'90 BMY - stumbles/cuts out on acceleration

[MontanaBighorn]

I picked up a '90 BMY 5 ton M923A2 (10,000 miles roughly) a few weeks ago and it has done great for me until this morning. While driving around town the truck is doing fine, but once I attempt to accelerate on the on-ramp to get on the highway the engine starts to cut out like its being starved for fuel. When I let off the accelerator the performance comes back, but when I press the accelerator to try to get highway speeds again it starts to cut-out again. I had no problem driving on the highway at -22F last week so I really don't think fuel is gelling at 10F.

My first thought is a lift pump issue because I've had several '01 era Cummins powered Dodge trucks exhibit this same behavior as a result of the failed/failing block mounted lift pump. I'd like to either confirm or eliminate this as the cause of my problems before spending the money to repair it. My local Cummins shop quoted me $450 to replace the pump. I could buy one for $60 and do it myself but with temps currently averaging around 0F degrees I don't know that I want to start an outdoor project like this. I've had friends suggest fuel filter but they aren't familiar with the M923A2.

Is there a way to know for sure before I start replacing parts? Is there a tutorial available on how to change the lift pump? The local parts guy couldn't be sure which lift pump I need because he said there were two different ones to choose from. I provided the engine serial number but it still didn't help. Any part numbers would be appreciated as well.

Thanks!

 

[Suprman]

I would replace the filters and put some diesel 911 in a fresh full tank.

 

[doghead]

Have you ever serviced your truck?

Have you been adding fuel additive?

 

[MontanaBighorn]

Hello,
Truck was serviced at diesel shop by previous owner. Still on the original tank from previous owner, running whatever fuel additive that he used. I know he added a lubricity additive, I just don't know which one he was using.
Thanks,

 

[doghead]

I would start with a new fuel filter. Also add in some 911 additive.

 

[tomcata3]

My M931a2 was doing the same thing, I replaced some fuel lines ( they were sucking air in to the system) and bypassed the fuel tank selector switch ( on driver seat floor) So i was only running one tank.

 

[MontanaBighorn]

Thanks much for all the suggestions; they are appreciated. Is there a test to eliminate the lift pump as being the cause? I have no surging at idle which in the past has proven a good indicator that the issue is water in the fuel. Also, before I checked for more updates I had already filled the tank and dumped in 81oz of Seafoam. Would you run the 911 additive in addition to the Seafoam, or does the Seafoam have it covered?
Thanks,

 

[SETOYOTA]

Start simple. Replace both fuel filters.

 

[MontanaBighorn]

Start simple. Replace both fuel filters.

I'm attempting to do this now, but spent the last hour laying in Montana snow under this truck trying to find the second filter. Where does that one live on the M923A2?
Thanks,

 

[Floridianson]

I'm attempting to do this now, but spent the last hour laying in Montana snow under this truck trying to find the second filter. Where does that one live on the M923A2?
Thanks,

Thought there was just the one canister on the A2 driverside under cab left foot.

 

[doghead]

Why guess, when you can read the TM?

 

[Floridianson]

Been reading the TM's on my M931A1 have not gotten to the A2 yet. Hoe Hoe Hoe

 

[MontanaBighorn]

Thought there was just the one canister on the A2 driverside under cab left foot.

I'm not finding one, but since he recommended changing both and that I'm new to this platform I deferred to greater knowledge.

 

[seano11]

there is the big canister 1 under the fender then there is one mounted on the engine. Its about the size of a car oil filter should be drivers side its the first thing your fuel line goes into after the lift pump. Did you check your transfer case lever if mines moved a bit the truck will sputter and miss

 

[SETOYOTA]

The big canister under the driver side fender and one on the back driver side of the motor. Looks like an oil filter.

 

[MontanaBighorn]

Why guess, when you can read the TM?

Time frame. I was trying to get this done before the next snow storm started and have so much to learn that I'm trying to gain the basics so that I understand what I'm reading. At this point I see lots of references to the M939 series but do not know how much of that applies to the M923A2. I'm hoping to find a "Newbie FAQ" at some point to give me the absolute basics that I can build upon with the TM.

 

[MontanaBighorn]

there is the big canister 1 under the fender then there is one mounted on the engine.

Thanks much. Have you a part number for this filter by chance? I'm in town now and if I have a part number I can go ahead and pick up the filter and save a trip back into town later.

Did you check your transfer case lever if mines moved a bit the truck will sputter and miss

I didn't, but don't understand the connection?

Thanks,

 

[doghead]

If you just open the TMs, and look at then, you will see that the A2 has it's own sections where needed.

In a time crunch, I prefer to get the facts right and get the job done correctly the first time. Often asking a forum for information is a crap-shoot.

In this case it took 2 days for a helpful(assuming it is correct) answer. Surely, it would not take 2 days to look at a TM and find the info.

I suggest you download the M939 series truck TMs, and get familiar with them. They are quite easy to use.

If there is one thing I have learned from the Internets, it's that a forum(with 500000 members) almost never gets the facts right(just how would you know if each poster is correct?).

 

[doghead]

33472 for the filter on the motor. WIX or any other brand you like.

 

[doghead]

CUMMINS 256476 for the big one under the fender