M923A2 - Loss of Power While Driving

[crolfe1984]

So I'm starting this thread to keep track of my findings and advice/solutions to the problem below:

My 1990 BMY M923A2, about a month ago, started acting oddly when being driven up a steep hill. I would notice a slight drop in RPMs and a definite change in the exhaust note. It sounded more muffled and a lot lower in tone. Didn't think much at first, but the problem has been getting worse. Its to the point that while driving today on flat ground the RPMs suddenly dropped from 2000 to 1000 with no response from the throttle. While I didn't totally lose power I was going no more than 15 MPH. This would last about 30 seconds or so and the truck would slowly gain engine speed. The exhaust note once again is very low and muffled. This issue is absolutely most obvious while driving uphill.

The past 900 or so miles have been trouble free, the gauges all read correctly (including oil pressure), the truck has fresh diesel in it, idles fine, and shifting from the transmission is on point. Aside from a small exhaust leak at the bottom of the muffler I can't trace any readily apparent issues.

My tool selection is somewhat limited and I don't have the space for huge projects (engine swaps etc.), but this summer I'll have time to work on it and funds for spare parts as needed. Any ideas or insight from people with turbo 5-ton trucks that have lost power while on the move?

 

[fuzzytoaster]

Starting off simple here...have you changed your fuel filters? It's possible gunk could have clogged your filters and settled when the truck sits only to be stirred back up and clog again.

 

[crolfe1984]

Going through my log book tomorrow to see when it was replaced. I've got TM 9-2320-272-23-1 downloaded and, as time permits in the coming weekends, I'll work through WP 0014-1. I don't have a lot of experience with these trucks, but I'm willing to learn from those that do!

I'm most curious what would cause the loss in power AND the drastic change in the exhaust note.

 

[crolfe1984]

Well today I replaced my fuel filer. Used a Baldwin 1226 and it replaced the FRAM P8043 just fine. Re-primed the motor (per WP 0239-2 steps 1-4) and it fired right up with out issue. Let it idle around 700RPM for 20 minutes while I check the transfer pump, fuel filter, injector, and injector lines for leaks. Couldn't find a single leaking drop.

I tested the truck on flat ground, reverse, forward, idle some more, and saw no issue. Decided to take it for a test run and sure enough on my first hill I got the odd exhaust note again and by the bottom of the hill the engine slowly ground to a halt. Odd thing is it started up just fine again and I got it turned back around to its parking spot.

Any thoughts or members with similar issues? I'd really like to get this one diagnosed!

 

[dmetalmiki]

Well seems to me if any inclanation of the vehicle causes power loss (and of course then the engine/exhaust sound would change) Something is "clogging up" somewhere. Have you checked the tank? and filter cases?.(water). I would start the vehicle chock it securely and them Jack It up to replicate the fault, from where you can trouble shoot/analyze further. Keep us informed of progress on this one.

 

[VPed]

Just for giggles, have you checked around the base of the turbo where it mounted to the exhaust manifold? One of my trucks had a leak due to loose nuts but the guy that spotted the problem (experienced) told me that blown out gaskets are common. Fairly cheap and easy to replace if that is the cause.

 

[dawico]

I would start at the tank and work toward the engine. The pick up tube may be grabbing something but then letting it go when it shuts down.

 

[crolfe1984]

Going to take today and try and work through these issues! I've made a valve-fuel cap so I can pressurize the tank, I'll sure to to spend some time investigating the fuel tank and tubes, and I'll also inspect the turbo more closely. I'll (hopefully) have results to report back.

 

[M35A2-AZ]

Be sure to only go to 3-5psi.

 

[dawico]

Going to take today and try and work through these issues! I've made a valve-fuel cap so I can pressurize the tank, I'll sure to to spend some time investigating the fuel tank and tubes, and I'll also inspect the turbo more closely. I'll (hopefully) have results to report back.

Be sure to only go to 3-5psi.

Yup. Park the truck on an uphill slope and disconnect the fuel line at the IP. Blow fuel through the system and see if it gets plugged up.

