clayne

Let's examine the myths surrounding fuel cut.

First, has anyone ACTUALLY lost an engine or otherwise detonated as a direct result of the ECU cutting fuel due to excessive manifold pressure or engine speed?

dubulup

I want to say the ignition is cut too.

I was thinking the same thing the other day, "How are all these people losing engines to lost apex seals?" I hit fuel cut every now and again...(electronic problem with venting the wastegate...solution I back the vent value down after a spirited run.)...but anyway, if my boost creeps up, the ECU stops from denotating, granted I have fuel cut set to a pretty safe level, 2psi above desired boost, and I run rich at high rpms where my boost tends to creep.

from all the bashing Mazda engineers get for the 13B-REW, they've saved my motor a couple times...but I do still have beef about coolant seals

tomaszjc7

My engine blew shortly after i hit fuel cut, I was on I55 in 4th gear, at 7k it hit fuel cut... then i switched to 5th and at about 140mph it blew.

911GT2

Never hit fuel cut. I bounced off the rev limiter once due to a broken tach. That was an interesting experience...

Mahjik

iTrader: (1)

What mods were on your car at that time and how many miles on the engine?

ZeroBanger

I have nearly 80 runs at the drag strip, I had been plagued with boost spike going from 2nd gear redline to 3rd gear. about 2/3's of the runs (probably 50) I hit a fuel cut from 2nd gear redline to 3rd at transition. I never, ever had any problem with engine damage.

The last time I went to the track I didn't hit any fuel cut, I think I solved my problem.

areXseven

iTrader: (1)

What causes fuel cut-off?? Is it a ECU pre-programed safety feature before detonation??

FCO has happend to me a few times. And it's not a funny thing when it happens.

DamonB

I have hit fuel cut a few times but it was at low rpm. My precontrol solenoid was failing and so the primary turbo would overboost and immediately hit fuel cut. Since I didn't know what was wrong I kept flooring it at low rpm and the engine kept bogging due to fuel cut. Then I noticed 15 psi on the boost gauge Each time the rpm was under about 4,000 rpm and the engine was fine.

ZeroBanger

Also, with my boost cut, my engine had no power until I shifted gears. Kinda weird.

adam c

iTrader: (2)

I hit fuel cut a couple of times when overboosting. The boost is now under control, and it has not happened in a long time.

I have not noticed any problems due to hitting fuel cut.

mad_7tist

it is far safer than ignition cut that used to be on cars

maxcooper

I think this is not quite what was asked, but I have bounced off the rev limiter under boost many times. I don't keep it bouncing against the limiter, but hitting the cut didn't seem to harm anything.

The stock ECU has a tricky overboost cut policy. This may not be 100% correct, but I seem to recall that it was related to RPM and how-long-have-you-been-over-the-limit. For instance, if you are over 11.8 psi for more than 1.2 seconds at 6200 RPM, you'll get a cut. I know RPM was a factor. I can't remember if the boost limit or time-before-cut varies with RPM; perhaps it was both.

I'm too lazy to go look for it, but if you really want the details, I think they are posted on http://www.ScuderiaCiriani.com/ somewhere.

-Max

DCrosby

How do you figure !?

Ignition Cut = Lost power and AFR that's pig rich... maybe some backfireing...

Fuel Cut = Lost Power and AFR Lean, where detonation is going to be the only thing you hear

Fuel & Ignition Cut = Slower car...

Kento

The term "fuel cut" is a misnomer; the ECU cuts both fuel supply and ignition, for the aforementioned possible overly lean AFR scenarios that could result from just stopping fuel delivery-- especially with the Wankel's somewhat poor combustion chamber flow characteristics opening up the possibility that some unburned intake mixture could remain and be ignited in the next rotor/crank revolution.

clayne

Thanks for all the feedback guys.

The premise was really what Kento was referring to. How much of the horror stories are just hearsay? Does ignition get cut as well? In addition, even if ignition was not cut would the car even detonate? It would seem to me that you'd need a pretty perfect scenario of injectors closing at exactly the right time to blow the engine with JUST a fuel-cut and not supplemental ign-cut.

ZeroBanger

I dont know, I cant imagine it being bad for the engine. The stock ecu and apexi (based on stock ecu) do this to protect the engine. I believe if you boost 25 pct over your target boost. I have done this so many times at sears point and sac raceway that I would have killed my engine already. I *THINK* I solved this problem finally.

DeaconFrost

just curious what kind of problems you were having with boost and how did you fix it? I have been having overboost issues on my 2nd turbo and have failed to be able to fix it without porting the wastegate.

ZeroBanger

I have had 2 sets of engines and 2 turbos, both have done it. It only happens from redline in 2nd to a hard shift into 3rd. I will know forsure at the next track event. I have 3 things I did. 1) I got a new OEM transmission
2) I set my power FC to 1 bar and set my duty cycle to .38 Since the map sensor is max of 16.X, .25 is more like 17 PSI so the car in theory should never have that issue. (although I did this in the past and it still overboosted)

3) water injection. This is the first time I used water injection at the track.

Take your pick, Im lost.

Snook

iTrader: (12)

i agree...unburnt fuel vs no fuel for the fuel cut option...id rather go pig rich and have it bog