2G Slow Acceleration, Bad Mileage, Erratic Boost

[1slowhatch]

Now I am having another problem (with my '97 Talon TSI AWD Auto- stock aside from boost controller, free mods) I seem to have fixed all the boost leaks (used boost leak tester to 20psi). The car still feels slow. Took it to the track (high elevation, lots of heat) and it ran terrible. I couldn't get it to build any boost at the line, so it was running mid 16's at 83? mph? I do have a boost controller on it, tried turning it up, but didn't seem to help. I put a boost gauge on it. Now, it seems like the boost is very erratic. It takes 3 or 4 seconds to build any boost foot braking it, will spike to 18, then fall to 13 or 14. Part throttle you'll see 15+. Very slow to pull out into traffic etc. The mileage is also terrible (around 9 mpg). There are no CEL codes. The only thing I can think of is maybe the ECU is pulling a bunch of timing? You can feel it slow and speed up, sometimes feel like you're hitting a wall, even though the boost gauge shows 15+psi. Heat soak??? Bad turbo?? (does have some in and out, and side to side play). Partially plugged cat?? Also, I only have 91 octane available.The engine runs very well otherwise, idles smooth, no overheating problems, no serious boost leaks, etc.

 

[19gsx91]

Have you checked your wastegate to make sure it's functioning properly? Are you sure that your manual boost controller is hooked up correctly? Do you have any exhaust leaks that you are aware of? What do you mean by "free mods" if you give us more information on the mods you've done it might help.

 

[1slowhatch]

Have you checked your wastegate to make sure it's functioning properly? Are you sure that your manual boost controller is hooked up correctly? Do you have any exhaust leaks that you are aware of? What do you mean by "free mods" if you give us more information on the mods you've done it might help.

I bought this car with a broken timing belt. I have since rebuilt the head and reassembled everything. I do not believe there are any exhaust leaks. I used new gaskets on turbo to manifold, down pipe, etc. It runs idles/sounds just like a stock car.

Free mods are trimmed the bov recirculating tube. I replaced the stock bov with an all metal evo 8 bov. New plugs gapped to .028. ARP head studs, felpro gasket. All new timing components. The cams are dot to dot, and appear to be in the correct position. No smoke out the exhaust. Runs and drives well, just doesn't seem to make the power it should and the boost is not constant.

How do you check the wastegate?

 

[1slowhatch]

I'm going to remove the boost controller and see if that helps any. I'm wondering if high boost spikes are forcing the ECU to pull timing and/or heat soak the intercooler quickly.

I've also done boost leak test, fixed all the obvious leaks, cleaned out the stock intercooler with gas, etc. All new intake manifold/t body gaskets.

 

[19gsx91]

No I understand you've done a BLT but I don't think you having a boost leak will cause the issues you're describing. I'd pull the MBC off and see if it runs any better and do some searching on making sure the wastegate is functioning properly. With a t25 and a stock exhaust I don't think you should be experiencing boost spike, which is where my recommendation to look into the wastegate comes in.

 

[1slowhatch]

No I understand you've done a BLT but I don't think you having a boost leak will cause the issues you're describing. I'd pull the MBC off and see if it runs any better and do some searching on making sure the wastegate is functioning properly. With a t25 and a stock exhaust I don't think you should be experiencing boost spike, which is where my recommendation to look into the wastegate comes in.

Removed the boost controller, but did not hook up the factory BCS. The boost spike is mostly gone (will spike 12-13 psi) at first, then fall to 10-11 psi. But it does NOT pull smoothly or quickly through the RPMs. It feels like I'm hitting a "flat spot" off and on. Boost gauge show good boost (10psi+) through all the "flat spots". Could it be a bad knock sensor? Maybe torque converter problem!??

 

[19gsx91]

Would you say it's sputtering under boost?

 

[1slowhatch]

Not really. I thought I was experiencing spark blow out when I had the boost set higher (breaking up on hwy pulls). But now that the boost is lower, it just feels really slow. It will sometimes pull well for approx. 2k rpm window, then feel slower again. It also feels like it slows down in the upper rpms, like it accelerates better at 4500 rpm than it does at 5500.

 

[black97spyder]

Sounds like your stock t25 isnt enough turbo for you. They dont like to pull real hard, and max out completely at about 17psi. Get a front mount intercooler to help with heat soak of the stock side mount and make sure all couplers are tight and leak free. You have no mechanical issues it doesnt sound like. The higher the rpm that small turbo will drop psi because your motor is becoming more efficient and the tiny turbo cannot keep the intake system pressurized enough like a larger turbo can. You will feel the boost "hit" and all the torque when the turbo first comes in and after about the 5k rpm mark most of the torque will be gone with that stock turbo and it will continue to revv... IMO swap a 14b or 16g turbo on it, VRSF front mount intercooler and turn the boost up to 14psi (anything higher and you risk hitting fuel cut) and it will run like a champ to 7k rpm. Wont need a tune with those mods or any fuel upgrades (though i still highly recommend dsmlink v3 to get the most out of the car).

