tuning help, rich idle, stumble, rich decel.

[Facime]

Ive been trying to iron out a few wrinkles in the tuning of my 7M. If you dont already know Im working with a Lex AFM, 550cc injectors, AFPR, T-58 turbo, AEM wideband, and otherwise stock sensors. My only means of tuning is the AFPR and the SAFCII. My fuel pressure is at 38lbs with boost reference, and to be honest I forget the non-referenced pressure. (I will record that tomorrow).

Anyway, my problem is basically that I cant seem to find a happy medium. At idle its pig rich, but has a nasty off idle stumble. Also I go pig rich under deceleration (both boosted and not) and lean spike whenever I raise the throttle input. This is all under the SAFC's low throttle map which Im using 30% as the break point.

For the rich idle I can dial out fuel to reach a reasonable ratio, but I have to take out 25-30%. Whenever I do that the off idle stumble is worse. Currently I set the 1000rpm point to -25% and the 1600 to +5% and then take fuel back out to -20% for the rest of the map. When I do that I minimize the off idle stumble and its really pretty much drivable.

For the "High" map I am taking out roughly 35% of the fuel load with the SAFC under WOT and she pulls real hard and A/F ratios are stoich and stable under 12-15 lbs of boost. At least until I get out of the throttle and then I lean spike but then immediately settle back into pig a rich condition that nearly stalls the motor.

Am I just going to have to bite the bullet and go standalone or at least a more sophisticated piggyback, or is there something I can do differently that could help balance the issues and give me better drivability?

Lastly, yes I already know about the issues associated with putting a piggyback in the air/fuel system that cause more delay. Yes I probably should already be using a standalone but I really dont have the money for one right now, so Im hoping to just find a happy medium. More fuel pressure? Less pressure? ditch the SAFC altogether and let the stock ECU handle the fuel maps? switch the SAFC for something else?

OH tuning gurus! Give me some ideas here! Thanks

 

[bwest]

Are you logging vf? By tuning under WOT (or low maps on the safc), the safc is fighting the tccs. I would set the low maps back to 0, check VF, but my guess is you fp is too high hence the richness.

In the FAQ section there is a post on how to tune for VF with the lex/550 combo.

 

[Facime]

I dont have any way to datalog. I figured at around 38 lbs I was close to stock but also have enough extra fuel to stay out of fuel cut at 15lbs.

Also one other point I want to make here is I do in fact intend to have the car professionally tuned on a dyno. Im just looking for some basic help to make it drivable until I reach 1000 miles or so.

 

[935motorsports]

key questions as well:

- do you have a walbro?
- is your j tube (the metal fuel drain connection) drilled out or bypassed?


One thing that concerns me is that you say your AF is stoich under WOT? You should not be at 14.7 (stoich) under WOT. Perhaps you can elaborate on that first, before anything gets broken.

The lexus and 550s is supposed to cancel each other out, roughly. So if you are taking out 35%, you are about 55-60% less then stock. That seems like alot and might explain the "stoich" under WOT

Let's be safe and shoot for something under 12:1 for WOT, 11.5-11.8.

What you REALLY need is some data logging if you don't have it. Trying to watch the AEM under WOT can be really difficult. A computer log will let you look at things on the computer safely in your home and you can easily see where the rich spots are.

For reference, my 7M to4e setup had lexus / 550s, walbro, j tube drilled out, -15% (pre-boost) on SAFC and ran great. No stumble issue. So I think the stumble might be related to some other hardware issue like TPS or something not related to fuel.

 

[bwest]

from the way it sounds you have more than enough fuel on top. fp is not going to impact fuel cut unless taken to an extreme low, where you have to add fuel - but by that time it will run so poorly (if at all) at idle that I wouldn't worry about that issue at all.

Hook up a MM to the diag block, start the car and watch vf. hell, make fp adjustments right there and look for changes in vf... Without watching vf, its hard to know what the tccs is doing.

 

[Facime]

Ok, first questions answered, yes I have a walbro and the J-tube is bypassed (-6 AN from fpr to return via barb fitting). Also to address your other concerns I just replaced the AFM electronics because of a code, and while I was at it put in a new TPS and adjusted it to spec. Also, because of some other posts I read about the common off idle stumble I did bypass the pump resistor via the "12v mod". However, for other reasons I still suspect my fuel pump to be a problem and have a new genuine Walbro on its way.

I think I understand about the Vf, I will see if I can rig one up to read in the cabin at cruise and under various conditions. Also I believe my fuel pressure was set too high to begin with but I had an unreliable gauge (non-liquid filled Aeromotive) That has actually now been replaced as it suffered some kind of failure because the needle fell off and its now full of fuel. Yeah, so much for aeromotive quality.

Under WOT when I said stoich I guess I meant to say that I definately wasnt leaning out even at high RPM. I was at least in the 14's and until I took out nearly 35% I was so rich I was crapping out and losing power. I have since reduced my fuel pressure (thanks to a reliable new gauge) to around 38lbs. When I did that I definately became more lean under hard boost. I will cut back the SAFC settings and try to get closer to the zero mark.

All of that aside I think I get what you are saying about the Vf. I read the post Mike wrote about Vf and some of it sunk in. If I understand correctly now you are saying that without knowing what the ECU is doing to compensate I shouldnt be using the SAFC to adjust what Im seeing on the wideband. Fair enough, I'll work on that a little.


Im still trying to grasp what makes the a/f peg rich on decel. Oh and if I read my markings on my injectors they are actually 580cc if that means anything.

Edit: I read somewhere about using one of the wires on the SAFC to tap the Narrowband and be able to read voltage right on the unit. Would that be useful to me fr monitoring purposes?

 

[Rajunz]

Hey Pete. Did you drill out the block off on the Lexus and adjust the screw all the way out? This really helps smooth the idle.

 

[Facime]

Hey Pete. Did you drill out the block off on the Lexus and adjust the screw all the way out? This really helps smooth the idle.

Ya know I really dont remember if that was done or not. I'll look into it. It would be nice if there was someone here in Houston that was good with this stuff that could spend a little time teaching me. Like I said though Im planning on getting it professionally dyno tuned when I hit 1k miles. All I need for now is a safe reliable street tune that isnt a hassle to drive.

 

[Poodles]

pig rich on decel usually means TPS isn't seeing the throttle closed when it really is...

might be sticking (mine was) but you said you replaced it...

 

[Facime]

yeah, second TPS and it wasnt affected. I managed to make some headway today. I turned the pressure down and tried to get as close to zero baseline on the SAFC, then up just enough to make it cycle between very slight rich/very slight lean. Im at 40lbs at idle with the vac/boost line on and 50 without. This seems to be a good compromise between low throttle driveability and WOT safe levels.

I think Im ok for now, thanks guys.

 

[bigaaron]

38psi at idle with the vacuum line connected to the manifold would mean about 50psi without it connected. It should be much lower at idle then 38psi with vacuum. I think your fuel pressure is too high, which shows in your having to take out about 30% average with the AFC across the whole range of rpm.

Also, it's ok for it to be lean at lower rpm before it hits boost, and it's really hard to tell what it's actually doing from watching numbers jump around on a wideband gauge, as someone previously stated.


edit: oops, i responded to your first posts, and I just saw the one above ^^^