Lexus/550 Wideband questions

[Compton74]

I know this topic has been extremely beat to death, but after constant searching and reading information I feel the question I have has not been covered. 91 GTE, Lexus/550, aeromotive fuel pressure regulator with j tube block off, mk4 fuel pump, 57 trim, full 3 inch exhaust with BIC DDP, cat less. After reading a mass amount of threads about the lex mod, I know a wideband is needed to make sure things are up to par. I ended up buying a innovate mtxl and installed it yesterday. Car runs well according to the wideband at full throttle at 14lbs it's running anywhere from 10.5 to 11 which is not totally rich, but rich nontheless. During cruising it reads anywhere from 14.7 to 15, which is acceptable, correct me if I'm wrong. But at idle it's running around 20, which doesn't bug me a lean idle isn't a horrible thing, but my idle is pretty jumpy and bad at times. Now my question is, is the only way to adjust my afrs is with a piggyback such as the safc/neo, or is their a way I can use the fuel pressure to make things a bit clearer. I will do whatever is necessary to make my car run correctly just wanted to know if I needed to spend the money, and maybe the reason why my idle is lean and crappy. Fuel pressure is at around 38 with vac off, as the CEL will come on for a lean condition if any lower then that, and if I raise it the CEL comes on for rich. Any help would be greatly appreciated.

 

[shipkiller]

11 to 11.5 is the acceptable range for WOT under boost

 

[Dan_Gyoba]

Sounds like your base fuel pressure is low, what does the gauge for your FPR read at idle with vacuum disconnected? Cruising throttle, the ECU will compensate via the O2 sensor to get you close to the 14.7 mark, and WOT is pretty much always going to be richer than that.

The other possibility is that you've got an unmetered vacuum leak at idle.

 

[Compton74]

Base fp with vac off at idle is 41

 

[Dan_Gyoba]

FP sounds good (That's where mine is set, too) so a vacuum leak then? I'd guess between the AFM and the ISC valve, since it seems to only affect idle AFR and not idle RPM.

 

[Compton74]

Not sure I'll check it out, thanks for the info I'll report back

 

[Compton74]

Sorry it took so long to report back, realised i didnt come back and im trying hard to not take peoples time and info for granted. So went through the whole car vacuum wise, found a number of small problems and fixed accordingly. Also installed the silicone accordion hose with nice big clamps to route out a leak in the stocker, and replaced the throttle body hose with a nice new thick silicone one. Afrs are still pegged at idle, but I see a little scarring on a rubber cap I used to cap the stock bov, so I have to run out get new caps and put them on. Thing is my boost gauge reads in the -10-11 range at idle. As far as I'm concerned, that still means I have a vac leak. So I think I'm going to go through it all again and check. But correct me if I'm wrong but afrs at idle at least, can be affected by a vacuum source that is not being read through the boost gauge or basically from afm to turbo?

 

[Dan_Gyoba]

Idle manifold pressure will be directly linked to idle RPM. Higher pressure will make for higher RPM.

A leak in the intake between the turbo and throttle body will leak boost, but isn't really in the equation when the throttle body is closed. Anything here large enough to cause idle AFRs to be really off would be a HUGE boost leak when the turbo is working and cause even bigger issues then.

Your boost gauge has zilch to do with AFRs. It's the AFM that tells the ECU how much air, therefore how much fuel to add. What throws it off is if air is coming in or escaping between it and the intake valves.

To have very high AFRs, this means more air than the ECU has been told about, or less fuel than the ECU thinks it's delivering.

Injectors being a trifle slow might do something like this, if they take a couple ms longer to open than the ECU thinks, this might be significant at the low duty cycle of idle, but less so at the high duty cycle of even normal closed-loop operation.

An intake leak in the piping to the ISC might do this by introducing too much air.

Some weird flow through your AFM might under report air, if the air is somehow not flowing as much near the KV sensor at low speeds. If you have the honeycomb grille at the front of your AFM, this shouldn't be the problem, but if you're removed it, then you can get some very strange effects in the AFM.

What I'd check, in order:

Look at front of AFM for damage to honeycomb grille. If damaged (or missing) repair.

Check tube from accordian hose replacement to ISC. Ensure leak-free and good condition. (I'd be surprised if this is it by now, but I'd check anyway.)

Try rotating the AFM to different orientations and observe. (If the air isn't coming in near the top, it's coming in SOMEWHERE.)

Monitor injector duty cycle, (And AFM output) and look for correlation.

Are these high impedance (IE: RX7) injectors? Maybe have them cleaned and flowtested?

 

[Compton74]

Alright i will go down that list and report back. All the information for testing injector duty cycle and AFM output are in the tsrm correct?
The injectors are from the RX7, and when i put them on around 3000 miles ago i hand delivered them to RC and had them cleaned and flowtested and all the numbers came out perfect. I trust their work at RC but for some reason at the back of my head im thinking it has something to do with the injectors, maybe a bad O-Ring somewhere.

Interesting you bring up the issues with the honeycomb grille, i remember it having a decent dent in it when i originally installed it. Figured trying to picking it out would have made things worse so i left it. Never knew that it could cause something like this. Can i just get a replacement honeycomb or do i have to get a whole new AFM?

 

[JSeaman]

A jumpy idle is quite normal if the ECU is using the stock narrowband output it can often bounce between (slightly) rich and lean

 

[Compton74]

well, i know it wouldnt be a concern in normal situations but my afrs at idle are so so high! Most people wouldn't be questioning but i just want to know why. Thanks for all the input thus far

 

[Turbo Habanero]

My car does similar things that i hav not found a fix for.

I figured it was a vac leak but can't seem to find the leak.

Boost gauge reads -14vac at idle
Afr's read 16.3-18 at idle.

 

[Sik89supra]

maybe leaking BOV, weak spring could be allowing the bov to open at idle vac when the vaccum is the highest, and while driving or under boost it would close because vac is low or boost is pushing it closed.