 

[Boomdeeze]

To be honest, I don't think heat soaking the side mount on a t25 is the problem. Modifying an auto is a little different than the typical manual build(Just got done with an auto build). What are you expecting to build boost wise while spooling it off the line? Tuning an auto for getting up on the converter is a key. I'm not 100% sure on what the stock tune will allow for building boost on the line is but I highly suggest you invest in a way to tune the car if you plan to run this at the track. The tuning system will also allow you to monitor everything that is going on in the car so it can point you in to a direction of what may be happening. It also sounds to me as though something is going on with your wastegate. A faulty wastegate can cause problems with building boost.

Second, get a transmission temp gauge and possibly a fan on the cooler if you want your trans to last (If you already didn't do damage to it since it was hot when you were at the strip).

 

[1slowhatch]

To be honest, I don't think heat soaking the side mount on a t25 is the problem. Modifying an auto is a little different than the typical manual build(Just got done with an auto build). What are you expecting to build boost wise while spooling it off the line? Tuning an auto for getting up on the converter is a key. I'm not 100% sure on what the stock tune will allow for building boost on the line is but I highly suggest you invest in a way to tune the car if you plan to run this at the track. The tuning system will also allow you to monitor everything that is going on in the car so it can point you in to a direction of what may be happening. It also sounds to me as though something is going on with your wastegate. A faulty wastegate can cause problems with building boost.

Second, get a transmission temp gauge and possibly a fan on the cooler if you want your trans to last (If you already didn't do damage to it since it was hot when you were at the strip).

The car will build plenty of boost when its cold. If the car has been driven for a while, it won't build more than 5 psi on the stock turbo.

Do most people go to a larger cooler or just put a fan on the stock one?

I don't think the trans is hurt, it drives like it always has, no slipping, have not seen the a/t temp light on.. etc.

 

[1slowhatch]

Sounds like your stock t25 isnt enough turbo for you. They dont like to pull real hard, and max out completely at about 17psi. Get a front mount intercooler to help with heat soak of the stock side mount and make sure all couplers are tight and leak free. You have no mechanical issues it doesnt sound like. The higher the rpm that small turbo will drop psi because your motor is becoming more efficient and the tiny turbo cannot keep the intake system pressurized enough like a larger turbo can. You will feel the boost "hit" and all the torque when the turbo first comes in and after about the 5k rpm mark most of the torque will be gone with that stock turbo and it will continue to revv... IMO swap a 14b or 16g turbo on it, VRSF front mount intercooler and turn the boost up to 14psi (anything higher and you risk hitting fuel cut) and it will run like a champ to 7k rpm. Wont need a tune with those mods or any fuel upgrades (though i still highly recommend dsmlink v3 to get the most out of the car).

I'm trying to get a 14b to swap on it this weekend and see what happens. Hopefully it will pull smoother and harder through the rpms. Will it work on the stock 2g exhaust?

 

[19gsx91]

Let us know what you discover, good or bad on the turbo swap, I still think there's something mechanically up with your car if your running 16s on a turbo dsm, even in stock form I wouldn't describe my 1g as "sluggish" by any means. I'm not really sure black97 read the entire post to be honest as the reply has me completely confused.

 

[1slowhatch]

Let us know what you discover, good or bad on the turbo swap, I still think there's something mechanically up with your car if your running 16s on a turbo dsm, even in stock form I wouldn't describe my 1g as "sluggish" by any means. I'm not really sure black97 read the entire post to be honest as the reply has me completely confused.

You mean the part about there being a possible problem with the wastegate?? I understand what you're saying, but I figure if there is a problem with the wg (likely cracked housing) it will just about require a turbo swap, so why not just try the 14b now?

Is there anything else I should check?

As far as the slow quarter mile times, I totally understand and share your concerns. I believe the 2g auto awd cars are quite a bit slower than a manual 1g or even auto 1g for that matter. The 60 ft times were beyond pathetic, without any way to build boost, it took almost 3 seconds. If i had let the transmission cool for a while (30 min) I bet it would have cut half a second or more off the times (leaving with 15 PSI) footbraked.

 

[1slowhatch]

Just got a CEL PO170 Fuel Trim Bank 1. Any ideas??

 

[19gsx91]

When did you last change your upstream o2 sensor? A quick search on tuners came back suggesting that it may be the issue. Fix the CEL first. Do you have a 16g swap kit? because the 14b is not a direct swap for your car.

