Grant01

I'm hoping some of you stock sequential experts can help me out on a problem.

My FD is running the stock ECU and under primary boost build beyond about 40% throttle there's an excessive amount of stumbling.

Under full boost with secondary fully on I have zero stumbles and it pulls all the way to Red line with ease, and nice and silky smooth

I started trying to dig into this and of course the first thing I do is I put a vacuum gauge and it is around 490mmhg

Numbers seem reasonable, so have hooked a smoke tester into the brake booster port with the primary and secondary turbo inlets blocked off and cannot seem to find any obvious leaks.
I have also isolated the vacuum chamber and other hoses and I'm finding no leaks there either.

I have performed the vacuum chamber test and the charge actuator cycles the six times it needs to according to the test sequence. The turbo control does not it cycles only when the car has been turned on but will not do it without the car being on. I assume something is wrong with this vacuum side but I can't seemingly find anything wrong with it. Boost transitions pretty much at 4500 RPM but the boost dip loses probably like 5psi, so something not right there.

For the love of God can anyone help me.....

DaleClark

iTrader: (55)

First off, I seriously doubt it's something with the turbo control. If your secondary boost is working properly you are good there. Most turbo control issues just mean you are primary turbo only, no secondary.

So, that said, it's a general "this engine isn't running well at low RPM under load" issue.

Are you sure it isn't the 3000 RPM hesistation? Some cars it's especially obnoxious.

Also worth doing a fresh set of plugs and wires and making sure spark plug wires are hooked up right.

Dale

Grant01

Yeah, I don't have a huge concern about the turbo actuator but could be potentially pertinent. Secondary boost hits at 4500 gear 2+ every time and it's a fairly quick transition minus what's I go into below. In first gear without a launch, secondary hits around 5200, which still doesn't seem too unreasonable.

And the stumble does happen at 3k or so, but if I am under a long gear run. Say 3rd gear from 1800+ rpm, it will stumble 3-4 times before secondary comes on.

I installed my power FC again to watch boost readings and it builds boost seemingly smoothly on the charted mode you can view, even if it's stumbling.

Boost transition is a huge drop, about .3 bar (5 psi), but builds strong and smoothly even after the dip and secondary spools

Using the reference of the boost dip I smoke tested the intake elbow off he primarily turbo and the fittings that provides vacuum and that elbow on the face of the primary has a pretty obvious leak and that does provide vacuum to the pre control, so that probably explains the heavy boost dip but doesn't explain a stumble
given that boost appears to build smooth, I suspect sensor or ignition.

Wires are NGK, unknown age but are in good shape. Coils have been replaced with a good used unit, plugs have 9k km on them. They have a slightly rounded electrodes but not outrageous. I'm using the BUR plugs so gap is near impossible to measure. But comparing to new plugs it appears to be gapped out by around .007-.01in on Leading and Trailing.
​I will put the new plugs in today and see how it responds
the TPS reads in spec with vta1 closed reading .44 WOT 4.34 and vta2 is .97 closed and 4.97 wot. (Or really anything beyond 20% throttle). The wot vta2 is just ever so slightly out of spec. I found a aftermarket sensor and it'll be here Friday.

j9fd3s

iTrader: (3)

so it stumbles even with the Power FC?

mine does too, i'm thinking mine is a not happy ground, as it does the 3200 hesitation too. yours sounds more like ignition, you might measure the wire resistance (should be under 16K Ohms/meter), and just put new plugs in it

DaleClark

iTrader: (55)

What mods are on the car?

When you say "stumble' is it a drop in power? Describe better what it feels like.

The 3K hesistiaton is really only a problem on the stock ECU. PowerFC fixes it. With the stock ECU you can upgrade grounds for a somewhat-fix that typically makes it less. I've driven cars that had a bit of a dip in power at 3k and some that did a hard buck at 3k.

OH, big one - do you have the air pump?

Dale

Grant01

*ninja edit for dales reply* When i say stumble I would best describe it as small dips of power, or the car cutting out half way for just a moment. So rather than a smooth power band, it sort of feels like the car has good power and then half second points where it has half power, then full power, then half. it only does this under low RPM high gear situation, so think 3rd gear rolling around a neighborhood, you roll onto the main road and roll into the throttle to accelerate and as it begins to build boost on the primary turbo, the car will sort of misfire, or have variations in boost that are small or whatever is causing it. It will also do it on the highway in 5th if you roll into the throttle to pass someone again moments of full power, mixed with half second moments of half power. RPMs dont seem to have a clear corrilation to anything, BUT as soon as boost builds that is when it is first does it.... so around 2k, then again at 3, then at 3500 then at 4200 then never again. As soon as the secondary turbo comes alive its full smooth to redline. Car engine wise is bone stock with a full and complete rats nest that has been redone with airpump. Air pump on idle cycles off without much fuss.


yeah, with the stock ECU, its quite fussy. With the power FC back in, it stumbles SOME, but nothing like the stock ECU. So whatever the PFC is able to adjust for its working... and based on what i know of the stock fueling, the small stumbles are pretty normal from fueling and turbo transitions. With the PFC, it should be mostly smooth short of the variations of boost.

It certainly feels ignition or sensor related if I had to go with my gut feeling. I ordered a cheap set of Orielly plug wires that should be here tomorrow to least rule out the problem even if they don't last more than 2 days . I will pull the wires when I get home this afternoon and run a resistance test on them.

Is dielectric grease used or recommended on these coils? I am fairly certain (like 99%) they are not greased at all. I guess there could be a chance I have carbon tracked the ignition coil and under heavy load it archs out and it needs cleaned. I could always have a friend boost build it for me, pop my hand in there and see if i get the **** shocked out of myself.... or take a slow mo video, that sounds far less painful

Ill report back tonight after plugs and using a multimeter on the wires.

