ZeroBanger

I never hit the fuel cut on the street, but on the track I do. I have tried many settings on the power FC, out of 30 runs I have hit a fuel cut 16 times. I found success last week by changing the settings, but when it got cold tonite at the track I hit the fuel cut. It always happens after transition in 3rd gear.

So my question is if I get a profec B or some other, will that prevent me from getting a fuel cut? It seems with the power FC I have to guess.


Thanks!

jspecracer7

Yes, you will still hit fuel cut. The PFC reads boost and when you're over your boost limit, it will cut fuel no matter if it's controlling boost or a Profec B is controlling it.

Just turn your boost limit higher and slowly adjust your actuator% higher.

ZeroBanger

So your thinking I should still keep the power FC and not use a boost controller? or use a boost controller and set the power FC to its limit so it doesn't over boost?

I have settings like this

80 68
90 64

when I had 70 degree intake temps this was fine and I ran a 13.0 @ 107. Same settings with 50 degree intake temps later that night I hit the fuel cut. I am so confused.

Thanks

jspecracer7

70 degree intake temps!...My God that's high. Do you have an intercooler?

Anyways, what do you want to boost?

rx7tt95

All you have to do is raise the boost level on the PFC past the limit that the Profec B is set at. If you never reach that boost level, you'll never have fuel cut. So under setting A, set it for some rediculous number (on the PFC). If the Profec B is in charge of boost, you're not even using the stock solenoids. They're completely out of the picture.
Michel

ZeroBanger

I have the blitz SMIC, u know when you have 300 cars infront of you waiting to run and you are in stop and go for 30 mintutes that happens. On the highway I am like 40 or so.

I want close to .85 without going over. but I hate to have to change it every time it gets cold out. Sometimes I hit the damn cut and it shows that I only boosted .77, yet I have those settings above, make sense? hell no.

Thanks!

jspecracer7

Right on! But don't raise the boost level too high because if something happens, you may **** yourself(I've boost 1.6 kg/cm2 on stock twins because of a wastegate line popping off )

rx7tt95

The numbers you've listed are for duty cycle. You need to change the actual boost limit as well. It's listed as kg/cm2. Set both the PR and the SC boost levels. What boost would you like to run? Add .5kg/cm2 to that on the PFC. Set boost with your Profec B. If you choose to stay with the PFC's boost control (using the stock solenoids), you'll have to lower your duty cycles to avoid boost spike. This is the reason you're hitting fuel cut. The PR duty cycle of 80/90 is pretty darn high.
Michel

ZeroBanger

the 80/90 is the boost its measusred in .5 increments. the other #'S are the duty cycle I thought. the book shows .80 and then .90 but I hit fuel cut evertime with that.

jspecracer7

If you want to run higher boost than stock, then you'll have to raise the boost from .80/.90 to .85/.95 or .90/1.00

...You start to experience boost creep in 3rd gear as well. I noticed this with the stock sequential system and cold nights.

ZeroBanger

doesn't the .90/1.00 give you like 14.7? I would blow up, LOL

jspecracer7

Yes it would...

...so what do you boost when you're using your settings during the day?

...because if you're hitting boost cut at .80/.90 in 3rd gear, then you're hitting boost cut because of BOOST CREEP. I had the SAME exact symptoms after I went full exhaust/FMIC/PFC and intake. Boost creep in 3rd gear on cool nights.

ZeroBanger

It doesn't matter what my settings are on the street I never hit fuel cut. I never run my car like I do in the 1/4 either.

I ordered the profec B I hope it helps. I can for example I had my settings exaclty as in the power FC book for the 12 lbs of boost and I hit fuel cut in warm weather even. Then I changed them to 80 66 90 62 and I ran 4 runs without any fuel cut, in both cold and warm weather....I hit .81 on my power FC. Then I changed my to 80 66 90 66 and had no fuel cut, it hit .85 last night but was still warm out. My next run same setting I hit fuel cut.

The other question..I notice my power FC gives me different boost in every gear. I may be at 9 or 10 in first and hit 12 by 3rd or 4th. Will the boost controller keep me at a consistent 12 regardless of gear/turbo?

