Fuel Cut: What is it? How do I fix it? [merged]

[Slanted J]

All fuel cut threads are combined here.

I've tried doing a search but to no avail.

I was just wondering what Fuel Cut is. I've heard it tossed around alot, but do not actually know the details behind it. And, naturally, I can gather that its when the fuel is cut off, but when and why.


Thanx,
Jon

 

[Defiant]

Fuel cut is like when that dog is chasing Foghorn Leghorn across the barnyard and he gets to the end of his rope.

Yours doesn't sound like fuel cut.

Start with a boost leak test. Then, plugs (and gaps) and wires.

 

[snailpower]

I am having the same problem in my car, at 4500 rpm the car "stutters", misfires, and backfires pretty much simultaneously. It really sucks when your trying to show off and it happens, people just stare at you like your car is a turd.

 

[Denji]

did you do a leak test on your intercooler pipes?

 

[oldman]

Check your fuel pressure, sounds like you're running rich.

 

[Denji]

sorry, just realized that it was already said... for some reason i thought i was the first to reply... i think its because i clicked on the link for the person who last posted from the forums page.

 

[Gen1boost]

well if i was running rich wouldn't i be shooting black smoke out of the exhaust? i mean it just backfires like crazy donkey ballz

 

[MR2_Turbo]

After searching and reading for the last hour, I still didn't find one answer that I was looking for.

I just bought myself a 93 tsi awd and its hitting fuel cut at around 5k rpm and only at WOT. I am no stranger to turbos but I am pretty new to DSM's. My other car is a 91 MR2 Turbo

So my main question is... Is there a simple way to disable FC on DSM's? I know on my MR2 there is a boost pressure sensor that you can just unplug in order to disable it (which I have done so I can run over 12 psi).

Is it possible to hit FC like this on a bone stock 1g? Keep in mind the temp here in MN is around 0 degrees right now.

I also read about how the DSMlink can disable FC and/or boost cut, but I am trying to avoid spending $500 on something I may not need.

Besides that, my only other problem is that the throttle has a tendancy to stick at 4k rpm, but a quick blip of the throttle will bring it back to normal. Is this a common problem also?

Thanks in advance for any help or advice guys. I'm really looking forward to starting this new project!

 

[Quasimondo]

Don't disable the fuel cut. That's a very handy engine saving measure to have.

Check for boost leaks along your intake piping. That's usually the most likely culprit for fuel cut. When the stock MAS sees too much air coming through it will be overrun and cause fuel cut. The MAS will see too much air if the turbo is working harder than it normally does to maintain boost because of a leak. Track down the boost leak and your fuel cut problems will go away.

If your car has cruise, check to make sure that the cruise throttle cables aren't causing the pedal to stick. Check for kinks in the cables as well.

 

[MR2_Turbo]

Thanks quasi. Could this have anything to do with the temp outside? The guy I bought it from said it doesn't do it in the summer, but then again, he also told me thats because the air is THINNER in the summer. Don't know where he got that one from.

 

[Quasimondo]

Air density increases as the temperatures drop, so he is correct, but that becomes a factor when you turn up the boost. Increased air density means higher karman readings and increased chances of hitting fuel cut, but that shouldn't be a problem if you're running stock levels of boost, so it points back to a boost leak and your turbo working harder than it should to compensate for the leak.

 

[Darksyne]

I used to have a 93 MR2 Turbo so I know about the ridiculously low fuel cut. BTW.. Did you know that the Boost Pressure Sensor from a 93.5- MR2 Turbo has the fuel cut set at 16psi?

You definitely have a boost leak somewhere, run a boost leak test to find your leaks: http://www.vfaq.com/mods/ICtester.html

BTW.. Turn your engine over the TDC or BTDC to close the valves so you can pressurize the intake easier.

I would take care of your throttle sticking ASAP. Pull the intercooler hose at the throttle body and make sure there isn't a bunch of crud hanging onto the butterfly

I loved my MR2, but in MD I'd have to park it for half the year due to snow

Good Luck, and welcome to the community!

 

[MR2_Turbo]

Air density increases as the temperatures drop, so he is correct, but that becomes a factor when you turn up the boost. Increased air density means higher karman readings and increased chances of hitting fuel cut, but that shouldn't be a problem if you're running stock levels of boost, so it points back to a boost leak and your turbo working harder than it should to compensate for the leak.

Thanks again quasi!

I used to have a 93 MR2 Turbo so I know about the ridiculously low fuel cut. BTW.. Did you know that the Boost Pressure Sensor from a 93.5- MR2 Turbo has the fuel cut set at 16psi?

You definitely have a boost leak somewhere, run a boost leak test to find your leaks: http://www.vfaq.com/mods/ICtester.html

BTW.. Turn your engine over the TDC or BTDC to close the valves so you can pressurize the intake easier.

I would take care of your throttle sticking ASAP. Pull the intercooler hose at the throttle body and make sure there isn't a bunch of crud hanging onto the butterfly

I loved my MR2, but in MD I'd have to park it for half the year due to snow

Good Luck, and welcome to the community!

Your name here sounds so familiar. I swear I used to know a darksyne. I think it was yahoo pool, or maybe just AIM or something.

Anyways, yeah in 93 they changed the fuel cut to 16psi. I still would have to disconnect it though since I run 20psi on my new turbo.

So check the TB for crap build up. I will do that. I'll look for a leak in the IC piping. What if I don't find the leak there? Also, is there anything else that can cause the throttle to stick around 4k? Or is the TB the only thing that can cause that?

