UrS4/S6 Stutter/miss-fire/hesitation!!!

[Andyh-R6S]

Hi all

I have noticed that rather a lot of UrS4/S6 owners have had similar problems with acceleration stutter over the forum, me included. (Manual and/or automatic versions0

If you assume (All replaced with new kit) that the MAF, WGFV, coils (034 High output and no separate Power Output stages), Fuel pump, vacuum hoses (Good steady 2.2 to 2.3 boost), earthing, plugs (Sealed correctly) are all operating as they should and other changes are supposedly decent with respect to the ECU (i.e. software remap, etc), then the exhaust is changed for a bigger one, free flow cats and a RS2 manifold is fitted. Is it the case that the standard remaps might just not be up to the job? My car still has this little stutter in top, around ‘3300rpm (ish)’ and ‘1.3 to 1.7’ bar (Instrument) but then on other occasions it is not evident, especially if the car is relatively cold or accelerated through the rev range slowly and not at full throttle. It’s like the car’s ignition is trying to catch up if you know what I mean. In my case, the car is slightly better, but I know it is doing it slightly still but it is bearable.

Could it be suggested that the cars need to be setup/remapped (Fry up) as a custom operation?

I think there are lots of us who have done bits ‘n’ bobs to our cars would like guidance here, especially if we are all looking at custom re-maps instead of ‘off the shelf’ electronic engineering, etc.

[iain1067]

Not a bad point at all, a trip to MRC perhaps???

[Animal Mother]

around ‘3300rpm (ish)’ and ‘1.3 to 1.7’ bar (Instrument)

That level of boost on the OE instrument gauge means your car IS NOT boosting. That looks like limp home to me. Should be boosting to 2.2-2.5 bar.

Boost leaks are also a big possibility.

[Andyh-R6S]

I think we need to understand that the car does actually attain full boost if accelerated gradually and/or on some full throttle occasions. The odd occasion it does it, its limiting the boost, almost like its miss firing (Making its mind up) and it eventually gets through it and goes up to full boost if a little roughly. Although I would agree it would be limp home mode if it did it all the time, mine does not and has similar attributes to other cars on the forum that do almost the same issue. The stupid thing is, if you back off the throttle (let the speed drop slightly to go through the same rev range) and floor it again it sails straight through it, with no hesitation. There are no boost leaks as I have had a dead weight tester attached to the car. (Loaded air supply)

I did not really want to try another ECU re-map as the Mrs is pressurising me to build the bathroom up and there will be no sympathy for me here from her.

I would really like somebody to plug into the car and I take them for a spin to see what variables are changing or not as the case may be, when the phenomenon occurs. I think this is the only way to sort this issue, especially as the ECU is showing no code with the E281 scanner plugged in.

The biggest improvement was changing the MAF and the WGFV for new kit but it is still slightly there.

I am half tempted to take up the offer of a ‘home fry’ but it will have to be covert; otherwise I will be dead meet.

[lune]

I have a custom MRC (Minhea Laptop Special) re-map and have had and still have some of the problems before and after re-map that you describe.
In my experience it's just a case of constantly chasing the weakest link, it's part of the 5 pot turbo charm You wait and long for the day that it actually runs perfectly and I honestly think I've only experienced this for a couple of month's out of the four years of ownership.
I have 3 good friends locally with either S2's or an S6 and after driving them all now and then non of them have been 100% in fine tune

My accelaration stutter was lost for a while after having the cylinder head gasket replaced along with some head work, I don't think it had as much to do with the actual new HG, more that everything from the top end of the engine was either replaced or cleaned up and refitted, including hoses (vaccum, boost & water) sensors and various other bits n bobs. Then over time the occasional stutter or hesitation has crept back in
Apologies I haven't really hit on anything constructive in my post other than keep persevering with leak checks and replacement parts. As for the custom map this will not solve any existing problems and the likes of MRC will not start on a re-map until they are confident that a car is running 100% in it's original form. I guess plugging into an ECU and looking at the live data might give them a clue that somethings up but generally I think it's down to old fashioned fault finding and replacing suspicious parts.

[UrS4boy]

Andy: Despite what you said about plugs and coils being "good", in my experience (93 S4 since 1998), missing and hesitation is almost always related to poor spark, either because of sparkplug issues or coil issues. In the 034 high output thread:

http://www.s2forum.com/forum/showthread.php?t=27684

you show a photo with your 034 high tension leads all bundled together. I would start by separating them with spacers. It could also be that you have a bad coil (or a burnt pin or something as shown in that thread).

When this problem shows up on AudiWorld, I send people to a testing procedure that I wrote. Usually it shows up the problem. While it was written mostly for the OE POS and coil-on-plug system, you might want to go through it and check a few things out, just to eliminate them (e.g. the 034 high output coils) from further suspcision (never assume things are okay):

http://forums.audiworld.com/s4s6/msgs/149788.phtml

You could also have a punky injector or two.

What is the state of your waste gate spring? When I ran too much compression on my 034 1.9 Bar WG spring, I had missing similar to what you are experiencing. Solution was to back the spring perch ALL the way up. Now its just fine.

Good luck.

Dave F.

[Andyh-R6S]

Dave,

It’s funny that you quote the ‘wastegate’ as mine has been totally wrecked by the previous owner some years ago. (It not screwed down though but it does have about three complete turns of spring compression though)

Although I have owned the car for nearly three years I have been going through most of the bits I would have considered to be ‘over the hill’, etc. The wastegate is the last item I intend to change, or should I say, when its replacement comes from Germany this week/next. (eBay) I cannot even take for granted that the wastegate spring in the old or used wastegate is standard, so I will get a new standard part and that area will be totally standard for the time being. (Although if a ‘1.9 bar’ spring is recommended, I will do the same as you have done, although standard at first) The top of the wastegate will then be standard and the spring compression will be back to factory specification. (Picture attached) The only other item I considered, was changing the Oxygen sensor as it is now ’10 years’ old and done ‘111600 miles’ as well.

The spark plug leads are just done like that to keep them out of the way until my spacers arrive. However, the slight hesitation did occur when they were not grouped together and each plug lead has some high voltage insulation (Tape from HV switchgear) a ‘red type clear tape/cellophane’ and then each lead has amalgamating tape wrapped round them, then tied loosely together. But I get your point, just waiting for the stuff to arrive.

I do intend to go through all the ‘034’ kit this weekend to see if any issues exist and I will apply your write-up as well. It’s just a shame that it still does what it did before, with the old falling to bits ignition kit!! (Cracked wires all over the show, etc) The new high output kit did not sort it!

Many thanks for the information, Saturday will be a fun day I am sure.