95 GST backfires at 4500 rpm

[boosted954g63]

Hey guy, I have been having a problem with my 95 GST for over a year now. When ever I rev the engine up to 4500 it backfires on me. I have done many tests and replaced alot of parts to try and fix it but, nothing is working for me. Here are the things I have tried so far:

New o2 sensors
New but used turbo (14b turbo)
Intake
Spark plugs
Spark plug wires
Rebuild the head with new valve seals/ New head gasket
New BOV
Boost leak tests everytime I put a new part in
New fuel filter
Many OBD-II scans that come up with no codes

What do you guys think that I should try to do next? The only thing I could think what else it could be is the fuel pump or the ECU going bad. What are your guys thoughts on this.
Thanks a bunch in advance!

O ya mods are up to date in my profile.

 

[joe]

Did you gap your spark plugs before putting them in?

 

[boosted954g63]

I had them gaped at .28 for a while and I researched it and on here its supposed to be at .31 so, they are at .31 right now.

 

[oldman]

I had them gaped at .28 for a while and I researched it and on here its supposed to be at .31 so, they are at .31 right now.

They are both way too big, gap them at .028". Which plugs are you using?

 

[boosted954g63]

Oops my bad . I will have to put them back down to .028. I am using the NGK BPR7ES.
Thanks again for the help.

 

[oldman]

I am using the NGK BPR7ES.

How much boost are you running?

 

[pur97tsifwd]

probably fuel cut does it make a loud bang and jerk you?

 

[boosted954g63]

I am running stock boost. I have never ran any thing but stock boost.

Thats what I was thinking fuel cut. When it hit 4500 it backfies and it feels like you are hitting a brick wall.

 

[oldman]

I am running stock boost. I have never ran any thing but stock boost.

BPR6ES.

Thats what I was thinking fuel cut. When it hit 4500 it backfies and it feels like you are hitting a brick wall.

If you're sure you're hitting fuel cut then we need to talk about all the details of your boost leak tests.

 

[boosted954g63]

What I do when I do my boost leak test is hook up the boost leak tester to the turbo inlet and put around 20psi into it. After it gets the air into the system I listen for leaks. I also check to see if it is holding the pressure too by squeezing the lower intercooler hose. Am I doing somthing wrong when I test?

Should I go out and get the BPR6ES?

I am not sure if I am hitting fuel cut or not. Are there any tests that i could do to find out if i am?

Thanks again for all of your help.

 

[oldman]

What I do when I do my boost leak test is hook up the boost leak tester to the turbo inlet and put around 20psi into it. After it gets the air into the system I listen for leaks. I also check to see if it is holding the pressure too by squeezing the lower intercooler hose. Am I doing somthing wrong when I test?

How did you measure the 20psi? I'm guessing that is what your compressor regulator gauge is set to.

Should I go out and get the BPR6ES?

Most definitely, you don't need the 7's until about 18-20psi.

I am not sure if I am hitting fuel cut or not. Are there any tests that i could do to find out if i am?

Not really, you may be able to see signs if you have a logger, it's generally pretty hard to mistaken bogging for fuel cut.

Thanks again for all of your help.

No problem.

 

[boosted954g63]

Yea the air compressor had a psi guage on it.

Would that becausing the problem having the 7's other than the 6's?

I dont have a logger so I guess i really could not tell.

 

[oldman]

Yea the air compressor had a psi guage on it.

Then you're going about it all wrong, setting your compressor regulator to 20psi doesn't at all mean that you pumped 20psi into the intake tract, you need to monitor your boost gauge during testing to figure out how much the intake tract is actually holding, it's not at all uncommon to see no more than 5psi on the boost gauge while the regulator is set to 20psi. You need to re-visit the leak test, I believe that is where your problem is as boost leaks is the #1 cause of fuel cut. Here is what I've posted in the past regarding boost leak testing which you may find helpful.

1. Disable your mbc.

2. Turn your motor to 30* ATDC to avoid valve overlap.

3. Start your test at the TB elbow and focus on area behind the TB first.

4. Spray soapy water at TB gasket, BISS, TB shaft on both sides, IM gasket, injector insulators, brake booster, afpr and all vacuum lines/connections.

5. Open your oil cap and listen for leaks. (PCV, valve seals/guide, rings)

5. Listen to your tailpipe for leaks. (EGR, valve overlap, jumped timing, bent/unseated valves)

6. Once all leaks are fixed, move the tester back to the turbo inlet.

7. Spray down the compressor cover (known leak), BOV return/flange (DO NOT TAP YOUR BOV LINE FOR YOUR MBC!!!), IC end tank/fins and all connections. Re- test.

8. Note that you will leak air into the crankcase through the turbo seal but do not panic, this is normal during a static pressure test as long as there are no shaft play.

The desired test result from the begining of the LICP (bypassing turbo) is around 20psi (on boost gauge) with the compressor set at 30psi, while taking no less than 30 seconds to bleed down to 0.

As a reference, my last test on my 500 mile new engine, I was able to pressurize the system to 25psi, bled down to about 16psi (my 1G bov) in about 30seconds, then took about 3 mins to 6psi and just kinda lingered there for a while. It's not easy to do but the point is it's possible. My next goal is 30psi After motor break in and Dodge modding my BOV. A boost leak test is one of most pita but important regular maintenace task, the key is patience and endurance, have fun.

Would that becausing the problem having the 7's other than the 6's?

Most likely not but you should still go back to 6's gapped at .028".