Fuel Cut #3

sleepydsm · 08-15-2008

92 TSI AWD 5spd

The car hits fuel cut. I know it's fuel cut. It even fuel cut on the dyno at the last dyno day. The car stopped hitting FC, found out there was a big boost leak before the maf, once it was fixed it hits FC again. Sounded like one or two smallish boost leaks from the throttle body area also.

I notice when it hits FC the wideband is like at 12.8

WHY does this happen?

Fresh 6 bolt
14B (15psi)
AFPR at stock FP
GM MAF/MAFT in blow through
"fuel cut" switch is "off"
FMIC
255HP
Disconnected FIAV coolant lines

**Shane@DBPerformance** · 08-15-2008

It's possibly fuel cut, if you are on stock injectors. The MAFT can't truely get around fuel cut. The only thing it could do is clamp the signal going to ECU, to try to avoid fuel cut, but that has the very dangerous side effect of causing the car to run lean, because it has stopped reporting the real airflow.

**scheides** · 08-15-2008

Dude, exhaust, FMIC, and a decent intake is enough to max out the stock maf and injectors on just the stock 14b. 12.8 is lean, this is another sign of this

I have a set of evo 560cc's off of my car...slap them in, you will be set! Dial back the MAF-T one or three clicks and it'll run like a kitten.

sleepydsm · 08-15-2008

SO I should slap that "fuel cut" switch back to the on position I guess.

Will boost leaks after the GM MAF affect anything?

Is the solution to this problem find some way to let the ECU read or allow the current airflow, and provide adequate fuel for that siuation?

**scheides** · 08-15-2008

THE solution is to provide more fuel, or turn down your boost (so you don't require as much fuel).

With the MAF-T, you can read as much air as you need to, but if you don't have enough fuel to go with that air, you will fuel cut (or blow up your motor by disabling it).

123abc · 08-15-2008

If you know you have boost leaks, I would fix them before upgrading to larger injectors.

I have much of the same setup as you except I have the stock pump and maf. I hit fuel cut around 5k under boost, but I know I have a couple leaks at the tb.

**scheides** · 08-15-2008

Sleepy, If you upgrade to the evo 560's, you can turn the boost up to 18

**Shane@DBPerformance** · 08-15-2008

Boost leaks after the MAS, whether it's a stock setup or a blow through MAFT setup will make the car more likely to hit fuel cut and make it run richer, because it's reporting more airflow to the ECU than is actually making it to the engine. Boost leaks before the MAS on a blow through MAFT setup would just make the car lose power and be more prone to knock because the turbo is having to work harder than normal.

You don't want to use the "fuel cut" clamp hack of the MAFT, it's a very poor solution. As Chris said, you need to put in bigger injectors and then dial down the MAFT. It's the same trick that people have been doing with the SAFCs to avoid fuel cut forever.

Or you could get an EPROM ECU in there with fuel cut removed. The stock 450ccs can handle a decent amount more power once the fuel cut in the ECU is removed. Fuel cut has nothing to actually do with fuel supply problems, it was designed as a way to save the car from a wastegate/vacuum line failure that would cause a serious overboost.

A//// Guy · 08-15-2008

The maft really doesnt disable it, like it should if you flip that switch.

Upgrade your injectors, switch the settings on the maft to acknowlegdge it, and then turn up the boost. Thats the only way to get rid of fuel cut. Then throw it on the dyno and get her tuned.

**Shane@DBPerformance** · 08-15-2008

If you are just barely on the edge of hitting fuel cut, then you might be able to take a different route, since you spent money on an AFPR. If you cranked the base fuel pressure from the stock 1G 39psi to 55psi, then you would turn those injectors into 534cc injectors and then might be able to lean out the MAFT.

**scheides** · 08-15-2008

Ooh, good idea shane!

Sleepy, try this, if you have a fuel pressure gauge to go with that AFPR

sleepydsm · 08-15-2008

Yes, the FP gauge is mounted on the AFPR. I will try to increase the FP, but should I then use the MAFT to lean it out a bit or just let it be with a higher FP?