 

[MR2_Turbo]

In case anyone cares, you can see my mr2 here....

http://img123.exs.cx/img123/518/54fr.jpg
http://img123.exs.cx/img123/6330/153wn.jpg

 

[MR2_Turbo]

Hey guys. If there isn't a boost leak, what else should I look at? ECU or MAF?

Also, we ruled out a stuck throttle body being the cause for the 4k rpm "idle" after a WOT run. The gas pedal still comes out all the way. So what else would you recommend I look at for that too?

 

[Defiant]

So my main question is... Is there a simple way to disable FC on DSM's? I know on my MR2 there is a boost pressure sensor that you can just unplug in order to disable it (which I have done so I can run over 12 psi).

DSM fuel cut isn't brought on by boost pressure. It's determined by the amount of air coming into the engine, and adjacent factors:

http://members.shaw.ca/costall/ECUprimer/ECU_ch7.html

And no, you don't want to disable it.

 

[Jlb8434]

i got this same problem, could changeing the plug wires, and plug fix this too. i' working on getting an logger. With the logger how could i use it to adjust airflow or fuel flow?

 

[MR2_Turbo]

DSM fuel cut isn't brought on by boost pressure. It's determined by the amount of air coming into the engine, and adjacent factors:

http://members.shaw.ca/costall/ECUprimer/ECU_ch7.html

And no, you don't want to disable it.

Thanks for the link.


OK, so does this mean the only reason I am hitting fuel cut is because of a boost leak or a stuck wg? Nothing else can cause this? I will be changing the plugs also.

 

[Darksyne]

Thanks for the link.


OK, so does this mean the only reason I am hitting fuel cut is because of a boost leak or a stuck wg? Nothing else can cause this? I will be changing the plugs also.

If you had a stuck wastegate you would be able to see that on your boost gauge.

A boost leak is the number one reason to hit fuel cut on stock boost. Run one before exploring other causes.

 

[MR2_Turbo]

If you had a stuck wastegate you would be able to see that on your boost gauge.

A boost leak is the number one reason to hit fuel cut on stock boost. Run one before exploring other causes.

Thanks again! I will check that out this weekend when the car gets back here.


Still looking for insight on the throttle problem.

 

[rally a 4g63]

Hey guys. If there isn't a boost leak, what else should I look at? ECU or MAF?

Also, we ruled out a stuck throttle body being the cause for the 4k rpm "idle" after a WOT run. The gas pedal still comes out all the way. So what else would you recommend I look at for that too?

A friend of mine has a 93 that we pulled the A/C pump out of, while we did that we binded up the throttle cables a bit causeing the throttle to stick at about 4000-5000 rpm. We straightened them out, and the problem was fixed. Take a look, wiggle the cables a bit and see if that helps.

 

[boostedinaz]

The stock boost gauge doesnt read boost. Get a real boost gauge and see what you are actually runnign boost wise. If you have a stuck WG then yes you will hit fuel cut becasue you are drawing in too much air.

As far as the throttle check the cables and possible rebuild the TB to get all the crap put of it. You may also want to replace the TB O-rings while you are at it. It is most likely the cables that are causing it to function poorly.

 

[DSMjrv]

i was just wondering what causes fuel cut? i have heard from some that upgrading ur fuel system will stop it, and then i have heard it has nothing to do with the fuel system? i am getting fuel cut on my car at 15psi and once in agreat while it will happen when i have it set at 14psi, will a rewire of my fuel pump help this? what can i do? im kinda in debt now so i cant go buy some ecu that completely eliminates it...

btw any1 have any links to where i can see how to do a rewire?

 

[MR2_Turbo]

I'm hoping it is just the throttle body or cable and those are the first things I'll be checking out. The only thing that makes me wonder though, is the fact that the gas pedal itself still comes all the way up when this happens. Still sound like the cable/throttle body to you?


Update on the fuel cut situation:

Well we have a new thought about why it has been happening. My alternator belt was squeeling after 3k rpm, and especially at WOT. So since the alternator wasn't giving its full output, maybe this was causing the fuel cut? It actually feels like hitting the rev limiter but only at 5k rpm. Is that still fuel cut on a DSM? Or is fuel cut going to be the usual hiting a brick wall feeling?


Also, my alternator belt tensioner gave out a couple days ago. The belt is so loose I can twist it around a full turn. I haven't driven it since it got loose. I'll be replacing the belt tomorrow probably.

 

[RallyxDave]

If it feels like you're hitting the rev limiter at 5k then you most likely have a spark problem. Bad plugs, wrong gap, bad wires, alt. crapping out, etc... Fuel cut feels like you hit the brick wall, much more severe than the spark/rev limiter type problem.

 

[boostedinaz]

I'm hoping it is just the throttle body or cable and those are the first things I'll be checking out. The only thing that makes me wonder though, is the fact that the gas pedal itself still comes all the way up when this happens. Still sound like the cable/throttle body to you?


Update on the fuel cut situation:

Well we have a new thought about why it has been happening. My alternator belt was squeeling after 3k rpm, and especially at WOT. So since the alternator wasn't giving its full output, maybe this was causing the fuel cut? It actually feels like hitting the rev limiter but only at 5k rpm. Is that still fuel cut on a DSM? Or is fuel cut going to be the usual hiting a brick wall feeling?


Also, my alternator belt tensioner gave out a couple days ago. The belt is so loose I can twist it around a full turn. I haven't driven it since it got loose. I'll be replacing the belt tomorrow probably.

If the pedal comes back then it is the cable.

YOu will know when you hit fuel cut because it is just like hitting a brick wall. I would imagine that your ignition system isnt getting the full voltage it needs to operate. When I had a bad alt I could see that I was only getting about 12.5 volts and after I got to about 4700 and above it would start tp break up a bit. Our ignition systems need a good solid voltage source to work properly.