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LH2.4 3" 012 AMM rich spike on tip-out

T

turbochimp

Member
Joined
Nov 2, 2011
Installed the following on my 1990 740 B230FT LH 2.4:
15g (from 13c)
012 AMM pre turbo - replaced stock air box with cone filter
48lb high Z injectors @ <3 bar (e85) - bypassed resistor pack

Now I get a rich spike when I let off throttle. AFRs read between <11-12 for a period of around 3 or more seconds. This does not only happen off boost - it will happen if I let off from ~0psi. Idle, cruise, accel and WOT all work great - just the prolonged rich spike when I let off.

I initially thought this was due to the stock cbv leaking. I have replaced the cbv with the forge piston style cbv and pressure checked the entire system - no leaks.

Any ideas? Halp!
 
Hi

This has to do with the chip programming.
Since the LH has no direct input from the TPS other than the idle switch the reaction to changes in airflow has to come from the AMM.
No matter how quick you shut the throttle the air will still have some momentum and continue rushing past the AMM, the when it hits the closed throttle plate it will bounce backwards to a degree and this air will also be metered.
I would suggest you transplant the accel and decel settings from a bin that uses the 012 AMM
like the 950 bin to make it as good as possible.

YS
Jaybee
 
Aren't the injectors way too small for 3" amm AND E85, especially if your fuel pressure is LESS than 3 bar.

2.5" AMM 337cc@3bar injectors
3" AMM 470cc@3bar injectors
3" AMM and E85 630cc@3bar injectors
Injector size +/- 15% (estimated lh2.4 correction ability)
 
OP is this when you lift completely off the throttle, like throttle plate closed and the only airflow is from the idle control valve, if so check your TPS like I said.
 
I did inspect the physical wiring on the TPS and didn't see anything amiss - didnt get around to checking electrical function yet. Based on AFRs at cruise the TPS does seem to be functioning correctly.

The behavior seems consistent with Jaybeeze's explanation - if I tap the throttle immediately after let-off it will return to normal quicker.

Unfortunately, programming LH is beyond me. I am running Mike's chips - is this something he may have a solution for? The only other thing I can think to do would be to maybe adjust the throttle plate to be a bit more open at idle - would this make sense?

mark: these injectors are more than adequate for the 3" AMM. You seem confused (or maybe its me).
 
337cc@3bar x 1,3 x 1,42 = 620cc@3bar (30% bigger AMM, E85 needs 42% bigger injectors).
Lower limit is 587cc@3bar injector (55lb@3bar)
Upper limit is 700cc@3bar injector (65lb@3bar), 337*1,3*1,6 = 700cc

But maybe i misread and you have 48lb@2.5bar injector, which equals 55lb@3bar.
In that case they should work allright.
 
If he uses chips with integrated o12maf map your formula is wrong ;) but 440 would be nice then.. Anyway.. 630 are needed if you do some tuning..
 
BTW.. i talked back with my ECU buddy..

I have this Problem too.. sounds absolutely logical to me having the wrong deccel and accel maps, cause we started with a 937 bin..

But has anyone tried fiddling with the IAC? Cause mine definately starts controlling the idle too late.. motor dies or almost dies falling back in idle from high rpms.. (everything above 2500) It falls back to 700rpm before the management does something.. where a normal B230FT controls at 1200-1300...
 
I'm telling you your TPS switch is not telling LH that the throttle plate is closed, I had this problem, making the TPS work properly is what fixed it. Car would run fine but when I lifted my foot and the throttle plate closed I would get these rich AFR's 10-12 nstead of the blinking 20 that that I get now.
 
Guys, you really need to use the 012 translation map programmed to make it run correctly.
Tip-in maps comes later. If you just put 012 AMM in stock bin made for 016 you can't expect it
to work properly, even if you "match" it with bigger injectors.
 
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