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

 

[Boost95]

Just got done with the compression test and its 150-152 across all 4. So thats not a problem. What next?

 

[oldman]

Just got done with the compression test and its 150-152 across all 4. So thats not a problem. What next?

With good compression numbers, air out of exhaust can only mean two things.

1. Valve overlap, both intake and exhaust valves are open. To avoid this, turn the crank to 30* after TDC.

2. EGR valve.

 

[Boost95]

Well, what should I check next. Its a big leak. It wont hold any psi at all it wont even build past 15ish. And it goes down to 0 within 5 seconds. I cant FEEL air coming from anywhere. I ran my hands under the intake mani also. What can I check next. Im getting ready to start breaking stuff I will regret later WTF

 

[oldman]

Well, what should I check next. Its a big leak. It wont hold any psi at all it wont even build past 15ish. And it goes down to 0 within 5 seconds. I cant FEEL air coming from anywhere. I ran my hands under the intake mani also. What can I check next. Im getting ready to start breaking stuff I will regret later WTF

Like I mentioned above, turn the crank to 30 degree after TDC then check if hissing continues at the tail pipe.

 

[Boost95]

I dont know how to put it 30* after TDC. This would have nothing to do with my car hitting fuel cut tho, would it?

 

[oldman]

Do you have a service manual? If so, which?

 

[Boost95]

I have one, but its for my 2G's. I was just looking in there but I dont have a socket that big. Is that something I NEED to do to figure out my leak? Its gotta be something huge to leak that fast therfore I should be able to find it fast

 

[Boost95]

BTW, im still in the garage trying anything. So anything you tell me to try I will try and post immediatly.
Thanks,
MIke

 

[oldman]

I have one, but its for my 2G's. I was just looking in there but I dont have a socket that big. Is that something I NEED to do to figure out my leak? Its gotta be something huge to leak that fast therfore I should be able to find it fast

Pull the mpi fuse and crank the car just a little at a time until the leak stops. You are not trying to find a leak, you're re-positioning the motor to avoid valve overlap (or TDC on any of the cylinder) so you can continue the leak test.

 

[Boost95]

UPDATE: I blocked off my EGR and now the car holds some boost. It is still leaking some but it is at least hodling it for some time.

 

[Boost95]

After blocking off the EGR it was holding better. I used to be able to pump so much air in and it would not even build past 15. Now built so much pressure that it blew the top off my boost leak tester. Got the car back 2geather and I went for a long ride. The car was now hitting 20psi, so I turned it down and its boosting like crazy. Sometimes it will sit @10psi other it will go up to 20PSI without adjusting it. I made the boost controller from home depot but I built the same one on my 90 GSx and I had no problems.

 

[oldman]

Bypass the mbc and run the pressure source directly to the actuator. If boost holds steady at 10-12psi, the mbc is the problem.

 

[Boost95]

Ok, so now. I would just run the vacum line from the wasegate actuator to what? I used to haev my BCS but I wook it out. Thanks

 

[oldman]

How's the mbc hooked up?

 

[Boost95]

WG Actuator-MBC-BOV T

 

[oldman]

WG Actuator-MBC-BOV T

Then go from bovT to actuator.

 

[Boost95]

Wouldnt that just give it all the air it wants and hit 20psi? Because stock it used to go to the BCS right?

 

[oldman]

Wouldnt that just give it all the air it wants and hit 20psi?

No, that will make it boost at the actuator spring rating of approximately 10-12psi. mbc and bcs operates under the same principle, delaying of the actual pressure from reaching the actuator, this will cause the actuator/wastgate to open later resulting in a higher boost level.

 

[Boost95]

Ill give it a shot in the morning. Thanks for the help 2day

 

[Boost95]

Alright, I hooked it up that way. WG Actuator directly to the BOV T. Took it for a ride and boosted right up to 20psi and I got off it. What is causing that to happen. The car always ran 10 PSI before I removed teh BCS and never put a MBC in it.

 

[oldman]

Alright, I hooked it up that way. WG Actuator directly to the BOV T. Took it for a ride and boosted right up to 20psi and I got off it. What is causing that to happen.

Does it shoot straight up to 20psi or creep to 20psi?

The car always ran 10 PSI before I removed teh BCS and never put a MBC in it.

Was that before or after the 3" exhaust?

 

[Boost95]

The boost shoots directly up to 20psi. As for the boost b4 or after the exhaust you have me stumped there. I dont remember What shall I look into next

 

[oldman]

What shall I look into next

If you're sure the hose to the actuator is leak free, the only thing left would be a defective actuator that never opens or a flapper that's physically stuck closed, more likely the first.

 

[Boost95]

The car used to boost to 10 psi and stay there. So im hoping it the VAC line. I will check it in the morning. So if thats good the only POSSIBLE things it can be is the Actuator or the flapper? Thanks for the help. If thats the problem I may still make it down the track 2morrow night.

 

[oldman]

The car used to boost to 10 psi and stay there.

Keep in mind that this can be because you were boosting with a huge leak through your EGR. Good luck.