R32 GTR Drivability issue

[HellBent]

I'm having trouble with my R32 GTR. Under part throttle, (maintaining speed) the car seems to surge or hunt. It is noticeable any time I try to maintain a set speed in any gear.

I recall having a similar problem in my mass air flow sensor equiped Mustangs. Sometimes it was a vaccum leak other times it was an EGR valve issue.

Although I heard that blow-off valves that vent to atmosphere can cause this issue as well. Check my car today, and sure enough, there are a pair of HKS BOVs that vent to atmosphere. Cool sound! But is this giving me part throttle drivability issues?

Thanks,

AL

[SkylineUSA]

Al,

Try cleaning the MAF, I just worked on one last week that was doing the same thing. Shot some carb cleaner on the elements, car drove solid after the cleaning.

Tony

[SkylineUSA]

Oops, I posted before I read about the BOV. I do not know why people change those out, unless they are pushing well over 500hp, the stock ones are good. I would go back to stock, if was my car

[HellBent]

Originally Posted by SkylineUSA

Oops, I posted before I read about the BOV. I do not know why people change those out, unless they are pushing well over 500hp, the stock ones are good. I would go back to stock, if was my car

I wish I knew more about turbo cars...

The BOVs I have are HKS units that vent to atmosphere. Since my car is also equiped with mass air sensors, I believe the air lost when the BOVs operate is at the heart of the problem.

From my experience playing with my mass air equiped Mustangs, any loss of measured air resulted in a drivability issue. The computer sees the air that is measured but does not get all of it. This most likely results in an overly rich condition when measured air is lost to the atmosphere through the BOVs. The O2 sensor detects the rich condition and reduces injector pulse width. The car then goes lean as the BOVs close. I believe this causes the car to hunt abck and forth to get back to a normal A/F mixture.

It could also be a vacuum leak somewhere... just wish I had more time to check it myself. That engine bay is pretty cramped though. I've also heard that leaking BOVs can be a problem as well.

Any thoughts?

-AL

[Gtr2.7L]

Do you feel it? Or hear it?

Part throttle, especially uphill, tends to bring on boost shuffle in these cars. The turbines seem to fight each other.

When you experience it, have you ever let go of the throttle, then give it around 3/4 throttle? Does it go away? If you go straight to 3/4 throttle in this case, it will get worse. When I ran the car at Laguna, it was fine until after turn 6 where I would sometimes float the corner rather than brake and accelerate. Then as I went up the hill to the corkscrew, I would get this shuffle unless I completely dropped engine load and stomped on the gas again.

HKS makes a set of manifolds that have a cross pipe between them that seems to solve the problem. I haven't gotten them because I'm cheap. Sean Morris says they do a pretty good job though. Sometimes he wavers between this being a turbine balance problem and a BOV problem.

For reference, I have the stockers and have "this" problem also.

When the flow meters begin to go...your car will actually "bobble". The car will make almost no power, and if you let go of the gas, will stall.

Originally Posted by HellBent

I wish I knew more about turbo cars...

The BOVs I have are HKS units that vent to atmosphere. Since my car is also equiped with mass air sensors, I believe the air lost when the BOVs operate is at the heart of the problem.

From my experience playing with my mass air equiped Mustangs, any loss of measured air resulted in a drivability issue. The computer sees the air that is measured but does not get all of it. This most likely results in an overly rich condition when measured air is lost to the atmosphere through the BOVs. The O2 sensor detects the rich condition and reduces injector pulse width. The car then goes lean as the BOVs close. I believe this causes the car to hunt abck and forth to get back to a normal A/F mixture.

It could also be a vacuum leak somewhere... just wish I had more time to check it myself. That engine bay is pretty cramped though. I've also heard that leaking BOVs can be a problem as well.

Any thoughts?

-AL

[SkylineUSA]

I have delt with MAF problems on a few GTRs, and I can say, they do not all act the same.

Clean your MAFs, and then go from there.

[Gtr2.7L]

Maybe I should have quantified that with "both"....

Originally Posted by SkylineUSA

I have delt with MAF problems on a few GTRs, and I can say, they do not all act the same.

Clean your MAFs, and then go from there.

[HellBent]

Thanks for the input guys.

I will check to make sure everything around the BOV is tight. The car is going in to Nissan for the timing belt and waterpump change. They said they will look it over good.

Hopefully they will come up with an answer.

If not I'll be crawlin' over it next weekend.

-AL

[HellBent]

Finally got the low down.

As I suspected it is caused by air that is measured by the computer but lost through the Blow Off Valve (BOV). The computer is basically trying to figure out why it's sensors aren't lining up as they should, causing the computer to guess and re-adjust. (This is why the stock set-up recirculates the vented air back to the inlet of the turbos.)

A knowledgeable local tuner recommends against BOVs that vent to atmosphere while using a stock computer. So the ding dong (previous owner) that put it on my car did it for the cool sound effect. Got to wonder about these people...

-AL

[RazorGTR]

Originally Posted by HellBent

Finally got the low down.

As I suspected it is caused by air that is measured by the computer but lost through the Blow Off Valve (BOV). The computer is basically trying to figure out why it's sensors aren't lining up as they should, causing the computer to guess and re-adjust. (This is why the stock set-up recirculates the vented air back to the inlet of the turbos.)

