240koukiSX

Ok guys I'd really appreciate some help on this. The car is a 97 kouki with an S15 SR. I just got it tuned and the car has run great and makes really good power. The problem is that sometimes right at 5K rpms it'll stop making power and act like it's hitting a rev limiter. The rpms will drop and it'll make a lot of power but then hit 5k-5500 and lose it again. It only does it if you go from lower rpms to pegging it at WOT. It drives perfect under all other driving conditions and only cuts out sometimes not every time. I'm trying to figure out where to start and what possibilities I can rule out so I don't waste money. As always any help is super appreciated and thanks a lot!

1nasty240sx

I actually had the same problem happen to my car with an sr20det literally like two weeks ago. I changed two things which was my stock fuel pressure regulator and my timing was all the way retarded so I advanced it to where it should be and it hasn't done it since. Hope that helps!

240koukiSX

Hey man thanks a lot! I'm gonna try it but do you mind telling me what fuel pressure regulator you upgraded to?

Croustibat

It has mostly nothing to do with the fpr. That fpr problem strangely enough happens only to zilvia members, everywhere else in the world, oem FPRs are fine on the SR20s.

Anyway i'd strongly suggest to bring it back to the tuner and have a little chat with him.

Because either you are extremely unlucky, and your fuel pump gave up after he was done mapping, or he "mapped" without using an AFR gauge and sensor.

Depending on the boost you are using, gapping the plugs a little smaller could help.

But clearly, if you can rev fully except on WOT, that is your fuel pump dying (and your engine running ultra lean)

240koukiSX

It would be just my luck that my damn fuel pump craps out after I get my car where I want it. The tuner definitely used an AFR gauge and sensor. The dyno sheets also show what the AFR was from idle to redline. I'm thinking im just going to go ahead and change my fuel pump, put a new fuel filter, and just go ahead and get a new FPR :/ then hopefully all my troubles will be solved

Croustibat

Try lowering your plug gap a bit first. It is free.

If your problem happens "most of the time but not always", chances are the plug gap is a bit too big (and of course, it could be both)

Also, it is much better to change things one at a time. Otherwise you dont know what was the problem (or what caused a new problem)

Check the voltage at the pump too. The oem pump wiring is very thin and sometimes pump voltage drops to 10ish V (instead of 14).

I happen to had a mix of these problems, to get correct AFRs i was at 100% duty on 1000cc, with 1.2bar boost which was not right at all. Changing the wiring allowed a 10% duty drop to get the same AFRs, which was good but not enough.

Then we plumbed a fuel pressure gauge and i saw my pressure go down when reaching boost ... new pump allowed the duty to drop to a normal 65/70% duty.

Funny thing too; with big injectors like these, a Z32 fuel filter will create bubbles, that can go through the injectors. Which dont really like that ... i had to change the filter to a metal one.

But i am still running an SR20 oem FPR, with 1000ccs and an uprated fuel pump ... nothing these cant handle.

I really dont recommend changing the FPR, as they mostly dont have the same response (changing it means updating the fuel map... )

240koukiSX

Cool man, I'll try it when I get off work. What gap do you recommend? I'm running 15lbs of boost with an almost stock motor. Only upgrades are bolt ons.

Croustibat

With 15lbs of boost you should be ok at .30. That should be your normal gap. If you know your coils are aging, you can reduce it a bit to compensate.
I had to go .25 when i reached 18psi on that turbo, and i sometimes boost up to 23psi now without problems. But i run e85 so have no det or temp problem. You would start to have issues doing this with regular fuel.

As far as the pump goes, get a walbro (a real one) GSS341-HP (High Pressure) is the one you want, it is nearly bolt on.

Dont forget to buy a new Oring from nissan for the fuel tank, because you wont be able to put back the fuel pump assembly with the previous one (it expands a lot. You could also cut it but ... meh.). cost is around 12$ .

240koukiSX

Thanks for pointing me in the right direction man. I'm going to try this and see if it helps!

inopsey

how old is your fuel pump? if its original to the car change it out. had the same problem with a 110k mile fuel pump on my 97.

240koukiSX

I have no idea if it's the original one or not in there to be honest. If the gap thing doesn't work that's what I'm gonna buy next

ultimateirving

Could a bad TPS cause an intermittent Flat spot in his RPM range.

