Need help with cut out issue, at wits end

[Tom N]

I am at my wits end with trying to figure out a cut out issue the car has above 21psi.
98 240sx w/ stock long block S15 sr20det, rewired walbro, fmic, 20g turbo w/ internal gate, enthalpy tuned ecu, z32 maf, 3in exhaust and progressive methanol injection.

Ok heres what it does. under 21psi it runs perfectly fine. Pulls to 7800 with no problems.
If i try to turn the boost up past 21 at wot it will cut out right about when it hits full boost. It will cut out then back in like twice then start pulling again.
I have tried adding additional grounds to the engine as well as a coil pack grounding plate, replaced the coil pack harness with a new one from wire specialties, tried swapping in some 350z coils, closed the gap up to .020.
tested to see that the harness is getting proper voltage to the coils, ran 12v power to the harness strait off the battery, voltage stays about 13.3-13.5 through the pull. I`m starting to think this issue is not spark related.
a/f is good. Ive tried leaning it down a bit as well as richening it up some through the alcohol injection just for something to try.

None of these thing made any difference at all. Still will cut in and out if i go above 21psi.

would love any suggestions that maybe i`m not thinking to test.

[mr.nismo.]

I'm gonna take a stab and say it's the tune. Im guessing above 21 psi it's hitting "dead spots"

[Tom N]

I'm gonna take a stab and say it's the tune. Im guessing above 21 psi it's hitting "dead spots"

What do you mean by " dead spots "?

[mr.nismo.]

Ok IIRC enthalpy is a mail tune yes? You just give him what's on your engine and he makes a tune. Well my guess ( again I could be wrong) your ecu isn't compensating for above 21 psi because it doesn't know how to. Or your injectors could be maxing out, idk. When it cuts out what is the AFR while it's doing that?

[Tom N]

Ok IIRC enthalpy is a mail tune yes? You just give him what's on your engine and he makes a tune. Well my guess ( again I could be wrong) your ecu isn't compensating for above 21 psi because it doesn't know how to. Or your injectors could be maxing out, idk. When it cuts out what is the AFR while it's doing that?

I live by Martin. He did the tune on the dyno.
Afrs are good and constant through the pull. Also I am spray I good amount of alcohol to compensate for running pump gas.

[mr.nismo.]

I live by Martin. He did the tune on the dyno.
Afrs are good and constant through the pull. Also I am spray I good amount of alcohol to compensate for running pump gas.

How is that monitored? When it cuts out does it backfire?

[Tom N]

How is that monitored? When it cuts out does it backfire?


How is what monitored?

When it cuts out it doesn't back fire. It's just like if right about full boost if you happen to lift you foot off the throttle then floored it again then lifted again the floored it again.

[mr.nismo.]

The alcohol injection

[Tom N]

The alcohol injection

I know at what psi it's cones on (6 psi ) and at what psi it is spraying full out (12 psi). It's a progressive system. I monitor afrs through a WB.
I don't see how the alcohol can be the problem. If it was the cut out would happen at 20psi also.

[mr.nismo.]

How is your boost managed?

[Tom N]

How is your boost managed?


Blitz ID spec r and also hooked up a turbo smart manual boost controller in its place to make sure my electric boost controller want causing a issue. No changes with either.

[mr.nismo.]

Are you watching what your boost gauge does? Assuming you have one

[Tom N]

Are you watching what your boost gauge does? Assuming you have one


The blitz will log boost with its play back feature. Ill have to actually look at what the boost does exactly. I assume it drops when the engine cuts out but haven't actually confirmed that.

[mr.nismo.]

What's the AFR in full boost?

[Tom N]

What's the AFR in full boost?

I've tested it from 10.5-11.5

[mr.nismo.]

If your afrs are fine the whole time then the only thing I could think of is that MBC might be fucking shit up past 21 psi for whatever reason. Check the boost logs

[Tom N]

If your afrs are fine the whole time then the only thing I could think of is that MBC might be fucking shit up past 21 psi for whatever reason. Check the boost logs

Only problem is it does this with my electric boost controller hooked as well as the manual boost controller hooked up.

[mr.nismo.]

Is the boost controller the only gauge you have? How are they setup? Is it vacuum source>EBC solenoid>MBC>waste gate? Or vacuum>mbC> Ebc solenoid> waste gate? Where is the ebc getting its vacuum reading from?

[Tom N]

No I have a boost gauge also.
I have hooked both the mbc and EBC getting vacuum from the intake manifold as well as the turbo compressor housing to see if one works better than the other as a vacuum source. Didn't notice a difference.
I did not use the EBC and mbc at the same time. I used them seperately to rule them put is a cause.

[mr.nismo.]

Ahh I see ok. I thought you were running them both at the same time so I just wanted to rule out an MBC issue. Is it only in wot when it happens? Does it do the same thing if you slowly let it hit full boost?

[Tom N]

Ahh I see ok. I thought you were running them both at the same time so I just wanted to rule out an MBC issue. Is it only in wot when it happens? Does it do the same thing if you slowly let it hit full boost?

