Hi All,

Been a member here for years, however barely post as I can find what I need via the search mostly - I loathe posting about yet another seq twin issue however I can't find it myself...

Had intermittent boost issues since owning the car (mainly on the secondary) so I bought a new S7 solenoid box and the two green solenoids (waste gate control and turbo pre-control) and replaced the rat's nest.

Now it's all back together and the primary comes on early and strong at ~11psi, the switchover at 4.5k rpm however drops to roughly 5psi and then slowly builds up to 8 or 9 psi by redline on the secondary depending what mood it is in.

Car is stock apart from I'm running an S7 Power FC on the base map. I've tried swapping the stock ECU back in however it ran worse again.

It is also running rich, you can smell it pretty strong at idle, I have dyno graphs too which I'll post pics of.

If anyone can support me solving this I'd be very grateful, have just been driving as it is for 6 months or so as I'd more or less thrown in the towel... Also to note I tee'd in to read boost just on the secondary and it seems the secondary is indeed making low boost.

Parts replaced (including one way valves and hoses):


Dyno info:




FYI:
0.8 Lambda = 11.8 afr
0.75 = 11.0
0.7 = 10.3



Thanks for reading

 

Don't have a S7 FD so I cant comment on the black box but I can say that you may want to check the actuator rods and see if they are connected. The clips that holds them to the flapper doors can fall off and the rod will pop off (circled in red)
I do know the the S6 FD's have restrictor pills in the lines shown - but on the later models they were build into the turbo housing instead (not sure if this would apply to you)

The pre control actuator works with both pressure and vacuum so if one of the pressure tanks or vacuum tanks have a leak in them (or any of the vacuum lines for that matter) you may have a partially working precontrol actuator.

Also check the charge control valve in the y-pipe

I've had a problem similar to this in the past and im pretty sure one of the actuator rods popped off due to a lost circlip.

 

I would verify the turbo control door is opening and the TCA is moving. That's hands down the top problem for no secondary boost.

Dale

 

Is it possible the new twin duty (green) solenoid set is malfunctioning? [How long have those NOS solenoids been bumping around in parts bins?]

Have you done a "smoke" test?

Its nuts that those little C clips can cause havoc. What do they cost $.05? Best to check those on a regular basis. I've seen them disintegrate with a little poke from a screwdriver.

Checked either of your blow-off valves?

Does the Power FC account for the extra air dumped in ahead of the O2 censor by the stock air control valve? Could the Power FC be getting a false lean reading and adding fuel as a result?

Do you have access to a JDM code reader? (Likely not useful with a Power FC; put stock ecu back in a run codes?)

Check the direction on your map censor filter.

Fins on the secondary turbo OK?

 

Holy thread revival time!

It is possible the green solenoid set is malfunctioning I guess, one test I haven't tried yet is unplugging the pre-control side of that solenoid and seeing if it makes any difference.

How would I "smoke" test?

MAF sensor filter is in correct direction.

So I've checked the C clips with the exception of the wastegate actuator as on the RHD versions the steering column means I can't remove the heatshield, however I'm fairly certain wastegate actuator is functioning as I get 11psi on the primary.

I used a vacuum pump and a bike pump to verify that both sides of the Turbo control actuator are working and both the wastegate and pre-control actuators.

Checked the air bypass valve and CRV, the CRV was out of spec so I replaced but no change at all.

Verified that the pressure tank and hosing holds boost and the same for the vacuum tank and hoses holding vacuum, KOKO test works as expected.

Got a feel of the secondary turbo blades, no play at all and spins freely.

Also worth noting that I ran the stock ECU for a week, ran even worse but didn't throw any error codes

So at that point I decided to give it a rest for a while as life and work got far too hectic.

Pretty tempted to rip the lot out at this point, rebuild the motor and go single SXE like everyone else, unless anyone else has any bright ideas?

Oh there was one other symptom, I can hear a high pitched whirring noise that sounds like it is coming from inside and builds with revs, fuel pump perhaps? Not sure if that would cause a low boost issue though, would anyone know what stock injector duty cycle should be relative to the top half of the rev range?

Thanks to all who have helped to date

 

Did find precontrol and wastegate solenoids are the most reliable on the car, simple to test as long as polarity is observed - and alligator clips help there. Dgeesaman(sp?) did have a comprehensive test protocol on all that twin stuff ages ago, which wouldn't go astray for your troubleshooting.

Smoke generator goes up either the intake or tailpipe. Ideal to find boost and exhaust leaks.

 

Our local shop that does about 75% of our local cars refuses to try and save the sequential set -up. However, if you can its nice to have the sequential.

Do you have the correct version PFC? Maybe try another one?

Watch out how your ignition coil leads are attached S7 and S8 connection pattern is different than shown in the USDM LHD manual.

I had a bent rubber oring in my fuel pump, which was the root of many evils.

But it was the miss attached leads that cost me a corner seal (or two).

(Hint: If you hit 6000rpm and hear a loud mechanical bang, pull over and call your banker. Your engine might be trying to run backwards.)

 

Decided last night to rule out a blocked catalytic converter/exhaust, so I unbolted the downpipe where it attaches to the cat, I didn't take the exhaust off completely just left the gap of about 2cm, enough to test the theory, don't worry it cant fall due to bracing and hangers.

Be warned if you do this to test your low boost secondary, even with the PFC boost control set to 7psi (0.5kg/cm²) and at only 3/4 throttle, on transition at 4.5 - 5k rpm the boost almost immediately hit 12 psi and the PFC thankfully fuel cut! Also it is loud AF

Anyway I now know that the issue was backpressure, probably from a dead cat which was causing the secondary boost issue, now to find a de-cat If only I tested this before shelling out ~$2k on parts and dyno time