I too feel it is fuel related, especially if he is on oem fuel pump.

just trying to throw out some other ideas

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one-sil-via13

I'd say fuel pump, friend had the exact same problem at the same rpm range....changed the fuel pump and voila! Don't think adjusting your gap will do much.
Edit: are you running a stock turbo as well?

240koukiSX

What fuel pump did he have in his car? And what did he put in? And yes its the stock turbo

Kingtal0n

sorry if I missed it but, what computer was used to tune it? what turbo? How many PSI of boost?

and please dont say SAFC + 550's + S15 turbo @ 18psi

__________________
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https://tinyurl.com/turbo240

240koukiSX

Na man you missed a lot haha. Apexi neo with almost stock S15 SR (just bolt ons) running 15lbs of boost.

Kingtal0n

So it is a SAFC. What size injectors you forget to add that.

And BTW your problem is most likely a boost (fuel) cut. turn the boost down to around 13 PSI and remove the SAFC to cure the problem. Reinstall the OEM S15 injectors.

Once the AFC is removed you may be able to go back to 15psi but I would advise against it for the longevity of the turbocharger and the engine.
In the past I have seen those engines detonate (from running lean) without the owner knowing and it will eat up the head and deck and trash the engine.

An SAFC is not officially a "tuning" device either.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

240koukiSX

It has the stock injectors already. I read your post and drove it till it fuel cut and when it did I noticed that it was at 17lbs!! I have an adjustable actuator in it. Maybe I need to adjust it down more first before I go and get a new fuel system upgrade... Any thoughts?

Croustibat

Ah, i missed that.

Bin the SAFC. That is not a tune.

SAFC works by tricking your ECU , it changes the MAF signal (and probably the temp signal too). It leads to having the ECU read another value in the fuel table ... which would be great, if it was the only thing it did, and the only thing to be done.

The problem is you need to change timing correctly, and an SAFC cant do that, because it has no way of knowing the timing .

The biggest concern is that by altering the MAF signal, it also forces the ECU to go and read another value in the timing table. Usually one that you dont want at all. Unfortunately, no (affordable) sensor will tell your timing is no good...

Bin the SAFC, get a real tune. If you know someone who has a nistune, get him to map your car by installing his ECU in yours. Then you can burn the resulting program in a couple of EPROMs and install them in the car.

Depending on his ability, It should also reward you with a lot more HPs mid and top range (timing makes power, not AFRs). I'd say 10 to 20...

240koukiSX

The timing is right on. I asked the tuner and he said he had to adjust it and the cams while it was on the dyno because they were off. He told me its running like it should and it made great power. 280rwhp and 280rwtq. I really don't want to get rid of the neo if it's not messing anything up... What else should I check to see if the neo is affecting it negatively?

Croustibat

The timing is off, because your tuner cant adjust it with an SAFC. The SAFC changes the timing everytime it changes the AFR and there is no real way to predict if it is going to be good or bad (although bad comes to mind as there is no way to set it).

What your tuner did was set the base timing correctly.

If you have a boost controler, i suggest you set the actuator arm to 10-11lbs, then use the boost controler to get a stable pressure. With just the actuator, your boost pressure will change depending on temperature and elevation - and timing and AFR (leaner = hotter, retarded timing = hotter, both making more boost). A boost controler is able to account for these and give constant boost.

If you are hitting 17-18lbs then it may be the spark plugs getting blown, so lower the plug gap a bit and get the new fuel pump.

Until you change your fuel pump though, do NOT boost the car, ever. You will run lean every time you do, and this kills an engine quickly.

Kingtal0n

#1 How do you know the timing is "right on"? Since there is no display, and no way to adjust it, that is impossible.

#2 The SAFC can not adjust timing. Therefore, you tuner is a liar? Unless you have ANOTHER piggy back capable of adjusting timing, and even THEN you have no clue where it "begins".

#3 the CAMS? You mean that you PULLED the valvecover and installed adjustable camshaft gears and while on the dyno you repeatedly pulled the valvecover and made small incremental adjustments to the camshafts? Doubt it. Plus, that is not a "bolt on" modification and you should have mentioned it much earlier. Remove the adjustable camshaft gears if you are using them.

#4 The GT28 from the S15 sr20det is best used around 13PSI for longevity purposes

#5 anything over 15psi and you risk damaging the engine (with oem injectors/turbo). It will pit the head and deck and make the engine UN-rebuilable, that is, trash the engine permanently. I have seen it happen enough to know. That is why the engine is fuel cutting on you; it is trying to prevent you from doing permanent damage.

