tonycosta1984

So I've been having a problem lately with the 93 s4, it won't accelerate properly, particularly on the freeway or if I have the pedal to the floor. It seems like a big miss, and almost has a bucking type motion. Any ideas on where to look? Ps. I don't think its a coil problem because i'm running 4.2 liter coils with the apikol plug and play kit.

UrS4boy

Never say never. How is the idle?

If you have a 1.8T/2.0TFSI/4.2L V8 coilpack installation, it is both easier and tougher to diagnose. If the problem is oil under high load (RPM and boost), you won't be able to figure out which coilpack or plug it is. Wait a bit until the miss starts to happen at idle.

If you seem to have a rough idle, it will be one cylinder. Pull the injector electrical connectors, one at time (and then replace). When you pull a connector and the idle gets worse, the issue is NOT on that cylinder. Replace the connector and move on. When you finally pull an injector connector and the idle doesn't get much or any worse, you have found you culprit. Replace the connector and make note of the cylinder.

Stop the engine. Pull the "problem" coilpack and swap it with an adjacent coilpack. Reconnect the coilpack connectors and start the engine. Go through pulling the injector connectors again, one at a time. If the problem cylinder becomes the one where you moved the "problem" coilpack, then it is the coilpack. HOWEVER, it the problem cylinder is the same one as before the coilpack swap, the issue is that cylinder, either the plug or the coilpack wiring or potentially (hopefully not) a burnt exhaust valve causing compression issues. Confirm with a warm engine compression test (all plugs out, dry and then wet).

If the compression test shows up that cylinder as the problem and there isn't much increase in the wet compression numbers on it, then it would confirm burnt valve or potentially a ripped head gasket.

These are the steps I would take.

UrS4boy

After my first post, a guy on a UK UrS forum who can't get his UrS4 to rev more than 4000 RPM in 5th or 6th (OE 6 spd) (been on-going for weeks), finally posted this photo and wondered whether it would be the problem.

Umm... very probably. Crimped/twisted line (because somebody changed the filter without holding the filter with a wrench when tightening the fitting on the fuel line). Restricting the fuel flow significantly. One poster nailed the diagnosis on the head: Lack of fuel = It will go lean, knock and the ecu will retard ignition and try to add more fuel, it will basically just hold back.

Sound familiar?

tonycosta1984

I haven't changed the fuel filter since I got the car in 2012. (I guess it's about time) I'm gonna try the coil/injector test as you mentioned and do a compression test too.

P.S. The idle seems fine as of now, but the problem does seem to only occur under heavy load.

tonycosta1984

I did a compression test first (cuz I was nervous) and it all checked out. Which is good news. I changed the fuel filter, just cause I had one waiting to be installed. I'll see if that makes a difference.

GoHeels

I've had this problem for a while. I've learned to live with just easing into the throttle enough to trigger the boost and back off a bit before it starts stuttering. I'm mostly on the highway and I've learned how to get the boost without the hesitation by going a bit easy on the throttle.

To me its always felt like my S4 did when the vacuum hose was coming off the moisture trap, so I've replaced some small vacuum hoses. And when my oem coils started acting up 4 ys ago, and Dave helped me asses, I got the LS2 ignition from Marc. But that was serious limp mode, the car would barely go down the street.

So hope you get yours sorted out. I'm likely in the market for a new anyway. At the moment I'm actually thinking 2012 328i sedan with a 6-speed. About the same size as a C4 with a tuneable turbo, sport seats etc. and 30+ mpg. Not sure I'm capable enough to work on it myself like the S6 though, with so much computer stuff these days. The S6 has been wonderful otherwise. I've driven an S4 for 4 years followed by an S6 for 5 years with very few issues. Almost all they ever needed was routine maintenance, most of which, with the help of Dave, Tom and this forum, I learned to do myself with my simple box of tools. Thx to all for the great help of course.

tonycosta1984

it feels kinda like an over boost fuel cut off situation, I'm not sure if there's a boost leak, but I'm gonna try to check it out. PS. the fuel filter helped a little bit, but the miss is still there for sure.
good luck with your situation . I hope you stay in the s car gang.

tonycosta1984

still can't figure it out. It's seems to happen in every gear except for first and only at wot and pretty much only between 3000-4000 rpm (roughly) I've changed the fuel filter, air filter, oil and oil filter. and also cleaned the maf. I inspected the michelin man hose and it seems fine to me. Also, checked the plugs and they seemed pretty decent for being about a year old. I'm running the ngk iridium BKR7EIX.

I ran the idle test that dave mentioned in a previous post and I couldn't seem to pinpoint a problem with one specific cylinder. e.g. When I pulled injector connector the idle seemed to get just a little shaky, but it seemed the same at every cylinder.

I also just did the basic check to coils to make sure each one had spark, which they did, and listened to each fuel injector with a long screwdriver (old school test lol) and each one seemed to be working the same.

Any ideas on where to check next. The part that gets me is that the miss doesn't really seem to happen in first gear, but it does in every other gear, but its only at wot and it's not Intermittent. It happens every time. which makes me think that it's an electrical or sensor type of issue.

UrS4boy

The MAF is definitely become the number 1 source of running problems. I put it as the first thing to check when diagnosing missing and hesitation issues a while back:

One missing and hestitation diagnostic procedure:
Click HERE

GoHeels

Does it do it when the engine is cold and you first pull out of the driveway... I don't like to do it but mine will usually boost like hell till things warm up. Last thing I replaced with the N75 valve, but nothing changed.