New Turbo Install: Lags & Won't Boost

[Fearra]

Hello all,
Though this is my first post here, I've been lurking around for a while using the information on these forums. A little about myself: I'm schooled in mechanical engineering and have been working in the aviation industry since I got out of school. I was never too interested in cars until I got my first one, and that's when the interest started kicking in. I picked up a local '88 Supra Turbo to use as a fun project car and to learn with (I was originally looking at the Mk4s, but since I had very limited knowledge at the time and knew I wanted to do modding I figured I'd pick up a vastly cheaper mk3 to experiment with).

Anyways, introductions aside, I've been working on my '88 Supra with the help of the TSRM and the information available on this (and other) websites but now I've run into a problem and questions I haven't been able to find the answers to.

Summary:

The car & mods:
1988 Supra Turbo (7M-GTE)
R154 Transmission (auto to manual W58 done by previous owner, W58 to R154 done by myself)
Apexi Power intake
V8 Lexus AFM
550cc RC injectors
Driftmotion Turbo kit (PT6262 turbo; .84 AR)
Driftmotion intercooler kit
Magnaflow high-flow cat
HKS Super Dragger cat-back exhaust

Symptoms
- manifold pressure quickly builds to ~1 psi but holds until 4k+ RPM where it will rise again to only ~4 psi
- adding regulated pressure to the top port in the wastegate improves the boost numbers, but it still takes 4k+ RPM to spool the turbo, and the boost is ~ 15 psi lower than what is expected (10 psi to top port + 10 psi wastegate spring yielded ~ 7 psi of boost at around 4500 RPM)
- AEM UEGO reading low 13/high 12 while in WOT, slightly rich at idle and normal running conditions (mid-low 14s)
- exhaust temps at ~900C at WOT (only done short pulls though, nothing prolonged so it's possible it could go higher), ~650C at cruise, ~ 500C at idle.

Troubleshooting already done:
- previous compression checks turned out good on all cylinders
- all boost leaks have now been fixed - large one found at first, now repaired with minimal impact to the boost problems
- post-turbo exhaust back pressure reads 0 psi (I blew into the gauge to make sure it worked and it does; got 2 psi blowing hard); I can get the needle to twitch a bit revving to 4k RPM, but still stays around 0 psi
- moved my boost gauge from the intake manifold to read off the wastegate signal line and found it topping out at ~7psi
- tried disconnecting wastegate and running the car at WOT (very cautiously, and only after I confirmed the boost leaks were fixed), and the car spiked to ~15-16 psi but only at ~ 4500 RPM.
- tried running the car with a make-shift boost controller and managed to increase boost, but not response (details noted in point 2 of the symptoms)
- repaired some poor welding (on my part) on the exhaust manifold to eliminate pre-turbo exhaust leaks
- pressurized the exhaust of the car to 10-15 psi, found the wastegate leaks slightly (don't notice it with the screamer pipe on, but with it off I can feel air getting by the valve) and also there was air coming out of the turbo exhaust housing. I'm not sure if it's normal for a small amount of air to get through these areas, or if they should be completely air tight.
- tested the wastegate valve, and it cracks open at ~10 psi, fully open at ~15 psi

According to my research on the PT6262 before I decided to purchase it, I should be seeing full boost by ~3500 RPM and moderate boost long before that. This turbo should also be able to push 20+ psi through a 7M no problem, but it's not. I was very confident it was a wastegate problem when i found I could increase the boost I was seeing with a boost controller (and it was still below the wastegate spring's rating), but I just finished testing it with regulated pressure and it appears to be opening fine and the valve doesn't leak too much. The only leads I have on the problem now are: There's a bit of air escaping around the wastegate valve and also some air coming from the back of the turbo exhaust housing when I pressurize my exhaust system.


Would anyone be able to lend their expertise to my turbo woes?

Thanks,
Jon

 

[NewAgeMA70]

Where are you located?

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[supraguy@aol]

That was an extremely well written synopsis.
As for the cause of the problem, not sure. Initially i wanted to say exhaust blockage. If you have a catalytic converter, its possible that the substrate could be partially blocked/ melted. I know you test exhaust back pressure, but i'm not sure if that would be a definitive test(depending on method). Other than that, i would suggest removing the intake pipe and physically spinning the turbo impeller, just to confirm that there's no unusual friction/ resistance.

Hope that is of some help.

