* * I need a list of everything that can cause fuel cut

[habitatguy187]

I'm seriously on my last nerve with my car. I have had a boost leak (or very similar symptoms) since I bought the car last august. I have searched many threads and made many threads and have never found my problem.

So I need a list of everything that can cause fuel cut, everything.

I have done many boost leak tests, used gallons of soapy water, used hvac leak finder, and even used a fog machine. I have absolutely zero leaks to the atmosphere, so it has to be past my IC piping. I've changed TB shaft seals and installed a EGR blockoff the correct way. The only thing I haven't done is a compression test, but my car doesn't smoke at all. I've also replaced my fuel pump, fuel filter, fuel injectors, plugs (twice) and wires.

I'm in desperate need of some help, I've learned so much about these cars and can help everyone else fix theirs but I can't get mine to work right. Any wisemen out there that would dedicate some time to someone who's dedicated, please please please help me figure this out.

 

[JEFFREYCASTGSX]

Well it doesnt have to smoke to mean you have low compression.

 

[e85_4g63]

To much air causes fuel cut, a boost leak causes the car to "stutter'' or "fall on it's face". Did Jeff program fuel cut eliminate into your chip? Are you sure it's working? How many lbs of boost are you running.

 

[habitatguy187]

Well it doesnt have to smoke to mean you have low compression.

Ok I'm going to do a compression test then tomorrow morning, but I'm going to do it when it's cold so that I don't strip the threads. Would enough blow-by be considered a boost leak and cause fuel cut? I figured it would. I'll post results tomorrow.

To much air causes fuel cut, a boost leak causes the car to "stutter'' or "fall on it's face". Did Jeff program fuel cut eliminate into your chip? Are you sure it's working? How many lbs of boost are you running.

I don't have a chip, and I totally understand what causes fuel cut, too much air being seen by the ecu and all that jazz. I am running a 2Gmaf with 550s. And since the 2g maf reads less airflow it should push my fuel cut limit back quite a bit. So I'm currently running 17lbs of boost.

I was hitting fuel cut before the maf and injectors swap on wastegate pressure. (9psi for me) Thanks for the suggestions so far guys, I'm really fed up with this.

 

[MY1GDSM]

Check your ECU maybe you have some leaking caps...

 

[habitatguy187]

Check your ECU maybe you have some leaking caps...

+1, will do. Although I've never heard of a bad ecu causing fuel cut, but it makes sense of course since the ecu induces fuel cut. Also might be good to note that my logger shows my fuel trims at 81%, meaning that I'm constantly running rich, I replaced my o2 sensor and still the same thing.

The reason why this is weird is because with a 2gmaf/550s and no tuning software my car should actually be a little lean, this may also be an ecu issue.

 

[MY1GDSM]

I've seen a few ecu's that had leaking caps act like they were hitting fuel cut in a certain rpm area say 4-5k..

 

[habitatguy187]

I've seen a few ecu's that had leaking caps act like they were hitting fuel cut in a certain rpm area say 4-5k..

See that's the thing, when I turn my boost down I'll get to a higher rpm before I hit fuel cut, if I turn my boost up I'll hit it sooner. I guess it could still be an ecu problem though, I'll check it out along with the compression test tomorrow morning.

 

[Redfwdsm]

See that's the thing, when I turn my boost down I'll get to a higher rpm before I hit fuel cut, if I turn my boost up I'll hit it sooner. I guess it could still be an ecu problem though, I'll check it out along with the compression test tomorrow morning.

what are your fuel mods? how big are your injectors? and pump

 

[jrohner]

You say you were running 9psi before, but how much boost are you running currently? That's about the most important thing in a discussion about fuel cut. Have you turned it down and at what psi do you get rid of fuel cut?

 

[JusMX141]

The reason why this is weird is because with a 2gmaf/550s and no tuning software my car should actually be a little lean, this may also be an ecu issue.

Not necessarily. There's a good chance you'll be far too rich and some point in the curve.

I ran a 2G MAS on my FWD with the stock 450's and a Big 16G at 12psi for a little while and aside from being a little lean at idle, the air/fuel was just about perfect under hard acceleration. If I threw a set of 550's in there with no additional compensation, it would've been pig rich.

