Boost leak or other?

[joesansone17]

I have a 1997 GS-T Spyder. When I drive regular, I get good boost and I can shift at 4500rpm. The more I get on the gas the car begins to stumble and backfires at about 2500 rpm. Basically it feels like the car wants to shut down. Ive gotten some suggestions of boost leak and some of a fuel pump. The guy that owned the car before me did a boost leak test on the intercooler piping but found nothing. But who else had this problem and what did you do? thanks.

Some Facts of the car:

86000k
Greddy uicp and licp
Hks ssqv (vented)
hks 3in downpipe
3in testpipe
greddy SP catback
K&N filter and aluminum intake

 

[streetlegends]

I have a 1997 GS-T Spyder. When I drive regular, I get good boost and I can shift at 4500rpm. The more I get on the gas the car begins to stumble and backfires at about 2500 rpm. Basically it feels like the car wants to shut down. Ive gotten some suggestions of boost leak and some of a fuel pump. The guy that owned the car before me did a boost leak test on the intercooler piping but found nothing. But who else had this problem and what did you do? thanks.

Some Facts of the car:

86000k
Greddy uicp and licp
Hks ssqv (vented)
hks 3in downpipe
3in testpipe
greddy SP catback
K&N filter and aluminum intake

This is what it sounds like to me, that you are not getting enough fuel when you are going into high boost. Check your fmu, and if you have a data logger and you check program your fuels. A matter of fact do you have a Air/Fuel ration gauge??? That will help you alot too see what the mix is under high boost. I hope this helps you out and I am pretty sure that will an expert that will you give you info as well.

 

[hottboost]

If you are venting to the atmos. then that is probally your problem. You have to do the gm mas conv. if you want to vent to the atmos. Other wise YOU HAVE TO RE CIRCULATE IN ORDER FOR THE CAR TO RUN PROPER. THE ECU HAS ALREADY ACCOUNTED FOR THE AIR RE CIRCULATING SO IF YOU VENT THE ECU DOESNT KNOW THAT, THERFOR YOU ARE GETTING A RICH MIXTURE. Hope that helps. Get a Greedy type s or 1G bov.

 

[kenamond]

If you are venting to the atmos. then that is probally your problem. You have to do the gm mas conv. if you want to vent to the atmos. Other wise YOU HAVE TO RE CIRCULATE IN ORDER FOR THE CAR TO RUN PROPER. THE ECU HAS ALREADY ACCOUNTED FOR THE AIR RE CIRCULATING SO IF YOU VENT THE ECU DOESNT KNOW THAT, THERFOR YOU ARE GETTING A RICH MIXTURE. Hope that helps. Get a Greedy type s or 1G bov.

The venting issue wouldn't show up if he stays on the throttle. When you shift or let off the gas such that the IM sees vaccuum, it opens the BOV, and at that point, the vented air will have been metered by the ECU. The result is that you'll have rough engine performance after shifts or letting off the gas and getting back on it.

If you stay on the gas, the BOV will be closed, and all of the metered air will make it to the engine, and you'll be running properly.

Nevertheless, it isn't a good idea to vent if you're using the stock MAS, but I don't think that this is your only problem.

If you have a logger, do what streetlegends recommended and check things out. If it's fuel cut, you'll see high injector duty cycle. This could be due to a boost leak, low fuel pressure (bad pump or fuel pressure regulation) or probably other things.

Without more information, we're just guessing.

I think you should be doing boost leak tests on a regular basis anyway, so maybe you should bite the bullet, get/make a tester, and see what happens. Just because it used to not leak doesn't mean that it hasn't developed a leak since.

And if you don't have a logger, you should get one.

 

[joesansone17]

It hooked up an after market boost gauge and Im running 15 lbs of boost. Tha t could make fuel cut right?

 

[president95]

http://www.dsmtuners.com/forums/showthread.php?t=186971.

