1998 GS-T 132 FWHP Stock? What could be wrong?

[andrewzpsu]

Hey guys, I just bought a 1998 GS-T today, it is my second GS-T, I used to own a 95 back when I was in highschool. This one felt substantially slower so shortly after buying it I brought it back to my shop to dyno it. Well, not to my surprise, dynoing in only 3rd gear, it only put down 132 fwhp with a pig rich AFR... under 10.0 AFR.

Well since I knew a thing or two about tuning (I work on GM cars), I removed two honeycombs from infront of the MAF... the side ones specifically. The AFR bumped up to an acceptable level, starting at around 12.4 and ending at around 11.6 at redline. The horsepower went up to 150 then and I decided I didn't need to try to dial it in more as this was close enough.

The car seems to be in good shape, but I'm not sure why the power is so low.

I'm going to hook up a boost gauge probably next week... just a cheapo one from advanced auto or something just so I could get a reading on the boost level.

One of the things I noticed is that compared to my old GS-T, the boost takes forever to come on.

Maybe my wastegate is stuck open? How could I fix that if that is the root cause of the low power?

I'm also going to run a compression check.

Anything else I should look into?


Thanks a ton! I'm excited to have one of these cars again! =)

 

[JMiller]

Did you remove the restrictor in the BCS. Should get between 13-14psi with it removed and hold around 10psi after 4800rpm. Also you could get a manual boost controller and turn the boost up to 16psi and see what numbers you get. CAUTION only change boost levels if you have a REAL boost gauge not that factory pos.

 

[daren_p]

Very common for the stock T25 to not hold boost as the rpms increase, the stock 12ish psi is about the most it can hold, no matter what you initially spike to. Dropping to 8psi seems abit low, the first thing you should do is a proper boost leak test, with a tester & soapy water. Go over any line that has pressure in it, not just the IC piping. You may be surprised with the leaks you find, when you didn't think you had any.

If boost leak checks fine, it may be a turbo issue itself. If your cars higher milage, it may just be tired. WG actuator could also be another issue.

 

[jrohner]

The stock T25 turbo is a tiny hair dryer, so it's not a big surprise it can't hold boost. Free-flowing exhaust would probably help some. I've only driven one 2G with the stock T25, and I could barely tell it was a turbo car at 14psi; it's a pretty lame turbo.

 

[andrewzpsu]

@Jmiler. I am using a MBC and a real gauge.

@daren_p. What I have been doing is clamping a boost leak tester to the turbo and listening for leaks while watching pressure drop. I haven't checked it lately, but I only found some tiny leaks..

It is the stock turbo. And I have suspected that the turbo is shot due to longer spool times than I remembered on my 95 GST. I will try to replace it when I get the $$$$ to do it.

 

[defury]

Did you check for shaft play I don't remember reading whether you did, check the exhaust for leaks too as well as the intake.

 

[andrewzpsu]

Did you check for shaft play I don't remember reading whether you did, check the exhaust for leaks too as well as the intake.

The shaft seemed perfectly fine. But I'll look at it more next time I'm down the shop.

I can't possibly see how an exhaust leak would cause such low boost (if the leak is after the turbo).

Definitely saw the turbo spike to 20 psi too and then drop down quickly and all the way to 8. So it seems like the turbo can spin...




Maybe the wastegate is the problem. Any suggestions on how to fix/test?

 

[JMiller]

What psi are you testing it? Also if you plan on getting a new/better turbo in the future, why not see how much you can get out of the little t25(like at 20psi) just for the heck of it.

 

[andrewzpsu]

What psi are you testing it? Also if you plan on getting a new/better turbo in the future, why not see how much you can get out of the little t25(like at 20psi) just for the heck of it.

I will try... but for some reason right now it is bleeding off boost dramatically.... only producting 8psi by redline... actually probably by 5500 rpms.

So thats a problem in getting to 20 psi

 

[EclipseTical]

What psi are you testing it? Also if you plan on getting a new/better turbo in the future, why not see how much you can get out of the little t25(like at 20psi) just for the heck of it.

This is a stupid idea that could very well lead to massive engine failure in addition to blowing the turbo. Unnecessary risk for zero gains to be made. at 20psi the T25 will be blowing ridiculous amounts of hot air and [most likely] causing an insane knock count that if you're lucky won't lead to the motor grenading.

OP-- conduct your boost leak test with soapy water; just listening for leaks will not find all of them. I've had pinhole leaks in couplers that made zero noise but showed themselves when sprayed with the soapy water.

 

[AlaskanDsm]

An easy way to track down boost leaks is to start testing at the throttle body. spray everything to shit with soapy water (TB gaskets, TB seals, injectors, intake manifold gasket area, etc). Then if you find no leaks and pressure is holding, then move to down towards the intercooler. If you do it in steps. you will be able to find out if it is only a certain section that needs to be looked at. Also, you might want to do a compression check just for hell of it to see how healthy she is.

 

[BoostedPhoenix]

This may sound simple and stupid but, is the Stock exhaust still on the car ? With the age of these cars i have encountered 2 of them that had plugged catalytic converters. Not uncommon if the car has ever had a sparkplug issue it does not take much to destroy that catalyst. Catalytic converters that are obstructed present them selves with two symptoms in turbo charged cars, Slow spool time and Low power output =P Both seem to be problems youre having, not that you should not do a tune up and fix the formentioned boost leaks but restrictions in the exhuast are not friends with turbos

 

[andrewzpsu]

This may sound simple and stupid but, is the Stock exhaust still on the car ? With the age of these cars i have encountered 2 of them that had plugged catalytic converters. Not uncommon if the car has ever had a sparkplug issue it does not take much to destroy that catalyst. Catalytic converters that are obstructed present them selves with two symptoms in turbo charged cars, Slow spool time and Low power output =P Both seem to be problems youre having, not that you should not do a tune up and fix the formentioned boost leaks but restrictions in the exhuast are not friends with turbos

I will get a test pipe put in place of the cats to test. Thank you for your suggestion.