 

[habitatguy187]

what are your fuel mods? how big are your injectors? and pump

Rewired 190 and 550s

You say you were running 9psi before, but how much boost are you running currently? That's about the most important thing in a discussion about fuel cut. Have you turned it down and at what psi do you get rid of fuel cut?

Before I swapped to the 2g maf I couldn't get rid of fuel cut, 9psi was wastegate pressure so that was as low as I could go. Once I switched over to the 2g maf and 550s, I can now run 15psi w/out getting fuel cut, but I should be able to run a lot more than that since the ecu sees less airflow because of the 2g maf.

I've spoken with some ppl who have done this mod and they said that you won't hit fuel cut until you're past 20psi.

Not necessarily. There's a good chance you'll be far too rich and some point in the curve.

I ran a 2G MAS on my FWD with the stock 450's and a Big 16G at 12psi for a little while and aside from being a little lean at idle, the air/fuel was just about perfect under hard acceleration. If I threw a set of 550's in there with no additional compensation, it would've been pig rich.

Why would this be? I mean there must have been something wrong for your car to work correctly with just swapping over to a 2g maf right? And would being so rich cause a symtom like fuel cut?

Congrats on becoming a Wiseman by the way.

 

[JusMX141]

Why would this be? I mean there must have been something wrong for your car to work correctly with just swapping over to a 2g maf right?

I don't think there was anything wrong....someone had installed a new EPROM ECU when I bought the car which was functioning perfectly, and I had added the Supra SMIC with a Dejon Upper Intercooler Pipe at the time with zero boost leaks as well.

I ran the car like that for a year or so without a single problem. On colder days it tried to stall if you didn't keep your foot on the accelerator until the car warmed up a little, but that was the only noticeable driveability change when I switched to the 2G MAS.


What's going on with the Logger when you're getting this fuel cut? Are you seeing weird timing pull or knock?

 

[habitatguy187]

What's going on with the Logger when you're getting this fuel cut? Are you seeing weird timing pull or knock?

Not seeing any knock, I need to make another log because I didn't really pay attention to timing, I'm still new to tuning. The thing is though my palm battery is dead, so I can't do anything. I ordered a new battery though yesterday so once it gets here I'll log a run and post it up.

Could someone please explain to me how you can have bad compression and not be blowing smoke out your exhaust? Thanks

 

[JusMX141]

Could someone please explain to me how you can have bad compression and not be blowing smoke out your exhaust? Thanks

I would guess worn compression rings coupled with an oil control ring that is still in fine shape.

I ran into this alot on the newer 4-stroke Motocross bikes that I rebuilt before I got into DSM's. The compression rings would be so badly worn that the engine wouldn't be able to start on it's own...it had to be bump-started. It literally didn't have enough compression to suck a fuel charge into the cylinder. Once you got it running, the bike wouldn't smoke at all, but if you rode it hard enough it would quickly drain the contents of the crankcase out the vent tube and all over your back tire, which coats the underside of your rear fender nicely. This was due to the increased crankcase pressure caused by the worn compression rings.

 

[habitatguy187]

I would guess worn compression rings coupled with an oil control ring that is still in fine shape.Once you got it running, the bike wouldn't smoke at all, but if you rode it hard enough it would quickly drain the contents of the crankcase out the vent tube and all over your back tire, which coats the underside of your rear fender nicely. This was due to the increased crankcase pressure caused by the worn compression rings.

I do keep blowing through oem pcv valves, I wouldn't think that too much crankcase pressure would cause that. Either way the compression test I'm doing tomorrow will tell me right?

 

[Maglin]

Here is a stupid sounding question. Do you have your breather tube attached to the intake after the MAF? If not or you have it just venting that would definitely be a large part of the problem. It would just be blowing air through the PCV and out the breather. It could also explain the trims as well. It would be in connection with excessive blow by.

You really need to post a datalog showing IPW, MAF, Timing, RPM, O2, Knock. You should actually attach it. I would want to see some idling in the log at operating temp and some cruise as well along with WOT hitting this fuel cut.

