Boost vs. RPM
 

This is weird, so bare with me.

Typically I can get about 5 PSI steady at half throttle around 3-4k RPM. It ramps up quick. Then it maxes out around 8-9 PSI steady around 6k RPM at full throttle.

Then there are times I have to flog it and can't get much power as if it is held back. In 2nd, the boost gauge slowly ramps up in sync with the tach to redline, but it doesn't max out at 8-9 PSI. It feels like the ECU is limiting the time to "fully" open the throttle, but limits how wide to open as well. I notice this after a warm start, and it gets a little better after a few minutes. Then there are times the "problem" comes back, and I can't get the car moving even with additional pedal travel.

I did get the brake switch replaced a few months ago, and I was able to get the car to scoot crazy fast in 2nd. Max boost picked up well before 4k RPM instead of ramping up slowly. The < 2k RPM slow pickup or hesitation is coming back. I recently filled it up with non-ethanol fuel, and it seems to improved response and reduced minor roughness at idle.

Just curious since I don't have a datalogger for turbo boost.

[EDIT] Forgot this might have to do with the ECU throttle tables. I'm still running the canned tune from GTM. My car never got dynotuned after the kit was installed. Possibly need updates to the throttle tables.

Any boost controller? Sounds a little bit like it could be a sticky wastegate.

Or a leak...

check for boost leaks and fix any leaks, if that doesnt help then check the BOV for leaks, and if that still doesnt help, you might need new wastegates or turbos

Here is a link to Ron's post about his TT having some boost issues: http://www.the370z.com/members-370z-...ml#post2263418
Slightly different than yours, his was more idle but might be something to look at.

Sounds like a boost leak Digi.

Thanks. Not sure how to check. I sprayed maf cleaner all over the place and don't see anything. I do notice a slight hissing sound around the bov area when it builds up boost. Think it's too loose or venting too early?

BTW this is starting to make sense in regards to slightly rough idle.

Ok here's what I felt, and it's weird. The car did it again in which it wouldn't rev so fast as if I couldn't open up the throttle. At 3-4k RPM there wast no boost even with my foot to the floor. All of a sudden I felt and hard a faint clunk, and the boost jumps to at least 5 PSI. Throttle response returned, and I was able to get the car going fast as the pedal went further down.

Think something's sticky? I've felt this a few times.

Maybe take off the throttle bodies and see if they're gummed up?

Here's an interesting question. I think everything looks good, but now I wonder about my HFCs. I've had the F.I. HFCs installed brand new at the same time the turbos were installed. I'm pretty much past 30k miles with the kit and the HFCs.

Think the HFCs clogged might be the reason for the slow spool or slow revving? Also, maybe it's the reason for the engine dying at idle on startup at times?

That's entirely possible.

I would definitely rip them off, even with my SC I blew out a factory cat after awhile, I really need to invest in some TP.
I know when mine blew I heard a slight rattle, almost like the clutch, from under the car when I would be in neutral and gave it a slight rev up to 1200.

I think that's what I'm starting to hear and feel. Response is getting pretty weak especially as the cats are still "cold." It's a wonder why I smell fuel at times. All starting to make sense now. I couldn't get it to hit boost on the freeway again, and it was laggy.

Priorities is keeping me from making the full switch to 3", so I might have to get another set of HFCs. I can do TPs, but the smell makes me nauseous.

I am not to sure about the cats, unless the engine is going into a sort of limp mode because of them. A plugged or shot cat would not cause the engine to come in and out of boost like you are experiencing (unless of course the ECU is doing funny things because of it). Do you have uprev? a simple log would tell you exactly what is going on (if its not being caused by a stick wastegate or something similar).

Yea, it's UpRev flashed with GTM's kit. I've not started having these funky issues till recently, and it feels like it is progressively getting worse. For the past several months I notice a faint whine which appears to come out of the passenger side turbo. The clunk feeling I felt from the lag sounded like it came from underneath on that side as well.

Also I wonder if this is why I've not been able to consistently get 8-9 PSI, and that I had to dial up the MBC a little bit the past few months. The boost gauge needle is steady, so it doesn't jump all over the place.

Exhaust note as of this morning, much quieter than usual. I'm waiting to hear from Tony in regards to options.

Definitely think the HFCs could be a culprit. And a reasonably easy thing to check.

Yea, no CEL so far. I'm going to see what options I have for the short time being. It can be simply HFC, or test pipes and HFC in the x-pipe area like the 3" TDX setup.

Here's the condition of the passenger side turbo. That oil feed location has been "moist" since day 1. My techs torqued it a couple times in the past year or so and noticed the bolts needed more torquing than the driver side turbo. It doesn't appear moist further above it.

I'm going to have my tech look at it again tomorrow while doing the oil change. If you guys have suggestions for stopping this leak, please don't hesitate to advise me.

Thanks!

I'm still leaning toward a fried cat.

