Ok. This its my first post so take it easy on me please.

Here's my car info: 01 a6 6speed, 116 k, fresh timing belt, double platinum plugs, apr 93 octane tune, 2.5" downpipes w/ high flow cats, billet bypass valves, stock cat back for now.

I had the apr flash done last week and the car ran fine. It was warmer though. Just got the car back today after the timing belt change/ tune up and the downpipes added . It ran great earlier today. We had about a 30° temp downswing this evening. Now I get a CEL with a misfire. I hooked up my diagnostic tool and I'm getting a cyl 1 misfire code. If I change back to stock ecu settings it runs fine.

Do I need to upgrade my fuel pump?

Any help here would be great.

 

Its strange to me that a tune like an APR flash would cause a misfire. If its not the performance tune causing the misfire, I would think its a fouled plug, a plug that not gapped properly, a bad coil on that cylinder or a malfunctioning injector. You can easily narrow the troubleshooting by checking that plug and swapping the #1 coil with another and see if the misfire code comes back and moves to the cylinder you swap to. That will at least narrow down a pausible cause. If it returns your problem may be with the tune or a failing fuel injector. I wouldn't think the fuel pump would be the cause being that the misfire is isolated to only one cylinder.

 

Ok. I'll check it out. I changed to the stock tune today and the misfire started to creep in under load as well. It was just not as bad. It isn't running as strong in either tune today. Just to be sure. What is the recommended plug and gap for slightly modded 2.7 t's?

 

Use the factory recommended gap. It should be in the owners manual.

 

Spark plug type? I ask because on a couple other turbo cars I've had, all copper or iridium worked best.

 

Don't use the factory gap for a chipped car. Gap the plugs down to .028" and you should be fine.

 

Ok thanks. I'll check it.

 

Ok. Did some checking. Plugs are fine. Swapped coil on no 1 and cleared CEL. Warmed up and cooled off, then test drove. Did another code check, and have a little more clarity. Multiple cylinder misfire and one of the cats are not heating up fast enough. The latter existed before the downpipe and cats. One new find is that 2 air box clips were missing. They were there 2 days ago. I ordered new ones just in case. Could that be the problem? The misfire is only under load.

 

Also I thought the mechanic put in platinum plugs. He actually put in iridium plugs. Pre-gapped.

 

Did you regap the plugs to .028"? When you say multiple cylinder misfire, which ones are misfiring? The missing air box clips won't cause your trouble - any air seeping in through the box lid still goes through the MAF and is measured. You can get some MAF cleaner and do that as peace of mind but it probably won't be a fix. The cat warmup is also unlikely to be related - in all likelihood that's a failing secondary O2 sensor on that side. I'm leaning toward what TwinTurboC5 said about a potential injector issue.

Try moving more coil packs around if your plugs are gapped at .028". If you're still misfiring, try closing the plugs down to .026" and drive it. If it boosts and fires properly, that tells me your coils aren't putting out enough juice to ignite the mixture at the proper plug gap, and that you may be looking at a bad ignition control module (ICM) - if I recall correctly the 2.7T has two of them.