Do a boost leak test. If the problem persists, than we can at least eliminate that aspect. Although venting isnt going to be affecting your car while on the throttle, it is still an issuing worth adressing. (recirculate it)

 

[kenamond]

It hooked up an after market boost gauge and Im running 15 lbs of boost. Tha t could make fuel cut right?

With your mods, it might be fuel cut. A logger will tell you if its fuel cut. You really should have a logger before you start pushing the boost on your stock fuel system, or you're risking your motor.

Try turning the boost down and see if the problem goes away. Find out what boost it can run with. If you still have a problem (problem doesn't go away at 11psi boost), it may be something other than your increased airflow rate overrunning your fuel system.

 

[diablos991]

Also, have you checked your spark plug gap lately?

 

[kenamond]

Also, have you checked your spark plug gap lately?

Question on this (trying to learn something), and I don't think it's thread-hijacking, as it should explain why you're asking him to check his gaps :

Based on my understanding of spark plugs, the more you compress the air-fuel charge in the cylinder (higher compression ratio and/or higher boost), the more resistance that charge has to conducting electricity. There's the normal compression due to the compression ratio, but then the boost multiplies this, more or less. So if your plugs are gapped too large, then you may be fine at lower boost, but at higher boost, you might reach the limit where the spark can't jump anymore and the cylinders stop firing causing a fuel-cut-like situation. Because the charge wasn't burned in the cylinder (spark never happened), fuel ends up in the exhaust which can ignite causing backfires. Is this the issue with plug gap in this situation? Also, if you move to higher boost, do you want to decrease the gap on your plugs?

Thanks!

 

[diablos991]

That makes sense to me. I know that when they are gapped too widely they won't spark when under boost, causing a fuel-cut type sensation. This has happened to me before.

I am not sure about decreasing your gap when under high boost situations though.

 

[oldman]

If you stay on the gas, the BOV will be closed, and all of the metered air will make it to the engine, and you'll be running properly.

Not if the mbc is hooked up to the BOV line.

With your mods, it might be fuel cut. A logger will tell you if its fuel cut. You really should have a logger before you start pushing the boost on your stock fuel system, or you're risking your motor.

Hitting fuel cut has little to do with his fuel system, fuel cut is a function to gaurd against run a way boost, not fuel starvation and it's triggered by air count. Think of it like the gas pedal which controls air, not fuel.

 

[skinnykenny84]

hey oldman, this thread looks mighty familiar huh??

did you give up on me?? http://www.dsmtuners.com/forums/showthread.php?t=220655

 

[kenamond]

Not if the mbc is hooked up to the BOV line.


Hitting fuel cut has little to do with his fuel system, fuel cut is a function to gaurd against run a way boost, not fuel starvation and it's triggered by air count. Think of it like the gas pedal which controls air, not fuel.

I thought fuel cut was triggered by injector duty cycle.

 

[skinnykenny84]

I thought fuel cut was triggered by injector duty cycle.

well the only aswere I get is boost leak (wich I am aware of) but there has to be other things that can cause fuel cut.

 

[Spoolio]

well like ive been mentioning to some other guys on here, ive had a problem where i thought my car had a boost leak, i was gettin a real bad studdering and popping it wouldnt do anything above 5psi, comes to find out my timing was wayy off, some of you guys have to start telling people to check thier timing, this is another reason why some people think they have a boost leak, they get a boost leak test and come up with nothing., im not saying your timing is off, also check the voltage on your battery going out to your fuel pump, (check with a voltmeter) also check your plugs see what color they are, i was losing boost my plugs were white, i had a blown turbo housing gasket, made my car run lean and cut out at 9psi. just some tips for ya

 

[kenamond]

well like ive been mentioning to some other guys on here, ive had a problem where i thought my car had a boost leak, i was gettin a real bad studdering and popping it wouldnt do anything above 5psi, comes to find out my timing was wayy off, some of you guys have to start telling people to check thier timing, this is another reason why some people think they have a boost leak, they get a boost leak test and come up with nothing., im not saying your timing is off, also check the voltage on your battery going out to your fuel pump, (check with a voltmeter) also check your plugs see what color they are, i was losing boost my plugs were white, i had a blown turbo housing gasket, made my car run lean and cut out at 9psi. just some tips for ya

You can't adjust timing on a 2g with stock ECU/ignition and no DSMLink, right?

