Multiple cylinders misfiring

I just bought a 2000 manual coupe with under 40k on it (only been driven 1000 miles in the last 8 years the guy before me had it.) Of course on the way home CEL went on. Anytime I am above 4000 rpm the engine doesn't seem like its running right and at 5000 rpm the CEL starts flashing. Ran the codes and got multiple misfires in 1 and 4. Got new OEM beru spark plugs and switched the coils from 1 and 4 to 3 and 6. Took it out after and still had the same issue so ran the codes again, 1,2,4 and 5 are misfiring, still only above 5000 rpms. So its not the coils or the plugs. Sometimes it will be 1 and 4 other times 1,4,2 and 5 It runs perfectly fine under 4000 rpms but once you get up past there it doesn't have as much power. Since it is both banks, both cats aren't likely to go at the same time so ruling that out. Next thought is fuel. I ran seafoam through the gas, but no results. Since it hasn't been driven and is both banks and seems to be limited to the last cylinders, my guess is not enough fuel pressure to supply all cylinders and just not getting enough gas to the last cylinders, although I'm not throwing any other codes(either weak fuel pump, injectors or fuel filter?) Next step is to test fuel pressure. Anyone else ever have this happen or have any suggestions?

NVM Re-read OP.

Switched coil packs around yesterday (1 and 4 were misfiring so switched 1 and 4 with 3 and 6 which weren't) 1 and 4 were still misfiring and 3 and 6 weren't so ruled the coil packs out

Bad injectors? Seafoam and fresh gas.

I was thinking that as well since it has obviously sat for a while. Did run a half of bottle of seafoam through with a half tank of fresh gas. Filled up again with fresh gas and still misfiring. May throw another batch in or pull the injectors and clean them

was a PPI or test drive done before you drove the car home? NTL, best of luck sorting your car out. P.S. Just a WAG: dirty MAF?

Fuel pressure and flow rate. Fuel filter, MAF and Durametric.

kromdom, after looking at rennlist that was my first mistake. It was the first car I've bought, saw the miles, jumped too quickly and now I've learned the hard way but lesson learned for my next porsche. Took a test drive but never took it over 5k. Ordering a durametric soon but in the meantime planning on cleaning MAF tonight and checking fuel pressure. MAF should affect all cylinders though and I haven't seen 3 and 6 misfire yet

Wait until you can scan it and ONLY then start cleaning things. You can introduce another problem and then you'll be chasing your tail forever. Next time take the car up to redline during the test drive.

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1000 miles in the last 8 years... Well, you have eliminated stale gasoline. However, I'm not sure the fuel filer and fuel lines and injectors escaped some varnish forming in them. BTW, I'd be tempted to replace the coils just to have the plugs and coils new. But the coils are probably not the problem. Short of replacing the fuel filter (and possibly the pump), the fuel lines and injectors, about all I can recommend would be to use Techron. Use a bottle according to directions and then if you notice an improvement use another bottle. Be sure to change the oil/filter after you run the last of the fuel with the Techron added out of the tank. You can check fuel pressure and delivery. Be aware the brass cap that seals the fuel line test point is not reusable. If you remove the cap you must replace it with a new one. Before you dive into the fuel pressure/delivery thing though be sure you give the car and the engine compartment a good going over for mice sign. A car that has been visited by mice (or rats) can manifest all kinds of engine and electrical problems.

Finally got my durametric last week! In the meantime I cleaned out all of the fuel injectors. That brought it down to only cylinder 1 misfiring. Logging the data on the durametric, it was showing mostly high rpm misfires in cylinder 1 but several low end as well depending on rpm. Cylinder roughness was also higher on this cylinder (10 vs -3). Pulled the spark plugs again and saw oil on the diode of cylinder 1. Decided to do a compression test on all cylinders to rule out bad cylinder. Got good compression within 10 percent on every cylinder. With that, my guess is bad valve seal most likely. Looks like the engine will be coming down soon. I was planning on dropping the transmission anyways to do IMS/RMS so not a ton more work. Still winter for a while here in Wisconsin so I have nothing but time. Any other suggestions before I drop the engine?

