RB25DE NEO with Haltech ECU

[Haggerty]

I seem to the be only person that is using a Haltech 2500 on an NA motor, I've installed a Bosch DBW throttle body to the OEM intake manifold and am having problems maintaining AFR even with the wideband o2.  It will run extremely rich at idle and up to redline, but under load it will go extremely lean in the 20s and i'm essentially having to rev it over 4k and feather the clutch to get it up to speed.  I've read a few other threads of about the butterfly, it seems removing the vacuum to it is supposed to have it remain open, i've noticed no difference under 4k with the vacuum line to it plugged. 

I'm hoping someone here has had luck using the NA manifold with Haltech, and if they happen to have a tune for it.  

[MBS206]

You very likely need to get it on a dyno and tune it.

My assumption is, you've got an RB25DET tune in it, which has a different manifold, different injectors, and different cams as a minimum.

What O2 sensor are you running?

 

When you say it runs extremely rich from idle all the way to redline, is this just free revving it you see that?

[Haggerty]

Yep, the closest base tune available was for the GTT, I went with that and made all the logical changes I could find to convert it to Naturally Aspirated.

It will rev fine in Neutral to redline but it will be cutting nearly 50% fuel the whole way.  If I let it tune the fuel map to start with that much less fuel it wont run right and has a hard time applying corrections.  These 50% cuts are with a fuel map already about half of what the GTT tune had.  I was having a whole lot of bogging when applying any throttle but seem to have fixed that for no load situations with very aggressive transient throttle settings.

I made the corrections to my injectors with data I found for them online, FBCJC100 flowing 306cc.  I'll have to look to see if I can find the Cam section.

I have the Bosch 4.9 from Haltech.

My manifold pressure when watching it live is always in -5.9 psi/inHg

Edited Sunday at 01:43 PM by Haggerty

[Murray_Calavera]

@Haggerty This seems silly to ask, but are you confident in your ability to tune the Haltech?

 

[GTSBoy]

Shouldn't need a "base map" for anything other than guidance to ignition tuning. You just need the engine capacity right, the injector size right, and something, almost anything, for a VE map.

On an NA engine, fuelling is almost completely a function of load signal & rpm. It should run and drive with a completely flat fuel map. It will be too lean under load, but that's easily fixed.

We used to tune all ECUs without any base map. There were no such things (until someone had tuned a near stock engine on one, and then they had a "base map".

[Kinkstaah]

For fuelling the Haltechs have O2WB fuel controllers. Very useful for helping tuning VE and correcting for *small* mistakes.

Of course if your injector/cam/trigger/sensor data is just wrong (or for a GTT which is not a GT) then you will get impossible reactions to things.

I am sure you know this already but the reason people don't typically put haltechs (or any Aftermarket ECU) on GT's is because there's practically no real gains to be had - So this knowledge won't be commonplace.

[Haggerty]

As far as I can tell I have everything properly set in the Haltech software for engine size, injector data, all sensors seem to be reporting proper numbers.  If I change any injector details it doesnt run right.   

Changing the base map is having the biggest change in response, im not sure how people are saying it doesnt really matter.  I'm guessing under normal conditions the ECU is able to self adjust and keep everything smooth.  

Right now my best performance is happening by lowering the base map just enough to where the ECU us doing short term cut of about 45% to reach the target Lambda of 14.7.  That way when I start putting load on it still has high enough fuel map to not be so lean.  After 2500 rpm I raised the base map to what would be really rich at no load, but still helps with the lean spots on load.  I figure I don't have much reason to be above 2500rpm with no load.  When watching other videos it seems their target is reached much faster than mine.  Mine takes forever to adjust and reach the target.

My next few days will be spent making sure timing is good, it was running fine before doing the ECU and DBW swap, but want to verify.  I'll also probably swap in the new injectors I bought as well as a walbro 255 pump.

