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

 

[steve]

Hey guys, I have read through a few topics on fuel cut but nothing has really led me to a conclusive fix.

Perhaps that's because short of a EPROM ECU and the software changes to eliminate fuel cut or a standalone there is no conclusive fix, just a bunch of bandaids.

Most people hitting fuel cut do so because of boost leaks but it's also possible to really hit it by pushing enough air to trigger while making HP from that air.

Steve

 

[rota92]

Perhaps that's because short of a EPROM ECU and the software changes to eliminate fuel cut or a standalone there is no conclusive fix, just a bunch of bandaids.

Most people hitting fuel cut do so because of boost leaks but it's also possible to really hit it by pushing enough air to trigger while making HP from that air.

Steve

Hmm...

When you guys say boost leaks, how miniscule are they? I guess I dont really understand how less air can cause fuel cut, unless its after the MAF (in my case just two couplers, and about 6" of pipe until the TB) in which there would be less air into the motor than the MAF told the injectors?

I got screwed buying an Eprom ECU a few months back, and dont really want to do it again I cant find someone local with a 90 Eprom.

I went to that one link that does the ECU mods, but I think since I drive the car so much I would rather have DSM link on it (From what I can see its similar to Neptune or hondata for hondas, and they are great programs that utilize the stock ECU) for more tunability

I guess I had my question answere long before I asked perhaps?

thanks again!

 

[mhuffman]

I have a 1991 FWD GST and im getting bad fuel cut above 4k rpm's at full boost, so i did a pressure test and my turbo seal is blown, air was leaking out very quickly. Hopefully replacing that will cure my fuel cut.

 

[Raymos24]

Hey guys, I'm new to this forum and was reading up on "Fuel Cut" and was having a similar problem and I can't tell whether it is Fuel Cut or just the spark plugs. I have a 97 eclipse Gst with the following mods: Greddy FMIC, Greddy Type-S Blow off Valve, All the Greddy Piping for the turbo, Evo 3 16G turbo. I have no fuel mods but I am still running stock boost. I dont even turn the boost control on because I have no idea how to deal with it . Ok so here is the problem. When I redline the car in first gear, it bossts fine and goes through cleanly. Then when I shift into second, I reach 5000rpm and stutter, then pick up again at 5500 and stutters then I shift at around 6250. Then in third the stuttering starts a little earlier at around 4000 something. Then in 4th the stutering starts earlier but I haven't pushed it. I dont think its fuel cut, but I was told that with those mods and no fuel mods it is probably fuel cut. What do u guys think. By the way I recently did a boost leak test and fixed a humongous leak in my head gasket so I don't think I will have any leaks. Thanks for all your help in advance.

 

[oldman]

When you guys say boost leaks, how miniscule are they? I guess I dont really understand how less air can cause fuel cut, unless its after the MAF (in my case just two couplers, and about 6" of pipe until the TB) in which there would be less air into the motor than the MAF told the injectors?

The intake tract doesn't end at the TB, the last possible leak in the intake tract is the valve stem seals in the intake ports of the head.

Hey guys, I'm new to this forum and was reading up on "Fuel Cut" and was having a similar problem and I can't tell whether it is Fuel Cut or just the spark plugs. I have a 97 eclipse Gst with the following mods: Greddy FMIC, Greddy Type-S Blow off Valve, All the Greddy Piping for the turbo, Evo 3 16G turbo. I have no fuel mods but I am still running stock boost. I dont even turn the boost control on because I have no idea how to deal with it . Ok so here is the problem. When I redline the car in first gear, it bossts fine and goes through cleanly. Then when I shift into second, I reach 5000rpm and stutter, then pick up again at 5500 and stutters then I shift at around 6250. Then in third the stuttering starts a little earlier at around 4000 something. Then in 4th the stutering starts earlier but I haven't pushed it. I dont think its fuel cut, but I was told that with those mods and no fuel mods it is probably fuel cut. What do u guys think. By the way I recently did a boost leak test and fixed a humongous leak in my head gasket so I don't think I will have any leaks. Thanks for all your help in advance.

