Did you guys upgrade MAP sensors when first adding turbo? I dont think my car is adding fuel to compensate for boost. Most of you guys ahve heard my story.

Fuel System
/Wahlbro 255lph fuel pump
/450CC injectors
/Holley 12:1 FMU
/SAFC II
*always 93 octane gas

Ignition Mods
NGK (non-iridium)spark plugs
MSD Coil Pack
MSD wires


This is a long story but it's been a problem for two years since I've installed turbo. The first month I had the turbo on the car, fuel response was perfect. After that month, I would give the car high throttle and it wouldn't increase speed very fast at all. I assumed my clutch was going out so I had it replaced with a high performance clutch.

After this, the problem continued, so I thought to look at my gauges when the problem was happening. It was leaning out. By this time I had increased boost to 10lbs so I was certain the stock injectors were going out. For this I replaced the injectors with the 450cc set and installed an SAFC II. Still the problem continues.

At 60mph in 5th gear, if I apply more than 20% or so extra throttle at a time the car will lean out and start stuttering. This also occurs at highway speeds if I ease into boost at 5th gear. My solution to this WAS dropping to 3rd gear and pinning it. Up until last week, if I dropped to 3rd at 60mph and gave it full throttle, it would lean out for 2-4 seconds and then get the fuel it needed. Last week, I dropped to 3rd and pinned it, and it wouldn't give it fuel at all. It stayed lean and started popping so I let off and drove as easy as I could.

If I'm in the lower gears, the fuel tends to respond better. First gear from stop, for example, rarely leans out. But second gear is starting to lean out as it increases in boost UNLESS it's at full throttle. But 3rd, 4th, and 5th have to increase speed VERY slowly to keep from leaning out. It's like the fuel isn't responding... I mean I have the fuel system for this. Currently I'm set at 10lbs of boost, but it was doing it at 5lbs of boost. I really need some help with this.

have you tuned the fuel curve on the afc. check fuel pess. im at 7psi on my 96 rst with no missing link. walbro pump and a bell engineering sfmu. the voltage clamp made my a/f rat. lean out at random. the missing link made it lean out at 4psi. no problem now.

What year car is yours? There is no specific turbo map sensor so you dont have to worry about buying any. Do you have a missing link installed on the map sensor? Just trying to ask a few questions to eliminate things.

Well my specs that i listed are wrong. For one thing my FMU is a 4:1 not a 12:1. Also I pulled the SAFC. It made the car run worse.... I would try to adjust it to send in more fuel and it just wouldn't do it. I had some guys get the car on a dyno to tune it and they aborted at 4k RPMs because a/f mix was 15:something and the best they could get it to with the SAFC was 14:something. I'm sure part of the problem is the 4:1 rise rate. I can't really figure out what I need as far as rise/rate because I dont understand Corbin's fuel calculations when it comes to pressure. I'm very good at math so that's not the issue, i just dont understand like "old pressure" "new pressure" etc... he doesn't take the time to explain that on his site. That doesn't really matter now anyway because I've decided to move to buying a preassembled MS kit and forgetting about increasing fuel with a rise/rate regulator. But it's still just very funny because as soon as the car had been turbocharged it ran great. It would respond instantly. Just trying to see what kind of problem i have before i invest in the MS and all it's accessories. Can't tell ya what fp is going down the road under boost bc i dont have a fp gauge.

The car is a 1999 RS by the way.

im not an expert or anything but isnt a 4:1 rising rate not enough for 10 psi shouldnt you have a 12:1? also do you you have a fcd of any sort? and is ur notor built? good luck!!!!

yea 12:1 if you had stock injectors in which he has 450's.

Dude, congrats on the MS thoughts. Buy it :P

if the fmu isn't raising the FP the diaphram is probably shot or the thing just plain doesn't work. I'm leaning towards that cause you said it was fine in the first place.

Get MS, tell it what inj size you have and actually TUNE a fuel map specific to your boost pressure.

Shit, you have no idea how good the car will feel after being tuned ;) but i';m sure I already told you that ;)

EDIT: if i was in your shoes i'd either

a) buy MSnS
B) buy an actual Vortech SFMU.

Many a members run 450's with the sfmu and have no problems at all.

there is a missing link installed right
because your problems sound like fuel cut

if your MAP sees any boost it starts pulling fuel

what i dont understand is how the dyno tuners were able to add fuel with the safc. with our cars you can only take fuel if i remember all of my reading correctly

that it why the majority of the tuning is done with fuel pressure and fine tuned with the safc

makes me appreciate my portfueler even more

Originally posted by baxsom
there is a missing link installed right because your problems sound like fuel cut if your MAP sees any boost it starts pulling fuel what i dont understand is how the dyno tuners were able to add fuel with the safc. with our cars you can only take fuel if i remember all of my reading correctly that it why the majority of the tuning is done with fuel pressure and fine tuned with the safc makes me appreciate my portfueler even more

I think it could be fuel cut also.

Motor is built (or else it probably would be blown by now, lol) I do have a missing link. I think im gonna go with blizare's theory of the fmu being shot. I'm set on going with MS in hopes that ditching that FMU will take care of my problem. Not only that but I'm wanting to run 15lbs and might need to pull timing a bit, which MSnS will take care of. Hopefully my 450s will be sufficient for that much boost. Thnx for the help guys :)

Since you do have a missing link, i am leaning more towards bad fmu also. But i am running close to 15psi and i have ran 17 with my super 16g without pulling any timing. I dont think you need to pull timing at 15psi. There have been people run 20psi without pulling any timing.

It sounds like a bad fmu to me too. that fact that it doesnt add fuel fast enough would make me lean towards that. that afc on our cars just adds or subracts MAP voltage, but we cant really add MAP voltage since if we go over about 4.7 v it does fuel cut, so an afc can only lean the fuel system out. Cant wait until you get MS thats gonna be sweet.

If you invested in a fuel pressure gauge, you'd have known this a long time ago ;-)

Originally posted by DarkOne
If you invested in a fuel pressure gauge, you'd have known this a long time ago ;-)

I think I said that a month ago :)

megasquirt or portfueler is the way to go

i run stock fuel pressure on the stock injectors at idle
under boost the 1:1 aeromotive doesnt raise pressure any more than necessary
and i am doing 15psi daily and so far have always logged 15-18 degrees of timing
on the untuned hahn map

i am also using a water injector so that might help a bit

the safc has blown a lot of engines
the local ricer tuner here has blown 5 engines that i know of with one and he is the supposed expert
ditch it

Originally posted by baxsom
the safc has blown a lot of engines the local ricer tuner here has blown 5 engines that i know of with one and he is the supposed expert ditch it

Idiots that can't tune blow engines. The tools they use aren't the determining factor, they are. I ran on an SAFC, 3:1 riser, and 440's for years.