[kpgubert]

The engine is just a NA 5.0 GT40 build (etc. etc.) with a TFS Stage 1 camshaft. I've been battling a "past idle and die" when coming to a stop. I noticed yesterday if I unplugged the vacuum line from the FP regulator it seemed much more likely to catch itself when returning to idle and not just die. I'm using a QH, BE, EA, and a Innovate wideband. While this definitely isn't a radical "build," because of the camshaft profile being significantly different than the stock cam, and thus affecting intake vacuum, would I have an easier time tuning this beast with an adjustable FP regulator? It seemed to me that taking vacuum out of the fuel pressure equation might make my life easier. Oh, and I have 30 lb. FRPP injectors. I've been playing around with the high/low slopes. Right now I have them at 30/32.

Thanks for any insight!

[cgrey8]

I don't think an adjustable FPR is going to be the solve to your problem. The issue is the fuel just hasn't been dialed in yet. If pulling the vacuum makes it catch easier, then this would suggest that it needs more fuel on closed throttle and pulling the vacuum gives it that. But you'll have the same problem with an adjustable FPR.

In the old days of tuning where people didn't have great control over the EEC, an adjustable FPR was necessary to get things just to run OK. But today, their only purpose is to make slightly undersized injectors flow a little more. The catch is raising the rail pressure puts more stress on the fuel pump and while higher pressure might make the injectors flow more, if it's a heavy boost application, you may find the fuel pump simply can't flow enough fuel to attain the pressures the adjustable FPR is demanding of it. If this is not a boosted application for you, that's hardly going to be a concern. But it's still not going to solve any problems. What will is dialing in the fuel so closed throttle, decel, and dashpot (i.e. dropping RPM) conditions are being properly fueled. This will likely be a mixture of MAF tweaks and transient fueling changes. Depending on how much you trust the injector parameters, it may also require you tweak them a tad too. And of course if you've racially changed the spark at CT neutral idle conditions, that could also be a source of issue. Hopefully you haven't been messing with that stuff too much at this point.

[kpgubert]

It isn't a boosted application, but I can definitely see what you're saying. No, a haven't messed with the spark at all at this point. I do have the base timing at 10°.

Yesterday I actually put the stock MAF and TB back on with the hopes of making making a basic tune easier, but no nice (I had a 75mm Pro Products TB and an 80mm from a V8 SHO on before). I'd stick the stock injectors back on too, but unfortunately I gave those away many moons ago. I checked for any vacuum leaks and I'm certain there are none. I'm just trying to rule out any external/mechanical problems before blaming everything on an inappropriate tune.

It does sound like it may be starving for fuel. Sounds logical to me. I wouldn't think I should need to mess with the MAF curve at this point, being the original MAF. Besides the injector slopes, BP, and dashpot, is there anything else I should be looking at? Speaking of which, what about my minimum PW? Can this be set too low?

Thank you very much!

[cgrey8]

Don't be quick to avoid MAF curve tweaks. There's a few different stock tunes from Ford where the exact same MAF hardware was used on the various vehicles, but the MAF curve in each stock tune was a little different...not a lot, but enough to be different. And enough that regardless how confident you are in your MAF's flow curve on a bench, in your vehicle, things are just enough different that you will most likely need to tweak the MAF to correct fueling issues.

[kpgubert]

Don't be quick to avoid MAF curve tweaks. There's a few different stock tunes from Ford where the exact same MAF hardware was used on the various vehicles, but the MAF curve in each stock tune was a little different...not a lot, but enough to be different. And enough that regardless how confident you are in your MAF's flow curve on a bench, in your vehicle, things are just enough different that you will most likely need to tweak the MAF to correct fueling issues.

Ah, okay. Note taken. I was playing with the 80mm curve when I was using that (I started with the '96 Cobra MAF curve in EA) and it seemed to improve my situation.

you might wanna give this a read

http://info.efidynotuning.com/fuel101.htm

Thank you, I will do so. I've read thought the "Idle Air 101" a number of times.

Thanks to both of you!

[kpgubert]

Ah, so I think I am finally seeing the light! I can't count how many times I have read through this article over the past two years:

Tuning Injector Slopes

Tonight things clicked, and I really think I definitely understand what's going on! All of it! Also, I have taken heed of the one note at the end about the injector offset being generous in stock form. Plus, I have underdrive pulleys. I'm sure that doesn't help my low RPM voltage drop case (yes, I'm going to start logging VBAT and pay attention to it).

It appears that the reason it was dying going to low RPMs is it was flooding itself out. I was actually able to get it to run "driveable well" the other day, but the lowest 1/3 of my MAF curve was pretty "lumpy." I'm not happy with that. Next time I play with it, I'm going to put the MAF curve back to stock. I'm then going to raise the low slope to 38.5 (it's at 35 right now) and start to play with the injector offset table.

I just wanted to give an update. Thanks again!

[cgrey8]

Yeah underdrive pulleys will run you into the "not charging" range. My engine has standard pulleys on it, but when it idles around 600, it blips down into the 550-575 range where the alternator just isn't producing as much and can't maintain the voltage. I can watch the voltage on the dash fluctuate as it idles. Tap the gas to get it above 650 and it's solid. As it drops back down, the voltage fluctuates again. So it wouldn't surprise me if underdrive pulleys get the alternator to that point at say 700-750 thus making the effects of the Injector Offset curve much more noticeable.

[kpgubert]

I just wanted to post an update to this so I'm not one of the "take the info and run" people.
Before I put the car away I played with the injector offset. I had the high/low slopes at 30/34.5 and the MAF curve unchanged. I even tried removing any injector offset (=1.000 across the board) and it would still fuel rich kill itself when ramping down to idle.
Well, the car is hung up in the barn for the winter, but when spring rolls around I'll jump back on this. I'll keep this thread up to date and tell what I figure out.

[kpgubert]

Ooops, that might be a problem. Guess what the first thing I will try this spring is? Thank you.