Kevin 1G Drummer · 08-15-2008

You'll wanna lean it out a little with the maft.

sleepydsm · 08-17-2008

Tonight, I turned the FP to 55psi and the car ran lean as hell. I was, uh, testing, and at wot it went to 14.1:1(knock city). I felt the car pulling major timing (i'd hope so at 14.1:1) and was slow as shit. I set the FP back to w/e it was supposed to be stock and then i was back at 11ish:1 at WOT, but with my pal Fuel Cut.

Refresher:
255HP installed about 4 months ago
Stock 450's
Stock EPROM ECU
Aeromotive AFPR
GM MAF/MAFT with fuel cut switch on, (will be switched off tomorrow)
I will also do another boost leak test tomorrow.

I am considering just getting some evo 560's and doing e85 with a chip burnt on the dyno.

Anyone know if Shane can eliminate fuel cut on the chips he can burn?

123abc · 08-17-2008

FWIW, I figured out thanks to twack that my sputtering at 5k was due to a 30 gap at the plugs. Gapped them down to 25 and she pulls to slightly past 6k. I don't need to go that high anyways.

**Shane@DBPerformance** · 08-17-2008

If you raised your fuel pressure and it went lean, then something isn't right. It could have been so rich that it misfired causing lean readings(misfires cause a lean reading due to the oxygen not being used) or something in your fuel system like the pump or filter is having a problem or something else is weird.

Evo 560s won't be big enough for E85, unless you don't plan on making any power. I turn off fuel cut when I do chip tunes.

sleepydsm · 08-17-2008

Did another boost leak test, found the TB shaft seals were leaking and two of the injector seals were pretty bad. I replaced all four injector seals, and I also flipped the fuel cut switch on the MAFT to allow factory fuel cut. (I misplaced my Instructions for the MAFT, so according to Tuners it's switch #3 needs to be in the down position, maybe someone can confirm that)

I just don't get why no one else has problems running 15psi on the stock fuel system/ecu.

Andrew7dg · 08-18-2008

Stock exhaust?

When I replaced my exhaust, major boost creep happened and it would go to like 19 psi. BOOM, fuel cut... But you Probably have a gauge to look at that.

I would get fuel cut all the time in my car just because of the exhaust

Do you have something with MMcd To see what the computer is seeing? Have you looked at your FTs? I had to adjust mine to the GM maf-t because it was off. Thats why there are adjustment knobs in the box. Every GM maf reads slightly different. GM ECU corrects this already but we are working off of this box.

These tuning knobs shouldn't be used for tuning bigger injectors. IMO they suck because they only tune LOW, MED and HIGH and there needs to be more points to tune with then just three. An SAFC ontop of the GM maf-t for tuning would be Ideal. If you were to do that though, the 2G MAS plus and SAFC reads much much better then the GM MAF-t (I have had bad experiences with the MAF-T). I believe the SAFC also takes into account Trottle position.

sleepydsm · 08-20-2008

Quote:

Originally Posted by Andrew7dg

Stock exhaust?

When I replaced my exhaust, major boost creep happened and it would go to like 19 psi. BOOM, fuel cut... But you Probably have a gauge to look at that.

I would get fuel cut all the time in my car just because of the exhaust

Do you have something with MMcd To see what the computer is seeing? Have you looked at your FTs? I had to adjust mine to the GM maf-t because it was off. Thats why there are adjustment knobs in the box. Every GM maf reads slightly different. GM ECU corrects this already but we are working off of this box.

These tuning knobs shouldn't be used for tuning bigger injectors. IMO they suck because they only tune LOW, MED and HIGH and there needs to be more points to tune with then just three. An SAFC ontop of the GM maf-t for tuning would be Ideal. If you were to do that though, the 2G MAS plus and SAFC reads much much better then the GM MAF-t (I have had bad experiences with the MAF-T). I believe the SAFC also takes into account Trottle position.

I have exhaust, the car is not boost creeping. I'm running 15psi and wondering why my ecu is seeing too much airflow, i just find it hard to believe I'm exceeding the max set airflow (which I know isnt a huge number, but still).

sleepydsm · 08-20-2008

I will get DSMLink soon enough, so I'll just quit bitching.

On another note I've been going throught a lot of the stock things and making sure they are ok. All maintenance things are done, I'm very good about that. Coil pack and transistor tested fine, I've been doing boost leaks like every day haha, I will check the injector pulse width soon, car has good fuel pressure, and a new fuel pump, a newer filter, etc. I'm just making sure everything is OK before I actually try to make modest power.