Hi everyone, I recently purchased a 2002 996TT. When I test drove the car it initially broke up a bit, but cleared up and ran like a champ to upwards of the end of 5th gear and a touch of 6th without a miss. After a day or so and a 16 hour drive home (FL to CT) the car developed multiple misfires and has been breaking up under load.

I immediately thought the issue was plugs, so I replaced them with NGK BKR7Es and gapped them to .025, shortly after I took it out, warmed it up and same thing, misfires when it sees load and more than .5-.7 bar. It seems to idle smoother, but still breaks up under load – Part throttle the car accelerates fine up to about .5-.6 bar, if I add a bit more throttle – immediate misfires and the car goes nowhere!

The car has the following mods:
Billet K16’s
EPL 72lb tune / injectors
997 Coils
2.5” inlets
2.5” custom exhaust
4.5” custom intercoolers
Silicone boost hoses
GT2 slave
Upgraded Clutch / FW

I purchased a Durametric (enthusiast) and scanned the car and came up with the following:

P0174 – Oxygen sensing adaptation idle range bank 2
P0300 – Misfires detected
P0301 – cyl 1
P0304 – cyl 4
P0305 – cyl 5
P0303 – cyl 3

So, now I’m thinking it’s a vacuum leak, boost leak, or possibly coils… I say possibly coils because when idling the car has a slight miss and an audible snap or arcing can be heard. The car will also slightly miss when accelerating at low speeds (RPM) in 2nd or 3rd or when under load.

Since I am new to the platform I am looking for any helpful input.

Thanks in advance,

Dave

 

if you have an audible snap or arcing you might want to check for proper ground...

 

I'd first do the coils....then check connections and do a pressure test.

 

The 996 coils are prone to cracking. The 997 allegedly fix that. (Worked for my car) If you buy new ones, they should automatically have the 997 part number.

 

The coils are 997, I verified that when I did the plugs. They have less than 4k on them at this point and did not appear to have any cracks.

 

With misfires and the classic sounds of high energy electricity arcing I'd have to say 'coils'.

Just because they have only been in there 4K miles doesn't mean one or more (4?) have not gone bad.

They may be the wrong coils, too, or installed incorrectly, and unless you saw them for yourself, they may not have been replaced at 4K miles.

Use the Durametric to look at short and long term fuel trims. If there's an intake leak the trims will be on the rich (+) side as the DME adds fuel to compensate.

If the leak is not real bad, when you raise the rpms up to say 1500, the amount of air the leak lets past compared to the total amount of air the engine is using drops and the DME will subtract fuel.

My reference doesn't list a P0174 for the Turbo. I find a P1130 which has a nearly identical 'description: "oxygen sensing adaptation, idle range bank 2" as P0174.

The MAF is suspect #1. Measure voltage at Pin III/23 and ground switch on the ignition and read 0.9v to 1.1v. If not replace the MAF.

Start engine. Read approx. 1.4v. If not replace MAF.

Check fuel pressure. Fuel pressure too high. Check the fuel pressure regulator an, vacuum connection and fuel return line, too.

Check fuel injectors for leaks.

Sincerely,

Macster.

 

I would say you have a bad O2 sensor. My failed primary O2 sensor caused misfires.

 

+1

Using a multimeter measure the resistance from the engine block to the battery negative terminal. Should be very near zero ohms.

Misfiring will mess up o2 readings

 

Thanks for your response. I did the plugs myself and verified that the coils were newer / recently replaced 997 units. I reinstalled them and all went smoothly.

The thing that makes me beleive that it might be the coils is the arcing and miss that I hear at idle. It could very well be a compund problem and I will be going through all the steps that you mentioned as well as pressure testing the car as soon as I can.

Thanks guys. Any more input is welcome.

 

i would check the maf first.

 

I would replace the MAF as well they are only 60 bucks on ebay

 

So I (formerly gtiman99) finally had some time to put another set of NGK BKR7E's in gapped to .025 and replaced all of my coilpacks with new units. The misfires are gone and the car runs hard! I am very happy and plan to Vbox the car this weekend.

 

I would say MAF, my first TT did the same thing as your describing and when i changed the MAF, it made a huge difference.

 

its your coils. i've had a set of 997 coilpacks go on me. i also did plugs and problem persisted, i thought to my self no way it could be the coils. but the symptoms point straight at them. so i replaced all of them and - problem fixed. good thing they carry 12mo warranty when you buy thru pelicanparts.

 

Tha't exactly how I felt. I am glad that the problem is gone and the car is running well now!