It is not clear the engine needs to be dropped or even opened up. I didn't read the thread again but are the coils and plugs new? Before I dropped the engine I'd throw new coils/plugs at the behavior. Are you sure the electrical connector/connection of the coil to the plug and the coil to the wiring harness is good? Unlikely a valve seal is the source of the misfiring. If the seal was leaking bad enough to cause misfires I think you'd see the engine smoke at times. I am not a fan of Seafoam. I am a fan of Techron. My advice would be - after you are sure the coil is good and the plug is good and the coil is connected properly -- would be to use a bottle of Techron as per instructions on the bottle. The SOP is you notice an improviement use another bottle. After you run the tank level down to say a quarter of a tank or so change the oil and filter. I am thinking engine deposits or fuel injector deposits are causing the misfires. At 40K miles I suspect the engine never got run much above 3 or 4K RPMs and probably is pretty loaded with deposits. That it sat for a while unused didn't help. You are sure the car is free of any rodent damage? You are running a top tier fuel and the proper octane grade and buying fuel from a busy station? Have you replace the fuel filer?

Are the cats original? If so, I would check them before dropping the engine.

Change the MAF. Don't just clean it, replace it.

This is what the plugs look like(maybe 30 minutes of run time on them) cylinder 1 vs 2 Macster, plugs are new, coils are not, but I checked for any visible cracks as well as switched coils around this weekend and no change in misfires. I believe the electrical connection is good as it runs with no misfires at midrange rpm and most of the time at idle. I will have to look into this however to make sure there not just a bad electrical connection before the coil. As far as fuel goes, it was filled up with the correct octane gas. Filter has not been replaced yet, but is on its way. I have switched fuel injectors 1 and 2 as well and no switch in misfires there. Durametric only has a single recorded stage 2 overrev so I don't think it was taken up very often. I don't remember the stage ones but it wasn't extremely high either. When removing the fuel injectors I looked over many of the lines and didn't see any rodent damage. I'll have to drain the seafoam filled oil and put some new stuff in with techron and see how it affects it Triple Black, cats are original. How would you go about testing these? Should the entire bank be misfiring with a bad cat? Flat 6, an MAF failing should cause most if not all cylinders to misfire if this was what was failing, correct? I'll check the MAF tonight on the durametric.

A bad cat should not cause a misfire. A persistent misfire might cause a bad cat, though. *edit* In my experience, I have never been able to attribute a misfire to a bad cat...

I just repaired a 997 that had been to 5 shops (2 dealers) with this issue 3 weeks ago. Al it needed w2as a MAF. The MAF can effect all cylinders, because issues were the MAF has a range with an issue will lean out, or enrich all cylinders to an extreme level, across the board. When this happens, the result is often multiple misfires, a flashing CEL, and random occurrences where the engine runs perfectly, then acts up, and quickly clears up. I have literally seen a bad MAF lead to an engine with 36 random codes.

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If the cats internals have deteriorated they can become plugged, which can lead to misfire at higher revs. One bad cat will cause a misfire on one bank, but there is the possibility of both going bad. One of mine was plugged and causing misfires on bank 2 (mostly just one cylinder, sometimes two). When they were taken off we found that the other cat was falling apart inside as well. This was on my 2004 with 24K miles just after I got the car about 3 years ago. I don't know of any test, other than removing them to check for rattles or loose internals.

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Not true, read my response below. A few years ago (you can search) I was having symptoms similar to the OP. I replaced my plugs, wires, MAF, and did every other piece of troubleshooting I could imagine. I would get a misfire every time I would try to rev over 4500 RPM. It was never consistent (in terms of the cylinder affected) either so it was really frustrating as I couldn't figure out why it was happening. Finally I gave up and took my car to the dealer. They tried quite a few things as well and finally decided to drive the car with the cats unhooked. Problem was gone! I ordered the cat x-pipe from Fabspeed and haven't had any issues since. So for the OP, do yourself a favor and check the cats!

Did OP ever find the answer to this? What ever happened?

How do you "check the cats"? Another cause from what I've read might be the cam timing being off from the chain pads wearing down. I have not checked mine yet - I am having these same issues with misfire on 1 bank after 5k RPM. Coil packs are good.

Last time the OP showed activity on the forum was Sept 2016...so we may never know.

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Based on what I read above, the dealer took the cats off and ran it without.

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I've been trying to track down similar misfires for about 6 weeks now... Getting pretty frustrating, seeing as I only get a couple hours at a time and I'm trying to troubleshoot in a systematic way. What does "cats unhooked" mean ? The O2 sensors unplugged? The cats themselves removed? That must have been crazy loud - where did they test it? I'm wondering if I can pull this off in my garage on a lift...

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On your new motor?

