lexus afm 550cc. Really bad idle and erratic fuel cut

Z06gette

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#1
I have an 88' 7mgte running 10psi with a manual controller. Boost gauge and UEGO wideband with HKS Super-AFR. I was running stock injectors and afm had zero issues with drivability. My idle was ALWAYS a perfect 14.7 and would gradually go richer under WOT down to about a 10.0-9.8 RICH.. I did the S-AFR first adjusted trims got WOT DOWN TO A 10.8. I Figured everything was perfect right where it should be so now would be the time to do the lexus mod with 550's. I have the Driftmotion Bosch low impedance 550cc injectors wired in with the ev1 plugs.
Immediately after doing the afm and injectors idle was complete trash 17.8-Off the chart.. checked all my vacuum lines with brake clean endless times and had zero boost leaks before and didn't touch the intake piping aside from 3000 pipe. Cruising at part throttle everything is fine afr's are 15-16 but get into boost and it goes 13,12,11.8 fuel cut... from 0-5ish psi... I work at a shop and my boss is a 40year master tech with a fox body in the 700HP range. So he helped me do my tps and calibration, checking resistance we are all good there. ITs my understanding that the afm cant really be "tested" as the TSRM test only tests the IAT.
Ive got new Toyota fuel injector insulators for the head that I am going to put in with vasoline and a new ISC valve gasket. Im really scratching my head otherwise...
I could use some direction Ive got the aeromotive afpr in bound but that would explain a slightly lean idle but doesn't make sense about the fuel cut, ignition cut out.

OTher notes- I have not messed with the screw on the afm housing, the cap is still on. I found exposed wires on the cps a couple of months back and repaired the harness
 

Z06gette

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#2
I’ll add I’ve read about every thread with people with issues after the Lexus mod and still got to where I’m at. It’s sad almost all the threads don’t have a follow up with a solution
 

Zazzn

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#3
Hello,

If you are seeing FCO at 5 PSI you definitely have a leak somewhere in the intercooler system. the turbo has to be pushing ALOT of air through the AFM to show 1500HZ -1700HZ of which will cause FCO. If your idle is garbage on the new injectors it could be the stock ECU on these injectors is not that good but I can't imagine that they are that bad. Maybe some of the injectors are clogged by dirt during install or something to that effect. But without a doubt, there is more than one issue going on here. If you put your stock AFM back in you should see FCO at like 3 PSI
 

3p141592654

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#4
The original 550/Lex mod required a custom "air screw" that replaced the screw in the original AFM housing. This was used to tune the idle. However, that is not a good solution. That screw adjusts some fundamental things about the way the KV sensor works. Someone on this site knows alot about this and hopefully one day will post that info.

The modern recommendation is to use an AFPR and adjust fuel pressure to get a good idle. I would suggest you go that route.

When I finally get my act together there will be a 3rd solution that gives factory drivability with this mod and stock pressures.
 
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Z06gette

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#5
ok, see across my research I came up with very mixed results on the adjuster screw. I saw that Supra SOnic club with the custom screw and then others saying it was a complete and total waste of time.

Now my IAC valve does the three clicks right after shutting off, but im wondering if that check valve is bad creating a giant leak under boost. Is there a way to check that beyond visual inspection? I did notice the BOV sounded more like a whispy airy noise versus the typical crisp sound even at similar boost levels.

So any more info on the screw would be awesome! Thanks guys for the response
 

Z06gette

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#6
Im waiting for the AFPR to get here install that and do RTV and paper gasket for the IAC and see what happens. Maybe I should head out the hardware store and find a longer screw for the afm adjuster?
 

Z06gette

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#7
Ok so i got the Lexus AFM screw turned all the way in today idle is still a little leaner than I would like 16-17 but does it ever pull. Still had it at 11psi today and at wot had an afr of 9.8.
Still waiting for the AFPR, but that was not the issue. I think my iac valve was leaking.. I took it off again and cleaned the surfaces and put some rtv on the paper gasket, wah-la.

Also in reference to the sudden “airy blow off valve” coincidentally on my last test run my intercooler coupler on the throttle body slipped partially off.
I removed it the other night when I was checking plug gaps and replacing wires.
 

Zazzn

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#8
BOV will make more flutter noises as you raise boost as naturally there is more air and it's stock it's not exactly the largest BOV for moving air.

Even with the Lex AFM screw completely out I didn't have lean issues at idle because the stock computer can adjust up to 30% fuel trims if the stock O2 sensor is there. This was with 550's which were Densos out of an RX7. It could be that the dead times on your injectors is simply nowhere near the same dead times as the stock Denso's which explains the lean idle.
 

Z06gette

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#9
Yeah I’m familiar with the blow off this was definitely a boost leak. But yeah idle is still 17’s but cruising it’s good and WOT I’ve got it pegged at 10.6 with my hks super afc
 

Z06gette

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#11
theyre the driftmotion 550cc bosch low impedance. THese seemed to be a good option based on the research I did. has anyone seem any issues with these injectors?
 

bountykilla0118

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#12
Driftmotions does a good job with getting the right parts for the 7m.