Thanks!

ech

The shortest answer to the first question is:

YES - you can install the profec B and then set your boost levels to be rather high. You probably don't want to change the first Turbo "base duty" too much though, because the Profec B is really just for the wastegate.

=====

BUT, I don't understand your settings. Why do you have the boost settings reveresed? The default is

.90 62
.80 70

with your settings of
.80 68
.90 64
you have a really high duty cucle for .80 on the first turbo. Secondly, your first turbo target boost should be equal or higher than your second turbo.

So before you go drastic try
.85 60
.85 66

If you still get cut < 4500 RPM then decrease the base duty on the first turbo
.85 58
.85 66

If you still get cut > 4500 RPM then decrease the base duty on the second turbo
.85 60
.85 62

and so on. You should be able to run more boost on the first turbo because RPM is lower, compression slower, and more fuel is availalbe too.

If you are not getting target boost due to the duty % being too low, you can always inch them up a little, as long as it doesn't bring back cut.

Hope that helps.
-Erik

ZeroBanger

thanks so much for your response, I appreciate it. I did order the profec. Here is my response:

With those settings (from the power FC book) I hit the fuel cut almost everytime I run the 1/4. It happens in third gear at transition. I never hit the FC on the street.
I guess my problem Erik is that yes your right I can adjust the duty cycle and I will not hit the FC in cold weather...The problem is that I never can just guess as to how much. For example, if I have settings that work in hot weather fine, in cold weather they hit Fuel Cut. Now I can reduce those settings on the duty cycle and maybe they will work, but in hot weather I will not get enough boost. Its like a stupid guessing game and I cant test this cause it only happens on the track not the street. I have even tried a "HOT" and "COLD" setting on my power FC and the weather just changes too much for me to guess correctly.

I'm hoping the profec B since it gets rid of the selenoids and crap will keep the boost stable more so than the stock ones. I'm only concerned to run 12 to 12.5 lbs of boost.

ech

And on your last post, changing the base duty UP will increase your chances of fuel cut, if you don't also change your target boost.

In lower gears you don't have as much chance for the boost to creep up.

Are you sure you are getting this in the second turbos? >4500 rpm?

On every run the PFC starts at the base duty (which will create some boost level) and then slowly adjusts the duty cycle to try to achive the target boost level. When you let off and go again it starts at base duty and then goes from there again. If at any point you go >.25 over the target boost it cuts.

So you can see that the base duty is really almost more of a determiner of the actual boost levels. If you are getting any boost cuts, always drop that number.

---

last comment and then I'll be quiet - and I'm not 100% certain about this one - having higher target boost on the first turbos seems dangerous because unless it pegs transition it could be trying for a nice high boost setting, then on transition the overboost threshold drops, and you could be more suseptable to cut. just a thought, I know the issue is complicated by the transition.

ZeroBanger

[QUOTE]Originally posted by ech
And on your last post, changing the base duty UP will increase your chances of fuel cut, if you don't also change your target boost.

In lower gears you don't have as much chance for the boost to creep up.

Are you sure you are getting this in the second turbos? >4500 rpm?


[QUOTE]

I am sure its happening at transition. On which turbo I don't know.

I don't know much but my theory was that when I had a lower # on my first turbo when the 2nd kicked it it boosted above the setting for the first turbo. The thing I cant explain is that sometimes when I hit fuel cut my power FC only showed my max boost at .77 yet my boost was set at the .90 and .80 for my turbos.

I don't know, I just hope that the PROFEC B solves this crap. Its not normal to have fuel cuts on more than half my 30 runs I have had.

nocab72

Once you install your profec, set the profec to 12psi, then set your PFC to 1.00. You SHOULD NOT hit fuel cut, if you do, there is something else wrong.

From your description, it doesn't REALLY sound like the profec is going to fix your problem. ie you are hitting fuel cut and only registering .77bar peak on your PFC, that tells me there is something else wrong, but you can try the profec, you might have a "nicer" transition boost curve with it.

