MEP 804b MPU source?

Steel Soldiers is supported by:

ehinlein

New member
23
0
1
Thanks for the quick replies! Just ordered but will definitely use the parts wanted section next time.
 

Guyfang

Active member
6,310
12
38
Member 155mm bought his from a truck repair shop, i I remember right. Send him a PM and ask.

Oh, whats wrong with yours?
 

155mm

Chief and Indian
888
2
18
Correct, the small mpu on 804 is the speed sensor on the tranny on an 03 379 pete, the large is on an 03 w900 kenworth tranny
 

ehinlein

New member
23
0
1
Hello Guyfang,

I didn't respond right away because I wanted to see if the speed pickup was the issue. It wasn't. The story. Nice clean 804b. Had for 18 months. From GP. Has always started and run fine. When I got it the fuel intake pipe in tank was bent upwards so required a fullish tank to run. Could be a hint that something was wrong and someone messed with it. Went to start it recently and it cranked fine but no start, no smoke. Thought maybe fuel. Checked at bleed and filters. Fuel good. Thought maybe pickup as this seems to be an issue. I swear I gently ran it in to stop and then backed 3/4 but after that upon crank, chewed it up. Live and learn. Anyway replaced that and get 2.8VAC on crank now. Only odd thing is that a couple of weeks prior to the no start condition I was moving it (no rear leg) and tipped it so it flipped on rear end, pintle to the sky for a short time (minute). Hadn't tried it since the tip. This was the first time. It was a gentle tip onto soft ground. Can't see this as cause but who knows. Any thoughts? I know. I know. time to break out the TMs.
 

robertsears1

Member
164
0
16
On my two 804’s if no smoke during crank, so far it has almost always been the MPU. On the A model, it has no fuel pump and it would lose the prime from time to time. Replaced the manual fuel pump doohickey and that part has been fine since, now the water pump is making bad noises with only around 150 hours total.

On the B, no problems in more than 500 hours of running and it seems more robust than the A, especially when running a FDECU-5 (5 ton heat pump). Since the B has fuel pumps, let it run for around 5 minutes and maybe crack some lines to see if it is moving fuel and bleed it. You should hear the return dribbling into the tank.

Yes, the TMs have some trouble shooting guides although the one about crank no start should begin with checking and verifying the MPU instead of near the end of the guide.

Robert
 
Last edited:

155mm

Chief and Indian
888
2
18
You can operate injection pump by hand, for troubleshooting. Takes 2 soldiers unless you have really long arms. My guess is mpu same as robert. Unless something got knocked loose with the tip over. Might check all relays behind control panel
 

Guyfang

Active member
6,310
12
38
Hello Guyfang,

I didn't respond right away because I wanted to see if the speed pickup was the issue. It wasn't. The story. Nice clean 804b. Had for 18 months. From GP. Has always started and run fine. When I got it the fuel intake pipe in tank was bent upwards so required a fullish tank to run. Could be a hint that something was wrong and someone messed with it. Went to start it recently and it cranked fine but no start, no smoke. Thought maybe fuel. Checked at bleed and filters. Fuel good. Thought maybe pickup as this seems to be an issue. I swear I gently ran it in to stop and then backed 3/4 but after that upon crank, chewed it up. Live and learn. Anyway replaced that and get 2.8VAC (where are you mesuring this? At the MPU, or at the A5?) on crank now. Only odd thing is that a couple of weeks prior to the no start condition I was moving it (no rear leg) and tipped it so it flipped on rear end, pintle to the sky for a short time (minute). Hadn't tried it since the tip. This was the first time. It was a gentle tip onto soft ground. Can't see this as cause but who knows. (Like 155MM said, check the relays.) Any thoughts? I know. I know. time to break out the TMs.
1. Charge your battery's. This set, like most TQG's work best when the batteries are in tip top condition.
2. Have someone try and start the set. You make the following tests.
3. See if you are getting 2.8 VDC at the A5 terminals 16 & 27.
4. Go to the A6 and see if you have 7.8 ohms across the coil, and 24 volts at the P10.
 

ehinlein

New member
23
0
1
I thought I should give an update. Did not have Guyfang's response and the voltage and resistance checks at the time. Summary is that it fires right up every time now. What was the issue? I don't really know and I hate it when "Things fix themselves" . At one point while I was cranking over and it wasn't starting I flipped the Battle switch while cranking and probably while releasing the crank switch also. Next time I switched to start it fired right up. And continues to do so. All I can think of is a corroded relay contact? I'm sure it will happen again when I need it most but it's tough to fix what isn't broke. Ill check those numbers anyway but guessing they'll look good since it's working. Been starting it for 5 days now with no issues.
 

155mm

Chief and Indian
888
2
18
I had a ghost also on a 805, got mad, disassembled whole control coupla, put it all back together. I didn’t fix anything, but this day, its the most reliable.

my guess is corrosion or bad connection, now the $10k question, which one.
 

Guyfang

Active member
6,310
12
38
This kind of thing drives me mad. You have got to test, test, test and test some more.

Like 155mm, when this happened to me, in the end, I simply took the whole freaking thing apart, and put it back together again. Cleaning, tweaking, bending, inspecting, testing and cursing. Its that, or just relying on my Fathers old saying. "I would rather be lucky then good".
 

Coug

Member
269
4
18
I hate doing the poking around trying to find the bad connection when working on customer units, because most of the time I never find anything I can point at and say "this is the problem, and now the problem is fixed, so it won't happen again"
It usually ends up "I tried finding what was wrong, moved a bunch of wires around and tightened a few connections, and it seems to be fixed for now. If it happens again give me a call and I'll come back because I can't actually fix anything if I can't find what's broken"
 
Top