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Diagnose turbo lag

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If it's not really about tuning or wiring. Then it belongs in here.


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Ok I recently got my car tuned and am finding there is a lot more turbo lag than there should be given the turbo size.

IE a GTX2867r with .86 T25 turbine. And it's hitting decent boost 14psi at 4000rpm before that is very little boost. Now the engine is a gen 3 3sgte. I have friends with gt35's spooling quicker.

Before I throw money at my tuner I would like to some how have a rough idea what the issue is. So how can one diagnose what's causing the lag with out a dyno?

I was thinking of adding a turbine oressure sensor by using my fuel pressure sensor with a long piece of hardline coiled up to remove the heat. But is there anything else I can do? Cars running a haltech. Controlling boost and it Ramps smoothly to 20psi. Echaust is magnaflow 100cell cat and straight through muffler. Full 3" echaust and pod filter straight on turbo intake. Pwr front mount.

Any ideas where to start?

Attached Files

A Gen 3 3S-GTE should be making much better and smoother power than that. Personally I would say it looks like the tune. It should also be making much better figures than that, I had one on my dyno last week which ran less boost on a standard turbo, standard ECU running pig rich made more power at the hubs

attached is the map if any one wants to look,

I've had a look through the closed loop boost settings and nothing seems out of the ordinary.

ideas before I spend another $1000AUD on a tune...

Attached Files

Have you tried pressurizing your intake/charging system to see if you have a boost leak somewhere? The most common cause for a symptom such as severe boost lag is a boost leak within the pressurized side of the intake system.

The problem is not JUST a high boost-threshold... its also making very low power for that kind of manifold pressure. It would seem that there is a significant flow restriction through the engine. But i'd be willing to bet its just an incompetent tuner!. I'd advise you to take it back and demand they re-do it free of charge.... but then again i wouldn't trust these morons. Or maybe they are competent... and they just ripped you off.

Im not familiar with that motor and do not know what kind of timing they usualy like, but that timingmap looks very conservative to me.

And your torque plot looks remarkable flat. Almost as if someone made it like that on purpose.

thanks guys. I suspect you are right.

due to my budget my plan is:

test for a boost leak.

attempt to tune the haltech closed loop boost control to improve the threshold slightly (maybe).

save my pennies get ethanol, get rid of the turbo adapters (ct26 flange to t25). and find a new tuner.

the tuner I chose came highly recommended, not sure what has went on, maybe he just is overly cautious since he doesn't tune 3SGTE's often.

thanks again.

could you ensure your wastegate/s are opening/closing like they should? If your exhaust flow is partially bypassing the turbine could be causing a slow spool-up?

A "tuner" who produces such dismal results should be out of business!. How much did he charge you for that??

Just disconnect your boost control altogether (wastegate permanently closed)... take the car on the freeway.... and in like 4th gear at 2000rpm plant your foot down and watch the boost curve. If boost comes on much sooner than normal... well then you know who to blame. You need to do it in 4th so as to have time to "catch" it from over-boosting. What your looking for is when the boost starts to climb. If you have data-logging capabilities... it makes it much easier.

Also... you might have a weak wastegate spring... and the exhaust pressure is pushing the wastegate open... well before target boost is reached. So make sure this is not the problem. You might be able to use some thin metal cable to "lock" the wastegate actuator arm in the closed position - to do this test.

Rule #1. Never use a "tuning shop" that has a dirt cheap website and no landline!.

ill try logging rpm, boost and AFR and block off the waste gate. over boost protection in Haltech should stop any risk of engine damage shouldn't it?

on the actuator alone it makes 12psi, so I didn't think that would be "too soft" to bring it on boost. actuator has about 2mm pre load.

I would rather not name and shame (not really productive especially to this forum) , Marek0086 if you are in Brisbane are message me and I will keep you in mind when I get a re tune?

Oh yeah... if you have over-boost protection function... make sure thats set up properly.

Im in Melbourne... and i don't have a dyno.

With the actuator alone does the boost perform the same as when it is plumbed in to the solenoid?

Closing the wastegate and trying to catch it if it overboosts or a safety system kicking in displaying Russian roulette, I would use a manual controller but never lock wire the actuator shut

Using a manual Tee-controller defeats the whole purpose of the test!. Besides, he already said he has an "over-boost" protection feature on his ECU.

What I usually find is that it is pretty difficult to mess up a tune so badly that boost response is completely destroyed. The turbo boost response is a function of exhaust mass flow and heat so provided you have the tune somewhere near the ball park you will be pretty close. Of course there will be a difference in response with a tune that is overly rich or overly lean, but in my experience this is likely to be a couple hundred rpm, not 1000 for example.

If your tune is completely messed up then the above goes out the window but you would expect see other signs of this in general driveability - Hesitation and erratic acceleration or trails of black smoke out the exhaust would be giveaways if this is the situation. Also this isn't what you would expect from any tuner who can do even a half capable job!

As has been mentioned by others, mechanical aspects should be ruled out first - Boost leaks, a wastegate that isn't sealing or even a collapsed flexi will effect both boost response and ultimate power. In particular I've seen more than a few collapsed flexi joints give problems that were hard to diagnose. The fact you are seeing 20 psi would probably rule that out for the most part but when there are a number of potential areas that could cause a problem, you need to tick each one off in an orderly fashion.

If I'm suffering boost response issues I always try disconnecting the wastegate from a boost source pretty early on during my fault finding to see how the boost responds with no wastegate control. Obviously this needs to be approached with caution as Marek has pointed out. If oyu have a boost cut feature, be sure to use it. This will prove if there is a problem with the boost plumbing or electronics or whether you are looking at something else.