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

 

[laserspeeddemon]

Honestly my bet is valve seals....

 

[auto2wd]

Pretty sure option 1 would be your option 3... eliminating the boost creep/leak.

 

[ddavisaf]

boost creep and a boost leak are two totally different things.

 

[auto2wd]

So out of curiousity, where did I get this boost leak that I wasnt aware of having?

 

[ddavisaf]

Right there

I'm not there, I have no idea. That's why you should test for one..... if you want me to completely fix it, bring it to North Dakota and I'll point it right out to ya.

If you don't have a boost leak, it's not fuel cut.
Especially at 15 psi.

I run an 18G, I've hit 17, 18 psi without fuel cut.

 

[auto2wd]

You've done this on stock fuel pump/injectors with no S-AFC?

I didnt mean for you to "point it out" I was more looking for why you thought I had one.

Guess i'll have to look into it some more.

 

[ddavisaf]

Stock fuel, stock pump.

Current setup is in the vehicle profile.

What is fuel cut?
Search for this topic now!

Fuel cut is cessation of fuel delivery and spark generation by the ECU. It is a pre-programmed response designed to save the turbocharger from utter destruction in the event of a catastrophic wastegate malfunction. For more details, read the ECU Primer, specifically the chapter on fuel cut. Also read Todd Day's Diagnostic Port issue on fuel cut, and the answer to "How do I prevent fuel cut" in this FAQ.

 

[auto2wd]

I already have a good idea what fuel cut is.

Stock fuel, stock pump.

Fuel cut is cessation of fuel delivery and spark generation by the ECU. It is a pre-programmed response designed to save the turbocharger from utter destruction in the event of a catastrophic wastegate malfunction.

Believed that was the problem im having because i have a small stock wastegate flapper, and O2housing.

Guess i was wrong, thanks for the help.

 

[Boost95]

Im not asking anyone to research for me. I have been thru every post on here anyway and I still have not fixed my car. Can anyone confirm that when doing a boost leak test you should not hear any sounds from the oil cap? If I had bad rings/seals etc my compression would be lower correct? I just cant figure the thing out. I have had the car for about 3 months now and have lots of mods waiting for it in the garage from my past DSM's .

 

[Boost95]

My actuator arm fell off once. I fixed that and the WG works properly. Thanks for giving it a shot tho

 

[Boost95]

Just that it wont show leaks @ the turbo seals.

 

[ddavisaf]

That's about the only thing left to do, would be a leak down test.

 

[oldman]

A leakdown test will not tell you anything about valve seals because a valve seal is not part of the combustion chamber.

Boost95, I know most of this has been posted before but let's do a recap.

1. Compression numbers both dry and wet?

2. Pressure level at turbo inlet and holding time?

3. TB elbow with pcv connected?

4. TB elbow with pcv disconnected?

5. Is the car smoking at all?

6. Have you try a different maf?

7. Have you try a different ecu?

8. steve was on the right track, a log of the fuel cut will tell us a lot so get that logger up and running.

Make sure the results are done at the same time and not days apart and that you address each question with as much detail as you can.

 

[Boost95]

A leakdown test will not tell you anything about valve seals because a valve seal is not part of the combustion chamber.

Boost95, I know most of this has been posted before but let's do a recap.

1. Compression numbers both dry and wet?

2. Pressure level at turbo inlet and holding time?

3. TB elbow with pcv connected?

4. TB elbow with pcv disconnected?

5. Is the car smoking at all?

6. Have you try a different maf?

7. Have you try a different ecu?

8. steve was on the right track, a log of the fuel cut will tell us a lot so get that logger up and running.

Make sure the results are done at the same time and not days apart and that you address each question with as much detail as you can.

I will go in the garage now and do all of the above. I will post as soon as im done. As for getting my logger up and running. I have it installed in my car and set up. Im running MMCD. I just dont have the software to review it. My computer is getting old and tired. I cant hotsync anymore and alot of stuff wont work anymore. So thats out of the question until I get a new computer. IS it possible for me to just look at my logger and give you the results when it hits fuel cut? Ill post soon with the results

 

[oldman]

You can take your palm and cable to a friend/neighbor/work can't you?

 

[Boost95]

Nobody wants me to d/l software onto their computer Here are the results I got. I didn't have time to do the turbo inlet because I gotta run. I figured Id post b4 I leave.

