Cat 3126 problem

2SteveWI · Jul 18, 2022

I know a cat 3126 is not a tractor engine, but I think there is an answer to this problem among the experts on this forum. I am a member of the local volunteer fire dept. We have a 2003 Freightliner with a cat 3126 responding from our sub-station. A couple months back, I responded to an early morning fire and the batteries were dead. There are 3 group 31 batteries in this truck. Batteries were less than 3 years old. Truck is on a battery tender. Tried to jump start the truck but no luck. Replaced with 3 new batteries from the local co-op as soon as they opened up and back in business. Since then the truck has been hard starting. If you turn the key the first time it will crank 30 seconds w/o starting. If you crank for 4-5 seconds and turn the key off and try starting a second time it will always start and run fine. No codes are stored, and the intake heater system is working fine. Believe the low voltage from the bad batteries damaged something. Has anyone in YT land had a similar experience. Thank you for any help. Steve.

danofarming · Jul 18, 2022

We just went through a sometimes no start situation with one of our trucks. Dead Batteries, No start Charge batteries start..... anyhow, turned out it was a Bad Ground Cable. I believe corrosion inside a crimped cable end.

Janicholson · Jul 18, 2022

The issue may be two things not one. The first encounter with a dead truck could be that lights or accessories were accidently left on. Or one or more of those original batteries was bad. I have encountered a brand new OEM battery in a new Nissan that would fail to crank the engin at all when first attempted over night. on the second or third attempt it would begin to turn the engine, then in about 10 seconds it would spin well enough to start. The battery was bad. it had an internal short that drained one cell to zero overnight. when starting the conduction through the other cells and the starter, charged the offending cell well enough to let it pass enough current to start the vehicle. The regional rep for Nissan had a difficult time with understanding the issue (read warrantee) until shown that it was the case by putting it in his car!. Before condemning the truck, volt test each battery before starting it. I bet one is going to show less than 11 volts. Jim

Steve@Advance · Jul 18, 2022

I agree with dano, a bad connection somewhere.

Immediately after a failed start, feel all the connections related to the batteries, cables, starter and ground. If any are hot, there's the problem.

You can also put a volt meter across each battery, directly to the posts. Read the voltage while cranking. If the voltage does not drop, that battery is not making good connection, while the others do all the work.

Sprint 6 · Jul 18, 2022

I had a 3126 in the shop with a glitchy injection pressure sensor that required two or more crank attempts to fire. The switch was causing the HUEI system to build pressure, then dump it. These engines run a similar injection system to the 7.3 Powerstroke (Navistar 444), in fact Cat developed the system for Navistar.

2SteveWI · Jul 18, 2022

I think you are on the right track. Many of the YT members that are also volunteer firefighters will probably agree that 3 years is common life for fire trucks. The old batteries were load tested and the voltage was over 13, but only 50 amps killed them. When cranking on the second cycle of the key switch you can hear when the injectors start firing and the truck starts running in seconds. Fire trucks also have a battery disconnect switch with a small keep alive wire feeding the ecm with an inline fuse (15 amp) on this truck. That keeps the ecm from having to relearn parameters every time started.

RodinNS · Jul 19, 2022

Id start with cleaning and checking the grounds and cable connections to the starter and ECM. I'd also install a ground disconnect switch on the floor of the cab at the drivers door and wire the maintainer/TIC/gas detector such that it's not disconnected when the switch is shut off.
Beyond that, if it's not a low voltage issue while cranking, then it's probably an HEUI problem as others have suggested. Could also be a bad crank sensor. First step in diagnosing that is checking primary connections...

Rod

Cat 3126 problem

2SteveWI

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danofarming

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Janicholson

Well-known Member

Steve@Advance

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Sprint 6

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2SteveWI

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RodinNS

Well-known Member

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