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.

Could it be a bad MAP sensor, knock sensor, the absense of a Missing Link, ignition problems?

i am not a expert but i don't think you can use a 12:1 fmu and the 450 injectors without a standalone. i don't think the safc can control those bad boys. i don't know of anyone that has got this to work right.

With that setup, it sounds more like your car is running pig rich, you've fouled the O2 sensor, and it is sputtering because it is drowning in gas rather then leaning out. I am very sure that a 12:1 FMU is much too great a rising rate for use with 450cc injectors.

What about a missing link or voltage clamp? I dont think I have either of these.

Will someone check this FMU to make sure it's 12:1??? It might not be.

http://www.holley.com/products.asp?product=512-505

Originally posted by evotunedscc
What about a missing link or voltage clamp? I dont think I have either of these.

You don't think?? :shrug

That is a very important part of the fuel system if your car is newer than 95' How could you have had the car turbo'd without KNOWING about signals above 4.7 Volts cause a fuel cut :shrug

I think the safc is useless regardless of your mods and the 12:1 fmu is TOTally wrong for 450cc injectors. lol You should be running like 3-5:1 with an SFMU or some standalone.....but not on stock internals.

The fuel delivery problem is partly because it takes a second to raise fuel pressures so you can't really FLOOR IT cause it will take a sec for the fmu to see the boosted condition and thus raiase the pressure. But thats not your problem.

Super dooper rich is your problem my friend.


EDIT: I can't tell you what discs are in the FP regulator you have cause it's not in front of me. Thats up to you to tell us what your running in there. What you have IS an adjustable FMU. So thats good. You just need to know whats inside. Do you have a fuel pressure gauge? If so, find out what you idle FP is and go boost and tell us what you FP is at 5psi or whatever.

Originally posted by Blizare

Originally posted by evotunedscc What about a missing link or voltage clamp? I dont think I have either of these.

You don't think?? :shrug That is a very important part of the fuel system if your car is newer than 95' How could you have had the car turbo'd without KNOWING about signals above 4.7 Volts cause a fuel cut :shrug I think the safc is useless regardless of your mods and the 12:1 fmu is TOTally wrong for 450cc injectors. lol You should be running like 3-5:1 with an SFMU or some standalone.....but not on stock internals. The fuel delivery problem is partly because it takes a second to raise fuel pressures so you can't really FLOOR IT cause it will take a sec for the fmu to see the boosted condition and thus raiase the pressure. But thats not your problem. Super dooper rich is your problem my friend. EDIT: I can't tell you what discs are in the FP regulator you have cause it's not in front of me. Thats up to you to tell us what your running in there. What you have IS an adjustable FMU. So thats good. You just need to know whats inside. Do you have a fuel pressure gauge? If so, find out what you idle FP is and go boost and tell us what you FP is at 5psi or whatever.

The Holly site says that it will raise pressure to a maximum of 4:1... so it may not be a 12:1 FMU. Do what blair said and check your fuel pressure at idle and then under boost to find out the real rate.

k, thnx for the help first of all. I know you're wondering how I can have all this stuff and not know everything about it. I had a small performance business in BG, Ky. We checked idle Fuel Pressure and it was 55-60lbs. Any suggestions?

Originally posted by evotunedscc
k, thnx for the help first of all. I know you're wondering how I can have all this shit and not know everything about it. I had a small performance business in BG, Ky. We checked idle Fuel Pressure and it was 55-60lbs. Any suggestions?

that is kind of high for normal idle fuel pressure. usually our cars idle at around 45psi.

So you think maybe the wrong disc in the FMU? Or would it be something with having no voltage clamp or missing link? Like I said, the first month everything was installed the car was running great... from fifth gear I could give it throttle and it would go. Now if i give it throttle in fifth gear it uses whatever it has in raw horsepower to increase speed but as it goes into boosting it starts all that leaning out (according to a/f gauge) and stuttering crap. It's like this happens when there's not much hp already built up and it has to build hp from boost. By the way, the car has a rebuilt bottom end with forged parts - rods, pistons, headwork, etc. So it should be ready for all this but this fuel issue has been haunting me since a month after turbocharging.