 

[Surfer240sx]

The t25 at 15psi is borderline maxing that turbo out let alone on a sidemout that should only see maybe 10psi. Still sounds like timing is getting pulled ide get a data logger palm logger they work wonders on figuring stuff like this out. Check the knock sensor readings it wont always pull a code if there is knock. Im guessing actual knock from too hot of air in that sidemount. Owned a s13 t25s t28s been there done that!

 

[19gsx91]

?These cars have made impressive power even with a stock sidemount. s13s are a whole different ball game then dsms. I STILL maintain that he needs to get his CEL sorted out and diagnose the sputter, I doubt at that level hes getting timing pulled on a 2g with a t25. They're timing maps are WAY more conservative then a 1g and I wasn't pulling timing on my 14b at 18psi on the stock maps. A logger isn't a bad idea but turning the boost up slightly on a mostly stock car isn't going to hurt anything as long as he is sorted out mechanically.

 

[1slowhatch]

Have some updates:

Popped the hood, and realized the turbo bolts had worked loose. I assume this had something to do with poor boost response/control, and also the fuel trim code (exhaust leak pre turbo). I have since retorqued cold, then hot to 50 lbs. I now can foot brake plenty of boost after 5 or 6 seconds (15 psi plus).

I have a cheap Actron code reader with live data. I was messing around with it tonight. Will it give me a any clues as to what's going on? It looks like I couldn't get the IAT's to show much over 105 deg. Its about 70 degrees outside, 18 psi spike, falling quickly to 14-15. ECT's were 190-210 after highway pulls.

I saw a little over 21 lb/min at WOT on mass air reading. It shows timing advance, but it seemed to be all over the place. A few times I noticed a - reading at WOT (like -2 degrees). At cruise it was much, much higher. Will this thing show me if I'm seeing knock??

 

[19gsx91]

Your boost spike then it falling quickly should have something to do with your wastegate, If You're still on a stock sidemount then your IATs aren't really that bad at all, trying blowing compressed air through each side of the intercooler to clean it out a little bit and help flow. ECTs are normal.

If you can monitor timing with that then I would guess it's knocking, the stock 2g map doesn't give a whole lot of timing through the higher load cell ranges (WOT) so enough counts of knock and you'd be negative, try dropping your boost a psi or two and see if that helps. At cruise the timing should be in the mid 20s-low 30s.

I can't answer your question about the actron code reader though.

 

[1slowhatch]

Your boost spike then it falling quickly should have something to do with your wastegate, If You're still on a stock sidemount then your IATs aren't really that bad at all, trying blowing compressed air through each side of the intercooler to clean it out a little bit and help flow. ECTs are normal.

If you can monitor timing with that then I would guess it's knocking, the stock 2g map doesn't give a whole lot of timing through the higher load cell ranges (WOT) so enough counts of knock and you'd be negative, try dropping your boost a psi or two and see if that helps. At cruise the timing should be in the mid 20s-low 30s.

I can't answer your question about the actron code reader though.

The IAT sensor is in the mass air sensor, correct? If so, how does the computer know IAT's after the turbo/intercooler?? I've noticed the IAT's really only climb when idling/stopped.

I lowered the boost pressure a bit. I now have 16 psi spike, falling to about 13 psi at WOT. Watching the timing advance on the reader:

High 30's part throttle cruise
First going WOT drops drastically to 6-8 degrees.
Slowly climbs with RPMS. As high as maybe 15 degrees!?

MAF reading still a little over 20-21 lb/min at 13 lbs or so.

Does any of that seem right? I didn't see an negative #'s this time.

I have read about finicky knock sensors on 2g dsms. This car has 118k miles, and I doubt it's ever been changed. Is this something I should be concerned about?

 

[1slowhatch]

I'm thinking about just buying DSM link. I already have an EPROM ecu. I have an idea this stuff is going to drive me crazy without a way to log. I also have a WB I plan to install soon.

 

[19gsx91]

The IAT sensor is in the mass air sensor, correct? If so, how does the computer know IAT's after the turbo/intercooler?? I've noticed the IAT's really only climb when idling/stopped.

Normal. Mine does the same thing. and yes for non SD cars the IAT sensor is in the MAF.

Look up shimming a wastegate, or a heavier wastegate.

Look at a timing table on a 2g. that seems to be normal.

 

[Spades]

runs fine, but just slow? Check engine compression

 

[1slowhatch]

runs fine, but just slow? Check engine compression

Good call. I'll check it tomorrow. It idles smooth, doesn't seem to use much oil, still has crosshatching in the cylinders. Rebuilt cylinder head, etc. etc.

What should the compression #'s be?? I'm at 4500 ft elevation, so they will show lower than sea level.