From what I understand you are using the stock fuel pressure regulator with 550's and you are pulling fuel with an SAFC...... it's going to be very hard to tune if that's the case. Even more so if you are using the stock fuel pump and regulator. The stock pump does not flow the same amount of fuel all the time.... its has a voltage switch meaning at idle the voltage is different than when it's under load, as the voltage goes up so does the fuel supply. It is hard to tune 7m with that setup. That's why we ditch the stock fuel pump once we start modding. I will share with you the notes I have on the Lex AFM/550 setup.

I assume you are using a wideband o2 if not ..... GET ONE.
https://www.jegs.com/i/AEM/017/30-4...Q2FxxGeMHq75ml3vkE06h-lPRPYzsNCBoC2fsQAvD_BwE

My suggestion:
SAFC average = -15% fuel corrections
base fuel pressure = 23psi
timing = 12
Your base settings are close to neutral, with a bit more timing. The advanced timing gives more power and helps the turbo spool. Having a higher advanced base timing = more power across the whole RPM range. Keep a close eye on A/F ratio during WOT keep it below 11-12 on pump gas.... 12.5 is pushing it on pump gas.

On the SAFC set the Low Throttle point to 69%, and the High Throttle at 70%.

Zero out everything on the Low throttle map.

I recommend getting a few things so you can tune before you pull fuel with the SAFC. You want to tune the fuel pressure first and pull fuel with SAFC second. Check for vac leaks and get your idle close to 14.7 (I saw 15 a lot) tune only your WOT setting to 11.5.
1. Walbro 255 fuel pump
2. Adjustable fuel pressure regulator with a gauge (Aeromotive is my company of choice)
https://www.summitracing.com/parts/...jyJkOuviuzPnphrGdeIlqfkdYWlsMIkhoCR7AQAvD_BwE
3. Back the screw on the Lex AFM all the back

With that setup the car should run pretty good.... each car is different, but this should give you a decent starting point.

Very quick run down:

At WOT, I would say generally 10.5 is where the stock ECU likes to be. 11.5 is a safe tune. 12.0 is a good performance tune. 12.5 is where things getting quite risky. 13.0 isn’t good. At WOT, the ECU ignores sensor inputs (open loop), so it isn't compensating. That's why you can tune with the S-AFC. At idle you should see ~14.7, cruising will vary across the board because of ECU control, throttle position and other variables. The stock ECU retards timing sharply at ~5,600RPM so SAFC tuning anything above 5,600RPM is relatively pointless.

SAFC advances timing as it pulls fuel due to the nature of dinking with the AFM frequency to trick the ECU into thinking that it's flowing less air, so it puts in less fuel, and puts in more timing advance. Basic SAFC 101. This is a good thing, and a bad thing. More timing + less fuel = more power BUT too much timing and not enough fuel are very bad. You probably have no way of knowing what your timing is once you're running, so set your base timing at 8-10 (for safety) and try not to advance the S-AFC farther than -20%. What you are doing is adjusting fuel while reducing the risk of over advancing timing (which can cause detonation). If you must go farther than -20%, then set all back to 0% and reduce fuel pressure to lean your motor.

You can go lower than -20%, but *I* prefer to try to keep the S-AFC as close to 0% as possible while maintaining proper AFR. You can always add timing later by increasing your base timing. While good in principle, I usually end up in the -18% range at the upper RPM.


The S-AFC is a TRIMMING TOOL, intended to FINE TUNE the fuel curve. It's not intended to be tweaked out -40%... Once you get your fuel dialed in, you can advance your timing a bit. Detonation is not your friend.

Disclaimer - All this assumes reasonable engine condition - boost levels - fuel and supporting mods... It's best to do this on a dyno, and with a professional overseeing your work. If you blow up your engine after reading this, it still 100% your fault.
 

Z06gette

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#13
thanks for the response good info there! Part of the confusing part too is everyone seems to use the saf-c ive got the hks version so the throttle response is set on a dial 0-100% where as the safc has the low and high setting and you set the throttle position.

Well at any rate ive got my afpr and a genuine walbro 255, just need time to get them in. I didn't want change too many things at wonce
 

Zazzn

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#14
I had a HKS S_AFR as well back in the day, but I don't remember the interface well enough to tell you how to tune.

I want to clear up a few things here.

The WHOLE point of a Lexus AFM and 550's is because the Lexus AFM allows 30% more air without being metered. To make up that fuel you add 550's. If you are really rich, it's because that's the factory tune. You effectively create the same situation is you remove 30% acorss the S-AFR everywhere and add 550's.

There the gain on the S-AFR is the amount of AFM signal you are adding, once you hit the limit you will hit fuel cut.

Anyways, regardless, I still stand by my original assessment, if you are hitting FCO at 8-9 PSI you have a boost leak.
 

Z06gette

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#15
Yeah no more fuel cut I’m set at 12psi no issues now, so thank you. I’ll update with some more info soon