You don't have fuel cut, you have hesitation/stuttering? Does this only happen when you're under boost? If so, check plugs (NGKBPR6ES @ .028") and wires then go back to the boost leak test. What exactly do you mean by you fixed a boost leak at the head gasket?

 

[DallasN2O]

Dont know if this is the right section for this but here it is.. I think my wastegate is stuck closed or something because the boost pressure on my aftermarket gauge is going up past 18psi and the car is NOT hitting fuel cut. Dont get me wrong, it pulls hard and feels great.. but its a freshly rebuilt motor with about 300 miles on it. 2g pistons, 1g rods, 2g turbo mani, stock 14b rebuilt turbo, stock 1g bov, stock exhaust. It idles and makes about 20-22 vacuum. Will this hurt my car if its not hitting fuel cut? I have no fuel mods whatsoever or any fuel control.

 

[oldman]

Dont know if this is the right section for this but here it is.. I think my wastegate is stuck closed or something because the boost pressure on my aftermarket gauge is going up past 18psi and the car is NOT hitting fuel cut. Dont get me wrong, it pulls hard and feels great.. but its a freshly rebuilt motor with about 300 miles on it. 2g pistons, 1g rods, 2g turbo mani, stock 14b rebuilt turbo, stock 1g bov, stock exhaust. It idles and makes about 20-22 vacuum.

Does it hit 18psi immediately or pausing at a lower setting, then creeps up as RPM increases? Which boost controller and how is it hooked up?

Will this hurt my car if its not hitting fuel cut? I have no fuel mods whatsoever or any fuel control.

Yes, this is how egines are blown. Fuel cut isn't there to guard against fuel starvation, it's there to guard against run away boost, you can definitely run extremely lean without hitting fuel cut. Stop thinking of fuel cut as "FUEL" cut, think of it as "BOOST" cut.

 

[Raymos24]

O ok I will check the plugs and the wires. When I bought the car it had a boost leak where the turbo connected with the manifold ( head gasket). It happened that only half of the gasket was there and I just had it replaced. Thanks for your help...I'll check the plugs and the wires.

 

[DallasN2O]

No. It immediately shoots straight up to 18-19 psi. There is no pause or hesitation. The car has no boost controller or any sort of boost control other than the stock system. What I'm worried about is.. at about 15psi the car should hit fuel cut, to keep from blowing itself up.. but it doesnt. I have hit fuel cut before, before I got the engine rebuilt I had a MBC and experienced it first hand when i turned it up past 15psi. I know its not the boost gauge malfunctioning because after about 12psi the tires break loose in first gear.

 

[oldman]

When I bought the car it had a boost leak where the turbo connected with the manifold ( head gasket). It happened that only half of the gasket was there and I just had it replaced.

That is not the head gasket, the head gasket is sandwiched between the top half (head) and bottom half (block) of your engine. The gasket you're refering to is the turbine gasket, you don't get boost leaks there, you get exhaust leaks. Besides the wires and plugs, you need to perform a BOOST LEAK TEST.

 

[oldman]

The car has no boost controller or any sort of boost control other than the stock system.

Describe exactly how the stock bcs is hooked up, IN DETAIL.

 

[Raymos24]

[/QUOTE]You don't have fuel cut, you have hesitation/stuttering? Does this only happen when you're under boost? If so, check plugs (NGKBPR6ES @ .028") and wires then go back to the boost leak test. What exactly do you mean by you fixed a boost leak at the head gasket?[/QUOTE]

Hey thanks for the advice. I was also wondering why does my car do the hesitation thing, only when im accelerating in a gear and the factory boost gauge ( the one near the speedometer) reaches its highest point, a little past the top line. Does this help pinpoint the problem or is that just normal timing for the hesitation to occur?