 

[Haggerty]

I guess one thing that might be wrong is the manifold pressure.  It is a constant -5.9 and never moves even under 100% throttle and load.  I would expect it to atleast go to 0 correct?  It's doing this with the OEM MAP as well as the ECU vacuum sensor.

When trying to tune the base map under load the crosshairs only climb vertically with RPM, but always in the -5.9 column.

[Murray_Calavera]

@Haggerty you still haven't answered my question. 

Many things you are saying do not make sense for someone who can tune, yet I would not expect someone who cannot tune to be playing with the things in the ECU that you are. 

This process would be a lot quicker to figure out if we can remove user error from the equation. 

[GTSBoy]

4 hours ago, Haggerty said:

It is a constant -5.9 and never moves even under 100% throttle and load.  I would expect it to atleast go to 0 correct?  It's doing this with the OEM MAP as well as the ECU vacuum sensor.

I saw you mention this earlier and it raised a red flag, but I couldn't believe it was real.

Yes, the vacuum signal should vary. It is the one and only load signal from the engine to the ECU, and it MUST vary. It is either not connected or is badly f**ked up in some way.

[Kinkstaah]

28 minutes ago, GTSBoy said:

I saw you mention this earlier and it raised a red flag, but I couldn't believe it was real.

Yes, the vacuum signal should vary. It is the one and only load signal from the engine to the ECU, and it MUST vary. It is either not connected or is badly f**ked up in some way.

@Haggerty this is your red flag. In MAP based ECU's the Manifold pressure X RPM calculation is how the engine knows it is actually...running/going through ANY load.

You are confusing the term 'base map' with your base VE/Fuel table. When most people say 'base map' they mean the stock entire tune shipped with the ECU, hopefully aimed at a specific car/setup to use as a base for beginning to tune your specific car.

Haltech has a lot of documentation (or at least they used to, I expect it to be better now). Read it voraciously.

[feartherb26]

I have an elite 2500 running an adapter harness on an rb25de neo r34. I took the butterfly out and removed all that junk. But I also went Plus+t at the same time. The butterfly thing works in reverse to the boost solenoid on the Gtt if that makes sense

[Dose Pipe Sutututu]

On 24/08/2025 at 2:11 PM, Haggerty said:

I seem to the be only person that is using a Haltech 2500 on an NA motor, I've installed a Bosch DBW throttle body to the OEM intake manifold and am having problems maintaining AFR even with the wideband o2.  It will run extremely rich at idle and up to redline, but under load it will go extremely lean in the 20s and i'm essentially having to rev it over 4k and feather the clutch to get it up to speed.  I've read a few other threads of about the butterfly, it seems removing the vacuum to it is supposed to have it remain open, i've noticed no difference under 4k with the vacuum line to it plugged. 

I'm hoping someone here has had luck using the NA manifold with Haltech, and if they happen to have a tune for it.  

post up screen shots of your injector tables

[Haggerty]

@Murray_Calavera  If I were an expert I wouldn't be in here looking for assistance.  I am extremely computer literate, have above average understanding on how things should be working and how they should tie together.  If I need to go to a professional tuner so be it, but I'd much rather learn and do things myself even if it means looking for some guidance along the way and blowing up a few engines.