And I guess ur right about the 4:1 fmu. For some reason I had in my mind 12:1. But this is my fmu, looks exactly like it anyway, haha.

could it be some sort of fuel cut issue? If he doesnt have a missing link installed, isnt that what you get?

What year is your car? that would help to figure out whether or not you need a ML or not.
I beleive if it is 95-96 it doesnt need one. correct me if Im wrong.

like all these guys said, the year of your car is going to affect what we suggest next. What year is it?

It's a 1999 RS.

definetly try a missing limk

Erg ... there are so many things wrong and so many things that you still need to tell us. A few things you need to tell us first ...

1. What are your settings in your AFC2? You can idle 450cc/min injectors on stock FP with the proper settings.

Oh BTW, 96+ idle FP is 52psi (roughly). It is not vacuum regulated at all! So it's 52psi ALL THE TIME regardless of how much you're on it. There is no vac line to the stock FPR that is located by the fuel tank.

2. So you have a Holley FMU. Are you still using the stock FPR? If you are I am suprised that you see 55psi and higher FP at idle. More info on the fuel setup please.

3. Get a voltage clamp or a missing link (I vote voltage clamp). You need to prevent the ECU from seeing the MAP sensor voltage higher than 4.7V. If it sees this condition you'll get fuel cut.

This doesn't seem to be your issue because you said it ran fine the first month. This isn't one of those things that just start magically happening. Are you sure there isn't some voltage clamp already on the car?

4. What is your FP under boost? This will be the only way to accurately determine what your current FP rise rate is.

5. Turn down your boost. Don't run 10psi if you have fuel issues. Especially on your stock motor. Run the least amount you can.

Originally posted by Avenger
5. Turn down your boost. Don't run 10psi if you have fuel issues. Especially on your stock motor. Run the least amount you can.

If you have an internal wastegate, remove or unhook the actuator arm from the flapper and your car will only boost under seriously heavy loads, and then for only 1 or 2 pounds. Hook it back up when you have confidence in the performance of your fuel system.

Okay. First question. Do you have any sort of voltage clamp or missing link. If you don't know what that is or does search "voltage clamp"
If you dooo know what it is then you should know where the Manifold Absolute Pressure sensor is and it's function so go out and look at the manifold and see what's there.

How do you know your running Lean or Rich? You don't have a wideband in your mods. Are you using an Autometer Gauge?

Are you one of those people that we all wish WE could sell our cars too :P

Just go, check out a car.

(GUY) yea it's got a aftermarket turbo but the cars a non-turbo originally
(YOU) Anything wrong with it?
(GUY) Nope.
(YOU) Cool, Does it make that sweet Pssssh!! sound?
(GUY) Yup.
(YOU) I'll Take it! Whoot! Car ya start it up for me now so I can hear the engine
(GUY) Sure, It's yours Man. (OMG WHAT AN IDIOT)
(YOU) YAYY look at me girls I go PSSSHH!!.........crash.


I'm just joking, but thats the only goofy thing about this post is that you have a model that NEEDS attention to the MAP sensor and you don't even know about it :P Did the person you got it from tell you all the involvement you'll need to have in this car to keep it running properly??

I'm bitchy cause I need Food. Sorry.

But if you can't realize we need to know more about this car to HELP YOU and I am committed to helping people. :dark so help us help you.

/end rant

Well I'm the original person to mod the car. It was my first car 6 years ago with only 20k miles on it. It was stock and I added body modifications and about the time the tuner scene got hot around my area there was a small performance company open up in bowling green, ky. I didn't know much about how to install my own turbo setup so I gave them the money to do it. At first everything was awesome, then slowly it stopped responding to throttle like it should. I do not have a missing link or a voltage clamp. I know what a missing link is, not too sure of it's functionality. And I have a basic understanding of what a voltage clamp does, but dont really understand how it installs or where to buy one.

