I have a 93 R1 with the following mods: RB intake, DP, MP, and PFC. Should I worry about fuel cut?

 

PFC as in power FC? No, just dial more full in if needed. If you can get to a dyno then tune it there.

 

Yes, PFC as in power FC. Reason I am asking is that I installed my MP yesterday and once under WOT I got a slight hesitation, a couple of small momentary cut outs.

I thought it could be detonation, but I didn't hear any pinging. My PFC knock levels have always been a bit high even before the midpipe.

I didn't think that the 3rd gens with a PFC had fuel cut. My boost is about 11.4-12.0 psi.

 

12psi is not high enough to hit fuel cut on a STOCK ecu and a PFC doesn't have a 'cut' - you may be having an Ignition problem or a poor primary to secondary injector transition. does the hesitation happen around 3500rpm? - that should be the transition area.

 

wrong,

The power FC will give you a fuel cut if you boost .25 over what your target boost is. If I don't have my settings exactly right I will hit a fuel cut when drag racing right after shifting into 3rd (at transition)

Its a real pain in the ***, I got a profec b but I don't think I'm gonna use it. The way to tell if your fuel cut is due to power FC....When you hit the fuel cut based on over boost it you will not get power back until you shift again.

 

You are correct the PFC will cut - But it is not at a FIXED level like the stock ECU. The description redbase gave of his prob. does not correspond to your description of the PFC fuel cut.

 

I understand. His description of a "Couple small momentary cutouts" does not exactly fit the description, I was just pointing out that power fc does have a fuel cut, believe me I have issues with it.

david

 

Actually the stock ECU isn't at a fixed level either. It can tolerate up to 13.3psi at the transition and 10.8 psi at 7krpm, sort of like a pyramid to account for spikes at the transition. Also, the ECU dumps a lot of fuel around transition for the same reason.

 

BUT it is a fixed map vs rpm, ie at any given rpm it is always the same, unlike the PFC where it is a offset from the Target setting.

and I know about the extra fuel also - My car puffs a big black cloud out the exhaust during transition at wot. just like stomping the throttle on an old 4bbl carbed muscle car.

 

The boost levels for my PFC is on the second setting: Primary .9 and Secondary .8.

 

well the next time you get a fuel cut, reduce the duty cycle like this. ...assume you have this set up

.90 .68
.80 .62

Change your duty cycle like this

.90 .64
.80 .58

That should fix it, if you still get it, reduce the DC further. its all dependant on how cold it is, so you can run a setting at one point and be fine, but then 2 hours later hit a fuel cut on the same setting. Its a pain in the ***.

 

It doesn't sound like a fuel cut problem. I've never experienced the fuel cut on the PFC, but with the stock ECU, when you hit the fuel cut you'll definetally know. The car will just fall flat on it's face. It sounds like more of an ignition problem to me.

 

neevosh
I agree (see my first post)
on the stock ecu, hitting fuel cut is like driving into a lake, a very sharp decrease in power, not just a slight hesitation.

 

Yup, the times when I have hit fuel cut, like during really cool/cold mornings it is just like you shut the car off....total loss of power. You definitely know it once you have felt it.

 

yes its a complete loss of power AND you cannot regain power until you shift. Thats the key.

 

I just rebuilt w/ port and it has been damn cold in tampa Just to add some knowledge, the PFC does have fuel cut. I hit it a few times when it is cold outside. I am not 100% sure, but I believe the problem comes from boost spikes. The base boost is set @ .28 for break in and if I hit it at all it overboosts and cuts. I can see my injector duty cycle is not hitting 100% so it has to be the boost differential. I would not say it is a differential of .25 but seems to vary depending on quite a few conditions.

 

Well you are right, thats exactly the problem. Mine has been solved too. I took my car to get dyoed and we hooked the boost pressure to the dyno and it showed I spike to 15. My fuel cut always hit when I shifted from 2nd to 3rd at the drag strip.

If I have these settings I will hit a fuel cut

85 78
85 68

If I do something like this....

85 68
90 54

or even this...

85 68
80 58


I will not hit it. It all depends on how cold it is, etc.

 

Ditto the responses re fuel cut. Like going from full throttle acceleration to hitting the brakes. Anything less is probably some other problem, BTW it's real disconcerting if you happen to be passing on a two lane road with oncoming traffic when it happens.
Ron A.