Fuel Cut Sensation

[Prodigyman]

I am just wondering what exactly happens when you are driving and hitting fuel cut? I read the FAQ and I know why it’s caused. My car running like shit now slower then N/A GS(160 HP?), due to boost leaks, very high gas mileage (16 MPG) and god knows what else. I am defiantly should have at least 80-100 + WHP more with my current mods (check my profile) and I am planning on getting 550cc, 190 FP (rewired), LC1 wideband, MAFT Gen II, GM MAS (blow through), 2.5” S intake pipe (no MAF, No BOV), and data logger then tune the car to my 320 WHP goal but before I do that I want to get the car running well and everything in order.

Current stats:
Stock Boost (Gage shows 12-14 PSI)
Stock Injectors
Stock Fuel Pump (+Stock wire)

When my car is cold and I just start to drive it actually pools very well due to ECU dumping rich mix for engine to warm up, only @ WOT in any gear ISP 2,3rd @ ~ 5-6k RPM (when it actually pulls well) I hear a BIG knock (or boom) sound form engine bay and exhaust, like car just hit a brick wall and slams my body forward a little, then I clutch it and go back in the same gear with almost closed throttle and it continues to drive normally. After car warmed up it drives normal (well if you can call it normal So is that exactly what happens during fuel cut or there is something else really wrong with the car?

[olmytsi]

Yeah that's fuel cut. You said you have some boost leaks, how about you fix them?

[Prodigyman]

Originally Posted by olmytsi

Yeah that's fuel cut. You said you have some boost leaks, how about you fix them?

I just did a test with boost leak tester I made (which licks too ) 2 days ago. Apparently its leaking somewhere around throttle controller area and maybe intake manifold gasket. I was using gas station tire pump so I didn’t have much time but even with that ON i would hit 5-7 PSI and stay at it. I never fixed boost leaks before so not sure what to do but I will disassemble that area when I will be installing GM MAF and replace all the gaskets to see if that helps.

[gsxin]

be sure your intake manifod gasket is leaking before you try taking it apart. I would try the throtle body area first. theyre known to leak there.

[olmytsi]

Honestly, you will need more than 7 psi to test it correctly. Test it up to what you run. I understand you don't have a compressor, so start looking for friends who do
The 7 psi test is a good start tho and better than no test.

It's most likely your throttle body or biss leaking...i had a leak there on 2 different motors so it's pretty common. You can replace the gasket easily. Extremepsi or jnztuning sell it in case you can't find it localy.
My gm maf also leaked so feel around that too when you leak test.

[Prodigyman]

Originally Posted by olmytsi

Honestly, you will need more than 7 psi to test it correctly. Test it up to what you run. I understand you don't have a compressor, so start looking for friends who do
The 7 psi test is a good start tho and better than no test.

It's most likely your throttle body or biss leaking...i had a leak there on 2 different motors so it's pretty common. You can replace the gasket easily. Extremepsi or jnztuning sell it in case you can't find it localy.
My gm maf also leaked so feel around that too when you leak test.

Actually I do have a compressor at home, I just don’t have a tire nipple nearness to connect to it, I just didn’t have time to go buy one for past few days. When I do I’ll do 15-20 PSI test.

Thx for your responses guys

[olmytsi]

Here's what i usually do. I put a cap on the turbo (no nipple). I unhook the hose from the pcv valve and stick air through that...works like a charm.

[Dred]

Wouldn't it leak through the cylinders if you do that? Woulnd't you hear the exhaust hissing which would make it hard to hear the other leaks?

[olmytsi]

It has always worked for me and i have boost leak tested countless dsms that way.