 

[Fearra]

NewAgeMA70: I'm located near Victoria, BC in Canada.

supraguy@aol: How I tested the back pressure was to unscrew my wideband O2 sensor from my downpipe and screw in an air hose (turns out the AEM UEGO uses the same 18mm thread as a spark plug) with a low-range pressure gauge (reads between 0 and 20 or so psi) screwed into the top of it. I then fired up the car, and the pressure gauge was reading 0 psi. I had my friend hold the RPM steady at 4000 which caused the needle to oscillate a bit, but the peaks of the oscillation were below .25 psi, and the average appeared to still be around the 0 mark.
I also rechecked the turbo impeller to make sure nothing happend to it. It still turns as easily as it did when I was priming it with oil prior to the first start up, and has no obvious signs of any wear-and-tear.

 

[Dirgle]

A couple of shotgun questions to cover a few possibility's.

1. Which method did you use for checking for boost leaks? Smoke or pressure test?

2. If the Pressure test what was the rate at which the system lost pressure after the air feed was cut off.

3. Which BOV/BPV do you have?

4. Which feed are you using to provide a manifold reference to the BOV/BPV?

 

[Enraged]

I have nothing useful to say about your problem, but I figured I'd let you know there are a few Supra owners here in Victoria, some with actual running Supras! We help if we can.

 

[BoostMonger]

Have you checked/retighten your bolts between head and mani, mani and turbo and mani and wg? Your exhaust needs to be checked for leaks as well as your ic pipes. exhaust that escapes before the turbo will affect your spool.



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[jdmfreak]

That was an extremely well written synopsis.
As for the cause of the problem, not sure. Initially i wanted to say exhaust blockage. If you have a catalytic converter, its possible that the substrate could be partially blocked/ melted. I know you test exhaust back pressure, but i'm not sure if that would be a definitive test(depending on method). Other than that, i would suggest removing the intake pipe and physically spinning the turbo impeller, just to confirm that there's no unusual friction/ resistance.

Hope that is of some help.

^^^this... Sounds like my first supra I was told it needed a new waste gate when I purchased it......that was not the case

the p/o had punched out the cat and the insides of it ended up in my muffler... Didn't drive any different but I wasn't able to make over 2lbs... I am not sure your method would show any back pressure without building boost but I found the problem when I removed my exhaust and it sounded like a rain stick... Maybe try doing a pull with only the downpipe... Not the rest of the exhaust

 

[Fearra]

Dirgle:
1. I used a pressure test to look for leaks. Since the car seemed fine up until positive boost I figured a smoke test may not tell me the whole story. I made a cap that clamped onto my compressor intake with an air fitting attached, then I popped off the piping leading to the throttle body and capped it off as well.

2. It was pretty much airtight when the throttle-body end of the piping was capped (and after I fixed all the obvious leaks); negligible pressure loss and no hissing at all. I also tried pressure testing with the intake hooked up to the throttle body/intake manifold, but of course then you get pressure loss via the vacuum tubes, exhaust via valve overlap, and the PCV pipe, so I didn't think was was all that useful of a test method. System was pressurized up to 30 psi when isolated from the throttle body/intake manifold, and 20 psi attached to the throttle body.

3. I'm using the HKS 'replica' BOV that came with the Driftmotion intercooler kit. Didn't seem to have any leaking issues once I seated it correctly (found out the snap ring wasn't all the way in at first when I was boost leak testing and it blew off my pipes and smacked me in the wrist ).

4. I'm using the stock BPV manifold reference. The Intercooler kit reuses the stock ISC piping assy, so I figured I'd keep the BPV/BOV referance where it was engineered to be.

Enraged:
That's cool, do you guys ever have meets or anything like that? It'd be nice to get some face-to-face advice from some Supra pros.

BoostMonger:
I have rechecked the turbo/mani and wastegate/mani bolts. I'm scared to check the mani/head bolts though, as I've already had to deal with one of the studs stripping the threads out of my header. When i pressurized the exhaust end of my car I couldn't feel any noticeable leaks at any of these junctions. There was, however, a bit of air escaping past the wastegate valve (not much, but detectable with the screamer pipe off), and a bit of airflow coming from the back of the turbine housing. I'm not sure if a bit of leakage there is to be expected or not.

jdmfreak:
Thanks for the tip; I suppose exhaust back pressure could work a lot like boost where you wont' actually see it until you're actually working the engine. I'll pull off my cat/cat-back and see if that affects anything.

