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Limp Mode

T

Trainedpro

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Have a 1996 K2500 GMC Suburban. Truck is going into Limp mode while towing uphill on the highway. Boost goes up to 10+ and stays there. Replaced the waste gate relay and the vacum pump and turbo boost sensor. What else is there that controls the boost?
Nick
 
Even new still may be bad MAP/boost senor on intake, reading higher than actual seen at gage, do you have access to scan tool to see what PCM is seeing and clipping fuel on high boost, are you getting overboost code ???, if not also possible you are seeing hight IAT, that will defuel and not code Are you sure you gat a boost sensor and not a Baro sensor, looks exaxtly like a boost but keyed so as to not easily hook up.
 
I bought the MAP sensor from a GMC truck shop and it hooked up easily. I do get a trouble code every now and then if I keep it throttled up on the highway p0236 - boost error. Truck runs excellent when I'm not towing but when I hit a big hill with a trailer on the Boost stays up around 10-12 if I keep it on cruise then goes into limp mode. I shut it down and it's fine. Does the map sensor have a gromet on it? There wasn't one on the top of the intake or on the sensor when I got it. The old one (installed by previous owner) had RTV sealer on it.
Nick
 
should be a seal grommet where it mounts to the intake, possibly RTV down in the sensor hole, not letting sensor to see true decrease in boost then it thinks it's in overboost scenario, tries to de-boost by opening the WG, that doesn't happen as the boost sensing tries to slowly respond to plugged boost sensing , and then tier 2 defense happens reduce fuel to control overboost, and you get defuel
 
Is 10-12PSI a scenario where it should be going into limpmode? I've been told that's overboosting!
 
Ya, these don't like sustained 10-12psi and what you are describing often happens. As mentioned before high IAT's also cause this a lot with our trucks.
 
No real setpoint that I'm aware of, part of the algorythm that compares boost-IAT-engine load etc, comes in at 10psi with some ambient conditions, and at 12 on others.

If it is boost that is causing the defuel, you'll need a fooler that tells PCM you are actually at a lower boost, or go with a reflash that gives fuel & boost gains so you can stay into "power" longer, reflash does away with the high limit boost

I see in signature you have a CAI kit, if it's pulling in underhood air, possibly on a hot day and your underhood is hot, your CAI isn't "cold", and causing IAT defuel to come into play also.
 
My truck is regularly boosting at 5psi at 68-70 mph, is this normal?
The grommet from the Turbo Boost sensor on the intake was missing, just picked one up but haven't had a chance to install.
 
Yes but as soon as I pass 72 it goes to 8-10 psi and goes into limp mode,
I think my boost is too high but don't know how to lower it without the purchase of a manul boost controller or a new ECU that doesn't have limp mode.
 
Good to know, thanks for the response.
Hopefully it's cheaper that the other parts i've replaced.
 
looks sensor related there TP 8-10 is std boost, you know anybody with a scan tool that can watch it while you drive to know wxactly what the PCM is seeing for both boost & baro. Also what is the 8th digit of your VIN S or F ?
 
"F", I still think my issue is overboosting, I get a P0236 error every now and again. I don't know anybody with a PCM, is it a common tool a shop will have?
 
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