B5 S4 NEED HELP. misfires at WOT and horrible MPG

[S4M]

well i'll start off by listing my current mods: used milltek downpipes and exhaust, used diverter valves, i put in a different ecu (same as my M box) with a giac chip in it (actual chip not flashed. opened it and date chipped was in 2004).

anyways, a few months ago i was just about to race an Evo and just as i stepped on it, i felt a little hesitation and the CEL starting blinking (this happened about 3 days after i put in the giac ecu). i pulled over and i heard a little rattling sound under the car which turned out to be the drivers side cat. i continued to drive the car and it seemed to run fine but when at WOT it it did seem to have lost a tiny bit of power. when i got home i read the CEL and it was "P0300 Random/multiple cylinder misfire detected". i thought maybe a cylinder wasnt firing. but the car seemed to run fine. i continued driving it and over the next few days or week it got worse and worse. it started to misfire and hesitate like crazy at WOT and it was the worse when the engine got warmed up. i than got CEL's "P0304 cylinder 4 misfire," P0306 Cylinder 6 misfire," and "P0431 warm up catalyst below threshold (bank 2)" (not all at once. i think over the next few days). it ran like crap for the next 2 weeks than all of a sudden it seemed to work fine, but once again not exactly all the power i had when i first put in the chipped ecu. i changed the primary O2 sensors anyways and i did seem to get a little better MPG. but than a few days later the problems started again. but it seemed to run nice and smooth with no problems if i didnt floor it. so i just kept driving the car every day. well now its still misfiring like crazy at WOT. it feeling to me more like the ecu is holding the car back (limp mode or fuel cut or something). it accelerates very slowly. the misfiring or whatever problem this is usually starts after 3,500 rpm's. now im getting horrible gas mileage especially after ive been driving it for a while and its all warmed up. it probably will get like 10-12mpg.

here are all the CEL's ive gotten in the order that the did come up ever since the first misfire:
-P0300 Random/multiple cylinder misfire detected
-P0304 cylinder 4 misfire
-P0431 warm up catylast below threshold (bank 2)
-P1131 Bank2-Sensor1 Internal Rsistance too High
-P0507 Idle Control System Higher than Expected
-P0306 cylinder 6 misfire
-P1392 Camshaft Pos.Sensor,Bank2 Open Circ./Short to B+

so far ive done all this and it didnt fix anything: cleaned MAF and also unplugged it (no dif), replaced primary O2 sensors, replaced ICM's, replaced spark plugs, replaced Bank 2 Cam shaft sensor, injector cleaner, checked TBB and its good, pressure test came up good. i am kind of stuck an need some help. ive done hours of research and it didnt help.

[RolledMySTi]

Have you tried swapping ecu's?

[S4M]

Not yet I will be getting my stock ecu back soon. You think that'll fix it?
I opened this one up and there's no physical damage or anything

[S4M]

so i just used a nicer scanner, i think its a VAG?, anyways, here are the codes i came up with:
P1458 - Exhaust gas temperature sensor 2 short to ground
P1556 - Charge Pressure Contr. Negative Deviation
P1461 - Exhaust gas temperature control bank 1 Range/Performance
P0441 - EVAP Emission Contr.Sys.Incorrect Purge Flow
P1548 - Boost Pressure Contr.Valve Open
P1426 - Tank Vent.Valve Open
P0102 - Mass or Volume Air Flow Circ Low Input
P0238 - Turbocharger Boost Sensor (A) Circ High Input
P0106 - Manifold Abs.Pressure or Bar.Pressure Range/Performance
P0305 - Cyl.5 Misfire Detected
P0304 - Cyl.4 Misfire Detected

now im not sure how old these all are, so i deleted them all and im gonna go back tomorrow or monday to see which codes came back. im thinking its a bad ecu though. thats alot of codes. im getting my stock ecu back tonight or tomorrow. see if that fixes it

[DiscoPotato]

You're timing might be off.. Check the timing for that bank of cylinders and also check if the cams are off on that head as you're cam tensior could be going bad... What's t
he mileage on the motor? Have you changed the tensioners or timing belt?

[SeaBass]

If these codes are current it definitely seems to be the ecu, nothing else controls all these different systems. It could also be a stretched timing belt, expanding when under wot load. Or you maybe running lean.

[S4M]

You're timing might be off.. Check the timing for that bank of cylinders and also check if the cams are off on that head as you're cam tensior could be going bad... What's t
he mileage on the motor? Have you changed the tensioners or timing belt?

Motor now has 88k. I have not done the timing belt yet. I planned on doin g it next month. But now I think it is the timing belt.

[S4M]

If these codes are current it definitely seems to be the ecu, nothing else controls all these different systems. It could also be a stretched timing belt, expanding when under wot load. Or you maybe running lean.