I've looked arond on the internet and keep finding random crap that doesn't help me out any. So can someone explain to me a voltage clamp and missing link and tell me how these relate to the Hahn FCD. Also, which of these three items can I use with an SAFC II?

Okay, I would take the SAFC out in my opinion.

Read this thread

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=8&topic_id=90261&mesg_id=90261&listing_type=search

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=8&topic_id=30633&mesg_id=30633&listing_type=search

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=8&topic_id=12821&mesg_id=12821&listing_type=search

and this thread

http://forums.2gnt.com/dcboard.php?az=show_topic&forum=8&topic_id=83897&mesg_id=83897&listing_type=search

But first I think I'd find out what your fuel pressure is while boosting cause it could also be that it's raising it too much or not enough....also, do you have a wideband o2 sensor? How do you know your rich or lean.

I think you should really bring the car to someone who knows what they're doing.

Take note kids. This is EXACTLY why it pays to do your own turbo installation.

Dude look, I've brought the car to a certified mechanic who graduated from NADC when they were an awesome school, he can't even figure out what's going on. If ya'll wanna sit here and hound on me about not knowing my stuff then just dont talk because it's not helping get the problem fixed. I'm not a total dumbass, I've listed the symptoms. According to the autometer air/fuel gauge and a narrowband O2 sensor the car just leans out when I give it fuel. This is the worst in 5th gear. It's not fuel cut because the engine continues to run.

Say for example I'm in 5th gear at 60mph. I increase throttle to 40% to pick up speed or climb a hill. As the needle crosses into boost it fuel cuts. However, if im at the same speed and in 5th gear and give the car full throttle, it will NOT fuel cut, but it will lean out really badly. The solution to this problem used to be to drop to 3rd gear where it already has power at that speed and give it full throttle.... it would lean out for 2-4 seconds and then go stoich like it should. As an indication the problem is worsening, the last time I did this... I dropped to 3rd, the car leaned out and then fuel cut. From there on home I drove the car as easily as possible. But normally it didn't fuel cut, it would just lean out for a little bit, then go stoich/rich.

I know you guys are telling me to check fuel pressure at idle and wot... but im at school and wont see the car till this weekend so I wont be able to check it until then.

I also have a large EVAP leak I cant get rid of if that helps any.

I just need to try and get it fixed so I can see about selling it. I've learned that if you want a fast car, buy one. Turbocharging a car that was never meant to be turbocharged just isn't worth it. I've fought with this problem for 2 years and I've just thrown in dollar after dollar for fuel system mods and engine rebuilds trying to get it running like it should, but clearly it's just not happening.

Originally posted by evotunedscc
Dude look, I've brought the car to a certified mechanic who graduated from NADC when they were an awesome school, he can't even figure out what's going on. If ya'll wanna sit here and hound on me about not knowing my stuff then just dont talk because it's not helping get the problem fixed. I'm not a total dumbass, I've listed the symptoms. According to the autometer air/fuel gauge and a narrowband O2 sensor the car just leans out when I give it fuel. This is the worst in 5th gear. It's not fuel cut because the engine continues to run. Say for example I'm in 5th gear at 60mph. I increase throttle to 40% to pick up speed or climb a hill. As the needle crosses into boost it fuel cuts. However, if im at the same speed and in 5th gear and give the car full throttle, it will NOT fuel cut, but it will lean out really badly. The solution to this problem used to be to drop to 3rd gear where it already has power at that speed and give it full throttle.... it would lean out for 2-4 seconds and then go stoich like it should. As an indication the problem is worsening, the last time I did this... I dropped to 3rd, the car leaned out and then fuel cut. From there on home I drove the car as easily as possible. But normally it didn't fuel cut, it would just lean out for a little bit, then go stoich/rich. I know you guys are telling me to check fuel pressure at idle and wot... but im at school and wont see the car till this weekend so I wont be able to check it until then. I also have a large EVAP leak I cant get rid of if that helps any.

