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Boost flutter

4K views 17 replies 7 participants last post by  Slowryd 
#1 ·
I posted about a month ago and thought my issue was a boost leak, but I really don't think that's the problem. Here's the issue (2005 SRT-4, stock except for exhaust): Totally works perfectly if I drive OFF boost. If I gradually increase the throttle, even up to near redline, it still works okay and will work up the boost to about 10 psi. If I boot it with full throttle to the floor quickly, the boost will start to climb and when it hits around 8 psi the engine stutters and the boost gauge shows a corresponding flutter/stutter. Sometimes this won't occur during second gear boost --- all works normally and it will achieve 12-13 psi boost. But when in any higher gear (3, 4 or 5), and I give full throttle boost, it stutters/flutters terribly, trying to get over 10 psi but cutting back the boost and physically shaking the car. So I'm wondering, is is a problem with the Throttle Position Sensor (TPS)??

I'm stumped on this one :frown:

Todd
 
#2 ·
Are you trying to achieve full boost while boosting through gears or are you in gear cruising and then punch it?

Pcm Boost?

Factory wastegate?

Vacumn line setup?

Please bear in mind in colder weather the Pcm will dial back boost. The only time I've experienced what your describing is if I happen to go WOT in 3rd, 4th, 5th at a low RPM without being in boost in a previous gear. If that is what you're doing I'm going to have to say that is normal.

If you are boosting from the previous gear and transition to the next while going WOT and run into that issue, then you may possibly have another problem.

If you can do so safely might be a good idea to post a video.
 
#3 ·
^^^True.

If it is different now than it was, the you probably have the spark blowout issue that happens when the plugs, wires or coil are the problem. So try those in that order and see if that fixes it.
 
#4 ·
I switched out the coil pack and that made no difference. The plugs and wires are fairly new so I'm doubtful that's the problem. I thought it might be the wastegate and I happened to have an AGP wastegate actuator, so I put that in. I made sure to adjust it so that max boost is still at 12-13 psi. Everything hooked up properly. But exactly the same problem as with stock wastegate. It feels as if the system "thinks" it is making too much boost then tries to cut back boost. As mentioned above, it will always do this in 3, 4 or 5 gears, and only occasionally in 2nd gear. I haven't tried it in 1st gear but my guess is that it will work OK in 1st. I'm at out to lunch by thinking it might be the TPS??
 
#5 · (Edited)
You're still not answering the other questions sir.... it's beginning to sound like your AGP wastegate is the problem. You would be better off selling it and getting a DSP to raise boost and join us in 2016. =)

Besides if the system was making too much boost you would either A. Pop a code or B. Peg your boost gauge.
 
#8 ·
#9 ·
Who's on First? :jester:

I've been wrong plenty of times, I read that as the AGP was the second wastegate so that's what he installed. Unless he is using a MBC or tune he doesn't have another way to set the boost at 12-13 psi.

In his previous thread he mentioned he is not on PCM boost, using the AGP, and blocked off his red line. That's why I'm asking him to let us know his setup. Although he's saying he's "stock" some changes have been made. I politely addressed that in his other thread also.

OK, I'll check the gaskets. I happen to have an AGP wastegate actuator which I'll put on in place of the stock one. Will see what happens....

TM
Checked all the gaskets -- seem OK. Put on AGP wastegate -- no change. Gets boost (about 12 psi) up to 4000 RPM then cuts back and stutters and hesitates. Anyone think it's a fuel pump or fuel filter issue??

TM
Not on PCM boost. But AGP wastegate instructions said to block off the red line where it hooks up to solenoid position #2 .
Well it's now fixed. Turned out to be a boost leak at the main intercooler charge-air pipe clamp where it comes off the bottom of the intercooler. But this whole exercise made me check everything else thoroughly, so that's a good thing.

Thanks guys for the tips!

TM
 
#12 ·
#13 ·
It could be plugs or wires. I will check these. Right now I have NGK Iridium (one heat range colder than stock) with 0.032" gap. They were working fine but then this problem started. I'll look at the wires and plugs closely. Re above replies, I only put in the AGP waste gate in order to see if my stock waste gate was not working. But I get the exact same problem with the AGP as with the stock one. I do prefer the stock waste gate and will put it back on. I'm not getting any overboost codes and I have all the colored vacuum lines from the 3 solenoids all hooked up correctly (reconnected the red vacuum line).
 
#18 ·
https://www.youtube.com/watch?v=1WUJMucIam4
https://www.youtube.com/watch?v=ZDntHUDldjY

So this started happening last month and I cant figure out what the problem is maybe someone can help. One video is with out the standard Diablo tune, and the other is stock

Car has no mods done to it, completely stock other than intake.

Maybe a boost leak?
Are you using a mopar coil pack and wires? Boosting while not under load is a bad idea.

Sent from my SM-T710 using Tapatalk
 
#15 · (Edited)
It looks like you are hitting full boost at a low RPM. The engine can't physically consume that much air at such a low RPM. I'm not sure if the noise is "compressor surge" (The turbo trying to spin backward) Or if you have a boost leak and it's only leaking at a high psi. What kind of Blow off valve are you using?

Also, On the second video, Are you keeping your gas pedal steady? OR are you lifting off the gas and pressing it? IF you are keeping the gas pedal steady on the second video. Check the Throttle position sensor voltage, key on engine off with the diablo. SLOWLY press the throttle down to the floor and watch the voltage. Make sure its slowly and and evenly changing voltage. If you find a "Dead spot" Where the voltage either jumps up or falls down suddenly then I'd say the TPS is bad.
 
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