 

[Siral3x]

I have a 1997 GS-T Spyder. When I drive regular, I get good boost and I can shift at 4500rpm. The more I get on the gas the car begins to stumble and backfires at about 2500 rpm. Basically it feels like the car wants to shut down. Ive gotten some suggestions of boost leak and some of a fuel pump. The guy that owned the car before me did a boost leak test on the intercooler piping but found nothing. But who else had this problem and what did you do? thanks.

Some Facts of the car:

86000k
Greddy uicp and licp
Hks ssqv (vented)
hks 3in downpipe
3in testpipe
greddy SP catback
K&N filter and aluminum intake

Since your car has 86k I'm assuming you changed the original timing belt.
I had a simillar problem.
You need too chk:
1.Timing belt(they are notorious on jumping 'teeth')
2.Spark plugs and wires.!.a lot of ppl omit the wires!
3.Boost leak test;
4.turbo for shaft play;
5.alternator and battery voltage;
You get the pic...chk the basic stuff out, then you go from there.
Get the results ,and keep us posted.
My problem was the timing belt..jumped big time.

 

[oldman]

did you give up on me?? http://www.dsmtuners.com/forums/showthread.php?t=220655

Yes I did for several reasons.

1. When ever I asked how many psi was shown on the boost gauge in leak test threads, I always have hard time believing when the answer comes back "20PSI" which is about 80% of the time, sounds to me like the person is just repeating what is being passed around on the forum. I have done many many many leak tests for many different cars, not ones did I ever get exactly 20psi. In your case, I also find it hard to believe that with the BISS screw leaking, you're still able to achieve 20psi unless you set your large compressor to 100psi.

2. You stated that you understood "fuel cut" and what causes it in your other thread but you continue to ask questions in both threads that tells me otherwise.

well the only aswere I get is boost leak (wich I am aware of) but there has to be other things that can cause fuel cut.

Bottom line, fuel cut is triggered by "air flow reading exceeding the pre-programed value in the ECU to guard against a faulty wastegate resulting in infinite boost". Let's go down the list of things that can cause high air count.

1. Defective ECU that is not able to received MAF readings correctly.

2. Defective MAF sending wrong signal to the ECU.

3. Defective wastegate causing infinite boost.

4. Boost creep.

5. Last and the most probable, boost leaks causing high air count due to losing metered air.

I thought fuel cut was triggered by injector duty cycle.

Nope, if that were true, there would be no need to log and tune, we can all just bump up the boost until we hit fuel cut. My old 16G setup use to creep up to about 24psi where I hit fuel cut, does this mean my stock fuel system will support a 16G up to 24psi? I think not. I think all the confussion surrounding this subject comes from the term "fuel cut", the proper term should've been "AIR CUT".

well like ive been mentioning to some other guys on here, ive had a problem where i thought my car had a boost leak, i was gettin a real bad studdering and popping it wouldnt do anything above 5psi, comes to find out my timing was wayy off, some of you guys have to start telling people to check thier timing, this is another reason why some people think they have a boost leak, they get a boost leak test and come up with nothing., im not saying your timing is off, also check the voltage on your battery going out to your fuel pump, (check with a voltmeter) also check your plugs see what color they are, i was losing boost my plugs were white, i had a blown turbo housing gasket, made my car run lean and cut out at 9psi. just some tips for ya

We are talking about fuel cut here, not "real bad studdering and popping", they are two different things. Problems with your ignition, fuel or lack of compression (like in your case) will cause bogging and lost of power but only air count can trigger "fuel cut".

 

[kenamond]

Bottom line, fuel cut is triggered by "air flow reading exceeding the pre-programed value in the ECU to guard against a faulty wastegate resulting in infinite boost". Let's go down the list of things that can cause high air count.

