1G 1991 GSX boost issue

[Db_datsun]

Hey everyone,

I recently picked up a 91 GSX and for some reason the car loves to go to 14 psi+ and hits a fuel cut at 5krpm, if I feather the throttle at 10psi it pulls and reves out as normal, I checked the vacuum lines,

turbo inlet pipe nipple ------ wastegate
I
I
BCS
I
I
AIRBOX NIPPLE

PCV valve is correct as well, so im a little stumped, the only thing modded is the 2.5in exhaust

 

[dwb]

Bad spark plugs & wires are often a culprit that people identify as fuel cut. It's not fuel cut. It's a spark issue.
A boost leak can be another.
Could be other things as well if you provided more information. A vehicle profile goes a long way to help us out.

 

[Db_datsun]

Bad spark plugs & wires are often a culprit that people identify as fuel cut. It's not fuel cut. It's a spark issue.
A boost leak can be another.
Could be other things as well if you provided more information. A vehicle profile goes a long way to help us out.

Bone stock other than a 2.5in exhaust.

 

[pauleyman]

If it wasn't violent, it wasn't fuel cut. Misfire is more likely. Look closely at the spark plug boots. Small white dots are where a spark jumped through. Electrical tape may buy you a few days if you find this. If you dont know age of plugs and wires a new set is in order.

 

[Db_datsun]

I'll start there, additionally is the bcs properly setup? Also is the stock boost 14psi i was seeing different places say different things.

 

[pauleyman]

I'll start there, additionally is the bcs properly setup? Also is the stock boost 14psi i was seeing different places say different things.

No. It isn't 14psi. Its 11psi on a 1g.

Concerning the boost solenoid you should have a line out of the turbo outlet to a T. One side of the T goes to wastegate actuator, other side goes to boost solenoid. The outlet of the solenoid goes back to the intake pipe before the turbo. The solenoid is just a factory bleed off. Many solenoid were modified also and those cars did achieve approx 14psi. It was so easy to do many of us did it because it take like 5 min to modify the solenoid.

 

[Adam]

Might be worth checking plug gap too. Could be too big

 

[We're on Boost]

Is there a cat on the car? Chances are, if there is a 2.5 inch exhaust system on a 1g, the cat may have been replaced by a "test pipe".
When that is the case, then look what happens. The red curve here was this otherwise nearly stock 1992 GSX but with an aftermarket downpipe and no cat.
Where the red curve ends at 5,000 rpm, that was fuel cut.
They said boost was 17 psi at that point.
Sounds a lot like what you are describing.
The blue curve was a previous run with the car nearly stock, for comparison.
These engines are extremely responsive to exhaust system upgrades.

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[Db_datsun]

No. It isn't 14psi. Its 11psi on a 1g.

Concerning the boost solenoid you should have a line out of the turbo outlet to a T. One side of the T goes to wastegate actuator, other side goes to boost solenoid. The outlet of the solenoid goes back to the intake pipe before the turbo. The solenoid is just a factory bleed off. Many solenoid were modified also and those cars did achieve approx 14psi. It was so easy to do many of us did it because it take like 5 min to modify the solenoid.

Awesome thats good to know! Im pretty sure the BCS is set right then, i just bought a boost leak tester so im going to try that today and go from there, so far the pcv valve and BCS checks out, seems to have a slight missfore as well I can barley feel it, so im swapping the plugs and checking the timing today as well

Is there a cat on the car? Chances are, if there is a 2.5 inch exhaust system on a 1g, the cat may have been replaced by a "test pipe".
When that is the case, then look what happens. The red curve here was this otherwise nearly stock 1992 GSX but with an aftermarket downpipe and no cat.
Where the red curve ends at 5,000 rpm, that was fuel cut.
They said boost was 17 psi at that point.
Sounds a lot like what you are describing.
The blue curve was a previous run with the car nearly stock, for comparison.
These engines are extremely responsive to exhaust system upgrades.

You must be logged in to view this image or video.

The previous owner said he purchased an aftermarket cat to pass smog so, I'll verify that claim

 

[We're on Boost]

The previous owner said he purchased an aftermarket cat to pass smog so, I'll verify that claim

Take a look at the downpipe too - see if you can verify whether it is stock or an upgrade. The pipe that goes from the O2 housing to the cat (or to the test pipe).

Sometimes people put a resonator in place of where the cat or test pipe would be. A resonator is larger OD than the pipe, so sometimes just looking at it from the outside, you might not know for sure if it's a cat or a resonator. But a resonator is open straight-through inside, so restriction to exhaust flow is pretty much zero, like a test pipe.

 

[Db_datsun]

I posted a new thread because this issue has completely become something else

1G - Dead Cylinder

Hello everyone, I'm stumped my cylinder #3 is dead. I checked compression which all cylinders came back good, checked the resistance on the injectors as well as made sure all the plugs to the injectors have power, verified injector #3 plug works on other injectors, verified fuel flow, verified...

www.dsmtuners.com

Take a look at the downpipe too - see if you can verify whether it is stock or an upgrade. The pipe that goes from the O2 housing to the cat (or to the test pipe).

Sometimes people put a resonator in place of where the cat or test pipe would be. A resonator is larger OD than the pipe, so sometimes just looking at it from the outside, you might not know for sure if it's a cat or a resonator. But a resonator is open straight-through inside, so restriction to exhaust flow is pretty much zero, like a test pipe.

I would love if you could take a look at this thread as this issue has become something else entirely