DaleClark

iTrader: (55)

The stock wires are of great quality and hardly ever have major problems. Those wires from O'Reilly is good for a quick test, but long term you should have proper wires. NGK makes fantastic plug wires for the FD that fit and work great and run about $25 for a set.

Could also be something injector related or wiring to the injectors.

Has the fuel filter been changed in recent memory?

Dale

Grant01

it has not been changed in the 10k KM i have had the car, but it only has 80,000 km on it one japanese owner before me. I like to think its been done before. But i feel if the filter was problematic it would be even worse higher up, not simple low down. Any noteworthy injector tests i can try. I have located a can of BG44k ill run through the system too

Currently the car has NGK wires in it now. so don't really suspect they are the issue, but for 10.99 its a cheap and easy test, but certainly not a permanent solution if that is the cure. I thankfully have new plugs ready to go in. Very hopeful its that since in my experience bad ignition system is often the big low RPM high load problem child.

Im going to check the FPR line and make sure not issues or pinches there. Ill see about pulling the filter and seeing if its dirty at the very least.

DaleClark

iTrader: (55)

It's worth doing the fuel filter just to make sure you are up on maintenance, especially when you don't have previous maintenance records. Read my 30 minute fuel filter change thread for tips and tricks. If you are going to look at it you are halfway to changing it, no sense pulling it out just to put the old one back.

I don't think that's the root cause but just a good thing to do.

Also make sure the ignition wires are hooked up right - if they are crossed or swapped you'll get all sorts of REALLY weird problems.

Dale

Grant01

I had actually found it and will be using that. Looks pretty simple to pull and then just back flow with come carb cleaner. The issue is getting a filter local in any reasonable timeline is essentially impossible it seems unless i want to pay 30 bucks in shipping. It doesnt look so hard to do even if i have to do it 2 times, Ill run some BG44k through it too just in case the injectors are mucked up.

I doubt the wires are crossed since it runs find, idles fine, drives fine, and even full boost is fine, just basically 2-4000 rpm under load is funky.

Grant01

Well, that would certainly be the issue.... You can see carbon build up on the spark plug end of the leading wire for the front rotor, and the resistance is 11 million.... I guess it's a good thing I ordered some wires

DaleClark

iTrader: (55)

Well that may not be the whole problem but it's not helping things .

Start there and move forward. No sense doing any other troubleshooting until you get the known problem resolved.

FYI, a rotary will do REALLY weird stuff with plug wires on wrong. It's not like a piston engine car. Sometimes it will idle and seem to run OK but with no power and the turbos glowing red hot. It literally takes 1 minute to check wires - of course, if you are putting new wires on, there you go.

The coils are labeled L1, L2, T1. T2. Leading is Lower spark plug. Trailing is Top spark plug. Rotor 1 is at the front, rotor 2 at the back closest to the firewall. The coils are labelled.

You can do it with just removing the throttle body elbow. Some of it is a tight squeeze but it's doable.

Dale

Grant01

I validated the install when I took them off and they were in right.

I tore the wire back and the graphite core was cooked for around in inch from the connector, so it has to have been making a huge arch in the wire making for a super weak spark. If any at all.

When I examined the plugs it was very obvious from a wear perspective that the training was hardly being used. A the other plugs have some wear in the electrodes (rounding tips) and this plug had a significantly more squared electrode.

My suspicion is the plug fired at a lowered voltage. But under a 50% throttle condition it probably had the voltage to arch out to the block somewhere. Plugs wires should be in today so will report back. I also found the pcv was clogged so probably not helping my case on running conditions with it drinking oil. Little carb cleaner fixed that right up though.

Grant01

Silky smooth

DaleClark

iTrader: (55)

So it's running smooth with the new wires?

Dale

Grant01

Yup, new wires and plugs and it pulls nice and strong.

One thing that's unrelated to the original post is that I still get an excessive boost drop at transition on my power FC. It's in the neighborhood of five to seven PSI it looks like. I couldn't immediately find any test sequence for the turbo pre control solenoid but I was able to test the actuator using my air compressor and cycling my finger over the vac side of it's and know that it works well.

You seem to be super knowledgeable on all things FD, dale, perhaps you could point me in the right direction for a good solenoid test?

DaleClark

iTrader: (55)

What exactly is your boost pattern?

There's tons of turbo troubleshooting guides out there. Also check the easy stuff - boost leaks are probably the #1 culprit of turbo problems.

Dale

Grant01

Using and vacuum/boost gauge at idle it builds the needed 4 psi when you rev to 5k. So check one there

PFC graph as my guide it builds quickly and smoothly o ~.7kg/mm2 and then as it transitions at 4500 it drops to about .2 then rebuilds again to the same peak of around .7kg/mm2. The PFC doesn't seem to have a sensor check for the pre-control solenoid so I can't watch to see if it actuates correctly.

I have done extensive smoke testing and vacuum line checking and specifically traced the line for the pre-control and found no issues with leaks that have not been already resolved. I have checked the boost chamber, vacuum chamber and turbo actuator cycles boost when it should with about how much it should... Except transition which it dumps a lot out.

​​​​​ I have removed the vacuum line going to the pre control actuator. Applied ~10 psi compressed air on the actuator and you of course feel the air cycle though the line and then when you cap the pre-control vacuum line, actuator moves smoothly and quickly.

DaleClark

iTrader: (55)

Are your check valves good? Does the pressure and vacuum tanks hold vacuum and pressure?

Dale

Grant01

Yes, vacuum and boost tanks hold pressure after the car has been turned off. Check valves are good and all were replaced about 12 months ago when I redid the nest