 

[crolfe1984]

Well I didn't even get to pressurize the fuel system. i started at the tank and removed the fuel supply tube to check for a blockage and it came apart in two pieces. It appears to have been removed once before a long time ago. I'm going to assume I need a new one (tube and elbow) so any tips on where to find one of these?

 

[MtnSnow]

Just resolder the pickup tube back into the elbow. (That's what I had to do to my M925a2 truck as I couldn't find an NOS complete pickup tube assembly

 

[crolfe1984]

Just resolder the pickup tube back into the elbow.

That's what I'll have to do, but I need a new elbow. Anybody have a spare or a source for one? Aside from a custom solution (new brass fittings, hose barbs, and a section of fuel hose line) I'd like to keep it stock. I'll gladly pay!

 

[MtnSnow]

If you do find a source please be sure to share it as I and others I bet would like to get a spare.

 

[M35A2-AZ]

Just resolder the pickup tube back into the elbow. (That's what I had to do to my M925a2 truck as I couldn't find an NOS complete pickup tube assembly

That is what I had to do to my M923A1 when i got it. Keep losing prime.

 

[crolfe1984]

That is what I had to do to my M923A1 when i got it. Keep losing prime.

So before I go doing something irreversibly stupid... Let me check with the community. As sourcing the reverse-flare brass elbow is next to impossible I've come up with this idea.

I've sourced a nice fitting combo for the fuel tube, but connecting it to the steel fuel line is not going to happen unless I cut off the portion with the compression fitting.

I'll then have to run 1/2" fuel line from a barb on the new elbow and triple clamp the new line to the steel line.

Yay or nay?

 

[silverstate55]

My local hydraulic hose supplier has hundreds of those fittings in stock...they brazed up various combinations for me at little charge. You could use a compression-to-compression fitting to fit the two lines together without clamping.

Look for your local Parker distributor, or anywhere that fabricates hydraulic hoses or hoses/lines for commercial vehicles. Take your pieces in with you & let them know what you need.

On the west coast, many NAPA stores no longer perform this service; don't know if it is the same in your area or not.

 

[M35A2-AZ]

So before I go doing something irreversibly stupid... Let me check with the community. As sourcing the reverse-flare brass elbow is next to impossible I've come up with this idea.

I've sourced a nice fitting combo for the fuel tube, but connecting it to the steel fuel line is not going to happen unless I cut off the portion with the compression fitting.

I'll then have to run 1/2" fuel line from a barb on the new elbow and triple clamp the new line to the steel line.

Yay or nay?

I would just resolder it up. The line running to the tank is copper not steel.

 

[dangood]

Loss of Power when driving

Hey guys, multiple times I have had this same issue of losing power after driving for a while. Last time I was driving a truck from Deleware to Utah and had it happen after 1300 miles. (clost to halfway, go figure) Most of the time it has been the before mentioned fuel filter, Or if the Truck has got the inline right before the IP, better throw a couple in the truck with you and a screwdriver as they dont last very long because of how small they are. The last trip I started losing power on the hills, and after spending hours on the side of the road going thru filters, lines etc it ended up being multiple issues, the Lift Pump (with the primer button) as a seal had gone bad and it was sucking air thru the button and leaking fuel. It also had a small air leak in the fuel line way under the fender and underside of cab that could not be detected until pressurizing the tank. Replaced with chemical grade transparent 1/2 hose from Tractor Supply so I could monitor the flow and air bubbles. Was getting small air bubbles from the draw tube of tank, so had to replace that when I limped it home. It had a small hairline crack right at the top of the inside of tank fitting. (its a wonder it made it over a 1000 miles without a hitch before!)

Good luck, let us know what it was when you figure it out.

Dan- Plan B Supply

 

[Rmtaunton]

Also just a tip , given only temporary but works . A can of bearing grease cost 7 dollars , it's a fantastic thing from bearings to coating fuel lines to seal pin hole cracks , ask me how I know