I haven't tried to let it build up to 21+ psi with out going wot.

[mr.nismo.]

And it does the same thing? That would rule out tps. You said you have a z32 maf. So n62 maf right? Not n60? If you have an n60 that would explain all your issues

[Tom N]

And it does the same thing? That would rule out tps. You said you have a z32 maf. So n62 maf right? Not n60? If you have an n60 that would explain all your issues


Wasn't aware there was more than one Z32 maf. Ill double check that.

[Tom N]

It's a N62.

[mr.nismo.]

Z32 300zx vg30dett used n62 maf. Maxima vg30 used n60. That wouldn't keep up with what your pushing. What color is the sticker on your maf?

[mr.nismo.]

Ok then it should be able to handle it. What's your inter cooler setup? BOV?

[Tom N]

I don't know the brand inter cooler. It's a good size one with 3in inlet and outlet.
BOV is a greddy rs vented to atmosphere.

[mr.nismo.]

Will it go past 21 psi? Need to check those logs. If it won't make it past 21 psi my guess that's the breaking point where something is being forced open (like the BOV) which would def make you surge like you were stompin on and off the pedal

[Tom N]

It will go past 21 but not with out cutting out. I've had it go up to 24 but anything over 21 and it won't pull to 7500 with out cutting out around the time full boost hits.

[mr.nismo.]

It has to be in the tune then man. Something is changing in the combustion chamber that the ecu wasn't told how to handle. I can't think of anything else that would cause it to do that. If it blips then gets right back on it something's changed. Or The way your waste gate is being told to bleed off before opening up for 24 psi is too slow and surges stupid high maybe. The boost logs would help a lot. If it was the maf, injectors, etc it should have issues above 21 psi period. Not just at 21 and then be like" k guys let's piss him off real quick then get back to work" my guess is the waste gate isn't opening up fast enough and it's surging way fuckin high that your setup can't compensate for. Get the boost logs and itl tell you for sure

[Tom N]

So I really think the problem is that fuel is being cut for some reason. When it cuts out boost does drop but its going to as the engine stopped firing.

car has a z32 maf and the ecu is tuned for it. Why what in the ecu would tell the car to cut fuel? I was under the impression the S15 ecu didnt have a fuel cut feature?

Maybe its time to go to nistune.

[mr.nismo.]

Is the ecu tuned for above 21 psi? What psi were you running on the dyno?

[Tom N]

Is the ecu tuned for above 21 psi? What psi were you running on the dyno?


To my knowledge it is. Has a Z32 maf that will flow far more air volume than a 20g can produce.

[mr.nismo.]

Yeah but if it was tuned for 21 psi that might be the problem. Did you get dyno sheets?

[Tom N]

Yes it was tuned for 21 psi. Problem is it wont go past 21psi with out cutting out.

[mr.nismo.]

Well there you go it's the tune. If I boost my stock ecu at 20 psi shit goes boom right? Well instead of you going boom fuel gets cut as a failsafe.

[Tom N]

Well there you go it's the tune. If I boost my stock ecu at 20 psi shit goes boom right? Well instead of you going boom fuel gets cut as a failsafe.

Except i`m told the ecu is tuned not to fuel cut at all. So aggravated right now.

[mr.nismo.]

I wonder if it's something to do with your boost controller. Your positive it's cutting fuel? Or it's just boost dropping?

[Tom N]

I wonder if it's something to do with your boost controller. Your positive it's cutting fuel? Or it's just boost dropping?

I`m not positive. Just leaning that way. Ive tried 2 separate boost controllers. One of them being a manual one and car reacts the same regardless which one im using.
Its not studdering, when i hit full boost above 21psi the car just completely cuts out. I doesn't fade off or spudder it completely cuts out.

[mr.nismo.]

Oh duh that's right. It's down to the tuneing man. Unless someone with more experience can step in that's all I can say. It cuts out after 21 psi and your tuned for 21 psi

[Tom N]

Its not tuned for 21psi. The tune should be good for a lot more airflow than the 21psi im stuck at.

[mr.nismo.]

Earlier you said it cuts out for a second then picks right back up?

[Tom N]

Earlier you said it cuts out for a second then picks right back up?

It has cut out for a second then hit again then cut back out then hit again and then continue pulling fine to 7500.

[mr.nismo.]

Sounds like the tune still. Dead spots. You have things called "cells" that you enter numbers into. Somtimes they could be not quite adjusted right. It needs to get back on the dyno. You should be you want to be able to boost 24 psi you should be running that on the dyno to eliminate any possible problems

[RedtopTech]

Do you have any method of dagta logging the "TP load scale?" It sounds like you are reaching load cut. Find out what Enthalpy set the Loadcut to.

[Tom N]

Do you have any method of dagta logging the "TP load scale?" It sounds like you are reaching load cut. Find out what Enthalpy set the Loadcut to.


It's set to max value. Pretty sure TTP is getting maxed out and the injectors are getting shit down. Going to put bigger injectors and retune them see what happens.