I just talkd to Tony@F.I. I think he's pretty amazed it took 30k miles for the cats to finally fail. Test pipes will be ordered first thing in the morning. Hopefully that'll remedy this issue and keep me going for while. Then eventually I'll switch the x-pipe out with one with HFC to cut the fuel smell. That will buy me some time before I can save up for the 3" setup and tune in about a couple of years... this house stuff pretty much eats up all my hobby funds lol.

I think that's going to take care of it. Cats that close to something as hot as a turbo is a recipe for failure.

Yea, it was a known issue. Nothing short of one off custom from Tony would resolve the issue at the time of installation since I still wanted cats. That's what lead to the design of the cats getting installed further downstream with the 3" TDX exhaust setup. Tony says he can fix me up with a 2.5" x-pipe with cats whenever I'm ready.

I love my 3" catted fi exhaust.

I'd like a 3" straight pipe. No catback :)
I got the Gtm 3" exhaust

I'm jealous. Two things I wished for... one of it was to wait to do any of this stuff knowing how awesome F.I. is hands down. I was the first to get a hold of the TDX 2.5" exhaust. Haha he calls me #1.

Pretty sad... TIAL EWGs sitting in a box all lonely.

Okay, test pipes ordered. It'll be a 3 week wait, but I might not drive my car as much till then. Turns out there's a 1 month wait at the body shop to get my car fixed as well.

It's making quite a bit of sense now after doing some research: sporadic engine start and idle problems, overheating last year when ambient was above 90F, sluggish response (still exists), slight raspy noise at idle heard echoing against a nearby object, and now barely any boost at times. I've not driven the car hard, but only for emergency at half throttle. Looks like I've been dealing with this for almost a year and now just noticing it.

So hopefully nothing's damaged. My tech will check the turbo exhaust side once the HFCs are pulled.

Thanks, all! Will report with status in a few weeks.

You could take off the cats and hollow them out for the time being.

Looks like the test pipes will be shipped out this week at the soonest.

I'm not exactly how much power this will free up since I'm currently sitting around 450 whp at 9 PSI, but I might dail down the boost controller and take it to a shop to get the AFR checked out as I dail it back up to about 9 PSI.

Any of you guys still running the 255 pump?

The walbro? Yeah. Works well enough.

Any plans to switch to Aeromotive 340 lph pump, Chuck? Are you still runnng the Bosch injectors as well?

When it comes time to start chasing more power, I'll swap to the aeromotive. I'm pretty content for now. I've got whichever injectors gtm ships with the stg one kit. Since its a daily driver, I'm not trying to make stupid power. I'm sure I'm in the 425-450whp range. That's good enough until the car becomes a weekend toy.

Haha good point. Can't wait to feel the response. I'm borrowing a '98 Civic and it has much more response than my car at the moment lol.

TP install progress:
Removed passenger side HFC. Confirmed from carbon deposits by the edge of possible leak due to lack of gasket to the downpipe. No wonder there's a whine noise. Last tech must have tossed it out after replacing the transmission several times last year. HFC surprisingly intact, but flash light test shows it is almost clogged.

Tech pulled oil line from turbo and is looking for a replacement gasket.

You're going to love it once you get the test pipes on. There's no telling how long you've been running with the cat partially clogged before it failed. Between that and the fact you're currently driving a car powered by an asthmatic gerbil, the Z is going to be a rocket ship.

Having a daily driver that was ungodly slow saved me thousands in mod money when I still had my STI. There was no need to keep modding it if you drove a 1991 Volvo 940 nonturbo Mon-Thurs.

You're right, Chuck. The the exhaust isn't any louder and there's no rasp. The tone changed a tiny bit, but has a more distinct VQ tone in the midrange. The boost setting is set low, so it's barely pushing 6 PSI. However, I'm getting boost at mid throttle at 3k in all gears. Throttle response feels much better. Also, the passenger side turbo whine is gone, but there's this nice faint turbo whoosh sound now as it spools up.

Well, the temps are 100F right now, but the engine didn't heat up like it did last year. Oil temps barely exceeded 200F, and the water temps remained.

It's amazing what getting rid of an astronomical amount of backpressure will do, huh?

I dialed the boost back up, so it's around 7-8 PSI. I was amazed as well and definitely felt an increase in power in my gutt lol. I took my neighbor for a drive, and it scared him. I told him this is the reason why I drive real slow and carefully on our street - not just for the safety of the kids around me lol.

Time to kick it up a tiny bit more... [evil grin] since mid throttle response feels so good.

You get to experience the thrill of going FI twice :tup:

Awesome dude! I'm glad you got it worked out.

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Glad to hear! Let's hear what she sounds like now! :D

My car is going in the shop next week to get storm repairs done, so I'll try to have a friend help me with some videos. It sounds so good. I just have to get over the fuel smell for now. The slight spooling sound is so cool I wish it was louder lol.