Possible weak battery info needed.

[chapmjw]

Hi,

I've had the 1990 M923A2 for about a year now and I think I have a battery issue that I would like to confirm. If I go a day or so without running the truck and then start it up, it will run like trash. It sounds likes a miss firing engine trying to die. If it has only been a day or so since last running it will usually only run like trash for a few seconds, then it will run perfectly. If it has been more than a few days it will only run trashy. I've never let it run like that for more than 10 seconds or so. To get it going again I have to charge the batteries and try again.

I have checked and cleaned all terminals under the seat.
I have checked for current draw when vehicle is off. (none found)
I have checked battery water level.
The batteries charge to 13Volts and show 12.9volts the next day.
The battery gauge before starting is just in the yellow on the dash gauge.
While running the battery gauge is right on the Gen when the battery switch is turned off.

Has anyone else experienced weak batteries doing the same thing?
What is not being powered correctly to cause it to run so poorly?
Any advice is greatly appreciated

Thanks
Jim

 

[simp5782]

Just cause a battery has volts doesn't mean it has a lot amps. If your not able to start it a day or so after then you have a bad cell more than likely you can have 13v and only 30amps rather than 900amps. The alternator may not be able to keep up with charging the volts which is in turn feeding back thru the PCB and causing it to run like crap. Some alternators are the same way. They can go flat out or they can just trickle charge the dang thing. You also need to check the connections at the starter since that's how your charging system operates. thru it and then to the batteries. I have seen some A2 trucks where NONE of the dashboard gauges or crap will work right with a dead cell on 2 of the 4 batteries. Take your batteries to have a real load tested put on them and find out which ones are bad.

 

[74M35A2]

Your battery situation should not affect the way the engine runs. It sounds like your losing the prime in the fuel line, and it is worse the longer it sits. When these trucks have air in the fuel system, that is exactly how they run.

 

[simp5782]

Your battery situation should not affect the way the engine runs. It sounds like your losing the prime in the fuel line, and it is worse the longer it sits. When these trucks have air in the fuel system, that is exactly how they run.

If its not getting enough amps or a battery is starving the system it can cause spiking at the fuel shut off solenoid. One reason i knew your alternator wasnt putting out amps cause it would act like it was sucking air but it wasn't drawing enough amps to the 2nd battery to sustain normal function. It also surged the ac system. His rough running may simply be a surging. He is south alabama and things mean different things there. Just ask our friendly SS members from South Mississippi.

Sent from my SM-G935P using Tapatalk

 

[tobyS]

When my battery's are low, the fuel shutoff solenoid will not pull in and the truck, while cranking, will not start and run. Once I manually push the solenoid in, it stays and starts up and will run normally. Check to see that the solenoid is going in and staying in.

I have to agree with 74M35A2 that it is probably a fuel line issue, sucking air. Use a fuel container and hose to the IP that you know is not cracked, bypassing all of the lines and the fuel filter and see if it starts and runs properly. Keep in mind that the fuel return line is pumping your fuel back into the truck tank, so it won't last long unless you run both pickup and return lines into your temporary tank.

 

[74M35A2]

A2 fuel cut solenoid has 2 coils within it, pull and hold, hence the 3 wire connector on it. The MW pump fuel cut lever driven by this solenoid is either in the run or stop position. It really can't cause rough running from hanging in the middle.

OP, as long as oil pressure shows above 0psi, run the truck longer and the roughness should clear. Press the accelerator a few times to help it. This will be indicative of air in the fuel suction system if it smooths out, as it should. Report back.

 

[Scar59]

Your battery situation should not affect the way the engine runs. It sounds like your losing the prime in the fuel line, and it is worse the longer it sits. When these trucks have air in the fuel system, that is exactly how they run.

Yep, head in this direction, good buddy's A2 did the same thing, longer it sat, the prime would be lost/drained off. He replaced all the fuel lines and returns. Now everything stays primed w/ fuel, fires up after a long nap.

 

[Jbulach]

He should be able to tie the fuel shut off solenoid back, and then start it, to determine if it is fuel or electrical system related, correct?

 

[tobyS]

He should be able to tie the fuel shut off solenoid back, and then start it, to determine if it is fuel or electrical system related, correct?

They usually stay in once you have them pushed back. But you have to have the switch in the run position, not the off position. Then it will release and shut the truck off when the truck switch is turned off. Keeps the local teens from just taking off with it too.

 

[74M35A2]

The mechanical shut down lever of the MW injection pump is spring loaded to default to the run position. The default position of the shut off solenoid is engine stop position, and is much stronger than the pump lever.

If any doubt, it is very quick to simply unplug and remove the solenoid. During extended cranking, the voltage drops, pull coil resistance increases as the coil heats, and the plunger will extend to the off position, preventing the engine from starting. I keep zip ties on board to lash the stop lever in the run position if need be. But that is likely not the case here.

 

[98G]

RED FLAG - "While running the battery gauge is right on the Gen when the battery switch is turned off."

Battery switch should not be in the off position while running the truck.

I also think you have priming issues...