If you have OEM injectors and OEM maf and OEM ecu and OEM turbo there is NO REASON to use any king of piggyback computer such an SAFC for any reason whatsoever. You spent $$$ on it for NO Reason and the "tuner" did absolutely nothing.

__________________
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https://tinyurl.com/turbo240

240koukiSX

The timing was off and the guy that tuned it fixed it. I know this because he told me and he's one of, if not the best tuners for sr's around. He didn't use the neo to adjust it. And no I don't have adjustable cams, I meant the cam angle sensor (I'm not the best at talking car tech, this is my first venture out into this world so I got a lot of learning to do lol) and as far as the life of the turbocharger I think 15lbs is a good mix between power and longevity. I'm thinking I might have a bad actuator or something since it hit 17lbs. I do have stock injectors, ecu and turbo but I have a z32 MAF. There's no way I spent money for no reason. My car feels amazing now all the way through the rpm range and it has so much more power. The tune got my car right where I want it. A little hiccup like this isn't going to discourage me from what all I had done man. I can feel that my car is so much better and is much happier. After I fix the occasional fuel cut I'm going to be 100% satisfied. I just gotta figure out what's causing it. I really appreciate your input so please keep it coming**

Kingtal0n

There is nothing more to say, you found your problem. turn the boost down.

and get rid of the Z32 maf there is no reason to use it. Or the SAFC, which makes your situation even worse.
I will not keep repeating myself. The engine comes tuned for 15psi without a SAFC or MAF required; those are mods for larger turbochargers, and a SAFC is more of a bandaid for cheap people that dont like their engines when using larger injectors. You dont even have larger injectors, therefore, a SAFC is completely pointless.

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https://tinyurl.com/turbo240

240koukiSX

Well hey man I appreciate your help a lot but nobody is forcing you to tell me anything. It seems like your getting a bit of an attitude or something... If I'm mistaken I'm sorry but that's how it came off. If I remove all that stuff and just crank up the boost will my car make the same power?

Kingtal0n

Drivability and fuel economy will increase and everything else will be the same, so yes it will make the same exact power and it will still fuel cut in the same exact spot, depending upon how much fuel was added with SAFC it may not fuel cut as early but instead will run leaner. Which is why you need to reduce the boost pressure.

To help you understand here is an example:
At 13psi of boost the maf may reach 4.4volts
At 15psi of boost the maf may reach 4.9volts
At 17psi of boost the maf may reach 5.1volts and FUEL CUT.

If you now install a SAFC and increase the "fuel" adjustment for 15psi, you will trick the ECU into thinking that there is actually 17psi of boost instead, and it will FUEL cut sooner because maf VOLTAGE input to the ECU is now higher.

A more appropriate way to eliminate any 12.2:1 or 12.8:1 air fuel ratios during 15psi of boost (possibly unsafe for an S15 turbo on the bleeding edge) is to bump the fuel pressure 5-8psi.

IMO that turbocharger will not last long at 15psi of boost.

__________________
5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

jr_ss

AFR's aren't the whole story. Timing plays a huge role in tuning as well. Since you can't adjust that, you only have half the equation.

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Croustibat

The boost controler is used to keep the wastegate shut longer, and then manage when / how it opens. It results in faster spool, and of course manageable boost. What is even more important is they usually have a warning setting that will open the wastegate and dump a variable %age of boost if you reach a set pressure. This prevents running 18lbs when you set it to 12.

If the AFR gauge says you are good and it is working fine, then you are not running lean.

You DO have an AFR gauge in the car ? What does it read off boost/ spooling / on boost ? What other gauge do you have ?

Did you have your EcU remapped or not ? Or are you just using an SAFC ?
As you are not remapped you could just be hitting the ecu load protection. It cuts fuel at a preset TP value. That value goes up, then down as your VE decrease. It must be peaking around 5/6k and is boost dependent... if you are right next to its limit, a little overboost or lower temp and there it goes, it cuts.



That.

AFR says how much fuel you burn. You want lean at part throttle, stoeich on some parts of the map, and 12 at WOT, basically. Go leaner and you get less power, higher temps. AFRs dont give power, they somewhat prevent you from accessing it. Setting AFRs is very easy, you just need a gauge and sensor

What makes power is timing, and this one is a bitch to set.

Set it wrong and it makes holes in your pistons (too advanced) or gives too little power and too much heat (too retarded, which is sometimes used to spool turbos faster, run retarded just when the turbo starts spooling helps).