I'm going to do another scan today after work. I put my stock ecu back in and I'm still having the problem although it doesn't seem to be as bad. But that's probably because I don't have as much power. A friend gave me a egt sensor and some coil packs. I'll try those out. But yea it's probably the belt or tensioner

[highPSI-S4]

so i just used a nicer scanner, i think its a VAG?, anyways, here are the codes i came up with:
P1458 - Exhaust gas temperature sensor 2 short to ground
P1556 - Charge Pressure Contr. Negative Deviation
P1461 - Exhaust gas temperature control bank 1 Range/Performance
P0441 - EVAP Emission Contr.Sys.Incorrect Purge Flow
P1548 - Boost Pressure Contr.Valve Open
P1426 - Tank Vent.Valve Open
P0102 - Mass or Volume Air Flow Circ Low Input
P0238 - Turbocharger Boost Sensor (A) Circ High Input
P0106 - Manifold Abs.Pressure or Bar.Pressure Range/Performance
P0305 - Cyl.5 Misfire Detected
P0304 - Cyl.4 Misfire Detected

now im not sure how old these all are, so i deleted them all and im gonna go back tomorrow or monday to see which codes came back. im thinking its a bad ecu though. thats alot of codes. im getting my stock ecu back tonight or tomorrow. see if that fixes it

I would start with the EGT wiring, check both sides and make sure the wires aren't cut or exposed. In all realness I'd check everything that has a code or at least look at what you can to determine everything looks to be in working and running order.

[S4M]

I would start with the EGT wiring, check both sides and make sure the wires aren't cut or exposed. In all realness I'd check everything that has a code or at least look at what you can to determine everything looks to be in working and running order.

Well I changed the bank 1 egt sensor. It seems to be running a little better but still misfires when the car warms up and bad mpg. On Wednesday I'm going to remove the cats cause they are bad and could be clogged. Maybe they were causing the egt sensors to heat up too much? Anyways, going straight pipe cause it's cheaper and don't want to mess up new cats if that doesn't fix it.
Maybe n75 valve is bad? I'm getting so frustrated

[S4M]

I think it's a boost problem now. I did get a code for something about the n75 valve.
Yesterday I was driving to Stevens pass and going up the mountain i barely had any power. I turned down my music and I heard my diverter valves repeatedly opening and letting the air out and I wasn't letting go of the gas at all.
So I'm thinking the cylinders aren't getting enough air and the fuel isn't all igniting so it's shooting into the cats.
I don't think it's a blown hose or anything. Maybe vac. A friend is gonna let me borrow his n75 to test it

[S4M]

Well you guys, I finally dealt with my bad cats yesterday by going straight pipe. I had a subaru shop in auburn remove my cats. The drivers side one was totally fucked. The first half of it was all busted up and the second half was all clogged up. I took the car out and oh man does it rip more than ever before. I'm in love with my car again lol. Anyways, thanks alot for the help guys.

[SeaBass]

Well you guys, I finally dealt with my bad cats yesterday by going straight pipe. I had a subaru shop in auburn remove my cats. The drivers side one was totally fucked. The first half of it was all busted up and the second half was all clogged up. I took the car out and oh man does it rip more than ever before. I'm in love with my car again lol. Anyways, thanks alot for the help guys.

congrats on figuring it out, great to have another B5 out of the shop and running properly. CHEERS TO NO CEL'S!

[S4M]

Still gotta delete my cel. But yea I'm happy. I've had the car for like 6 months and the last 3 months it didn't run right.

[Slavchob]

Good to hear it's fixed did your mpg's go back up or are they still at 10-12?

[S4M]

Mpg's seem to be back to normal. I've been pretty much flooring it non-stop since I fixed it yesterday and it's still doing better than before. Lol once I chill out and drive normal it's gonna feel like I'm driving a Honda (mpg-wise atleast)
Dude you have 3 s4!!! Send one over here for me haha

[asp s4]

ive had what sounds like the same problem for almost a year with my s4! tired pretty much everything with no luck, i only get around 400 kms ( or 250 ish miles)per tank and any time i go WOT i get crazy hesitation and i feel like there is no power. what do you think fixed your problem in the end???????

[highPSI-S4]

Glad you got it figured out OP!

These cars have tempers, in all when i had my S4 i replaced a lot of things chasing down Misfires.

It happened so long ago i almost forgot, My story is similar to he OP's. somehow my one of my ICM's became lose and disconnected, this cause the car to go in limp mode and it started smoking. when i pulled over i noticed the DP was red hot and was like WTF!! After i limped it home i noticed what was unplugged, i plugged the ICM back in and everything was normal so i though. Fast forward 3 months and my car is in limp mode again, Pulled codes and got almost the same as the OP. It turns out i cooked my catalytic converter as well as my front 02 and EGT sensor and this is when i went STG2+ all at once while replacing the sensors. Got my car back faster than before.

Spark Plugs, ICM's, Coil-packs, Front o2 sensor, EGT Sensor. Those are what i check first if i have misfires, then i check for loose hoses and boost leaks.