K

ZeroBanger

I don't know why my power FC recorded a .77 when I hit the FC. I can say other times I had a .80 set and hit it was .82 when I hit the FC. All I can say is Different settings on my power FC will make the FC go away, but when it gets cold I will hit the FC again. I have to believe since the profec doesnt use the stock selenoids that should fix the problem. I cant think of any other reason. when I get the fuel cut I find that if I reduce the duty cycle by a .2 or .4 the fuel cut does not happen. So it has to have something to do with the power FC and the boost settings. ITs just a PIA to guess whether or not I need to change the settings.

Beast From The East

I didn't see it mentioned in the thread so far, and I don't have my PFC manual in front of me, but IIRC fuel cut is hit when you boost .25KG/cm^2 over your boost settings for your primary turbo. That's 3.56 psi over your setting, which means you are spiking to beat the band. Get that spike under control or your motor is history - if the spike doesn't get you due to not enough fuel then the fuel cut will due to the lean condition it can cause.

I run an old Pettit boost control unit set to 1.13 kg/cm^2 (16psi), and run my primary setting at 1.5 to ensure no fuel cut. I have many mods to allow this (330 rwbhp with custom twins....waiting for 3 bar Apexi map sensor so I can go to 18~20 psi to get to 400rwhp).

Beast

Edit added - I took the time to read the thread more clearly, and you're saying you hit cut at .77? That's only 10.95 psi. You must have some other fuel delivery component problem. I'd be worried about fuel pressure - your pump might be going out, or your fuel filter might be clogged. Put an in-line fuel pressure gauge in your fuel line and run it up to hang on your driver's side windshield wiper. Do the run and watch if your fuel pressure is dropping off. When's the last time you changed your fuel filter?

You should not hit fuel cut at those settings you're describing. Your symptoms point to another problem.

ech

I agree with "Beast". I'm pretty sure that the reading you see on the PFC (peak hold) is what the PFC uses to determine boost cut. If it maxs at .77 to .83 and you are getting cut, then it is probably something else.

Nevertheless - please try the settings
.90 .58
.80 .62

just for kicks. That should not trigger boost cut at all.
On my prior post where I speculated on the transition - I don't know what I was typing - I got my arguments all messed up. One thing is that on the first turbo, it precontrol actuator is used to regulate boost, and the WG is held closed. So the higher the boost settings on the primary, the less air goes to pre-spool the second turbo. The lower the boost on the first turbo, the more air pre-spools the second turbo.

But I think that is a moot point, because if you are getting a boost cut and your ecu is healthy - then you should be seeing at least 1.05 on your peak hold!

You aren't running on 1/4 tank of gas or anything like that are you?

ZeroBanger

I'm getting my boost controller installed on 6/13 and I will report back to the thread after I take it to the strip. My rotary tuner said its because of the power FC and the settings. He said because of the change in temps. He is confident this will fix it as I am too. The fact is I did run 4 successful runs on that setting I pointed to, when I changed the duty cycle from .62 to .66 to try and increase the boost a little, It ran fine for my first run, but 1 hour later when it got cold I got a fuel cut. I know from experience if I had set it back to .62 that I would not have a fuel cut again. That makes be think its not a fuel pump. I would have that problem on the street also, and I would have it regardless of my power FC settings.

I've been wrong before, but like I said, every time I get the boost cut, when I set my power FC setting back, the boost cut goes away.

thanks!

jspecracer7

If it does trigger boost cut, it's because of boost creep that he's hitting boost cut.

SPOautos

sorry

SPOautos

When you turned up the duty cycle to up the boost did you also turn up the boost level??? You should find a duty cycle that keeps your car at the boost you want then you should be able to just adjust your boost. If you turn up the boost with the ducty cycle but leave the boost the same then your boost will go higher than what you have entered in and you'll hit fuel cut

Also - I dont know if you actually getting creap or not....I think your just getting transition spike. Its, been a long time since i had to control my boost since I run like 15psi and also since my car has been down for 4 months I'm getting rusty BUT I think the higher the % on the pri duty cyc the less of a spike you will have.

STEPHEN