Ok so my car was tuned to 20psi, everything was great all day. Near the end of the day I notice my boost is trailing off towards redline. Before this it would hold a solid 20psi all the way to 7500rpms.

Now, no matter what the boost controller is set it, it will lose 3-5psi as I get to redline. I've tried a new boost controller, redoing all couplers, etc. I replaced a few vacuum caps, and when I was out testing it I blew one of them off. And even with it off I would make 15psi, and then it would still trail off towards redline.

Anyone have any clue what could be causing this? What happened today makes me think it isn't just a boost leak. Any help would be appreciated!

 

Loss of boost is usually restriction in the exhaust. What kind of cat do you have? How many miles are on it? Are you running sequential?

Dave

 

No cat.. rx7store resonated midpipe. Running gotham racing gr63 kit.

 

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ignition system maybe? Have you tried changing plugs? Also check your coils as well.

 

Could ignition make you lose boost?

 

I've heard of it on this forum thats for sure. to the point where there would be zero boost actually. Its on this forum somewhere. It was the secondary coil. But if you think about it, it would make sense. If your not blowing up all of your fuel properly your losing power and that could be a reason for the lose of boost.

 

It just doesn't make sense, ignition or not, the boost would be there from the turbo. Doesn't really make sense at all, the turbo is completley seperate from the coils.

 

I'm not sure about that, myself. The moment boost goes down, the wastegate closes to use more of the available exhaust flow. You'd have to see a drastic reduction in flow for the wastegate to nearly close and all of the flow goes over the turbines. At 10psi and stock flow I'd find that hard to believe, but at 20psi and more flow, maybe. I'm not a tuner though so that idea is just conjecture.

The fact that you were getting 20psi, and still get 20psi before it tapers, suggests it's not a boost system problem. It suggests either 1) excessive flow restriction (could an intake pipe be collapsing?) or 2) something dragging down the whole system under maximum load.

I'd try in the single turbo section - it seems to not be getting much attention here.

Dave

 

Producing boost is a function of the heat energy available in the exhaust gasses. If there is an ignition problem resulting in misfires (you may not feel these at high RPM) or incomplete combustion, that reduces the energy input (exhaust gasses will be cooler) to the turbos and will result in lower boost, especially at the high boost level you are running.

In addition, ignition problems often appear at higher RPM's in conjunction with high cylinder pressures produced by high boost levels or high compression ratios (the spark has a harder time jumping the gap when more air molecules are present at high pressure, and the coils become saturated at high RPM's).

Therefore, IMO, it sounds like an ignition problem. Among other things, it could be excessive resistance in the wires, rounded electrode edges on the plugs, marginal coils, low voltage to the coils, or a combination of all of these.

 

Regarding the "high boost levels", the car did the same thing when I turned the boost down to 10psi, it would drop to like 5 by redline.

 

I don't know if you were referring to my previous comment in particular, but this could still apply at lower boost levels...

And even a resonator could collapse internally and block flow...

 

Yeah, I took off the midpipe, well unbolted it from the downpipe, and I think it kind of fixed the problem. It was losing less boost, but then it kind of fell and landed right in line with the downpipe, pretty much hooking it up again. I have to take it completely off to be sure, its just so hard to drive like that because its so damn loud.

 

Well I swapped plugs, same thing. Almost seems worse. IDK!! Help??

 

Are you absolutely sure your wastegate is functioning properly?

 

Are you using an ignition AMP? If so what kind? Is it hooked up to the stock primary or are you using a TII primary coil? I still think this sounds like a burned coil problem, maybe not totally burned out coil but somehting of the sort like DaveW said. BTW DaveW thanks for backing me up on that statement.

 

Xeros, you're welcome. Made sense to me.

 

I'm pretty sure, I have dual tials, not sure how to test them either. =/

 

I'm using an hks twin power on stock coils. I tested the coils before I got my car tuned and they were ok, oddly enough they couldn't get a good ignition reading when I got my car dyno'ed.

 

Sounds like an exhaust restriction, make sure your muffed midpipe is not falling apart inside and check your catback to ... I've seen the internal perf pipe section of some high quality muffs start to separate and extend into the exhaust flow if used as a mid muf, lots on heat on our car's exhaust.

 

Yeah, I took the midpipe off--ran open downpipe and it made no difference.

 

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