Mid-boost mid-throttle stutter

[Aaronbrook37]

Diagnosis:

Partial throttle and partial spool
RPM and load varies
Any gear from 2nd-5th inclusive
Very quick stutter between 0-2psi on the boost gauge

Progress:

Voltmeter reads a steady 14.7/14.8 volts at full load/operation.
Plugs cleaned and gapped to 0.031".
Cap and rotor cleaned and dried out.
Checked base ignition timing and coil resistance.
Checked air filter and new fuel filter.
Got the steadiest 22inHg I've ever seen.

Next steps:

1) Reset the ECU.
2) Fill up with fresh 91 octane.
3) Air blast electrical ignition components.
4) Delete boost controller temporarily.
5) Check the function of my blow off valve.

From there, I'll likely be building a boost leak tester and buying a fuel pressure gauge. Any thoughts?

[Aaronbrook37]

Resetting the ECU did nothing.
Filling up with fuel did nothing.
Air blasting the electrical components did nothing.
Deleting the boost controller fixed the problem! I had the knob set so out of whack that the car didn't know how to boost!

[Aaronbrook37]

Also, the BOV was starting to stick. Lubricated it liberally... and it opens significantly faster now. That means more PSSSHT and more fun!

[Aaronbrook37]

It's happening again unfortunately. Thinking boost leak or spark plug leads. Will test resistance and build a boost leak tester and report back.

[SiliconSoul]

I'd go over your vacuum lines with a fine tooth comb. Especially if it feels like its flat on the top end.

[Rocketman]

Do you have a stock ECU? Try turning the boost back to stock, and a stock ECU. See what happens.

[Aaronbrook37]

Darn... I can't quite recall where I put the darn thing. I'll try another boost controller delete though and see if I get the factory rated boost spec. I'm running a VJ11 full turbo with a VJ14 wastegate. Never had any problems like this before.

[Aaronbrook37]

I always say to myself that I finally have this car figured out and in perfect condition. Hopefully, unlike every day before this, I'm actually right today. I went manually hunting for a boost leak the only way I felt like trying given I've been having some terrible migraine headaches lately and didn't really want to use my air compressor that much. Over the course of a good hour or so, I disassembled everything in the intake stream from the air box and air flow sensor to the throttle body and idle air control valve. Almost obsessively, I combed over every single fitting, every single clamp, and every single piece of rubber/silicone/steel. It was all thoroughly degreased, cleaned, rinsed, dried, and torqued.

I took it for a spin after this feeling really sure that there couldn't possibly be any boost leaks anywhere in the system. Unfortunately, it was bad... not only bad, but worse. The stuttering was becoming more and more prevalent, particularly when the car was all warmed that. This and the fact that the idle was dropping down to uncomfortably low levels whenever I put the clutch in. It almost felt like the car was intermittently running on three cylinders... but I thought nothing of it and kept going as I had errands to run. Ten minutes later, with crazy amounts of grey smoke flying out of the tailpipe, I pulled into my girlfriend's driveway and popped the hood.

What I saw not only shocked me, but almost embarrassed me as well. One spark plug wire was loose at the distributor cap, and another had come completely off. Frustrated, I thought nothing of it and popped them back in quickly. What I neglected to of course notice was the goings-on of the actual spark plug wires inside their boots given they had been pulled back/out likely due to frequent install and removal. Figured that one out this morning when I was rechecking my plugs... noticing a shiny gold piece hanging out of one of the boots. Pulling them all back through completely, I feel confident that I had probably solved my intermittent spark issue and smoking problems.

[SiliconSoul]

Lol.. at least you hopefully have it figured out. It's always a little thing, but like a needle in a haystack you have to find it first!

[Aaronbrook37]

I have reason to believe that my exhaust fasteners have recently gone on strike. After I got the car up on four stands, I quickly discovered that essentially every single one of them was somewhat lacking in tension from a handful of the exhaust manifold nuts all the way back to the muffler bolts. It made these past few weeks rather loud, obnoxious, and smelly to say the least... particularly under heavy load and or high boost. Though it may not be related to my recent ignition stuttering, it's useful to make a note of for the search archives. Perhaps my old torque wrench is starting to fail... I can't say for certain. Either way... I gave them all every ounce of strength in my body this time. In the past, I've sort of always just assumed that the car would ooze smelly, noisy testosterone... but that's not good enough for me any more. I'm putting an end to smelly cabin pollution, migraine headaches, and exhaust drone!

[Aaronbrook37]

Took another look at the ignition timing... turns out I was off by a few ticks due to oil and goo build-up on the notches. I put it back to 13* BTDC. Here's hoping that clears it up. Boost leak tester going in shortly!

[Aaronbrook37]

Home Depot boost leak tester is a success. A few of my t-bolt clamps are oddly sized, requiring more than just a deep 10mm socket to tighten them sufficiently. Fortunately, 10mm closed-end wrenches got the job done.

The final boost leak is a big one... coming from the intake manifold fuel injector grommet on cylinder four. It certainly explains the intermittent nature of the misfire/stutter and the reality that it intensifies with heat/load/throttle/boost. Gonna leave it for another day though because I didn't feel up to working around gas fumes today.

[bhearts]

sounds like you need a flyingmiata voltage clamp. thats what iceracerdude always harped to me. those afrs try and change and closed loop operation isnt havin it.