Need help with 8V92TA stalling issue

jjb · July 22, 2016, 07:31:56 PM

I originally posted this ins the off topic forum but they recommended I put it here so more people would see it.

I have an 8V92TA in a Military truck that stalls occasionally once warm. I also notice it will run rough at highway speed almost like its not getting enough fuel. It idles very low and sometimes the tach reads 0. At cold start I get about 7-800 rpms.

Any ideas where I should start looking? I recently noticed some air bubbles in the racor filter bowl so I think the first order is replacing fuel lines but I'm not 100% sure this my whole problem as it seems fine when its still cold.

Its a military rebuild by Diesel Exchange. It has less than 300 miles on it.

I attached a picture of the truck its in. Not a Bus but I heard you guys on here are Detroit experts.

Geoff · July 22, 2016, 07:46:50 PM

Yes, air in the fuel will cause all the problems you describe. The racor gasket may be the problem.

jjb · July 23, 2016, 04:55:55 PM

Quote from: Geoff on July 22, 2016, 07:46:50 PM
Yes, air in the fuel will cause all the problems you describe. The racor gasket may be the problem.

I have a filter kit I will be putting in at some point but the fuel lines look badly dry rotted. On this truck that's like 20' of fuel line. I hope the kit includes a new gasket

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DoubleEagle · July 23, 2016, 05:04:56 PM

Looks like the engine has few hours, but has been sitting in the sun for a long time. It might have even been overseas previously. Clean everything out and replace every rubber line and all gaskets. Even if they are not causing the current problem, they could cause trouble in the future. That unit might have been in the first Gulf War for all you know, and the engine was renewed after it came back.

jjb · July 23, 2016, 08:53:50 PM

The engine that was in it was bad. It had a cracked liner likely from being overheated. That engine only had 14k miles on it. I put a new/rebuild in it.

I will replace all of the lines but I thought it seemed odd that it only happens when its at operating temp. Once its at operating temp the tach reads 0 at idle most of the time. I would expect the air would make it surge or run rough not idle so low it doesn't even read on the tach?

luvrbus · July 24, 2016, 07:58:07 AM

Is that a DDEC (electronic) engine ? another ? do you have Jake Brakes

HB of CJ · July 24, 2016, 05:04:48 PM

Consider changing out all the rubber fuel lines with one size larger replacements. Also consider adding dedicated fuel tank booster to engine electric fuel pumps. Consider dedicated return line from engine fuel pumps. Also consider replacing all the fuel filters. Finally consider a dash board fuel pressure gage. Also in very hot weather operation consider a fuel temp gage. Respectfully.

jjb · July 24, 2016, 05:23:47 PM

Quote from: luvrbus on July 24, 2016, 07:58:07 AM
Is that a DDEC (electronic) engine ? another ? do you have Jake Brakes

Mechanical and it has Jake's.

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jjb · July 24, 2016, 05:29:12 PM

Quote from: HB of CJ on July 24, 2016, 05:04:48 PM
Consider changing out all the rubber fuel lines with one size larger replacements. Also consider adding dedicated fuel tank booster to engine electric fuel pumps. Consider dedicated return line from engine fuel pumps. Also consider replacing all the fuel filters. Finally consider a dash board fuel pressure gage. Also in very hot weather operation consider a fuel temp gage. Respectfully.

The fuel supply lines are like a garden hose. I think they are 5/8".

I have considered a booster pump even if just to help with bleeding.

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luvrbus · July 24, 2016, 07:34:19 PM

Does that have the electric pumps supplying the DD gear pump and 1 pickup tube or 4 one on each corner of the tank ? you did install the .80 orifice fitting on the return line where the pump can build pressure

jjb · July 24, 2016, 09:33:13 PM

Quote from: luvrbus on July 24, 2016, 07:34:19 PM
Does that have the electric pumps supplying the DD gear pump and 1 pickup tube or 4 one on each corner of the tank ? you did install the .80 orifice fitting on the return line where the pump can build pressure

No electric pump. It looks like just 1 pickup tube in the tank. I reused the return lines from the original engine. Where does the orifice go? I will see if I can find it in the manuals.

jjb · July 24, 2016, 09:35:14 PM

Here is a picture of the truck its in.

jjb · July 24, 2016, 10:00:33 PM

Looking at the parts diagrams I do not see any orifices but I do see a check valve on the supply side on top of the fuel tank. Its #7 in the attached picture.

HB of CJ · July 25, 2016, 01:24:46 AM

Very nice military 8 wheel truck. It would make a great off road motor home. I was told when rubber fuel lines get old, the insides swell up under use with hot fuel. The inside diameter swells down to practically nothing. Very reduced flows. Outside visual inspection can miss this. The cure is new lines. That and you got probably air pockets in the works.

bevans6 · July 25, 2016, 05:02:51 AM

The check valve is usually a special fitting installed on the cylinder head outlet that returns fuel to the tank. The fitting has a pipe thread that screws into the head, and the return hose threads onto it. It looks like a normal fitting, but the internal diameter is reduced to 1/16" or thereabouts. That restriction is what allows the fuel pump to build pressure. It's often overlooked when swapping in a new engine since unless you look closely and know what to look for, you would mistake it for a normal full flow fitting. If you find the return line and trace it back to the engine, that should be it. The check valve on the supply is a different deal, it is there so that the engine holds prime.