 

[BoostMonger]

:thumbup: you could take your exhaust off and run it with just the downpipe to see if back pressure is the problem haha



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[jdmfreak]

... Maybe try doing a pull with only the downpipe... Not the rest of the exhaust

:thumbup: you could take your exhaust off and run it with just the downpipe to see if back pressure is the problem haha



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Haha beat you to it

 

[Fearra]

So, I just came back from a very loud trip down the street but to no avail. I didn't notice any improvements in the boost; I don't think it's anything in the exhaust.

 

[Beals]

if the wastegate is opening early it won't allow it to build boost. I'm having this problem with the my c12a's I'm going to port the holes and then shim the spring so all in all it works better I hope.

 

[Dirgle]

You seem to have done a fairly thurough job hunting down, possible pressure loss point. The one thing that still seems out of plaice is your AFR's. You say it's showing 13/high 12 at WOT. This is very lean. On the factory TCCS you will usually be in the 10's.

What is your fuel pressure?

 

[Nick M]

I would look at the wastegate and arm and not just the actuator function. Also, that turbo will not respond like a CT26, which I thought would be common knowledge.

According to my research on the PT6262 before I decided to purchase it, I should be seeing full boost by ~3500 RPM and moderate boost long before that.

I don't see how that is possible.

tested the wastegate valve, and it cracks open at ~10 psi, fully open at ~15 psi

That is also normal of mechanical actuators. They open before the limit. And if the limit is only 15 psi from the actuator, it isn't going to hit 20. And don't rule out an engine problem.

 

[Enraged]

Enraged:
That's cool, do you guys ever have meets or anything like that? It'd be nice to get some face-to-face advice from some Supra pros.

We have meets when we have running supras... hehe. My car needs a tune and a few other things, another local is Nashman (his engine blew on the dyno, hes rebuilding now), and there are a few others around.

 

[Fearra]

Dirgle: I've been running with a Walbro pump dropped in place of the stock one for a while now (since before I threw my hat into the T4 Turbo upgrade ring). The only thing that's changed with my fuel system since I was running ~ 7-8 psi boost on my damaged CT26 (impeller blades were chewed up for some reason) has been my fuel injectors, which are now RC 550cc ones. I would expect to be able to get at least the same amount of boost as I was before this upgrade on my existing fuel system. It is something I haven't checked yet though, so I'll see about picking up a fuel pressure testing kit and seeing if something's up there.

Nick M: I realize this turbo won't spool like the CT26, but nonetheless, the PT6262 is supposed to be a very fast spooling turbo. Maybe I'm being unrealistic about 'full boost' by 3500 RPM, but I should be at least be able to get ~ 10-15 psi by 3500 RPM and 'full boost' by 4k at most. From what I've read people with T70s and 67mm turbos report 'full boost' at 4000-4300 RPM, which is what I'm seeing on a 62mm turbo (except my 'full boost' is currently ~ 4 psi). I could get my previous CT26 (which had a damaged compressor) to start boosting before 2000 RPM, and would see it max out before/around 3000 RPM.

My wastegate is the Driftmotion HKS 'replica' external that comes with the Driftmotion kits. It's supposed to be a 10 psi spring, but I was testing it with an air compressor regulator (which likely looses a good portion of it's accuracy at those low pressures), so it's in the ball park of what it's supposed to be.

Enraged: That's cool, you should make it known once you guys are up and running again. By the way, do you know of any good, local performance/tuning shops? I know about 5252 Motorsports, but only by what's on their website. If I'm going to be looking at tuning and a stand alone ECU setup (possible engine building as well) are there any recommended local-ish shops that have a good rep?


Thanks for the advice/input guys. I'm going to see about following up on the fuel pressure thing. But I keep coming back to there being an exhaust-side problem (as most of the advice here suggests as well). I'm getting the feeling the problem is a whole bunch of little things that are all adding up. I think I'm going to just go and apply sealant on every possible weld/interface on my manifold and see if I notice a difference.

Keep the suggestions coming if anyone has anything else!

 

[Suprapowaz!(2)]

Anybody in your area have an external WG that you can swap and test to rule out the replica? I'm not dogging on replica's as I run one that works great. You just never know. Are you running off the WG spring alone, or do you have a boost controller? If you have a BC, what kind and brand? Manual, electronic?

Maybe you have a weak WG spring that's opening up with the exhaust pressure pushing on the piston. I don't know. Maybe if you order a stiffer spring it might help?

Perhaps the turbo isn't any good? Just because it's new doesn't mean it's perfect.

 

[Nick M]

Are you running the A340E or the R154?