Unfortunately yes. I've been working through this with Jake via email, so as not to create some big uproar/flame fest here (while quietly searching through misfire threads), but I just found this thread and it seemed interesting. Jake has been super responsive and helpful as I pick his brain relentlessly! The car was running absolutely perfect at the time I did about a 50 mile drive when I suddenly had some misfires (it sounded and felt like a VW power wise). I was close to home at the time, so I limped in shut it down and checked it with the Durametric - misfires on 1, 2, 5 & 6, with post Cat O2 sensor codes as well. Per Jake's suggestion, I ordered new O2 sensors (genuine Bosch) and cleared the codes. Upon clearing the codes, the car ran fine for another 2 weeks or so (without cleaning/replacing anything). Then it happened again - more misfires. In the mean time I had received the new O2 sensors and MAF - ok time to replace them...that should take care of things... Well, needless to say the O2 sensors were a real pita - they took about a week due to my work schedule. In the end, I removed the rear bumper and the CAT pipes so I could bring them to my shop, put them in a vise and get some air tools on them. Easy peasy - finished removing and replacing the sensors in about an hour including chasing the threads with an 18mm tap. The right tools are EVERYTHING when it comes to getting things done! Upon getting everything back together and starting her up, everything was great for about 10 miles - then it was back to the same old misfires again (this seems to be a pattern - the car runs fine when cool and starts to misfire when up to temp - anywhere between 6 - 10 miles). That was about 2 or 3 weeks ago. So far I've 1) Replaced upstream and downstream O2 sensors (no more codes for them so that was productive) 2) Cleaned original MAF and replaced original MAF with a new genuine Bosch unit (same part # - old '99 style) 3) Checked and cleaned male/female sides of X59 connectors (though I haven't pulled the pins on the female side to check there yet - that's next on my list) 4) Pulled/checked/cleaned plugs on the ECU for corrosion/bad connections - nothing obvious. I may go back in and open it up to look at the board itself - last time I did that, it cleared a CEL that "wouldn't go away"... (Also prior to doing this I disconnected the battery and did the "full reset" - touched positive and negative cable ends together)... 5) **So far, I've found no rodent damage which has been gnawing at the back of my mind (see what I did there? ) - but it's definitely still on my radar. This is where I am, and I'm heading back to the garage to work on it now - If anyone has any ideas, I'm open to 'em! Thanks in advance, and please no flaming/blame games...

I am sure most if not all of these have been thought of by Jake, I am just sit balling through some of the things I would check. When it misfires, is it always the same cylinders, 1,2,5&6 or is it different each time? Have you hooked up your scan tool, looking at misfire monitoring on each cylinder, than started the car and watch each cylinder misfire in real time? (Can durametric do this?) If so, what changed(if anything) when the misfires started? Did the secondary air shut off? Did you touch the throttle? A/C? you said it will only happen when the engine gets hot.. Does it seem to be when the oil or coolant get to a certain temp? Is it the same every time? Does it happen at the same time if the car is started and idling vs started & driven? Have you cleaned the grounds on both cylinder heads and the engine to body ground? Try looking at the battery voltage at the engine disconnect post while this is happening, any change in voltage? I don't know how long you have had the car, but have you confirmed that the MAF PN you got is actually for your car? I know there used to be numerous versions, I dk if that is still the case. How are your RKAT values? Any change before misfires? As crazy as this sounds.. have you tried a hard battery reset? Disconnect BOTH leads of your battery and touch & hold them together (you can use a jumper wire) for 30 seconds? I will keep thinking on this and post up I have anything else I can think of for you to check.

Bad ground? Mike

How's about have you checked,cleaned,retightened ground points #10 and 11? If that doesn't work ring out ignition coil sockets between X59/1 connector and coils. If that checks then pin side of connector to DME plug. Looking for faulty or broken down wires. Possibly a fault of some sort will show up.

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I'm not sure same cylinder misfires support this, but could have recently filled up on some crap fuel?

I'll answer generally as specifics would take me forever. 1) The misfires are random - ie: sometimes on the same cylinders, but sometimes not 2) The only real constant is that I don't get the misfires until the car is driven close to 10 miles (a little less if it's hot out side) - it seems to be temperature dependent. * Bad ground is a real possibility and I have so far checked the engine ground by the rear passenger side wheel. Cleaned both ends and both sides (engine and chassis) lugs and studs and re-tightened. No love... 3) Fuel? Mmmmm, I don't think so (although anything is possible) - I always use Shell V nitro plus 93 and mostly from the same station (I'm almost positive that at least the last 5 fills have been from the same station). How's about have you checked,cleaned,retightened ground points #10 and 11? If that doesn't work ring out ignition coil sockets between X59/1 connector and coils. If that checks then pin side of connector to DME plug. Looking for faulty or broken down wires. Possibly a fault of some sort will show up. ^^^This is what I'm working on now...

