Problem description:

Frequent and reproducible hesitation and misfire during maintenance throttle and mild to moderate increasing throttle in most RPM ranges. Most pronounced in the 1500 to 3500 RPM range.

Maintenance and troubleshooting history:

35,000 mile bone stock 2001 996 TT car showing no fault codes. Plugs and coil packs replaced at 30,000 miles. Vacuum leaks corrected at 34,000 miles. Cleaned MAF thoroughly with no effect. Disconnecting MAF had no effect on problem. Durametrics data collection attached. Results appear that misfire is random across all cylinders. I don’t know if this is normal but O2 sensors and lambda setpoint (column E, F and G) seem to go haywire (O2 values at 5, lamda setpoint at 1.04) at times (see counter positions 1204, 1383, 1581, 1842, 2059, 2100 etc, etc)

Next steps:

Need help on this. If the brain trust can read the data collection and glean something that would be much appreciated. Feel free to suggest other fields you want to see. Suggestions on the next steps are very welcome. I’m thinking that running some Techron through the system is a decent next step. Your thoughts?

Thanks,
Dave

 

if you've modded the car, you may want to read this post:
https://www.6speedonline.com/forums/...must-read.html

 

Thanks FDSS, the car is bone stock,

Dave

 

What kind of plugs? Maybe a boost leak?

 

Thanks Chad. The plugs a Bosch, all leaks were identified using a smoke machine and corrected.

Dave

 

What model of plugs? FR6? Were the leaks vacuum or boost?

 

the plugs are FR6 LDC

The leaks were in three locations

1. side port on aftermarket diverter valve unscrewed

2. O-ring at boost hose leading into left side intercooler

3. O-ring at boost hose leading out of left side intercooler

I don't know if these are just boost leaks or if these are alo vacuum leaks at idle/decel

Thanks for your help,

Dave

 

Guys,

really stumped with this one. Any more ideas?

Thanks,
Dave

 

I had misfires also, I changed my MAF, alternator, plugs, and ignition coils.

The damn thing was the O2 sensor (drivers side one after the cat) was touching a part of the aluminum plate of the engine and this was causing all my grief. I had the mechanic fix the mounting of the O2 sensor and for good measure the area it was rubbing against was removed.

This has stopped all my issues.

Good Luck

 

You gotta have it checked out properly.....FR6 LDC....not a good one....do your research

 

Thanks art4iza for your reply but I a bit confused by what you said. In the 16 or so spark plug discussion threads on this forum, no one had a particular problem with the Bosch FR6 LDC and some reputable shops recommend them. In fact, on 10/30/08 at 01:45 am in a thread entitled “spark plug selection” you state “I would go with Bosch, FR6LDC or LDU at that level.” This was for a car on the lower end of the boost/power range. So I've done some research and come up with only positive things for that plug. What am I missing?

Not sure what you mean by having it checked out properly. The car has been to a very reputable local shop twice, a full service when I bought the car and a diagnostic call to try and determine the cause of the hesitation. Those guys found the leaks. Any tool I don't have to perform diagnostics I'm willing to source or borrow, and I've opened the analytical discussion up to the world for input. What have I not done properly so far?

I suppose I could just dump the problem on someone else but that really is not my way and some would argue that's not the proper thing to do either. I could list why I think I'm qualified to work on this car, I think you would be satisfied.

 

I used to have FR6 LDC in my stage IV EVOMS two years ago....which was fine. Then changed to FR6 LDU which is used in GT2's and was great. The higher power you go, you need colder plugs like Iridiums. My suggestion to have it properly checked is to look into durametrics, assess problem, identify the cause, and find a clear solution.....Looks like you're heading toward the light.