Boost limits after long cruise at speed

[DMather]

OK, I've got a weird one that I do not see anywhere on the forums. It's not a dead petal. Here's the scenario.

Cruising at 70-75 on basically level, no hills, interstate with normal boost displayed on manual gauge. Then, when a hill that requires more power to maintain speed is encountered the throttle responds but the boost does not increase. I can hear the throttle change but the engine can't develop more power. This will happen whether I am using cruise control or not.

If I release the throttle and reapply the engine goes to no power and then returns to the maximum boost it had before..but...if I release throttle, disengage clutch and allow the engine to come to idle, then reengage, the boost comes back to life and everything is normal..... for a while.

I changed the MAP (Boost) sensor and the only change that it made was that releasing the throttle and allowing the boost to go to zero now resets. I don't need to disengage the clutch. I suspected the MAP as I have not seen this problem at 55-60 and concluded that the boost was being reported wrong to the PCM.

I changed the IAT and it made no difference. (the original was oil caked but tests ok)

Here's the setup.
-I have a smarty but changing programming makes no change in the problem.
-Waste gate is free and functional. (When running right it runs from 0 to over 35psi)
-APPS (TPS) is the genos replacement and is fine (and since this happens using only the cruise control the APPS is not in the circuit when the problem occurs.
-2002 5.9HO with 4" turbo elbow and exhaust
-pacbrake exhaust brake - that is full open and I have not used since trying to fix this.
-5volts test good in multiple locations

Thought about grounds this morning and am going to check the ground on the PCM but I am beginning to suspect that it may be the source of the problem.

Anyone have any thoughts or ideas on this? I'm running on empty for things to test.
Thanks

 

[Bob4x4]

Drive with fuel pressure gauge and scanner reading live data duplicating concern

 

[DMather]

Forgot to post - I have a fuel gauge... WOT 12PSI
Live data on android reveals nothing other than what I can sense without the gauge.
And....throwing no codes.
That's what makes it so puzzling. (and frustrating)

 

[DMather]

So... I pulled the ground off the batteries and turned the ignition on for about an hour. Then reconnected the batteries, performed a APPS calibration and cleared all codes.

Went for drive and the truck is now behaving perfectly. Smooth, consistent and boost is behaving the way it should.
However, when I got back I checked for codes and was surprised to find P1693.... and P0216.... ugh

Before I start shopping for VP44.... have I missed anything?

 

[DMather]

And now it gets really frustrating.....

Spent most of the morning running the truck at different loads, speeds and distances and can not get it to throw a code.

Is it possible that the computers were just so messed up that the codes weren't really there and after "rebooting" the computers it took a cycle or two for it to find itself and now all is well in the world???? In 55 years of wrenching I have never had something be so flakey, and I've seen some crazy sh*t.

Guess I'll just cross my fingers and hit the road and hope I don't get stuck on the side of the road for a third time this year. (broke the rear axle....twice)

Still open to idea, suggestions, oversights, insights, tall tales or large amount of unmarked bills......

 

[DMather]

OK.. now I'm looking for thoughts..

The ONLY time the codes get set is at startup.
I checked for codes...none.
I start the engine... 2 codes P1693 & P0216
I clear the codes.
I drive, drive, drive. 30,50,70mph, light acceleration, WOT acceleration in multiple gears. 26psi boost. I decelerate in 6th as well as downshift to push rpms up and bring throttle back in. Everything running as it should....
And...
Check for codes.... NONE.

Really scratching my head on this one.... Even tested the batteries to make sure they are not being pulled down and low voltage is causing the problem.

 

[Chief USA]

I think you best be prepared to replace the VP-44. Mine threw P0216 the last month of the engine warranty. The only reason I checked for a code is that the engine missed one time under a load accelerating. Diesels don't miss. My engine ran just fine and never gave me any problems but after reading up on the what exactly internally inside the VP-44 causes the code, it is a matter of time before the pump will fail. It could take years or it could take days. No way to tell. I took it to the Dodge dealer who saw the truck was running and asked me how I knew the VP set a P0216 code, so I showed him how to retrieve the codes cycling the ignition switch. After some denial and few phone calls they replaced the pump.

This may be helpful on understanding the P0216 code if you have not read this already.

https://www.bluechipdiesel.com/reading-codes

Your truck is not under warranty. If it is still running acceptably, I would continue to drive it with the knowledge that it should not be a surprise if the VP-44 eventually fails and leaves you on the side of the road. It may never fail or it could fail quickly now if you think we have jinxed it.

 

[petersonj]

@DMather, your original problem and the code you are now seeing just after start-up may be related. Over 15 years ago my original VP44 pump failed with an eventual 0216 code set (a timing related issue). Before I ever got the code, the engine would periodically go into "limp mode" (what you described earlier). It hardly ever happened at first and the ambient air temperature had to be above 95 degrees for it to happen. As the months rolled by, the limp mode began occurring more frequently and at cooler ambient temperatures. Over twenty thousand miles and a year later, I finally had it replaced under warranty.

No two trucks will show exactly the same symptoms. There are many things that can put the engine into limp mode and "actual timing not meeting commanded timing" is one of the them. The event may have to occur a specified number of times during a specific time frame before setting a code or triggering a limp mode.

- John

 

[DMather]

Thanks for the input. I've basically decided to just drive and keep fingers crossed.
There has been no other symptoms other than the "limp" mode. (for lack of a better label). Now, after the computer reset, the truck is running normally except throwing the code on startup.. although I have been noticing if I wait for the fuel pump to cycle it does not throw the code.
I am making 1300 mile trips about every 5 days so I'll know soon enough....or later. ;-)