 

[jrohner]

Unbolt the downpipe from the o2 housing and see how it acts.

 

[JMiller]

When you do a boost leak test what psi does your wastegate start to open, also have disconnected the coupler from your TB elbow and pressure tested the TB, in man, etc. You could also do a leakdown and compression test.

This is a stupid idea that could very well lead to massive engine failure in addition to blowing the turbo. Unnecessary risk for zero gains to be made. at 20psi the T25 will be blowing ridiculous amounts of hot air and [most likely] causing an insane knock count that if you're lucky won't lead to the motor grenading.

OP-- conduct your boost leak test with soapy water; just listening for leaks will not find all of them. I've had pinhole leaks in couplers that made zero noise but showed themselves when sprayed with the soapy water.

namonai baka, hitowarawase kokkei

 

[EclipseTical]

namonai baka, hitowarawase kokkei

sorry i don't speak Japanese, but I highly doubt it would be a foolish,insignificant,or trivial matter to the OP if he follows your idiotic advice and blows his engine due to running extremely lean thanks to your advice of running 20psi on a T25 with 450cc injectors.

WTF do you think the result of running too high boost with not enough fuel is? Is it definitely going to cause severe damage to a motor? No, but it is possible. To me that is an unacceptable risk, especially since a T25 would be well out of its efficiency range at 20psi and would be performing worse than it would at 15psi.

If you want to take that risk knock yourself out bro but it's irresponsible to advise others to do it as if there is zero potential for damage to their car to result.

 

[spooling 1g]

Could possibly be a bad knock sensor,or seeing as its a 2g with the boost spiking it could be seeing knock and pulling the timing equaling no power.

 

[andrewzpsu]

Could possibly be a bad knock sensor,or seeing as its a 2g with the boost spiking it could be seeing knock and pulling the timing equaling no power.

That is another suggestion I got from the shop behind mine. They said pull the knock sensor and see if it makes a difference.



I think my next two action steps are going to be to pull the knock sensor, check for changes. Then unbolt the downpipe or whatever to see if there is any kind of restriction making my life miserable there.

If neither of those improve the power I'll be looking into wastegate/turbo problems.

 

[jrohner]

You can't just pull the knock sensor; the ECU doesn't say "I don't see a knock sensor, so I'm just goona go ahead and assume there is no knock".

 

[BoostedPhoenix]

You can't just pull the knock sensor; the ECU doesn't say "I don't see a knock sensor, so I'm just goona go ahead and assume there is no knock".

Indeed this is true if you unplug the knock sensor you will get CEL and no timing advance. That surely wont be a way to make your car feel faster

 

[andrewzpsu]

So here is an update... kind of funny at that.

Instead of putting a test pipe in place of the cat, I simply just disconnected the down pipe. It was definitely on its way to making more power until it melted a strap and came off the dyno. My first time a car came off the dyno haha. Apparently the strap was right under the downpipe... my bad.

Well, coming off wasn't anything bad (especially because mine is in-ground) except I popped a tire. So its been a little while since I tried to play with it. In fact, it was at least 4 weeks since I had started it last, and to my surprise the car started right up.


Anyway, I think it could be the cats, but driving around the other day it simply started smoking pretty good. Frankly it seems like the turbo's seals went as I actually can see a little smoke coming from the turbo.

I'm going to replace the turbo (need to find a new one cheap) and just put a pipe in place of the cats for the time being.

Sometime this week or next I'd say.

Also, it looks like my timing is off a tooth on one of the cams, but I really can't be sure. It idles fine though. Which is something I wouldn't necessarily expect. Going to do a leak down test on it soon. That'll tell me if this engine with 25k miles is junk or not before I buy a new turbo.

 

[2slow4utsi]

So here is an update... kind of funny at that.

Instead of putting a test pipe in place of the cat, I simply just disconnected the down pipe. It was definitely on its way to making more power until it melted a strap and came off the dyno. My first time a car came off the dyno haha. Apparently the strap was right under the downpipe... my bad.

Well, coming off wasn't anything bad (especially because mine is in-ground) except I popped a tire. So its been a little while since I tried to play with it. In fact, it was at least 4 weeks since I had started it last, and to my surprise the car started right up.


Anyway, I think it could be the cats, but driving around the other day it simply started smoking pretty good. Frankly it seems like the turbo's seals went as I actually can see a little smoke coming from the turbo.

I'm going to replace the turbo (need to find a new one cheap) and just put a pipe in place of the cats for the time being.

Sometime this week or next I'd say.

Also, it looks like my timing is off a tooth on one of the cams, but I really can't be sure. It idles fine though. Which is something I wouldn't necessarily expect. Going to do a leak down test on it soon. That'll tell me if this engine with 25k miles is junk or not before I buy a new turbo.

You can probably get a used 14b for no more than $150 shipped.

 

[FLASH1970]

I will if the AFR at WOT is unsafe once I find this boost leak. (I suspect with 99% certainty that is what I'll be doing.)



My dynojet.

I have a shop in West Chester but only work on domestic cars.... for now.

With your Eclipse, you still are working on a domestic car...

 

[andrewzpsu]

With your Eclipse, you still are working on a domestic car...

Lol... doesn't feel domestic haha. So damn tight.

But turbo will be replaced once I find a suitable replacement.

 

[dsm-onster]

The eclipse was built as close as the chevy they probably tuned today. . . The "domestic" name is rather irritating.