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

 

[ddavisaf]

I still have 8 posts left

 

[Boost95]

Now you have 7 Im going to go to the dealer and get an OEM PCV valve and give that a shot since STEVE says they are usually bad. I will post with the results. -MIke

 

[ddavisaf]

Now you have 7 Im going to go to the dealer and get an OEM PCV valve and give that a shot since STEVE says they are usually bad. I will post with the results. -MIke

That one doesn't count, neither does this one!!

Yeah, I read up. Sorry, I've been trying to sell my car this weekend so I haven't been around much. I'll be around much more tomorrow. (I read Tuners at work, so that's when I'm most active)

 

[steve]

I'm going to go to the dealer and get an OEM PCV valve

Just disconnect the line from the manifold to the PCV and plug it. Then do another pressure test to see it that's how air was getting into the crankcase. If it is then it make sense to try and get a OEM valve. Ask then if they have any shop air to check the new one at the dealership. You may need to try a few.

Steve

 

[ddavisaf]

do another pressure test to see it that's how air was getting into the crankcase

If your PCV tests okay, then you're getting air into the crankcase via your turbo seals, or your throttle plate isn't closing all the way. Turbo seals run through your oil lines into the pan and up through your piston oil rings since they can't seal perfectly. If your throttle plate isn't closing all the way simply loosen the throttle cable a little bit until it's fully closed. Take off the throttle body elbow to verify this.

7 left

 

[steve]

If your PCV tests okay, then you're getting air into the crankcase via your turbo seals, or your throttle plate isn't closing all the way. If your throttle plate isn't closing all the way simply loosen the throttle cable a little bit until it's fully closed. Take off the throttle body elbow to verify this.

During a intake pressure test air will get past even a closed throttle plate and it should (think about how the car gets air at idle). So how would this cause pressure into the crankcase?

Also the throttle butterfly isn't supposed to close all the way. It's held slightly open by the Idle Position Switch. too far closed and the butterfly bights into the throttle bore and the can has issues on deceleration, too far open and the car idle surges. The adjustment of the IPS is critical to correct operation. Adjusting the throttle cable slack will make sure that the butterfly closed to the IPS stop but it shouldn't cause it to close all the way.

Steve

 

[ddavisaf]

My mistake, when I was trying to explain this I had the TPS 0% reading in my mind, which is what it should read at idle correct? It's not fully closed persay, however via the TPS is it.
Or am I totally off?

I couldn't remember what he was idling at but threw this up as a possible solution to the problem.

 

[steve]

My mistake, when I was trying to explain this I had the TPS 0% reading in my mind, which is what it should read at idle correct? It's not fully closed persay, however via the TPS is it. Or am I totally off?

On a 2G most dataloggers will scale TPS output just like a SAFC does. Also on a 2G the IPS is inside the TPS so there is a fixed Speed Adjustment Screw (SAS) to control how far the throttle closes (I forgot we were talking 2G here). The TPS is adjusted based on where the IPS opens and closes not by TPS output voltage which is why loggers scale the display so that 0% = the lowest voltage seen and 100% = the highest voltage seen. On a SAFC you can read the actual voltage using the Sensor screen.

Steve

 

[jkrause]

I have the safc, so i guess my solution would be to go get it tuned? Correct? I know im an idiot but work with me here.

 

[killakev805]

I have the safc, so i guess my solution would be to go get it tuned? Correct? I know im an idiot but work with me here.

I noticed where you are from, and it blew my mind, I graduated from OHS, class of 2001.

About your problem, try those links that diplomat put up for you. There is a lot of information on those sites (especially www.vfaq.com) if you do your research you will be able to tune it yourself. If you can't get it figured out take it to a dyno shop, hopefully one with some DSM knowledge and have them tune it for you.

 

[Boost95]

I got another PCV, this time I got the OEM from the dealer. I put it on and it still hits fuel cut. As for my idle my car used to idle fine but ever since I got this reman TB it sits at 1300 and sometimes surges. I just set the TPS yesterday. When You say TEST the LICP do you mean to test it at the J-Pipe? I hate this car

 

[Boost95]

I just ran another test from the TB Elbow with the PCV valve capped. Its still leaking so that is ruled out. Now when you say LICp you mean the J-pipe? testing from the LICP is doing nothing more than checking leaks at my intercooler and BOV. If my turbo seals were bad, wouldnt that car smoke alot? I always wanted to use that.

-MIke

 

[ddavisaf]

So we've ruled out the following correct? Add any I forget.
PCV
Injector seals and insulators
Throttle Body Shaft Seals
EGR
Boost leaks before the throttle body

You tested your MAF, and your ISC.
You've checked your spark plugs for spark
You've checked your fuel pump for proper operation.

You've run a compression test wet and dry, and all cylinders tested fine.
You're no longer running a boost control solenoid right?