[Slavchob]

Mpg's seem to be back to normal. I've been pretty much flooring it non-stop since I fixed it yesterday and it's still doing better than before. Lol once I chill out and drive normal it's gonna feel like I'm driving a Honda (mpg-wise atleast)
Dude you have 3 s4!!! Send one over here for me haha

Haha sure. Just send me all your info to my local Nigerian bank choose one of the following, and we can get a nice wire transfer going for the shipping. You don't need to pay for the cars, not like I want them anyway

[S4M]

My problem was 100% my bank2 catylic converter. I bought used milltek downpipes and exhaust from a friend. The car they were on was very low and you can see scrapes and dings on the dp's. Anways, the car ran fine for a few weeks with no chip. But 3 days after chip, the driver side cat went bad. I knew it was bad but thought another problem I was having made them go bad. I thought fuel was shooting into it and messed it up.i didn't wanna replace the cats before fixing my problem in case I would destroy new cats. So I ended up buying quite a few sensors and such to try to fix it. Them I decided to just delete my cats and see if that'd fix it. I had a feeling they were clogged. I could hear them rattle. Anyways, yesterday I took in into a exhaust shop and had them delete the pipes. They showed me my cat and it really surprised me how bad it was. The first price of it was totally busted up and the second part was stuffed and clogged from with debrie from the first.
I would post a pic but can't with my iPhone. Anyways it worked just about perfect as soon as I drove it away from the shop. I just need to gap my plugs smaller as well as delete the cel. Anyways, I have a cam shaft position sensor, bank 1 egt sensor, n75 valve, icm's, and coil packs for sale if it's not your cat. Let me know.

[S4M]

Haha sure. Just send me all your info to my local Nigerian bank choose one of the following, and we can get a nice wire transfer going for the shipping. You don't need to pay for the cars, not like I want them anyway

Idk man. It's too much trouble for an s4. I gotta go to my bank and blanbla bla with the ugly teller and whatever else. Can I just give you my account info and you take what you need?? That'd be Lot easier. Otherwise keep the dumb cars. Hahaha.
Dude they are sick though. I love those headlights. I have the clear corner ones. Got them before I found out about these led ones. How much do they cost??

[papuc14369]

Damn, my first impression of misfires is always a boost leak, then EGTs, then ICM but never would have thought of the DPs. Glad you fixed your problem.

[Slavchob]

Idk man. It's too much trouble for an s4. I gotta go to my bank and blanbla bla with the ugly teller and whatever else. Can I just give you my account info and you take what you need?? That'd be Lot easier. Otherwise keep the dumb cars. Hahaha.
Dude they are sick though. I love those headlights. I have the clear corner ones. Got them before I found out about these led ones. How much do they cost??

Umm... iirc they are roughly $250-$300 on ebay. They do need a little modification to get them to fit, but they do look sickkk at night. I got HID's for them, so theyre super bright at night also. Overall, I'm happy with the purchase Theres a lot of guys that are on here that hate on them, but idc. Pictures don't do them justice. They look great in person. I get compliments on them all the time from random people at parking lots, gas stations and whatnot. People think its a new car. haha. But anyways. If you're looking into getting a pair, do ittt

[S4M]

Sooooo.... I'm actually still having some misfires. And I just drove to the pass and looks like My mpg's are kinda shitty again. Definately not as bad as before but still happens sometimes. I'm gonna gap my plugs right and put in the ecs n75 that just came in the mail. Maybe my bank 2 egt went bad from too much heat or something. I cleared the codes and gonna check them again soon hopefully.

[asp s4]

any updates on this?

[S4M]

Yea. I galled the plugs to like .028 and put in the ecs n75 valve. It didn't make a dif so I sold the ecs valve and put the stock back in. I'm like 90% sure it's my bank 2 egt sensor though. I've been looking everywhere for a used one. Finally found one ima pick up on Sunday.

[S4M]

Oh yea and 1 plug was so loose that there was gas in the coil pack lol

[asp s4]

any more updates? lol

[bassist169]

I have been having misfire issues on WOT for almost a year now. Last week a friend and I put on new straight through downpipes and exhaust. I checked the codes and I was having a misfire on Cyl 4, some EGT faults and O2 sensor faults so while I was in there I went ahead and replaced both EGT sensors and the bad O2 sensors. After getting it running again I tried to hit WOT and still the misfires came. Checked the codes and now the only ones that come up are misfires on cyl 1 and cyl 4. I replaced the coil packs in both of those less than a year ago so this is getting very frustrating. I am going to try swapping out the different coils but I really have no idea what might be causing this. Any ideas? It is a 2000 S4 with ssac downpipes, testpipes (right now) and exhaust and the ecu was chipped by MTM......

[S4M]

try gapping your plugs around .28. if its coil packs i heard that they dont show codes. but i changed my egts and its running much better now. so my problem came frome both messed up cats and bad egts. i still have to delete the codes though. but ill do that after i put my own ecu back in. its out getting a different tune. and do you have stage 2 file? to code out O2's??
i actually dont have O2's coded out right now and i get "warm up cat below threshold" but its running fine. it should be in limp mode i thought. im running a stock H box instead of my M box

[bassist169]

ill try that

[fairbird]

Had the same problem for last month , exchanged coils , imc , plugs (gate 28 ) , pressure test is fine , egt off , o2 off , straight pipes . on low boost like 7-10 psi no problem , waiting for new soft from VAST .