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RB26 Custom spec - Haltech Elite 2500 - Funny VE Number, knock sensor, etc.

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Hi guys,

I have a RB26 newly built, on a 1995 R33 GT-R. I have been making adjustment myself and the car runs kind of okay on medium boost (10~15 psi) but it's not consistent.

Important spec:

OEM Crank, 86.5mm piston

Compression ratio 8.615:1

Factory intake, 6-throttle

Camshaft 260" 10.80mm lift

91 octane

ID1000, 276L/hr fuel pump, 3BAR fuel pressure MAP referenced

EFR8374 1.05, 6boost twin 38mm Tial wastegate

Obviously I use TPS + MAP tuning. It idles beautifully with close loop enabled. At idle with a hot engine, the VE number is about 66 (The cell at and around 0% throttle and 1000rpm), and my tuner thinks it is very abnormal. He explains a bigger, fatter camshaft usually results in lower VE in low RPM and higher VE in high RPM, which I totally agree. He suspects I may have an air leak between the throttle and the engine. The engine is blueprinted by machinist but I install the rest of the "stuff" myself. I use new MLS intake and exhaust gasket, and all vacuum hoses are new straight from Nissan, and I did not modify any idle mechanisms.

So my list of questions here:

1. Will an air leak after the throttle plate (possible the throttle shaft) result in higher VE number in low RPM / idle?

2. My knock 1 sensor picking up almost no noise but my knock 2 sensor picking up quite a bit of noise when I accelerate. Why would that be? I removed the paint on the block and used sand paper to clean the knock sensors and torqued it to spec.

3. What should the air temp correction setting be? If I use Auto V.E. air temp compensation, do I eliminate the Air Temp correction table entirely?

4. Is it possible my charcoal canister causes vacuum leak? I routed it like factory, but when I open a gas tank I can feel air rushed in and when I fill up at gas station sometimes the fuel filler automatically stops, sensing the fuel is full, when it's not.

Thanks for everyone's input! My first post!


I have a similar engine and my idle area Ve numbers are in the low 50s. you could have a vacuum leak or low fuel pressure. an easy test for vacuum leaks is a can of flammable brake cleaner. just carefully spray around areas of concern like the throttle shafts and see if the engine rpm is affected. also check if the base fuel pressure matches the setting in the ecu.

Hi Joey, I'll answer your specific questions below but first it's important to understand that the Haltech (as well as every other standalone) VE model is not necessary as precise as you might think. The final VE numbers are a function of all the other inputs and it's very easy to bake in errors that will influence the VE numbers needed to get your target AFR. All it would take is the injector flow not perfectly matching what the Haltech expects and you've got an error. The Haltech also doesn't include an overly complex or advanced injector model (nothing specifically wrong with that but it affects the VE numbers).

66% VE is probably a touch high at idle, however if you're at a sensible idle target (800-1000) then any vacuum leak is likely to be so small as to be insignificant. A quick test is to spray a product like Brakeclean (just make sure it's not a flammable version) along the interface between the head and inlet manifold/throttle bodies with the engine idling. If there is a vacuum leak the idle speed will drop. With that out of the way, onto the specific questions:

1. This part gets a touch tricky with MAP x TPS depending how the idle is controlled. If you were using dbw then the airflow is always a direct relation to throttle opening which is really what you need for this style of tuning strategy. On the other hand if you're using a stepper or ISC solenoid for air bypass then this creates issues as the idle airflow isn't related to throttle position and hence this can result in some required weirdness with the VE numbers. The reality is that most of this issue tends to be tuned around with the cold start enrichment tables since the ISC duty is going to remain relatively fixed at normal operating temp.

2. I'd be suspicious of wiring or the knock sensor. You should be seeing relatively similar signal levels from both. I haven't had any experience with the Haltech with dual knock sensors but seem to recall a similar complaint from a member a few months back.

3. It's up to the individual. If you choose Auto air temp correction then the IAT is accounted for in the main fuel equation and you should set the IAT correction table to 0. Alternatively many people (myself included) tend to find that auto correction can be overly dramatic, particularly after a hot restart. I choose to disable the auto correction and use the conventional IAT correction table. Try both and see which you get more stable results from. As a third option you can use auto correction with the comp table zeroed and then manipulate the correction table in the places you find the automatic compensation is too dramatic.

4. Anything is possible - The charcoal canister works in conjunction with a purge valve which would need to also be installed and operating correctly to preserve stock functionality here.

Thank you for the in-depth explanation!

Just want to share a little bit of what I have found......Although my car does idle beautifully, upon checking the idle control long term trim table, at 80'C Haltech almost trim off all duty cycle! After disabling charcoal canister, the duty cycle is back to normal range of base map (within 2%). Checking the idle control table may give you instant hint! I also think using propane/brake cleaner at throttle is an excellent idea. I haven't got around doing it yet.

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