Hi folks,

I need your help!

I have been chasing a high rpm boost flutter for months now and cannot figure it out to save my freaking life. Overall, the car runs & idles great. I am getting a 10-7-10 transition with recovery time of about 1-1.5 seconds in all gears (Well I didn't try 5th...).

However, once I pass 6000 rpm I get a rapid boost flutter between 8-10 psi gauge.

Other symptoms / facts:
- the engine does not hesitate, stutter, etc, - it pulls smoothly with slightly less power
- the engine note does not change
- The same flutter is visible on the PFC screen (in graph mode).
- The flutter always occurs and is always occurs at the same rpm. It stays till redline.
- The boost level never flutters above the target boost level, always below.
- knock levels get a little more erratic above 6000 rpm, but stay between 30-45
- vaccum at idle is 16-17. Idle is rock steady. compression is 8.0-8.3 on all faces.

I have run the following tests:
- Pressure chamber holds pressure
- Vac chamber holds vaccum
- If I disconnect the wastegate control solenoid (unplug it) to make the WG run on spring pressure alone, I get the same flutter at 6000 rpm - it just flutters between 5-7 psi instead on 8-10 psi.
- If I tap into the rear turbo housing (by the teeing the boost gauge into the line by the 1" charge relief hose), I see 11-12 psi all the way to redline, so the rear turbo is making good boost. I don't get the rapid flutter, but I do get a slower cycling of +/- 1 psi above 6,000. Pre-spool seems to work - I get 8psi by 4100 rpm or so in both 2nd and 3rd gears.
- turbo control actuator retracts when car is started

I have tried the following things to fix this:
Ignition / electrical (since it was at high rpm)
- Replaced spark plugs and wires
- Replaced leading coil with new one
- Installed PFC (Same behavior on stock ECU and PFC)
- replaced 02 sensor (it was bad)
- upgraded all grounds and added extra ones (4 gauge wire)

Vaccum lines / hoses
- rechecked all vaccuum lines, confirmed orientation & function of check valves
- vaccum lines are still secured to WG, PC, actuators, etc.
- confirmed that the pill is in the WG line AND put a clamp directly on top of it so it the hose cannout expand around it
- replaced one-inch hoses from y-pipe with new ones
- pressure tested the system to 15 psi (no leaks found)
- replaced UIM, throttle body and elbow gaskets anyway

Air flow
- Installed gotham high-flow cat (in case stock one was clogged)

At this point, I am running out of ideas beyond throwing money at an hks twinpower, catback, etc. The only things I can thing of left are a) the stock cat-back might be creating a restriction, but it is strange that it would do it at lower boost levels (the 5-7 psi on WG spring pressure), b) some other problem with the wastegate, c) still ignition related or d) some bizarre proble with the WG solenoid.

FYI - The mods on the car as it sits now are:

- Stock motor with 39K on it
- m2 intake
- Efini y-pipe
- Gotham high-flow cat
- stock sequential set-up with viton hoses / check valves
- pfs boost gauge
- PFC on base mod map (unchanged except for boost settings)
- stock factory cat-back
- Fluidyne radiator

Thanks everone for their time - I really appreciate the help.

- Phillip

 

yes.... but did you call your car a "dirty little girl" and promise her "candy" if she runs right.... works for me once in a while....

 

I didn't notice in your list of mods that you had a downpipe to replace the clog-happy pre-cat. Dunno if having a clogged, or mildly clogged, pre-cat on the car would cause a flutter, rather than just a drop in general, but it might be something to check out.
And if you do still have the pre-cat, this would be a great excuse to get a downpipe

 

Hi,
Thanks for the post. Downpipe is already in. Soooo frustrating.

- Phillip

 

I'm thinking your problem is ignition-related, since it always occurs at the same rpm.

I'm also wondering if perhaps your a/f ratios are a bit rich up top, overloading your stock ignition system at a certain psi in the higher gears?

 

What do you mean by flutter? Erratic Boost up and down? Or an actual fluttering noise?

My car had a fluttering sound that started when I put on my downpipe, I found that I didn't tighten the bolts enough and it was leaking only at high rpm (higher exhaust pressure).

 

Hmmm...I have not tuned the PFC yet, so it may be super rich...

The DP bolt idea is also interesting - I will re-check that again later.

The "flutter" is an erratic rapid fluctuation of the boost level. There is no change in exhaust or engine note when it occurs. Just the boost fluttter. Ironically, the boost gauge actually makes noise as the needle is moving pretty fast.

- Phillip

 

ok then that's different from what I had, mine was a flutter sound from the turbo/dp area

 

Is it possible something in the air intake path (hose collapsing, etc.) is fluttering partially shut at high air flow and blocking intake air flow and then releasing as the flow decreases, causing a "flutter?"?

 

Your downpipe being loose will not affect your boost levels.
You can hear the boost gauge making noise over the combined sound of exhaust and engine?

 

Hi,
Particularly with the windows up the boost gauge flutters so fast you can hear it rattle a bit....

DP is a long shot, but could make a difference if there is back pressure between the engine port and the turbos...