A knowledgeable local tuner recommends against BOVs that vent to atmosphere while using a stock computer. So the ding dong (previous owner) that put it on my car did it for the cool sound effect. Got to wonder about these people...

-AL

Well sorry he doesn't sound very knowledgable, at least about these cars. While your problem is more than likely caused by "leaking BOV's" not one(s) that vent to atmosphere.

My GTR had a Trust Type R that vented to atmosphere and I never had any issues such as you discribed. The car ran great except for a coil pack issue I chased for a while.

Changing the factory bov's to atmospherically venting one(s) will only give your a rich condition upon letting off the gas under boost. This isn't a bad thing and acutally does help cool the crowns of the pistons off a smidge or if you will helps when you quick shift to have a shot of gas ready to go upon applying the throttle again.

I'd like to know which sensors aren't lining up? You've got your MAF sensors which have already metered the air coming in. Your MAP sensor which only reads mainfold air pressure. Other than that the only other sensor is in the plenum which is a temp sensor.

There is another thing to watch which will also show up as leaking bov. That is the pair of intake mainfold gaskets. They get brittle over time and actually break off, causing a leak. The gaskets are located between the plenum and throttle bodies, and throttle bodies and head. Now this is a bad thing as it also sucks air into the system while crusing causing an additional lean condition.

[RazorGTR]

Originally Posted by Gtr2.7L

Do you feel it? Or hear it?

Part throttle, especially uphill, tends to bring on boost shuffle in these cars. The turbines seem to fight each other.

When you experience it, have you ever let go of the throttle, then give it around 3/4 throttle? Does it go away? If you go straight to 3/4 throttle in this case, it will get worse. When I ran the car at Laguna, it was fine until after turn 6 where I would sometimes float the corner rather than brake and accelerate. Then as I went up the hill to the corkscrew, I would get this shuffle unless I completely dropped engine load and stomped on the gas again.

HKS makes a set of manifolds that have a cross pipe between them that seems to solve the problem. I haven't gotten them because I'm cheap. Sean Morris says they do a pretty good job though. Sometimes he wavers between this being a turbine balance problem and a BOV problem.

For reference, I have the stockers and have "this" problem also.

When the flow meters begin to go...your car will actually "bobble". The car will make almost no power, and if you let go of the gas, will stall.

Sounds like you have one weak turbo.

The only times I've seen this happen is by one of two things.

1. One weak turbo, or the wastegate of one of turbos isn't working properly. Common when turbos are getting tired. A good way to tell is when the engine and turbos are cold and you are gentely accelerating you'll hear a bit of a whine or groan. You'll find you've got excessive play in the bearings or shaft of one of your turbo(s).

2. Unballanced turbo(s). Unballanced being the turbine wheel and compressor wheel are not matched up. In other words some yahoo who thinks he knows what he is doing builds a turbo using wheels that are not matched for eachother.
Or
Had the turbos reconditioned and the housing aren't machined the same.
Or
Exhuast housing and compressor housings don't match up.

Hybread turbos are a recipet for disaster.

[HellBent]

Razor,

Thanks for the reply. This is a distinct possibility. The car is 14 years old an could probably use an engine refresh. It could very likely a leaking BOV or gasket somewhere. I've also heard that a bad vaccuum hose leak can also cause the same problem.

The sensor issue I was talking about is the MAF sensor vs. throttle position vs. O2 sensor. If the MAF sensor measures a specfic mass of air yet more air is getting into the system, then this causes the computer air/fuel maps to be off. I ran into this while tuning Mustangs.

Basically, the MAF thinks it has "x" amount of air, and the TPS sensor also coroberates this with a particular throttle psoition. However, the O2 sensor picks up on a lean condition. The computer tries to adjust, but then the leak stops, and the car is now too rich. The O2 sensor tells the computer things are now to rich. This causes hunting of the idle and surging while driving.

I am definitely a begginer when it comes to Skyline issues, but I've been around the block with EFI Mustangs. My brother and I even engineered a dual mass air meter and dual throttle body set-up on a 1989 mustang back in 1992. Made a custom aluminum and plastic crossflow manifold. Pretty radical looking, but tuning and testing was a bear!

Like I said, I am definitely a begginer when it comes to Skyline issues. Any suggestions on the Skyline are welcome and appreciated.

-AL

[SkylineUSA]

Mustangs, Skylines, there all the same Same theory applies to a point.

[Gtr2.7L]

You'd think so. I have a set of 2540's, new from the factory. They did it from the beginning. When I did the bore-up, I sent both turbines back to HKS and they told me nothing was wrong with them.

Sean had the same thing happen with a new set of 2530's as well.....

Doesn't do it all the time, only under a specific set of circumstances....

Originally Posted by RazorGTR

Sounds like you have one weak turbo.

The only times I've seen this happen is by one of two things.

1. One weak turbo, or the wastegate of one of turbos isn't working properly. Common when turbos are getting tired. A good way to tell is when the engine and turbos are cold and you are gentely accelerating you'll hear a bit of a whine or groan. You'll find you've got excessive play in the bearings or shaft of one of your turbo(s).

2. Unballanced turbo(s). Unballanced being the turbine wheel and compressor wheel are not matched up. In other words some yahoo who thinks he knows what he is doing builds a turbo using wheels that are not matched for eachother.
Or
Had the turbos reconditioned and the housing aren't machined the same.
Or
Exhuast housing and compressor housings don't match up.

Hybread turbos are a recipet for disaster.