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

 

[urcnjoe]

There should be a way to automatically have a Boost leak test reply pop-up in these forums, so old man does not have to waste his time anymore.

 

[oldman]

There should be a way to automatically have a Boost leak test reply pop-up in these forums, so old man does not have to waste his time anymore.

But that will kill my post count..

 

[Boost95]

I dont have a boost controller installed. I did pin point it. It leaks behind the compressor housing.

 

[ddavisaf]

I can't think of anything that would be leaking from behind the compressor housing. Possibly a cracked housing?
Get a friend to help you. Spray down the turbo with soapy water, then run another boost leak test, crawl under the car and see if you can see it. Before you climb under it you might want to get a portable light so you can see better.

 

[DSM90AWD]

I dont have a boost controller installed. I did pin point it. It leaks behind the compressor housing.

Check the thermo valve's plastic "Tee" (screw-in fitting on the thermostat housing where the EGR vac line plugs into). I assume since you blocked off the EGR you capped these lines at the Throttle body source? If not, this plastic fitting is notorious for leaks

 

[Boost95]

I dont have a boost controller installed. I did pin point it. It leaks behind the compressor housing.

Sorry, I didnt mean to sound ignorant. I was in a rush on my way to work this morning.

 

[Boost95]

Can anyone specify, that when doign a boost leak test and you open the oil cap you should hear nothing at all? Also with my holding time at the TB elbow would it be good enough to keep me from hitting fuel cut if my INlet leaks were fixed?

Thanks,
Mike

 

[DSM90AWD]

Any logs yet?

I can't comment on the oil cap noise from an intake pressure test, but know when performing a leak-down test (similar process) noise would indicate worn rings. I uses my compressor pressurising at the turbo inlet with it set at 16psi to start and then go up to 25psi and listen for leaks.

BTW.. what brand Boost Gauge are you using and where is it tapped into for a boost signal?

 

[Boost95]

OK I have the boost leak tester hooked up one last time. Im trying to pin point it better. I can hear the leak more thru a vacuum tube when I put it to the left of where the oil line bolts into the top of the turbo. Right near the back side of the compressor housing
Thanks,
Mike

 

[DSM90AWD]

OK I have the boost leak tester hooked up one last time. Im trying to pin point it better. I can hear the leak more thru a vacuum tube when I put it to the left of where the oil line bolts into the top of the turbo. Right near the back side of the compressor housing

No offense, but several questions have been recently asked without reply and advice given seemingly ignored. Some of us are taking time out from work to try and help so please be respectful or the help will go away.

BTW.. we are on page 8 of this thread and you are still discovering boost leaks WTF.

 

[Boost95]

Your past few questions in your replys were ignored because they would have no effect on my leaks. When I made this post I had no leaks and one thing came into another and another. From looking thru the post you can see that we have ran into alot of problems but were resolved thankfully to Bruce and Steve.

 

[Boost95]

I'm telling you, valve seals! Between combustion cycles, out goes the boost, and in comes the fuel cut.

Bruce says with how long my car holds boost at the TB I should not hti fuel cut..

 

[oldman]

Let me be clear on what I said.

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.

What I mean here is that if TB test holds 20 psi for a while, although there are still leaks into the crankcase with pcv disconnected (I suspect the rings due to 30psi difference between dry and wet test, I don't think it's the valve seals), it's not enough to cause fuel cut at 12psi. With that said, I assumed you knew you had to go back to the turbo inlet and repeat test until you achieve the same 20psi at the turbo inlet. A leak is a leak whether it's before or after TB, sorry if I was not clear about it.

 

[Boost95]

Something im confused about is... On my 97 I had compression of 65 in one of the cylinders and I did not hit fuel cut with that car?

 

[oldman]

Something im confused about is... On my 97 I had compression of 65 in one of the cylinders and I did not hit fuel cut with that car?

Low compression numbers doesn't mean you'll losing metered air, you can have bent valves or blown HG, neither have much to do with fuel cut.