Keep the ideas coming...

 

I think Kento's right - ignition makes the most sense.

The trailing coils, ignition coil harness, igniter, etc should also be checked. Timing also I think. Maybe the Crank angle sensor.

I wonder if fuel pressure or injector problems could cause it also? Does your PFC show fuel line pressure? Might a failing secondary injector stick open when given high duty cycle inputs?

Dave

 

Kento,
You are right on the DP..it's after the turbos... I wasn't thinking.

Dgeesman,

How does one test the igniter / harness? The trailing coil testing thing I think I saw somewhere when I was testing the primary...

Additional info...
I tightened down the AWS hose with screw clamps and adjusted the tps sensor last night. No change in behavior.

I was also chasing the possibility of a leak at the CRV. I teed into the vac line from the CRV solenoid to the charge relief valve. Everything works as it should. Vac (20mm) until 4500, then 12psi pressure from the second turbo. Vac returns once rpm drops below 3000. Vacuum pressure holds overnight if car is turned off. Clamps are all on tight and hoses are new.

Overall, the rear turbo seems to do great..smooth even power at 12psi...at least when measured at the compressor housing.

Is there a good place to measure pressure at the primary compressor housing? If both turbos are making good pressure at the housings, that would seem to indicate a leak somewhere downline.

If, on the other hand, the primaries boost is erratic...that would seem to indicate a ignition problem with the primary rotor..what do yall think?

- Phillip

 

See section E of the Factory manual. The coil is basically a resistance test, which while imperfect is better than nothing. The ignition coil harness I would just test by checking the continuity of the harness. Then plug the ignition harness into the bigger engine harness and verify good continuity to the igniter connector. Factory wiring diagram should show these wires. To be perfectly thorough, then check continuity to the ECU terminals, but that's a long way to reach with test wires.

It looks like the igniter test involves a SST, so the only option I can think of is to find someone with a wrecked car and simply swap the igniter and igniter harness for a test drive. Unfortunately, this doesn't cover shorts or opens in the front engine harness, and swapping that is much harder.

Tee into either line running off the center of the y-pipe. One runs up to the pressure chamber and if you tee in between the y-pipe and check valve it should be easy. Above 4500rpm (CCV open), it will be be average pressure between the primary and secondary since their boost is immediately combined. There is no sure way to separatey measure their outputs unless the CCV is closed.

Another place is where the wastegate and precontrol actuators connect to the primary housing. It's a little hard to reach and you'd need to tee into the compressor end of the hose since the boost pills are in the hoses. I would only bother if the above location gives abnormal results.

A simple and conclusive way to check CRV and ABV function is to disconnect the output from the airbox during a test drive. They should be silent when under boost.

Compare this to the boost read by the boost gauge at the normal UIM location - offhand I'm not sure what it means, but it's a useful data point since it lies ahead of the throttle and intercooler.

The boost from the primary and secondary turbos is combined to go to the intercooler, and only split to the front and rear rotor in the UIM. So there is no relation between the individual turbos and individual rotors.

 

Dgeesman,
Thanks for the inputs, I'll try teeing into the primary turbo tonight and see what I get.

"The boost from the primary and secondary turbos is combined to go to the intercooler, and only split to the front and rear rotor in the UIM. So there is no relation between the individual turbos and individual rotors."

Hmm... I was thinking the exhaust side, but I may be mistaken...does the exhaust from the front rotor feed equally to both compressor housings? Or would the front rotor have more of an impact on the primary turbo? Might be insightful for tracking down ignition problems...

Thansk for taking the time to provide input...I appreciate it.

 

Have you physically checked the wastegate linkage and related components?

 

Hi folks,

Found something...I have an exhaust leak between the block and the turbo manifold. Exhaust is coming out right by the rear turbo compressing housing (by the oil line). Seems to be getting a little worse from all of the WOT testing I have been doing.

So what do folks think...any chance this is contributing to the boost flutter problem at high rpm? Maybe once airflow through the motor gets high enough?

I know the rear turbo is making steady 12psi boost despite this leak from my previous tests. I'll check the primary today...

Thanks again for your thoughts.

- Phillip

 

Any updates?

 

Just an idea, after reading a bunch about ignition information: there is an updated design for the ignition coil harness that runs about $40. The old one can cause accidental grounding which of course would affect spark.

Dave

 

Hmmm interesting.Any links?

 

https://www.rx7club.com/showthread.p...nition+harness

 

my 2 cents:
The PFC stock maps are made to run 11-12 psi, at 10-7-10/8 you are running rich through the whole map. that, in combination with a weak coil...
thats all i got

 

12 psi is only 8% more oxygen than 10psi, so in the rich-running world of FDs that's not very rich.

Dave

 

if you can get access to a hks twin power try plugging it in. It can "clean up" some minor or worn ignition related problems. Just an idea.

 

I just looked at the ignition coils i have from the 99 spec engine that i bought,and it seems that the only difference in the wiring harness is the grounding strap(dave's link says the same).The "updated" harness doesn't have the gounding strap that bolts to the engine block-everything else is the same.I might give it a try...