Hi

I'm trying to diagnose a blip in power that I'm getting with the NOS setup I have (Mods, please don't merge this with the Project Fast & Furious threads as this is a specific question)



At about 3400 revs, you see the dip in power.

I've been watching my MAP sensor readings using my scangauge and when I floor it without NOS, the MAP reading shows 14.4 (What the units are I don't know)

When I floor it using NOS, the MAP value goes to 14.9 and stays there until well into VTEC (7500rpm to 8000rpm or so) and then comes back down to 14.4

Could this be the reason it's doing this?



The lower line on the AFR being when I'm using NOS.

I know it's not the IAT sensor as I have moved that to behind the NOS jet and am still getting the same result.

Any ideas?

Thanks

Gary

 

A Map sensor is used to measure load and thus looked up the ECU map to dictate the amount of fuel and ignition timing to run in a typically 16x16 table based on load x revs.

I find those units strange its either PSI or KPA, but atmospheric is 14.7 so NA cars run about 0psi at full throttle, from tuning NA cars you get get upto 0.1/0.2 psi so its likely 14.9 is actually equal to ~ 0.1 psi.

Your AFR starts off at roughly 13.7 (tad lean but pretty good) pre 3400 rpm then nose dives at around 3600 to 10 AFR - far to rich even for a NOS setup.

For me at the end of the day your getting/need some form of ECU tuning, a VAFC2 might help correct this somewhat(get it into the 11's AFR) on the cheap problem is when you lean it out it add's timing - not really ideal for NOS. VAFC2's work well when leaning out which you need to do. Though just check for detonation. Your running stock map but references values which is doesnt quite expect nor deals with correctly because it doesn't have the scope too.

At the lower revs ranges the car isn't exactly pokey and is still running on the first cam with fuelling and timing to suit that range.

Its working so far (not yeilding its best power) because you are running incredibly rich AFR and the stock ECU has conservative timing.

Have you logged the IAT readings?

 

The IAT port is currently blanked off and the IAT sensor loose in the engine bay. I did that after the dyno run to see if it made any difference as the spraying of NOS was dropping the IAT by up to 25 degrees and I didn't know if that was causing the problem.

Moving it doesn't seem to have made any difference so I'll pop it back in place.

The NoS/fuel ratio through the current jetting is 1:2 nos to fuel. I may get hold of an AFR sensor and gauge and try playing with the jetting for now. The jets are only a fiver each so only a tenner to try a couple to see the effect.

I'm reluctant to get an ECU as the point of the kit was something to play with that could be lifted onto another car if need be and as the AFR sensor and gauge is only about a ton, I don't mind spending that to get accurate readings that I can keep an eye on.

Thanks for the reply. Very helpful.

 

The IAT sensor is used like PID, and is referenced in tables like compensation tables (thus add/minus timing etc to given maps) having it reading false reading could give erroneous readings/results and ill effects again depends what its reading etc.

I'd be worried about bore wash with an AFR of 10 that is incredibly rich.

I'm going to be brutally honest and don't take offence but it seems like a bit of hack riding on the edge, if you value the car/engine i would at least get a VAFC2 (last resort) or a GEMU if you want to better the situation without spending a shit load - at least then you have finer control, can yield more power and most importantly run the car safer, you could alter the jets too as you say but your results will come down and you'll still have the situation above albeit slightly better.

 

Thanks for the advice. I'll start hunting out a GEMU then I think.

Cheers.