*RESULTS*

Compression Test: DRY- 155 across the board
Wet Test(capfull of oil)- (4)185 (3)185 (2) 180ish (1)185

TB Elbow Leak Test w/PCV attached- 20PSI went from 20-0 in 40 seconds. It went down quicker from 20-10 than it did 10-0. Once it got to about 7-8 it slowed down alot. It then sat at about 2psi for a long time but that is not counted in the 40 seconds.

TB Elbow Leak Test wo/PCV attached- Everything ran very similar. NO CHANGES

"Is the car smoking at all" No , the car does not smoke at all. I had my dad behind it when I revved it hard in neutral and it had a little blackish like any car would. Under Boost it does not smoke. I cant notice anything inside and people outside said everything is normal. The car burns no oil either.

"Have you tried a different MAF?" Yes, I took the one I had on my 90 GSX and it made no difference at all. I'm sure it was working because it was fine on my 90.

"Have you tried another ECU" No, I did not try this yet. I didn't want to spend the money for it to make no difference.

Theres nothing I can glance at or have a friend look at as I hit fuel cut to help out?

 

[Boost95]

Any thoughts Bruce

 

[oldman]

Compression Test: DRY- 155 across the board
Wet Test(capfull of oil)- (4)185 (3)185 (2) 180ish (1)185

TB Elbow Leak Test w/PCV attached- 20PSI went from 20-0 in 40 seconds. It went down quicker from 20-10 than it did 10-0. Once it got to about 7-8 it slowed down alot. It then sat at about 2psi for a long time but that is not counted in the 40 seconds.

TB Elbow Leak Test wo/PCV attached- Everything ran very similar. NO CHANGES

I believe those numbers are good enough for us to conclude that the suppose fuel cut probably isn't related to boost leaks. The difference of 30psi between dry and wet test indicates that you're loosing a little of air though the rings but nothing to be alarmed about, many would kill for those leak test results.

Nobody wants me to d/l software onto their computer

The quicker you get the log on a pc the better, I'm sure you can get it done one way or another.

"Have you tried another ECU" No, I did not try this yet. I didn't want to spend the money for it to make no difference.

Use your 90 ecu and swap pin 6 and 14.

 

[Boost95]

Can you explain to me why you dont think my problem is related to fuel cut? So you mean, I should not be hitting fuel cut with it holding the boost that long at the TB elbow? I am talking it over with the G/F about getting a new computer so I can put logs online. As for swapping my ECU, I sold that ECU a few months back Can the ECu be causing a problem?

 

[oldman]

Can you explain to me why you dont think my problem is related to fuel cut?

Because I have helped many in the past who has mistaken fuel starvation with fuel cut though you seem to have a pretty good idea what a fuel cut feels like. Reason why with a log of the fuel cut and the help of steve, we should be able to figure out if it's a fuel cut and why.

So you mean, I should not be hitting fuel cut with it holding the boost that long at the TB elbow?

That is correct, especially not at 12psi.

I am talking it over with the G/F about getting a new computer so I can put logs online.

Good idea.

Can the ECu be causing a problem?

Considering fuel cut is controlled by the ecu, I think it's very possible. In a situation like this where normal cause didn't materialize, troubleshooting becomes process of elimination.

 

[crxp-o-s4now]

ok so i installed my new mbc because my other one was broken and could not be turned down all the way. So i turn this new one down AL THE WAY (to not add any psi), and for some reason, im still NAILING fuel cut like a brick wall and it feels like either my exhaust wants to throw itself to the ground or somehitng with the intercooler. (loudddd noise, maybe backpressure). So what could the problem be? i know it hits 15psi strong and then BOOM! fuel cut. i cannot run my car like this because it honestly sounds like its about to fall apart. So what do i look for..?? any help is apprecuated.

 

[vr6chris]

a buddy of mine had this same problem. he could never get rid of fuel cut even after going with a safc. it turned out his ecu was bad. might want to check it out

 

[oldman]

Start with a boost leak test, probably the number one cause of fuel cut.

 

[Boost95]

Well, after 2 hours in Best Buy we finally got a new computer. Next time I get time I will get a log in this post so you guys have a better idea whats happening. Does anyone have the MMCD player link off hand? Its about time I got a new comp. its been loooong overdue

Thanks,
Mike

 

[doug]

Yeah, what he said. And how about a mod list?