1. Defective ECU that is not able to received MAF readings correctly.

2. Defective MAF sending wrong signal to the ECU.

3. Defective wastegate causing infinite boost.

4. Boost creep.

5. Last and the most probable, boost leaks causing high air count due to losing metered air.


Nope, if that were true, there would be no need to log and tune, we can all just bump up the boost until we hit fuel cut. My old 16G setup use to creep up to about 24psi where I hit fuel cut, does this mean my stock fuel system will support a 16G up to 24psi? I think not. I think all the confussion surrounding this subject comes from the term "fuel cut", the proper term should've been "AIR CUT".

Awesome! Thanks for the info. I've asked the following in other threads to no avail: Where can I find a document that describes the 2g ECU? I'd like to know what it's doing, because it seems to be important in order to mod your car without blowing something up (e.g. fuel cut).

 

[skinnykenny84]

Yes I did for several reasons.

1. When ever I asked how many psi was shown on the boost gauge in leak test threads, I always have hard time believing when the answer comes back "20PSI" which is about 80% of the time, sounds to me like the person is just repeating what is being passed around on the forum. I have done many many many leak tests for many different cars, not ones did I ever get exactly 20psi. In your case, I also find it hard to believe that with the BISS screw leaking, you're still able to achieve 20psi unless you set your large compressor to 100psi.

Well, Bruce I meant that I run it up to 20psi and then start looking for leaks. And yes the biss screw is leaking VERY slightly but not fast enough to where I cant get 20psi into the system. Of course Im using a huge compressor at my grandfathers tire shop! .

So you ARE saying I could have a defective MAF?

Would that explain why it only fuel (air) cuts at a certain boost level? And if I lower the boost 1-2psi it does not fuel cut? I mean if it were a boost leak wouldnt it fuel cut at 13 as much as it would at 15psi?? I know, I know Bare with me here Bruce!

 

[skinnykenny84]

If I ever make it to a dsm meet and see oldman Bruce this is what hes gonna do to me... ..........

 

[oldman]

Would that explain why it only fuel (air) cuts at a certain boost level? And if I lower the boost 1-2psi it does not fuel cut? I mean if it were a boost leak wouldnt it fuel cut at 13 as much as it would at 15psi?? I know, I know Bare with me here Bruce!

First of all, you need to determine if you're truly hitting fuel cut, many mistaken bogging with fuel cut.

Secondly, 15psi = more air flow than 13psi which means you're closer to fuel cutting @ 15psi than @ 13psi. Let's pretend we are talking about a bouncer at a night club holding a counter at the front door representing the MAF and PSI (pounds per square inch) replaced by psf (persons per square feet), Which do you think will yield a higher body count at the door, 3 psf or 2 psf?

If memory serves, you were hitting fuel cut at 9psi in the other thread, you were swearing up and down about how you had no leaks when everyone told you to leak test. You then found leaks, fixed them and is now up to 15psi and again, you're saying you have no leaks while knowing the BISS is leaking. Are you sure you had someone in your car reading the boost gauge while you pump pressure air into the system and the 20psi you're refering to indeed came from the boost gauge, not the regulator on the compressor?

 

[skinnykenny84]

I have a spare boost gauge for stuff like this that I connect and leave under the hood so I can see whats going on. And you lost me on the night club analogy ;-)

 

[oldman]

I have a spare boost gauge for stuff like this that I connect and leave under the hood so I can see whats going on. And you lost me on the night club analogy ;-)

Which means you still don't fully understand what triggers fuel cut. If you understand that fuel cut is triggered by your MAF reading, why would you not understand that you're hitting fuel cut at 15psi (higher maf reading) but not 13psi (lower MAF reading).

 

[laserspeeddemon]

Do a tune up, sounds like either A) you are getting too much fuel or B) not enough spark.

It really sounds like the ignition is missing. Probably because you fouled them due to the vented BOV, go with NGK BPR7ES plugs gapped to about 0.026". Magnecore 8.5mm wires, etc.

Its actually hard to determine your problem without knowing if you are talking about a stutter or true fuel cut.