^^^ Interestingly, after cleaning and tightening the passenger side engine ground point #11 (no change in misfires) I moved over to the drivers side to check #10... ... ... Hmmm, no ground point #10! There is clearly a lug on the engine block and a point on the frame near the bottom of the motor mount. The point on the frame was pretty rusted and the stud was missing - it looked like someone had put some kind of sealer/goop on it. I cleaned it out and tapped it the best I could with a M8 1.25 tap. It was super difficult to get the tap wrench up the the spot... I finally went to Lowe's and got a tap wrench that allows the tap to be driven by a socket or standard ratchet handle with a long extension on it. Unfortunately, they didn't have a flat bottom/flush cut 8mm 1.25 tap. I'll probably get one a NAPA tomorrow (Advance didn't have it either - only a 8mm 1.0 ). In any case, I'm not expecting this to cure my problem as I'm sure there's never been a ground at this point (I had the engine out a few years ago before the full rebuild). According to the Bentley manual there are at least two more ground points in the engine bay - I don't remember seeing these either when I dropped the engine... I'm also planning on going back and checking the grounds at the ECU relay are as well...

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Same here. Removes the cats, problem solved.

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Wow! Interesting... seems bizarre, but the fact that I haven�t been able to figure this out yet is also bizarre. What did you replace the cats with?

Also bizarre is that I opened up X59 plug 1 and found that I�m missing the connection on pin/socket 11 (valve lift control cyl 4-6) strange no?

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Nothing!

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^^^ Not the case - I was reading the wrong page (The EWD pages are many, and slightly confusing) - I was looking at Motronic 7.8 when I should have been looking at 7.2... In any case, I won't be able to get back to it until tomorrow. Will post back then. Not sure if I want to drive around without cat's - how loud is it? Please compare to stock with cats (as opposed to "it's not loud at all")...

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I have these these 200 cell cats on my '99 C2 with FSI 3.6 Street Performer. I also have their headers. Along with the install I replaced the O2s with the Bosch Universals from Warehouse33. Not a bit of trouble with any of it so far with over 10k miles logged. https://www.topgear-eurosport.com/po...ll-sports-cats You would be in at about $750 for the CATS and the O2s.

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I'd probably be ok with something like that^^ if I'm sure that's my problem - the difficulty is in figuring it out... I don't want to spend $800 to find out I've still got this misfire problem...

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Oh, yes of course. I'm just sharing this, should the CATS be your problem. It is not a terribly expensive route if you have to go down that road.

Maybe someone on the forum can loan you a pair of CATless pipes or hollowed out pair of stockers.

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I can't speak to whether this is actually your problem, but I'll give a heads-up on the TopGear cats. (2004 C4S) My factory CATS were bad when I got the car (after some misfire issues that I fixed), and they rattled when I took them off, so definitely a problem. I then bought and installed these same TopGear Cats back in January of this year. They are beautifully made, nice welds, very light weight, and installed easily. I also installed 4 new Bosch O2 sensors at the same time. Within 30 miles, and continually after that, I got Cat efficiency codes for both bank 1 and bank 2. Used Durametric to monitor voltages, and the sensors are good, the Cats just don't do enough to attenuate the oxygen level. I tried to contact TopGear asking what they generally recommended, but I could never get them to reply. I had to install O2 spacers onto my after-Cat sensors. Finally got to that a month ago, and the code is finally cleared and gone. You can search the forums, some people haven't had an issue, but many have. If you DO have a Cat issue, my recommendation would be to either: 1) Be honest about it and just use a straight/test pipe and O2 spacers. The TopGear Cats really aren't doing much anyway. 2) Pay more for better Cats. (Would have been my choice, since I generally like having breathable air on the planet.) Good luck!

So far I’ve : cleaned & checked all engine ground connections (gp10 & 11) cleaned & checked ECU connections, cleaned and checked coil grounds and toned out all coil green wires to X59-1 plug (black) in engine bay. Unfortunately, I’ve only been able to do this while the engine is cool And of course the engine runs great while it’s cool 😩... How about the injectors? I suppose I should check for power to them as well... once again, not sure how I can pull this off when the engine is hot??? I’d be grateful for any ideas... Thanks

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I seem to remember Jake mention injectors acting up (leaking) when hot. Not sure if there's anyway to test them on your end though. Maybe try swapping some around and see if anything changes?