@GTSBoy  I was hoping it would be as simple as a large vacuum leak somewhere but I'm unable to find anything, all lines seem to be well capped or going where they need to be, and when removed there is vacuum felt on the tube.  It would be odd for the Haltech built in MAP to be faulty, the GTT tune I imported had it enabled from the start, I incorrectly assumed it was reading a signal from the stock MAP, but that doesn't exist.  After running a vacuum hose to the ECU the signal doesn't change more than 0.2 in either direction.   I'll probably upload a video of my settings tomorrow, as it stands I'm able to daily drive, but getting stuttering when giving it gas from idle, so pulling away from lights is a slow process of revving it up and feathering the clutch until its moving, then it will accelerate fine.  It sounds like I need to get to the bottom of the manifold pressure issue, but the ignition timing section is most intimidating to me and will probably let a pro do that part.  Tomorrow I'll try a different vacuum line to T off of, with any luck I selected one that was already bypassed during the DBW swap.  (edit: I went out and did it right now, the line I had chosen did appear to have no vacuum on it, it used to go to the front of the intake, I've now completely blocked that one off at the bracket that holds several vacuum lines by the firewall.  I T'd into the vacuum line that goes from that bracket to the vacuum pump at the front of the car, but no change in the MAP readings).  Using the new vacuum line that has obvious vacuum on the hose, im still only getting readings between -6.0 and -5.2.  I'm wondering why the ECU was detecting -5.3 when nothing was connected to the MAP nipple and ECU MAP selected as the source.

@feartherb26  I do have +T in the works but wanted to wait until Spring to start with that swap since this is my good winter AWD vehicle.  When removing the butterfly, did it leave a bunch of holes in the manifold that you needed to plug?  I thought about removing it but assumed it would be a mess.   I notice no difference when capping the vacuum line to it or letting it do its thing.  This whole thing has convinced me to just get a forward facing manifold when the time comes though.

Edited 9 hours ago by Haggerty

[GTSBoy]

Put the ECU's MAP line in your mouth. Blow as hard as you can. You should be able to see about 10 kPa, maybe 15 kPa positive pressure. Suck on it. You should be able to generate a decent vacuum to about the same level also. Note that this is only ~2 psi either way.

If the MAP is reading -5 psi all the time, ignition on, engine running or not, driving around or not, then it is severely f**ked.

Also, you SHOULD NOT BE DRIVING IT WITHOUT A LOAD REFERENCE. You will break the engine. Badly.

[Murray_Calavera]

35 minutes ago, Haggerty said:

If I need to go to a professional tuner so be it

You won't need to do that if your happy to learn to tune it yourself.

36 minutes ago, Haggerty said:

and blowing up a few engines

You 100% do not need to do that. It is not part of the learning process. It's not like driving on track and 'finding the limit by stepping over the limit'. You should not ever accidently blow up an engine and you should have setup the ECU's engine protection to save you from yourself while you are learning anyway.

37 minutes ago, Haggerty said:

If I were an expert I wouldn't be in here looking for assistance

Plenty of us have tuned their own cars, myself included. We still come here for advice/guidance/new ideas etc. 

What have you been doing so far to learn how to tune?

[Murray_Calavera]

17 minutes ago, GTSBoy said:

then it is severely f**ked

I'm hoping it's something as simple as the ECU is looking for an external MAP sensor, but he is trying to use the onboard MAP sensor.

[Kinkstaah]

3 minutes ago, Murray_Calavera said:

I'm hoping it's something as simple as the ECU is looking for an external MAP sensor, but he is trying to use the onboard MAP sensor.

This IS something you also have to configure in Haltech (or at least I did in the past when going from onboard-to-ECU map sensor and an external MAP sensor in haltech land).

[feartherb26]

1 hour ago, Haggerty said:

@feartherb26  I do have +T in the works but wanted to wait until Spring to start with that swap since this is my good winter AWD vehicle.  When removing the butterfly, did it leave a bunch of holes in the manifold that you needed to plug?  I thought about removing it but assumed it would be a mess.   I notice no difference when capping the vacuum line to it or letting it do its thing.  This whole thing has convinced me to just get a forward facing manifold when the time comes though.

If you take the top half of the intake off you can unbolt the flap off the shaft and leave the shaft in there blocking the hole. Then you can remove the little vacuum canister off from under the manifold and get a spare vacuum line to run to the ECU.
I can take some photos of it later. Probably best to get the vacuum source to the ECU sorted first though.

Mine all worked mint with the base map from the GTT an I've pretty much let the closed loop sort the fueling and took 1 degree out of the whole timing map.

Edited 8 hours ago by feartherb26