sometimes cheaper to buy a new longblock than build a used one. I have gone through a few 6.5's and 6.2's rebuilds and simply add good rebuildable (crack free) engines are hard to find anymore.

Pics. WE WANT PICS of the somewhat rare Yukon 1994 diesel!!! :woot:
 
Wow, thank you for all these responses! As you can tell, I'm very new at this kind of forum. My truck, a 94 GMC Yukon 6.5L 2 door 228k miles, was my grandma's truck. I guess what I'm getting at is no matter what, I'm keeping it. If I had to spend $20k to get it running again, so be it. It's been a great truck and I'm sure it will be again.
I had quite the issue with it 3 weeks ago. My wife took it to town, and when she got back, the ignition was stuck on. Wouldn't budge. the truck was still running, and I didn't know what to do. I pulled both batteries' cables. Still ran. About 5 minutes later, it ran away, meaning it went crazy and started revving up high and often. I panicked, told my wife "it's gonna blow" and started pulling fuses. I don't think the fuse pulling helped anything, but coincidentally after pulling the F/SOL fuse, it died.
This week I had time so I pulled the steering wheel etc. and got the lock cylinder out. Sure enough, it was bad. So bad that the key is still in it. Put everything back together, and it started up fine. Ran for 30 minutes, smooth like it always had. However, it then began to spit white smoke. Thinking about the high revving from earlier, I start thinking dang, it's a blown head gasket.
I can't find a leak along the heads though. So now, I'm wondering if I don't need to calm it down a notch and troubleshoot other systems. Aside from batteries and tires, etc., nothing has been replaced. It's ran well for a long time. I can't read fast enough on here, holy crap there's a lot of stellar ideas, like relocating the PMD and lift pump mods and such.
It's spitting white smoke, and the idle is rough. I took it to the corner and back, it sounded unlike its normal self and ran rough. Any ideas?
 
Many of us understand saving your grandpa’s truck and will help all we can.

Whenever this engine will not shut off- pinch the fuel return line coming out the front of the ip (injection pump) This is the 1/4” diameter line we always suggest be replaced with clear line to check for bubbles incase of air intrusion. This will stop fuel flow through ip and shut down engine unless it is in runaway from outside fuel source like engine oil, transmission fluid, natural gas in the atmosphere, etc. The only way to stop a runaway is block 100% air flow coming into the engine with a positive air shut off valve. Basically a valve in the air intake line before the intake manifold that stops all air flow. Most people after experiencing any kind of runaway go from thinking having one is a waste of money to deciding they want one. There are automatic expensive ones, or you could diy one a few different ways more affordably. That is something to consider after current issues are squared away.

White smoke is either unburned fuel or coolant.
Start truck, smell exhaust.

If you can video it running and post on YouTube, then copy and paste link on this thread. If you cant do YouTube, lmk and i will have you message video to me and I will post it for you.
 
So no one got hurt and that's the important part.

Clarifying what @Will L. said: Only pinch the return line if the engine is at idle. During run away the engine cooling fan can fail flinging blades off. Flung metal fan blades are like a lawnmower blade and can go clean through you. The hood normally contains this type of fan failure: Leave it down. Engine failure from Diesel run-away, well, the safest place is in front or behind the engine.

FWIW: what you did was disconnect the batteries and the alternator electrical noise went nuts. After the engine starts the batteries are a 2+ AMP DRAIN on the system. Batteries also stabilize the voltage and filter out alternator noise. The alternator is powering everything when the engine is running. So with crazy voltages and "noise" the ECM and PMD lost their mind. I am guessing biased on loosing positive battery post connections off-road and electronic things getting weird. (2009 year... Radio went nuts door and locks unlocking and locking.) Normally a run away is Condemn and replace the PMD as some are known to run away.

"Pulled F/SOL fuse, it died" ... Yea that fuse pull dropped the Fuel Shut off Solenoid (Or cut power to the PMD). It's the tall silver barrel on injection pump with 2 wires on it. It shuts off fuel to the IP when it looses power. This just cuts the fuel with key off. There is no ECM programming to do anything with it during a run-away event.

You were thinking of a rebuild: is the run-away why? I am not asking about "restore a classic." as that is different than rebuild/replace an engine.

However is it using any coolant?

Take the oil fill cap off and then start the engine: any blowby out the oil fill?

