OBS defuel?

MeTo · Sep 26, 2016

Will an OBS pcm defuel if boost climbs above ~25 psi?

ghohouston · Sep 26, 2016

I think it varies between tuners.

Swaan · Sep 26, 2016

Yes it will but usually closer to 35psi .

Mine did that so i put a regulator on the map line . Set it fir 25 psi prob solved

Justin@DP-Tuner · Sep 26, 2016

In a stock tune, yes it will defuel at around 24psi.

In an aftermarket tune it may not. Depends on the tuner. We eliminate the defueling from overboost.

79jasper · Sep 26, 2016

What would the signs of defueling be?
Like will you feel it?
And will a obs set a over boost code?

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Swaan · Sep 26, 2016

Oh youll feel it lol

Its like going from full fuel to someone turning the key off. It will buck like crazy

79jasper · Sep 26, 2016

Guess I don't have to worry about it since my hydra. Lol
Was just wondering.

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Garbage_Mechanic · Sep 27, 2016

Justin@DP-Tuner said:
In a stock tune, yes it will defuel at around 24psi.

In an aftermarket tune it may not. Depends on the tuner. We eliminate the defueling from overboost.

Huh, when did you start doing that? Cause my DP Tuner sure defuels around 30 PSI or so very violently. Had to put a regulator on it .

old man dave · Sep 27, 2016

Back in the day, some swore their trucks defueled and others said no way. I think it depends on the year and PCM code of the truck.

OBS California trucks get a turbo overboost code P-0238 and that cuts out the engine at 24psi at the MAP. Boost fooler or pressure regulator cures that. Had to set the regulator to 19psi static pressure to compensate for the dynamic pressure wave rise at full throttle to keep the CEL from coming on. this varies by the particular regulator you use.

Justin@DP-Tuner · Sep 27, 2016

Garbage_Mechanic said:
Huh, when did you start doing that? Cause my DP Tuner sure defuels around 30 PSI or so very violently. Had to put a regulator on it .

Jody has been doing it since at least the time I started (December 2012). When was the last time you had your tunes updated?

With our tunes, de-fueling from overboost is eliminated. However, without the use of an overboost annihilator you may still get the P0238 or P1249 codes. Each truck (PCM cal) seems to be different there.

Garbage_Mechanic · Sep 27, 2016

Justin@DP-Tuner said:
Jody has been doing it since at least the time I started (December 2012). When was the last time you had your tunes updated?

With our tunes, de-fueling from overboost is eliminated. However, without the use of an overboost annihilator you may still get the P0238 or P1249 codes. Each truck (PCM cal) seems to be different there.

Likely before 2010, can't remember.

I still remember discovering the overboost issue......

This is the wife's truck and when we first got it in 2003 she was unimpressed. Her hot rod 91 IDI would outrun it. So I put the usual stuff including a brand new set of AC injectors and DP tuner. Her comment was "so a set of injectors cost more than and engine rebuild on the 91? Why is a Powerstroke better? "
Just happened I got the DP tuner installed the day before the Diesel Power Show at the Tulare Ag Center. So there were a lot of hot rod diesel guys on their way there. So sure enough we were blowing by a 6.0 with stacks when we discovered the boost defuel. Thought it blew up of course since it shut down and relit about 4 times before she could get her foot out of it. so the next weekend a boost regulator went on and the fun resumed.

Krause · Sep 28, 2016

Defueling may have Nothing to do with the tuner ******** that parameter or not. OBS's (which have a frequency based MAP) typically can only throw an overboost code. The SD's on the other hand have a voltage based MAP, can all defuel. On OBS's in particular, the MAP sensor dosnt like getting crammed with boost, and starts sending erratic signal to the PCM, which causes the bucking. It is defueling, but not on purpose, it's a symptom of the MAP loosing connection with PCM for a second. The variety in this comes with the random condition of your frequency based MAP sensor, and whether it is feeling up to the task of keeping the signal or not, some seem to be more tolerant than others.

Install a boost fooler before the map to insure you dont find out how enduring MAP sensor is. Mine was not very.. ask me how i know...

Swaan · Sep 28, 2016

Lmao doh!!!!

Yup it sure bucks violently dont it..

Justin@DP-Tuner · Sep 28, 2016

Garbage_Mechanic said:
Likely before 2010, can't remember.

I still remember discovering the overboost issue......

This is the wife's truck and when we first got it in 2003 she was unimpressed. Her hot rod 91 IDI would outrun it. So I put the usual stuff including a brand new set of AC injectors and DP tuner. Her comment was "so a set of injectors cost more than and engine rebuild on the 91? Why is a Powerstroke better? "
Just happened I got the DP tuner installed the day before the Diesel Power Show at the Tulare Ag Center. So there were a lot of hot rod diesel guys on their way there. So sure enough we were blowing by a 6.0 with stacks when we discovered the boost defuel. Thought it blew up of course since it shut down and relit about 4 times before she could get her foot out of it. so the next weekend a boost regulator went on and the fun resumed.

Oh okay. Yes, if the tunes are that old you may not have the defuel disabled. You can send the chip in for a reburn to get the latest tunes if you would like.

Yes, the defuel is very noticable, especially at WOT on a track. Can only imagine what went through her head when it happened :wtf: LOL

m j · Sep 30, 2016

the map only reads to 35psi. if it goes over 35psi it sends a -30psi reading to the computer.
yes this makes it buck pretty hard.

Norgren part number R07-100-RNEA looks to be perfect and has a locking knob

R07
'-100' is 1/8 ports '-200' is 1/4
'-R'
'N' is no gauge option, substitue a G if you want the little gauge port
'E' outlet pressure range 5-50psi
'A' female pipe thread

direct from their webstore in the US were $24 when I looked but they are on ebay too I found one that is 'used' for $13 plus $10 for the ride to Canada
(most places want $40 for shipping to Canada)

MeTo · Nov 13, 2016

FWIW, I have over 37 psi boost with PHP tunes and NO defueling. By the density of the black cloud in the side mirror; there is no doubt it's fueling.

96F350KID · Nov 14, 2016

Depends on PCM code. As i found out some PCMs have a speed limiter of 116mph and some don't. All OBS trucks should have some sort of boost fooler on there. Diesel sites little one has worked on mine for years without an issue. Just have to oil it when the code pops up some times.

m j · Nov 15, 2016

MeTo said:
FWIW, I have over 37 psi boost with PHP tunes and NO defueling. By the density of the black cloud in the side mirror; there is no doubt it's fueling.

the MAP only reads to about 35psi boost. I have personally tested it with regulated shop air and using torqueapp.
the PCM will 'see' a -30 psi value when the MAP maxes out and the PCM takes a bit to recover from the overboost.

like most have said, get a regulator to prevent the sensor from maxing out, they are something like $30 direct from the manufacturer Norgren