2005 Jeep Wrangler 2.4 NGC3 Closed Loop Boost PE

I'm new to tuning, so you'll have to excuse my ignorance. I turbocharged my 2.4L Jeep and have some theory questions before I start messing with VE and spark tables. How do you get it to go into power enrichment under boost? The trigger for power enrichment in the tune file is throttle position and then you can scale it based on pressure ratio, but you can't trigger it with pressure ratio. The dilemma is (correct me if I'm wrong) in closed loop, the computer will still try and fight to bring it to stoich. Even if the VE table is set up to burn rich under boost, the ECU in closed loop will adjust STFT to bring it to whatever I set as stoich. Now I could make it run open loop all the time, but I would prefer not to. Engines have better life expectancy in closed loop. I could just lower the WOT threshold, but throttle position doesn't necessarily correlate to load/boost. I could lower stoich AFR, but then I'm burning rich all the time, not just under boost. Does anyone have any ideas or is this something I simply cannot do? It seems hpt added a function to alter the OS on some GM computers to allow for boost enrichment. Excuse the ignorance, but could I simply add that ability to my ECU somehow? For background, I have a Neon 2.25 bar MAP sensor and am actually only running like 5psi boost max.

Short of running open loop, unfortunately there is no way I've ever seen to activate PE off of MAP.

There is a work around you can do electrically. It's a little barbaric, but it will do the job. The idea is to use a combination of a hobbs switch and a 3.9v zener diode, and tap into your TPS wires.

1) Run one side of the hobbs switch to your +5v TPS supply wire
2) Run the other side of the hobbs switch to the TPS signal wire
3) Using the wire in step 2, tap the zener diode in with the black band facing this wire.
4) Tap the other side of the zener diode (opposite of the black band) into the ground wire of the TPS harness.
5) Run a manifold pressure source to the hobbs switch, and adjust to the pressure of your liking for when you'd like PE to kick in.

This will result in a 3.9v signal being sent to the PCM whenever you hit your hobbs switch pressure setpoint, which will activate PE mode.

Thanks for the response. That's a pretty creative solution and its actually pretty similar to some piggyback systems like the split second enricher that override o2 sensor voltage, but those are hundreds of dollars and a zener diode is like pennies. Also TPS is a little more reliable than narrow band o2 I feel like. I actually have a pressure switch set up to eventually trigger water injection once I get everything else smooth. I wonder though if overriding the TPS like that would have unintended consequences. Have you done this before on an NGC3?

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Originally Posted by tschmitt416

Thanks for the response. That's a pretty creative solution and its actually pretty similar to some piggyback systems like the split second enricher that override o2 sensor voltage, but those are hundreds of dollars and a zener diode is like pennies. Also TPS is a little more reliable than narrow band o2 I feel like. I actually have a pressure switch set up to eventually trigger water injection once I get everything else smooth. I wonder though if overriding the TPS like that would have unintended consequences. Have you done this before on an NGC3?

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I've never used it on any personal or customer cars. But it was a trick that many folks used on SRT-4s back in the mid-2000s (which use NGC3 PCMs). If you have an automatic transmission, I suspect it would cause shift points (including downshifts) to follow WOT/kickdown shift patterns. Probably trigger the A/C compressor to disengage, also. Other than that, it's obviously going to force you into open loop PE mode. That's about all I can imagine it will affect.

Makes sense. I'm manual and no AC lol. I'll probably do this but use like a 4.7V zener diode and set the PE thresh to 4.7 (It's at 5V stock, which is why these things will literally never go open loop). That way if I'm not making boost at 3.9V TP for whatever reason, the car stays closed loop, like it was designed. I'll post an update once everything is running in case some future turbo Jeep person wants to do the same thing. Thanks for the help, B00STJUNKY.

Hi, any updates to this?
I am also wanting to have a CL system but need the OL enrichment when in boost.

Any part numbers for this Hobbs switch and a sketch on how its in the system? All would be great.

Thanks.

any update if this worked?

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Originally Posted by keith Goosen

Hi, any updates to this?
I am also wanting to have a CL system but need the OL enrichment when in boost.

Any part numbers for this Hobbs switch and a sketch on how its in the system? All would be great.

Thanks.

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