 

[oldman]

Hey thanks for the advice. I was also wondering why does my car do the hesitation thing, only when im accelerating in a gear and the factory boost gauge ( the one near the speedometer) reaches its highest point, a little past the top line. Does this help pinpoint the problem or is that just normal timing for the hesitation to occur?

Damn it Raymos, BOOST LEAK TEST!!!

Your stock boost gauge doesn't measure real pressure, it guesstimates pressure using mainly your aifflow readings at the MAF. When you have leaks, air you lost is already counted so the airflow reading skyrockets causing the stock gauge to max out. Never go by the stock gauge, an aftermarket boost gauge should be everyone's first mod, why do you not have a boost gauge?

BTW time to update your profile.

 

[DallasN2O]

What does it mean when your car is stock and your boost goes up to like 20psi and never hits fuel cut?

 

[oldman]

What does it mean when your car is stock and your boost goes up to like 20psi and never hits fuel cut?

Sounds normal to me, I use to creep up to about 23psi with 16G before fuel cutting.

Fuel cut doesn't equal running out of fuel!!!

 

[DallasN2O]

Sounds normal to me, I use to creep up to about 23psi with 16G before fuel cutting.

Fuel cut doesn't equal running out of fuel!!!

I understand that... but why when I had a mbc and turned it up to 16 psi I would hit the cut.. but now that my wg is stuck closed and its hitting 20psi its not. It feels like the ecu is retarding the timing or something.. its not making power on boost like it should. Car was just rebuilt.

 

[oldman]

I understand that... but why when I had a mbc and turned it up to 16 psi I would hit the cut..

The setup must have been different, I bet if you turn it up to 20 psi, you won't get fuel cut, you probably had boost leaks before, not to say you don't have any now.

but now that my wg is stuck closed and its hitting 20psi its not. It feels like the ecu is retarding the timing or something.. its not making power on boost like it should. Car was just rebuilt.

Makes perfect sense, you were running lean which led to knock and timing retard. The knock sensor is what guards against fuel starvation.

 

[mhuffman]

My leaking compressor seal was causing fuel cut under WOT at 4500rpm's and up. I had to remove the center section of the turbo, remove the compressor cover, and replace the o-ring seal. No more fuel cut. Only $5 for the seal, but at least 5 hours of labor for a n00b.

 

[Raymos24]

Damn it Raymos, BOOST LEAK TEST!!!

Your stock boost gauge doesn't measure real pressure, it guesstimates pressure using mainly your aifflow readings at the MAF. When you have leaks, air you lost is already counted so the airflow reading skyrockets causing the stock gauge to max out. Never go by the stock gauge, an aftermarket boost gauge should be everyone's first mod, why do you not have a boost gauge?

BTW time to update your profile.

Ok I definitely think I have a boost leak because my auto-meter boost gauge shows that at most im boosting around 8psi even though I'm at stock boost. I have a boost leak tester that came with the car but I have no idea how to use it or where to put it. I looked on vfaq but the wording is a little difficult for me . Also I found out today my Greddy Type S BOV is venting to the atmosphere. I would like to know how that effects my performance and how I can fix that ( specifically where to put the hose to recirculate it to the air intake). My car doesnt seem to accelerate nearly enough at WOT so any help would be greatly sppreciated. Thanks

 

[oldman]

Ok I definitely think I have a boost leak because my auto-meter boost gauge shows that at most im boosting around 8psi even though I'm at stock boost. I have a boost leak tester that came with the car but I have no idea how to use it or where to put it. I looked on vfaq but the wording is a little difficult for me .

Something I posted in another thread.

1. Disable your mbc.

2. Turn your motor to 30* ATDC to avoid valve overlap.

3. Start your test at the TB elbow and focus on area behind the TB first.

4. Spray soapy water at TB gasket, BISS, TB shaft on both sides, IM gasket, injector insulators, brake booster, afpr and all vacuum lines/connections.

