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ARFFMAN · 05-21-2021, 06:56 PM

I have a Newmar MH with a Cummins ISM 500. When I bought it I would get out on the road and the turbo would only max out to 4 to 8 psi. I took it to a friend of mine who worked on diesel fire trucks. He used the Cummins Software for the ISM 500 and everything tested OK and No Codes. He told me to change the fuel filter and the test drive was full boost 28-31 psi. Problem solved. NOT. Took it home and parked it. Next day same low turbo boost. Changed filter everything good, till I parked it. I figured out that when I start out, I'll drive for about 20 minutes and no turbo boost. Pull over and turn off engine, restart engine and full boost till the next day drive. After no boost for the first 15 minutes, Shut down engine and restart and full turbo boost. Has anyone experienced this or can shed some light on what's going on. Something appears to be resetting after engine warm and then restarted. Pulled engine codes today and none found.
Please help! I'm drowning.

jacwjames · 05-23-2021, 07:34 PM

Not an expert, don't claim to be. But I do read a lot of the posts on several forums.

It almost sounds like a fuel starvation problem.

Couple things to check.

I'd check your fuel tank breather, have read where mud dabbers have blocked, this would explain why after it sits for a while your problem goes away.
I've read also of an instance where the fuel line degrading internally and a flapper (piece of internal hose) would block fuel.
Also read where internal fuel line would degrade and pieces block the fitting going into the primary fuel filter.

Again, not an expert, don't claim to be.

bubby124 · 05-23-2021, 07:59 PM

Are you using the engine pack brake I've heard of them sticking then unsticking

RS505 · 05-23-2021, 08:52 PM

Since the problem comes and goes with a restart, I would look for a glitchy wire or sensor. The throttle position sensor would be the first thing I'd look into and if your rig has a VGT turbo, the guide vane actuator would be second. bad ground wires are known to cause all sorts of intermittant problems.

I have a relatively cheap scan tool, and I can use the "live data" feed to check these sort of things.

ARFFMAN · 05-24-2021, 11:42 AM

Quote:

Originally Posted by RS505

Since the problem comes and goes with a restart, I would look for a glitchy wire or sensor. The throttle position sensor would be the first thing I'd look into and if your rig has a VGT turbo, the guide vane actuator would be second. bad ground wires are known to cause all sorts of intermittant problems.

I have a relatively cheap scan tool, and I can use the "live data" feed to check these sort of things.

Does your Scan gauge read the Throttle position gauge. I just got a Scan gauge
and it does have Live data. Just need to know what I'm looking for. (Value)

wolfe10 · 05-24-2021, 11:48 AM

Quote:

Originally Posted by bubby124

Are you using the engine pack brake I've heard of them sticking then unsticking

Nope, the Cummins ISM will not have an exhaust brake.

ARFFMAN · 05-24-2021, 12:02 PM

My Cummins ISM500 does have exhaust brake

wolfe10 · 05-24-2021, 12:06 PM

Quote:

Originally Posted by ARFFMAN

My Cummins ISM500 does have exhaust brake

An exhaust brake or an ENGINE COMPRESSION BRAKE.

Completely different.

Again, never heard of an ISM with an exhaust brake.

RS505 · 05-25-2021, 10:20 AM

I don't have a scan gage, it's a Nexus 102 I think. There's also a Road Relay 4 (Cummins) on the dash, but I don't think it reads TPS

texasrs · 05-25-2021, 12:16 PM

I believe Wolfe10 is correct. You should have an engine brake.
AKA "Jake Brake". Single, or 2-stage.

texasrs · 05-25-2021, 03:18 PM

In terms of function, Jake brakes and exhaust brakes are exact opposites. Whereas an exhaust brake traps compressed air inside the cylinders (inhibiting upward piston movement), a Jake creates a vacuum to inhibit downward piston movement.

wolfe10 · 05-25-2021, 03:29 PM

Quote:

Originally Posted by texasrs

In terms of function, Jake brakes and exhaust brakes are exact opposites. Whereas an exhaust brake traps compressed air inside the cylinders (inhibiting upward piston movement), a Jake creates a vacuum to inhibit downward piston movement.

Let me restate that:

An engine compression brake/Jake brake allows the engine to do all the "work" of compressing 18/20 volumes of air into one on the compression stroke and then at the end of the compression stroke, opens the exhaust valve to allow all that "work" to escape.

So instead of that "work" being returned as the piston pasts TDC, it is released.

SIGNIFICANT braking HP.

DirtyDodge · 05-26-2021, 08:58 AM

Could it be the turbo boost sensor?

TTD · 04-24-2022, 05:00 PM

Any news on this?

I have the same engine and the same problem. Going on 2 years now.

Basically, whenever the engine is cold (meaning it has not run for at least 3 or 4 hours), it does not have full turbo.

Drive it for 10 to 15 minutes, restart the engine and I have full power. It will stay working perfectly no matter how many times I restart it... as long as I don't let it get cold.

Cummins troubleshooters said it was the air controller that sends something to the actuator. I just swapped it with a brand new one (cost 1200 bucks) and no change. (yes, I plan to send that part back).