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.
Yes, air in the fuel will cause all the problems you describe. The racor gasket may be the problem.
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
Sent from my XT1585 using Tapatalk
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.
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?
Is that a DDEC (electronic) engine ? another ? do you have Jake Brakes
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.
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.
Sent from my XT1585 using Tapatalk
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.
Sent from my XT1585 using Tapatalk
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
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.
Here is a picture of the truck its in.
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.
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.
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.
Quote from: bevans6 on 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.
I installed all of the fittings from the old engine on the new one.
Sent from my XT1585 using Tapatalk
Quote from: bevans6 on 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.
I still have the old engine so I can double check. (Trust but verify 😃)
Sent from my XT1585 using Tapatalk
I had check valve on the brain when I wrote that, I meant to say "restriction fitting" not check valve when referring to the fitting on the engine that the return fuel line connects to. Just find that fitting, take the hose off and see if it is full ID or 1/16" ID. Sorry for the confusion.
Quote from: bevans6 on July 26, 2016, 04:33:36 AM
I had check valve on the brain when I wrote that, I meant to say "restriction fitting" not check valve when referring to the fitting on the engine that the return fuel line connects to. Just find that fitting, take the hose off and see if it is full ID or 1/16" ID. Sorry for the confusion.
there are many...here is one, they are normally engraved R-xx often 80 or 90 or ??
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fdieselpro.com%2Fmedia%2Fcatalog%2Fproduct%2Fcache%2F1%2Fsmall_image%2F9df78eab33525d08d6e5fb8d27136e95%2Fd%2Fe%2Fdetroit_diesel_engine_fitting_restriction_r80_8925042_fitting_restriccion_det.jpg&hash=1b77a0c95bd64fdb06061b482ae6b5212e806cd6)(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fdieselpro.com%2Fmedia%2Fcatalog%2Fproduct%2Fcache%2F1%2Fsmall_image%2F9df78eab33525d08d6e5fb8d27136e95%2Fd%2Fe%2Fdetroit_diesel_engine_connector_t_with_restriction_r80_025_per_031_ntp_8925027t_conector_det.jpg&hash=1e1d9e7785bed3a34f0d312fdd7b77dd568bd7ff)
Can you tell from this?
It looks like its 14 in the above diagram. Its part number 8924182. I'm pretty sure I put it on the new engine but i will double check.
Thanks for pointing that out.
If I was to suss out that diagram, I would say fuel comes out of the filter and into the rails on the head via thingies 19 and 4, and the return comes out of each head and is tied together at thing 13, so thing 14 is a real good bet. I take it the engine still isn't running well?
Brian
Quote from: bevans6 on July 27, 2016, 12:14:16 PM
If I was to suss out that diagram, I would say fuel comes out of the filter and into the rails on the head via thingies 19 and 4, and the return comes out of each head and is tied together at thing 13, so thing 14 is a real good bet. I take it the engine still isn't running well?
Brian
I looked up the part number for 14 "8924182 ELBOW, 5/16"-90 DEG. TUBE; 1/4" PIPE (.080" REST.) (W/SEALANT)"
I haven't had time to do anything with it. Its runs fine until it gets to operating temp :).
Give us some idea on how it sounds when it starts to stumble after warming up
Quote from: luvrbus on July 27, 2016, 08:12:39 PM
Give us some idea on how it sounds when it starts to stumble after warming up
it sounds fine they it sounds like its going to stall and it does or it will continue running normal but the tach goes to 0 which I would assume is because its idling too low to register.
When I hit the high idle switch it stumbles for a bit like its got air in the fuel but after a few minutes at high idle it seems to run fine.
I think I really need to make sure that orifice is in place and replace all of the fuel lines and filters and see what it does.
The other thing I forgot to mention is that the jake brake doesn't seem to work as good as it should. It seems like its on low all of the time. It has 24-28 volts like its supposed to.
There are o-ring (2) on each solenoid if you pinch one or lose one installing those it takes a while running but they will make a engine stubble as they build pressure and partially engage the Jakes and so will bad control valves in the Jake.
What do you use the vehicle for I bid on 1 on the Iron Planet site but missed it and had no idea what I could use it for but I thought it was neat
Quote from: luvrbus on July 27, 2016, 09:01:12 PM
There are o-ring (2) on each solenoid if you pinch one or lose one installing those it takes a while running but they will make a engine stubble as they build pressure and partially engage the Jakes and so will bad control valves in the Jake.
What do you use the vehicle for I bid on 1 on the Iron Planet site but missed it and had no idea what I could use it for but I thought it was neat
The engine was rebuilt by diesel exchange in 2010 so I would have no idea. I guess I have lots of work to do.
I honestly bid low never expecting to win :D. At least that's what I told my wife.
I use it in shows and parades and around the horse farm. Just a really big toy.
Sent from my XT1585 using Tapatalk