5. Open your oil cap and listen for leaks. (PCV, valve seals/guide, rings)

5. Listen to your tailpipe for leaks. (EGR, valve overlap, jumped timing, bent/unseated valves)

6. Once all leaks are fixed, move the tester back to the turbo inlet.

7. Spray down the compressor cover (known leak), BOV return/flange (DO NOT TAP YOUR BOV LINE FOR YOUR MBC!!!), IC end tank/fins and all connections. Re- test.

8. Note that you will leak air into the crankcase through the turbo seal but do not panic, this is normal during a static pressure test as long as there are no shaft play.

The desired test result from the begining of the LICP (bypassing turbo) is around 20psi (on boost gauge) with the compressor set at 30psi, while taking no less than 30 seconds to bleed down to 0.

As a reference, my last test on my 500 mile new engine, I was able to pressurize the system to 25psi, bled down to about 16psi (my 1G bov) in about 30seconds, then took about 3 mins to 6psi and just kinda lingered there for a while. It's not easy to do but the point is it's possible. My next goal is 30psi After motor break in and Dodge modding my BOV. A boost leak test is one of most pita but important regular maintenace task, the key is patience and endurance, have fun.

Also I found out today my Greddy Type S BOV is venting to the atmosphere. I would like to know how that effects my performance and how I can fix that ( specifically where to put the hose to recirculate it to the air intake)

Don't even think about not recirculating. Do you see a huge fitting on your intake pipe that is most like plugged up? Go to a auto parts store and find a molded radiator hose for best fit between the BOV and the huge fitting on the intake pipe. Also, if your MBC is connected to the BOV line, change it back to the compressor/j-pipe.

 

[Raymos24]

Hey thanks for all your help but I got one last question . When I get on WOT and I am boosting at full force, my car stops accelerating as strong. It bogs down alot on top of doing the stuterring. MY question is that if that bogging down is ###### caused by a boost leak or is that another problem I gotta fix.

 

[keithscianna]

Ok i am have the symptom of a fuel cut. I can get through 1st gear all the way then in 2nd around 5k it kinda cuts of for a split second and then it will keep going up in rpms with the cut off every second or so. And in 3rd 4th and 5th it does the same thing but it starts at about 3-4k. But if i hold the throttle about 1/4 of the way down it will go smooth through all the gears. I am pretty sure there is no fuel cut going on tho. I am running 15 psi on stock injectors and a walbro 190 fuel pump and i have an adujustable fpr. There are new NGK plugs gapped at .28 new wires new fuel filter. I am thinking it has to be a vaccume problem or something. My vac guage says about 16 and idle and goes to 20 if i rev to about 2k and let off gas then fall back to 15-16. Some times it is at 12 depending on my idle. The least owner of my car kinda F'd up my vac lines. I'm pretty sure the pvc vavle is not hooked up. , The pvc line looks like it is going to the catch tank.

 

[wvturbo2]

Fill out your vehicle profile. If you have an after market intake with out the nipple for the pcv valve the line should goto a catch can. I don't know what the deal is with your vacuum, but what are you using to tune with? I think your probably getting close to the limit of your stock injectors. My car used to let me smoothly pull through all rpms under real low boost or in vacuum, but if i pulled a decent amount of boost It would knock and feel like fuel cut around 4k. That could be why your car does this. Turn the boost down to 13psi and see if it still does it.

 

[romeen]

What you are describing sounds more like either a boost leak or misfire. I would start by doing a boost leak test. Remember that a boost leak can be (and usually is) a vacuum leak when you're not boosting.

Fuel cut is unmistakeable. It is rather violent. It has been described as feeling like you hit an invisible brick wall. The first time it happened to me it scared the crap out of me. I looked in my rear view mirror half expecting to see my motor laying in the middle of the street behind me.

 

[keithscianna]

I dont have aboost leak, I did a test today. It does feel like its hitting a wal but i just got used to it i guess. I dont have a MBC but i thought the stock boost control was limited to 13 psi. So im not sure why its going higher than that.