The GM manual starts with AIR in Fuel. X2 to start there with the clear line, check fuel lift pump in frame rail works, etc.

You just got this... Changed Air filter? Fuel Filter? Old fuel in the tank? Aka Did it sit a long time?

If it's cold out and ideling a long time it's possible to cool it off enough that the fire goes out in a cylinder. Low compression and other factors help. Summer fuel gelling in a cold winter?
 
WarWagon said:
Welcome! Yes, why rebuild? You will find these are a throwaway engine and it's sometimes cheaper to buy a new longblock than build a used one. I have gone through a few 6.5's and 6.2's rebuilds and simply add good rebuildable (crack free) engines are hard to find anymore.

Pics. WE WANT PICS of the somewhat rare Yukon 1994 diesel!!! :woot:
Click to expand...
I realize now that I haven't taken hardly any pics of this thing. I'll have to get on that. I also have a 87 Mustang GT convertible, but I have 100s of pics of it. Crazy. I'll fire the Yukon up today and see if I can smell what's in the smoke. Thanks again for any and all advice you may throw my way. It's greatly appreciated.Yukon1.jpgYukon2.png
 
Last edited by a moderator:
Nice rig. Interior pics would add to the diesel p0rn... :woot:

The biggest difference between a 350 and this engine is these DON'T go to 11. See the temp gauge? The RED should start at 210. After that temp rings start to loose their temper (and suddenly here comes the blowby) and things start to crack. 230 like the military runs in Hummers makes it a 30K life engine, maybe. Yeah IDI diesels get hurt at lower temps than gas engines or modern diesels. Towing or Rockies with grades that go for miles is the typical things that bring this 210+ problem on. Your area of the country may vary... (Ya haven't said.)

It has to spin FAST to start. Seriously 2 batteries to handle glow plugs, but, that 10 HP starter makes more torque than a 1 ton lug nut takes (to put on properly not break). If it isn't spinning over fast one day (A battery or starter brush failure can slow things down and still crank. S L O W L Y...) it likely won't start. If it doesn't start in 2-3 tries on 30 second cranking bursts: GIVE UP! Tow IT! and FIX IT! Burning the starter down on something that won't start just adds to the misery and costs more than a tow bill. AAA, your cell phone, auto ins... all have a towing plan cheap, Eh? A 350 can hardly turn over and the spark from A plug may get it going. Doesn't happen with a slow cranking diesel.

Don't even try ether aka starting fluid. Not unless you are willing to haul the engine out as scrap metal. Note: Disable glow plugs first in this life and death emergency where the engine IS expendable.

Good clean grounds and battery cables in good shape really matter on these rigs. The grounds near the auto trans dipstick are sensors and ECM: critical. You take grounds apart to check and clean them not just a visual on these rigs.
 
Oh that rig is no good. Afraid you are going to have to sell it to me! Haha. Love that rig- exactly color and nice chrome rims with tint windows just like I would want.

Don’t buy any parts without mentioning here first btw. We can save you tons of headaches and cash buy pointing you to better choices and away from many of the rip-off places out there.
 
Y'all are too cool. I really, really, appreciate the compliments. I was told by someone a while back that of all the trucks like mine built in '94, under 2% were diesel. I have no idea where they got that from, but there might be something to it. I never see the diesel ones.

It sounds like I need to start the truck and smell the exhaust before I guess anything else about the truck. Thank you all for the advice so far.
some questions I have right now though....
1. Should I relocate my PMD? I've read some posts that suggest it's a good idea.
2. Should I consider bypassing or replacing the lift pump?
3. Anyone know of a diagnostic plug in? I'm embarrassed to ask, but I've had vehicles with OBD1 ports, I don't see one on mine thogh.
4. Anyone familiar with GMTD ScanTech? Is this something I should look into?
Thank you to anyone responding to these questions. I'm way out of my comfort zone, but just being a part of this group gives me hope and confidence. Thanks again.
 
1. Yes
2. Need to verify if it's a working LP. If it is I'd definitely make or buy a relay harness and add in a WTS feature so it will run during WTS.
3. Yours being a 94 should have a diagnostic port just to the left of the steering column under the edge of the dash.

Nice Hoe BTW
 
2% Diesel... You had a hard time buying one new in the era gas, Diesel, or otherwise. GM could not keep at one point with demand. No 4 door diesels in Tahoe or Yukon. All 2 door.
 
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