Blair, quit hounding. You're not helping plus you're not giving him anything insightful to try past the "you need a missing link".

1. Fuel cut. When you experience fuel cut your engine will not stop. That's not what fuel cut is. You're right in your assumption that the ECU will not fire injectors during it but it doesn't continuously maintain the state. It goes off and on around where the MAP is seeing positive pressure. The car will feel like it's bucking more or less.

2. I understand that you're using your narrowband to check your A/F ratio. It's been discussed that it's woefully inaccurate on here countless times. It's why no one really trusts it. Also, one of the problems with using it is that as the o2 sensor fails it'll give you false readings which in turn causes the car to supply the incorrect amount of fuel which in turn again causes you to see all sorts of wierd shit on your A/F gauge. Endless cycle.

Another point on your narrowband A/F gauge. Your example of 40% throttle is a bad one. Why, because if you're only giving it 40% throttle you may or may not be going into open loop. This is determines how your ECU is supplying fuel. If you're still in closed loop your car will be trying to keep the A/F around 14.7:1 (using the o2 voltage). This translates out to seeing your blinky A/F gauge bounce back and forth between rich and lean. You should also see this condition under cruise.

In open loop, the ECU uses a predetermined fuel map and doesn't use A/F correction (o2 voltage) to determine the amount of fuel to deliver. This scenario tranlates to your blinky A/F guage pegging out over in the green side. If it still cycles you aren't in open loop.

3. A point about the AFC. Everyone one here NOW says "it's horrible, don't use it, it'll blow shit up" blah blah blah. But they forget that's what we all used initially. Anyway, it's got it's pros and cons. I'm also telling you this from a I used it and I know what the heck I'm talking about standpoint not a I read this on here and I'm just telling you what I read standpoint.

I'm sure that you already know that the AFC is a voltage modifier. On our cars the voltage it modifies is the MAP sensor voltage since our MAP sensor is the main value used to calculate the amount of fuel to deliver. As we've already also mentioned our cars have a fuel cut threshold that is directly related to MAP sensor values (voltage). It's just a hair before atmospheric pressure (roughly around 4.7V). Because of this condition, the AFC is limited to only REMOVING fuel! This means if your maps on your AFC have positive correction, you're only making your fuel cut issues WORSE!

For arguments sake though lets say your car is like a 95 that doesn't have fuel cut. Positive correction is still useless. Here's why. When you are in boost, your MAP sensor will be maxed out at roughly 4.7Vish (probably a little higher). As that value runs through the AFC, it will add X% of that value on top of that based on what you've programmed into the AFC. So say +10%, the output value will be 5.17V (4.7 + .47). This value then goes to the ECU. The ECU will see this and pretty much not have a clue what the hell that means because it expects MAP voltage to be between 0V-5V (its' a 5V sensor). So the ECU will just dump the largest value that it has for it ... which conincidentally will be the same at anything past 0psi. Pretty useless.

What some of us have done in the past, is to use it as a fine tuning tool and to increase ingnition timing. Using FP to supply a rich condition and then using the AFC to trim out little bits of fuel to run optimum power. People have varying results (some unpredictable) but most people tend to stay away from it now because there are products out there that are better and more predictable (which is what you want in tuning).

4. You mentioned something about stoich at full throttle. That's a BAD THING! You should never EVER be stoich at full throttle! It should read rich on your blinky gauge. That's exactly where it should be. WOT with boost you are really looking for somewhere along the lines of 11.5:1-12:1 A/F ratio.

Lastly, we're not trying to blast you or anything. You've mentioned your symptoms but this situation is not a clear cut ... it does this so it must be that. We are trying to help you but we just still do not have enough information to give you a definitive answer. So this weekend find out what you can and post back and let us know. That'll give us greater insight. It'll help us rule more things out and hopefully find your problem.