 

[oldman]

well why don't we do a boost leak at 90 degrees rotation each time, from tdc. It could be 2-3 shot valve seals on 1 piston.

Intake valve seals are located in the intake ports of the head, not in the combustion chambers. Rotating the engine will have no effect on whether the seals leak. In other words, all intake valve seals are exposed to intake pressure at all times.

 

[moparmadd]

so where would the fuel filter be on a 91 talon tsi awd. and do u have a link to how to do a boost leak test or can someone tell me? thanks guys

 

[v2ner]

http://dsmtuners.com/forums/showthread.php?t=169435

i believe the filter is on the fuel pump inside your tank but correct me if i'm wrong.

 

[ddavisaf]

http://www.vfaq.com/mods/ICtester.html
Make it yourself boost leak tester.



How do I prevent fuel cut?
I have [injectors/fuel pump/fuel rail] installed, but I still get fuel cut! Is there a fix?
Search for this topic now!

This question comes up a lot, mostly because people misunderstand what fuel cut is for, and why it occurs at all. For the answer to this, read this chapter of the ECU Primer.

The simple answer is that because fuel cut is pre-programmed into the ECU, there is no method of disabling it. There are no modifications that can do so, aside from an ECU upgrade that eliminates fuel cut. Upgraded fuel pumps, injectors, and fuel pressure regulators do nothing to avoid or eliminate fuel cut. NOTHING.

That being said, there are some methods (some cheap, some not) of postponing fuel cut. All the methods work on one principle: fooling the ECU into thinking there is less air entering the engine than, in fact, there is. This can be done by adding unmetered air, or by changing the sensor inputs used by the ECU to determine air mass. Of course, these methods usually mean the engines run leaner than stock. Again, read this section of the ECU primer for details.

Methods include:

removing the lower honeycomb from the MAS. See the FAQ Locator (look in the "Intake" section) and Jim McKenna's MAS modification page for more information.
'Gutting' (cutting out) the lower section of the MAS. This modification was first marketed by HKS, improved upon by Roger Hanson, Eric Typpo and Jim McKenna, and recently re-popularized by Al Blaha. This involves cutting out the entire lower section of the MAS - delaying fuel cut, but making the engine run leaner - and altering the intake air temperature sensor to compensate. Mike Jackson also does this - read his information here.
plumbing in a secondary air intake after the MAS. Use extreme caution!
the fuel cut defenser (FCD) by HKS
the dime-store fuel cut defenser (DSFCD) for 1G or 2G. Use appropriate caution.
fuel management computers, like a VPC or PMS. See the Glossary for details.
An ECU upgrade from Technomotive is the only way to really eliminate fuel cut.

 

[ddavisaf]

Useful links concerning fuel cut:
http://members.shaw.ca/costall/ECUprimer/ECU_ch7.html
http://members.shaw.ca/costall/ECUprimer/index.html
http://www.dsm.org/how-tos/JFM/MAF_Mod.html
http://members.rogers.com/mrjackson9/MAF_Index.html

Some of these links are for advanced tuners only. So be careful and research fully before trying anything. I posted these for an FYI only.

 

[ddavisaf]

http://dsmtuners.com/forums/showthread.php?t=169435

i believe the filter is on the fuel pump inside your tank but correct me if i'm wrong.

(I'm uping my post count too )
Fuel filter is located on the pump and also on the passenger side firewall. Inside of a black canister.

 

[v2ner]

i see..haha.

 

[oldman]

we've pretty much ruled out static tests period.

I would like to think so but not quite, he still has to figure out why the system is only holding 10psi at the turbo inlet. After he is able to pressurize close to 20psi at the turbo inlet and the problem still persists, that log of the fuel cut would come handy.

 

[ddavisaf]

Either a boost leak before the TB or bad turbo seals indicate 10psi at inlet and 20psi at tb elbow.

 

[oldman]

Either a boost leak before the TB or bad turbo seals indicate 10psi at inlet and 20psi at tb elbow.

How many posts is that now?