 

[Boost95]

Yes, all that is ruled out. AS for the others they dont relate to my problem. We now narrowed it down to leaking into the crank case. Its not the PCV so im guessing its turbo seals or a valve seal etc? I still dont understand how testing at the LICP is going to prove my turbo seals bad. If im testing at the Tb elbow that would rule the turbo out. Therfore

 

[steve]

Do you have a log showing the actual fuel cut?

Steve

 

[ddavisaf]

Testing from the TB elbow would be the same as from the LICP, I wasn't thinking clearly before.
You said the intake manifold gasket is good correct?
Well, we've ruled out every common problem...
Next here is what we need to do.
Clean the battery terminals. Make sure everything is grounded good. Rewire your fuel pump if you havn't done so already. Then make sure it's not receiving any power loss during driving. Make sure your timing belt isn't misaligned. Make sure your MAS isn't taking in excessive amounts of air. Make sure there aren't any misran vacuum lines on the throttle body.

If none of that works, then it's one of two things, with a possibility of a third.
One: You'll have you get a different ECU that can delay the effects of fuel cut, something like DSM Link...
Two: It's not fuel cut, or anything related to a car stumbling during acceleration
Three: I totally missed something, which I don't think I did if it has to do with fuel cut or stumbling.

 

[Boost95]

Testing from the TB elbow would be the same as from the LICP, I wasn't thinking clearly before.
You said the intake manifold gasket is good correct?
Well, we've ruled out every common problem...
Next here is what we need to do.
Clean the battery terminals. Make sure everything is grounded good. Rewire your fuel pump if you havn't done so already. Then make sure it's not receiving any power loss during driving. Make sure your timing belt isn't misaligned. Make sure your MAS isn't taking in excessive amounts of air. Make sure there aren't any misran vacuum lines on the throttle body.

If none of that works, then it's one of two things, with a possibility of a third.
One: You'll have you get a different ECU that can delay the effects of fuel cut, something like DSM Link...
Two: It's not fuel cut, or anything related to a car stumbling during acceleration
Three: I totally missed something, which I don't think I did if it has to do with fuel cut or stumbling.

You still must not be thinking clearly we have it narrowed down to leaking into the crankcase somehow. Why would I go around replacing all this stuff? As for having an acutal log of the Fuel cut. I have my datalogger installed in the car but I dont have the software to reply them. My computer is also messed up and wont let me hotsync. Is there anything I can look at on the logger to help you out STEVE?

Thanks
-MIke

 

[auto2wd]

So I got the car back last week and I put some miles on it and had it don't to get some things straight and was very disappointed with the 194hp.

Basically I'm getting fuel cut but cannot turn my boost down due to boost creep. It is set to around 12 psi but creeps to 15-16 because I'm running stock flapper on 16g and stock O2 housing on 3" exhaust/DP.

I figure I have two options *both will be done but I want some input on which to do first*.

Option 1: Upgrade my O2 sensor housing and wastegate flapper to 34mm so I can eliminate the boost creep and lower my boost to around 10-12 psi till I get the fuel setup.

Option 2: Get a 255 pump, S-AFC, and 660 Injectors and just stay at 15-20psi and worry about turning it down later on.

I was told option 2 would be fine to go with first because with that turbo there is no reason to be under 15psi, and I might as well just make the modifications to get the 15-20psi working correctly.

 

[ddavisaf]

I don't know exactly what is going on with you car. There are only two ways for you to leak air into the crankcase. PCV and turbo seals. Your testing at the TB and still hearing a leak negates the turbo seals.
You tested the PCV, it's good you said.
Bad intake manifold gasket would be the next thing to look at. But you said you already did...

As to your logger, injector cycle and fuel trims at time prior to and at your fuel cut problem.

 

[ddavisaf]

Or Option three, which is fix the boost leak.

 

[steve]

There are only two ways for you to leak air into the crankcase, PCV and turbo seals.

Four ways that I know of, turbo seals, PCV, valve seals, and rings. That's not counting holes in the pistons

Steve

 

[Boost95]

But my car has 155 across all 4. Thats almost perfect! When im doin the boost leak test and I open the oil cap that does mean its gettin in there or is that a sound you will always here. I dont want to miss anything.
Thanks,
MIke

 

[ddavisaf]

http://www.agpturbo.com/customer/product.php?productid=58&cat=55&page=1

There is one of the last things I can think of.
steve- Yeah you're right. Sorry.

 

[Boost95]

Thanks for your help. But fuel cut is there for a reason. All an FCD will do is let me run lean. Any last things OLDMAN/STEVE. I dont have any time to research being on my own now and going back to school and working everyday. So all your help is appreciated.

Thank You
-MIke

 

[steve]

I dont have any time to research being on my own now and going back to school and working everyday.

Sorry to hear that. I really don't have time to do your research for you. I hope you get it figured out.

Steve