Originally posted by evotunedscc
Dude look, I've brought the car to a certified mechanic who graduated from NADC when they were an awesome school, he can't even figure out what's going on. If ya'll wanna sit here and hound on me about not knowing my stuff then just dont talk because it's not helping get the problem fixed. I'm not a total dumbass, I've listed the symptoms. According to the autometer air/fuel gauge and a narrowband O2 sensor the car just leans out when I give it fuel. This is the worst in 5th gear. It's not fuel cut because the engine continues to run. Say for example I'm in 5th gear at 60mph. I increase throttle to 40% to pick up speed or climb a hill. As the needle crosses into boost it fuel cuts. However, if im at the same speed and in 5th gear and give the car full throttle, it will NOT fuel cut, but it will lean out really badly. The solution to this problem used to be to drop to 3rd gear where it already has power at that speed and give it full throttle.... it would lean out for 2-4 seconds and then go stoich like it should. As an indication the problem is worsening, the last time I did this... I dropped to 3rd, the car leaned out and then fuel cut. From there on home I drove the car as easily as possible. But normally it didn't fuel cut, it would just lean out for a little bit, then go stoich/rich. I know you guys are telling me to check fuel pressure at idle and wot... but im at school and wont see the car till this weekend so I wont be able to check it until then. I also have a large EVAP leak I cant get rid of if that helps any.

i dont care who your mechanic is or where he graduated from, most of the people on this site (EDIT: there's quite a few) are experts on the 420a platform and turbocharging it.

the autometer a/f gauge is useless. get a wideband


evap leaks contribute to vacuum/boost leaks. find that problem, it can screw with your fmu.

Dont get me wrong, I'm not trying to say anyone here is less knowledgable than the mechanic I've had working on the car recently. Blizare told me to take the car to someone who knew what they're doing. Clearly I've done that. This is my last resort, if anyone would know how to fix my problem someone here should. The only thing is I dont know a whole lot about the fuel system and I really dont wanna spend much more money on a wideband or portfueler or anything like that. It's just not worth it to me. Hopefully I'll get a car soon that was built to do what I want it to do, but for now I just want 15lbs of boost and I'm just trying to figure out what's going on. I've got the internals and mostly everything else I need for it. It's just this damn problem seems to be sticking around for the long run.

To keep this simple, check fuel pressure at idle and boost. Get a voltage clamp and ditch the SAFC. Anything else?

Originally posted by evotunedscc
To keep this simple, check fuel pressure at idle and boost. Get a voltage clamp and ditch the SAFC. Anything else?

No thats about it.

It could be something as simple as your Fuel pressure is't raising enough for the boost you are trying to run. I know I was trying to run 7 psi and I was only getting 75ish psi of FP at the rail when I needed around 100 for stock injectors :P Once I got the sfmu tuned properly it pulled like a muther compared to running soooo lean under boost :)

And seriousley, that narrowband means nothing AT ALL to me. I'd sell the SAFC and find a Zeitronix wideband to actually SEE what you a/f ratio is.

maybe your fuel pump is takin a crap if its not railing fp's

Originally posted by rs_smoked_you
maybe your fuel pump is takin a crap if its not railing fp's

that could also be a problem but we have no clue what the FP is :shrug

Update: I installed the missing link and it seemed to help a little. It no longer totally cuts fuel, but the fuel still isn't responding to the throttle in the higher gears at low RPMs. So that still didn't fix my problem. Still, in the higher gears (3,4,5) when I apply throttle, the only response is all turbo and not much out of the engine. The turbo spools really loud and the damn car just doesn't increase speed much at all. It just doesn't seem to get any power in these gears unless full throttle is applied at higher than 4500 rpms. Fuel response in the lower gears is good, but isn't reliable unless she's at wot. 40%-90% throttle in the lower gears is just unpredictable, sometimes the engine responds to the turbo like it should and sometimes it's all turbo and no engine again.

The next step is to check fuel pressure at idle and under boost. With my 450cc injectors I'm gonna turn fp down to 50lbs at idle and 110lbs at 9lbs of boost. I also have to check and see which disc is in the FMU, depending on which disc is in I might put one of the others in. Not sure why I'd need higher than a 1:1 rise rate tho?

