Maybe: Misfiring, bad plugs, possible vacuum leak...?

[jaywood]

Turbo m20
30lb injectors
Begi rrfpr
Turbo chip
Wideband
Boost/vac gauge
Oil pressure gauge
~7 lbs boost
Ngk plugs

I've had this setup for a couple months and it's been driving pretty good. I don't abuse the motor. Just recently (3 days ago) the idle started to stutter. I would let off the throttle and it would drop low on the rpms, then rise, then drop again, then rise and stay at ~800. I figured it was a vacuum leak...no big deal. So I was driving to school this morning and I was going down a hill and using 2nd gear as my brake (no gas, just cruising). I pulled up to a stop sign, waited for traffic, and slowly pulled away in first gear. That's when I heard these symptoms:

Bad idle
When idling and giving it some gas (holding it around 3k) it sounds perfect
Driving with light throttle it almost sounds like knocking/popping
It came out of nowhere
No easily visible vacuum leaks (looked it over for a couple minutes)

What could it be? Bad plugs? AFR is right where it should be so I don't think that's an issue.....


Thanks in advance r3v.

[Ceeker]

check 02 sensor..unplug it and see if the car drives better. if there is a change it is most probably that.

[jaywood]

Don't have an o2 sensor. Just the wideband (lc-1) with the narrowband output wire connected to the stock o2 harness (sending narrowband signal)

[jaywood]

Just drove it home from school. It had the same problems. At first it wouldn't start but it eventually did.

It only had symptoms when I was on the throttle. Say I was in 2nd going 25 mph, I let off the throttle and it sounded normal.

[ak-]

Those were my early symptoms of a bad TPS and cop/rotor. Eventually I hit a brick wall @ 3rpm with intense back firing/misfiring.

[Jaxx_]

Before we jump farther than spark plugs... what do they look like?

[jaywood]

Haven't checked them out yet. I will do that soon and post pics here.

[jaywood]

Pulled plugs today:

[Jaxx_]

is that oil or carbon? they look really rich.

Did you change the plugs after you did the initial tune?

[jaywood]

is that oil or carbon? they look really rich.

Did you change the plugs after you did the initial tune?

The tips are carbon.

No. These are the same plugs. I am just on a chip though...so I did fuel pressure, AFR, and other tuning on these plugs.

[jaywood]

Anyone?

[Kozworth]

Turbo m20

Bad idle
Driving with light throttle it almost sounds like knocking/popping

Thanks in advance r3v.

A knocking/popping would make me lean towards spark knock. Aka, you have detonation. Correct me if im wrong (just trying to apply what im learking in class) but carbon buildup could affect how gasoline burns if theres too much of it. Running a turbo with bad gas/wrong octain cannot have a high enough octane rating to reduce spark knock.

Did you just fill up before this started happening?

[HR2L]

Swap out your plugs, check your wires, rotor and cap, as well as coil. Looks like you have excessive carbon deposit but its glossy which indicates possible splash fouling (wet) from carbon build up on piston face during running shedding off and fouling up the insulator and strap. I'm under the impression your turbo set up is turned and AFR is being monitored? What do your AFR's look like @ cruise and WOT as well as warm idle? Could just be a weak spark, which is creating an incomplete combustion which is why you are hearing the popping sound at partial throttle (spark isn't as strong as it is @ WOT). If you haven't done an ignition overhaul in sometime, you may want to think about it.

Good Luck, and keep us in the loop about what you do, and what happens. :)

[jaywood]

I did just fill up, but I've been running the same gas (91) from the same station for a few months now.

Yes. I've got it tuned. When I start it in the morning it runs at ~10.5. Yes, you read right....10.5 at idle. It's only like that for a minute or so (motronic ignores the adjustments I did to the AFM wheel. It enters a pre-programmed map during warm up which is designed for 14lb injectors, not 30lb) When it's warmed up it idles at ~14.5-14.8. WOT it's in the 12's.

Stock ignition setup.