Defueling?

OBS73 · Mar 27, 2014

Just got done recently putting most the big mods in my signature on. I am now having this problem. If I slam on the accelerator, it will scream for about 3 secs and fall right on its face. I can also just very so slightly creep into the pedal and as soon as I get to 20 psi or so (I can sometimes get it to 25 psi or so) it will cut out and I loose all boost as well. Installed a boost fooler and have the same problem. My tunes are still setup for a stock truck, could this be a reason as well? I have my fuel pressure at 65psi at the moment and I can't check at the moment while WOT, need to get an in cab gauge so I can. Any insight would be great.

OBS-Addiction97 · Mar 27, 2014

Change your air filter ASAP.

OBS73 · Mar 28, 2014

Air filter is brand new

Powerstroke Man 6.4 · Mar 28, 2014

OBS73 said:
Air filter is brand new

Get new tunes. You can also try take the chip outta the PCM an see if it still does it.

OBS73 · Mar 28, 2014

Yeah, I am waiting to figure out tuning until after I get my new turbo setup hopefully by the end of the month. Guess I will just keep my foot out of it and in stock tune for now.

Obsledpuller · Mar 28, 2014

I ran into something similar with my mods in my sig almost was acting like a rev limiter. I called Larz at gearhead him and Matt do my tuning. He told me about a boost fooler. If your PCM is stock it's most likely seeing an over boost scenario and that's what is causing it. Just my experience with a similar problem.

Magnum PD · Mar 28, 2014

May also be a bad MAP sensor.

David N · Mar 28, 2014

What fuel pump? If you're dropping fuel pressure it will fall on its ass like that.

OBS73 · Mar 28, 2014

Bosch 044

OBS-Addiction97 · Mar 28, 2014

Check for boost leaks, and unplug your map and see if it runs better.

MAFoElffen · Mar 31, 2014

OBS-Addiction97 said:
Check for boost leaks, and unplug your map and see if it runs better.

Yes, unplugging the MAP would throw that into a default fuel map...

I would think boost leaks would not cause that, because the MAP would read lower, right?

Bad MAP sensor could cause that.

Reason I say that? Well- I'm OBS, running tunes and consistently max out with 25.6 pounds boost without getting decel conditions and without having to use a MAP line regulator. In fact, that is where a friend and I have figured is the point where it would be safe to set a MAP regulator if you needed one.

Me and a friend tested this condition with the MAP. He goes above 40 psi. He has a regulator setup. I am planning to go 40 PSI. We both have a vested interest. The external MAP sensor actually registers to just above 30 psig in varying the sense voltages, sending them to the PCM. (Yes, we thought that MAP reading limit would have been max'ed at a lower pressure, but we were wrong...) The PCM seems to trip a decel condition at around 27-28 pounds psig. (note that is all corrected to "psig")

So if the OP is really getting a decel condition... verified by an overboost DTC P0234 or for some reason was getting an underboost DTC P0299 code with good boost on the gauge... = Bad MAP sensor.

You have a manual Boost gauge right? And you are 20-25psi with stock tunes? With what Turbo and wheel? That is not noted in the sig line your are posting with... and you are not going to get that on a "stock" tune calibration with a stock TP-38 turbo... that would be very rare. I'm getting that with a TP-38, but with many heavy mod's to that. (just confused by that logic)

Do you have he ability to read live data?

On the suggestion of tunes or removing the Chip... Do you have a chip (and if so who's tunes for what?) I didn't see where you confirmed that you had a chip or not. That was confusing. You said you were still on stock tunes and was waiting on working out some turbo related issues before going to tunes. 160's will run without a chip... just not as well. But may be you meant that you are running tunes chipped for stock injector'ed calibrations... so that maybe the tuned calibrations for those are opening the larger injectors up too much? If so you would have black smoke from the A/F being off, right?

You also did not go into any details on the turbo related issues you said you were working through...

Just thinking out loud.

old man dave · Apr 15, 2014

Overboost defueling appears to vary by PCM code. Some do and some don't. Mine doesn't but there has been many posters who said theirs did.

Also I get the P0238 CEL at 24psi.