Any other suggestions? BTW, does anyone very knowlegable of this engine being turbocharged live within a 200 mile radius of Nashville, TN? lol
The motor has just been rebuilt with forged internals and high perf. parts and im afraid it might have to get done again if I dont get someone who knows a lot about the specifics of this motor and turbocharging it to look at my issue.

Originally posted by evotunedscc
With my 450cc injectors I'm gonna turn fp down to 50lbs at idle and 110lbs at 9lbs of boost.

Okay. stock idle FP is 45-47psi. 235cc injectors.

Why are you going to run 450's at a higher pressure. Search for sfmu setups with 440's. You have to run pretty low idle fuel pressures with anything that large, and fuel spray quality will be poor with idle pressures under 20 psi.

Just search. I don't feel like doing it for you right now. :P

EDIT: I think you'll need about a 3:1 raise in fp. so say 25 psi at idle static at around 32-35. then say 60-65 at WOT with 10psi. But then comes the "TUNING" part which you cannot do without a wideband 02 sensor.
So yea, the sfmu has some tunabilty to it but you can do any good without knowing where your at and whether or not adjustments are actually doing good.

AGAIN, this is not my fuel system, I am just guessing my the many threads i've read in the past on this issue.

Originally posted by Blizare

Originally posted by evotunedscc With my 450cc injectors I'm gonna turn fp down to 50lbs at idle and 110lbs at 9lbs of boost.

Okay. stock idle FP is 45-47psi. 235cc injectors. Why are you going to run 450's at a higher pressure. Search for sfmu setups with 440's. You have to run pretty low idle fuel pressures with anything that large, and fuel spray quality will be poor with idle pressures under 20 psi. Just search. I don't feel like doing it for you right now. :P EDIT: I think you'll need about a 3:1 raise in fp but i'm not sure how much boost your trying to push so i can't really tell you what your static & WOT boost shuold be around.

Damnit you people. Stock FP is 52psi if you're not a 95. 52psi ALL THE FREAKING TIME! I've already said this once. Argh ... I not even going into the rest of that reply. I'll do it later when I feel like dissecting everything.

okay. 52 psi then. I'm a 95, so sue me :P

Okay all i'm getting at is there are many people who run this setup. I don't but I'm just trying to keep this going and help this guy out.

.

Thnx guys I appreciate the help. Keep it up tho 'cause I gotta get this fixed!!!!! :)

anyone got any new ideas on this problem yet?

Originally posted by evotunedscc
anyone got any new ideas on this problem yet?

Hey man, I was having similar problems as you, give it gas but it felt like I wasnt getting the fuel and the car wouldnt go as it once did. CHeck to see where the vacuum line is on your intake manifold for the fmu, make sure it isnt teed off but connected right to it. I had mine on one tee, it didnt work, replaced the line, put it right on the intake, now it works great again. Sorry if this was already stated, I kinda just looked over the replies.

Yea that def. a good idea but you'd think since a custom shop did the work they'd know that :P

Thanks man, I'll give her a try. I haven't looked to see how they hooked that up, but it's def. worth a shot.

Any of you guys leave near ky or tn??

Any chance this could be caused by my BOV venting into open atmosphere rather than back into the intake??

Originally posted by evotunedscc
Any chance this could be caused by my BOV venting into open atmosphere rather than back into the intake??

No, dont think so, for our motors that is fine, think most people on here vent to atmosphere

THat only pertains to a car with a MAS (air flow sensor). We have a MAP sensor which reads the manifold pressure instead of air flow.

On the silvia I have it venting to the atmosphere and it uses a Z32 AFM from a 300zxTT. Everytime I do a WOT pull through the gears, it backfires and blows a little flame out the exhaust :P cause of a rich condition.

Some guys also suggested fixing leaks through a boost leak test and also getting a data logger to use when driving. Any suggestions on these ideas?