You should also try to just plug off the PCV at the intake manifold and try a run to see what happens.

Just to make sure it's actual fuel cut is it a very violent cut in power? I'm talking it feels like you broke something and the car feels like it's about to just come to a stop. Fuel cut is very very violent and if you kept hitting it you will eventually pop the HG. Also another common cause of a leak is the injector lower insulator seals. If they are hard they are bad and need replaced.

 

[habitatguy187]

Do you have your breather tube attached to the intake after the MAF?

Yes

You really need to post a datalog showing IPW, MAF, Timing, RPM, O2, Knock. You should actually attach it. I would want to see some idling in the log at operating temp and some cruise as well along with WOT hitting this fuel cut.

Will post logs once my new palm battery gets here.

You should also try to just plug off the PCV at the intake manifold and try a run to see what happens.

Tried it, same thing happening.

Just to make sure it's actual fuel cut is it a very violent cut in power? I'm talking it feels like you broke something and the car feels like it's about to just come to a stop.

Complete loss of motion, very violent jerk, if you keep the pedal depressed it won't pick back up for about 2 seconds, yeah it's fuel cut alright.

Fuel cut is very very violent and if you kept hitting it you will eventually pop the HG.

Really??? I've never heard anything about this? Why would it pop a HG?

Also another common cause of a leak is the injector lower insulator seals. If they are hard they are bad and need replaced.

I replaced all the injectors seals when I changed the injectors out, everything's sealed tight.

 

[Maglin]

You can pop a HG because Fuel cut will cause a very sharp lean spike that also brings some pretty damaging detonation. I've personally seen it happen. Guy kept wanting to show me his fuel cut.

 

[habitatguy187]

You can pop a HG because Fuel cut will cause a very sharp lean spike that also brings some pretty damaging detonation. I've personally seen it happen. Guy kept wanting to show me his fuel cut.

Yeah after thinking about it last night in bed I figured that was why, well I've hit it plenty of times I'm on my way to go get a compression tester so I'll post back shortly.

 

[viperlp01]

Do you have an eprom??? Just make a chip to eliminte it.. I had the worst problem with my 2g trying to get rid of fuel cut... I honestly did the socket myself and my buddy who makes chips for 1gs made me a chip that compensates injectors and elim. fuel cut... Thats all i needed to start pulling hard again... I know it is not a real solution but it looks like you have spent some money in places you probaly didn't need to... I mean honestly once you go with a device to tune it they all have boost cut elim. in them minus a safc...

Ya and if he does a boost leak properly and open the throttle body you will hear a leak from the injectors....

 

[habitatguy187]

Do you have an eprom??? Just make a chip to eliminte it.. I had the worst problem with my 2g trying to get rid of fuel cut... I honestly did the socket myself and my buddy who makes chips for 1gs made me a chip that compensates injectors and elim. fuel cut... Thats all i needed to start pulling hard again... I know it is not a real solution but it looks like you have spent some money in places you probaly didn't need to... I mean honestly once you go with a device to tune it they all have boost cut elim. in them minus a safc...

I completely agree that I would get a chip with the fuel cut eliminator in it, but I don't want to just cover up the problem, I mean something's obviously wrong here, so I'd like to fix it before I go upping the boost some more.

 

[habitatguy187]

After doing some more reading I decided to do the compression test hot, here's my results w/out putting any oil in the cylinders.

Cylinder 1: 139
Cylinder 2: 145
Cylinder 3: 145
Cylinder 4: 150

I'm glad that turned out ok, but what now?

 

[habitatguy187]

Looks like the ecu's caps have leaked a little. It doesn't look that bad but I guess it's the next thing to change since everything seems ok. I'll post back in a couple weeks once I save up some money to buy a new ecu. If anyone's got one for cheap let me know.

 

[toofast82]

Looks like the ecu's caps have leaked a little. It doesn't look that bad but I guess it's the next thing to change since everything seems ok. I'll post back in a couple weeks once I save up some money to buy a new ecu. If anyone's got one for cheap let me know.

any leaking is definitely repair or get another ecu.
My car was having intermittent issues while the caps were leaking as well