B7 S4 Misfire diagnosis help

B6/7 S4/RS4
#3

Continued…
I forgot to mention the symptoms in my first post. The car has a little miss at idle, but nothing major or significant. But under throttle, once you get over ~4k rpms, it has practically no power and a solid or flashing CEL and noticeable misfiring. There is NO rattling or clacking on startup like I’ve read about in other posts, and the tensioner and guides that are visible with the valve cover removed so almost no wear.

Codes are:
005495 Right Engine Mount Solenoid Valve P1577 - 004 - Open Circuit, Freq 1, 778rpm
000768 Random/Multiple Cylinder Misfire Detected P0300 - 001 - Intermittent, Freq 1, 4730rpm
000776 Cylinder 8 P0308 - 001 - Misfire Detected - Intermittent, Freq 1, 4730rpm
000774 Cylinder 6 P0306 - 001 - Misfire Detected - Intermittent, Freq 1, 4730rpm
001073 Warm Up Catalyst; Bank 2 P0431 - 001 - Efficiency Below Threshold, Freq 1, 2140rpm
005137 Secondary Air Injection System; Bank 2 P1411 - 002 - Insufficient Flow, Freq 1, 2267rpm

So I took it home, parked it in the shop and started thinking with new knowledge of the timing chain issue, as well as some reading about carbon build up.

I pulled the intake manifold to look for carbon buildup, and while a little dirty, there was nothing alarming, nor anything that was worse on any particular cylinder. So i took that off the list. Then checked the air filter and it was like new, no obstructions in the air supply, so ruled that out.

Next was a compression test. This was a dry compression test after the car had been sitting for a day or two, so I expected the results to possibly a little low, but I was surprised when I saw readings of 90-105psi on the entire left bank. The right bank checked out good at 150-160psi.

After that, I pulled the valve covers expecting to find a cam out of time by a tooth. But looking at the notches in the front, they are lined up pretty darn close. I’m assuming if the right bank is good and the marks are lined up, and the left bank looks to be good and lined up, then it isn’t necessarily necessary to align the timing mark on the crank? (though I know its a good sanity check)

So my best guess is that the mechanical adjuster is not working properly, and when the car hits a certain rpm/throttle condition, the right side is working properly, but the left side is not, causing the misfire. Is that a logical conclusion? And if so, how does that cause the low compression?

Thanks in advance for the help!

#4

You’ve come to the right place for help. You’ll get much better direction and support here. I’d suggest a few things. One try posting the entire compression test results per cylinder. That will help some of the guru guys. Also at first glance I don’t see any codes related to timing components. So I’d say there you’ve lucked out. It’s good searching the net but lots of websites have bad data.

I’m going to assume you don’t have a vagcom cable to look at values?

Other than what you mentioned is the car 100% stock?

Did the shop clear the codes you listed?

Currently when you drive the car it will flash the cel when trying acceleration over 4000?

#5

I do have a Vagcom that works with my 04 Passat TDI, but it wouldn’t connect to the B7 S4 because it’s not HEX-CAN like the newer/fancier cars.

Car is 100% stock as far as I know. One owner company car with excellent maintenance record.

Yes the shop cleared the codes. I also have a regular OBD-II code reader and have cleared the. Odes after fiddling and test driving. It doesn’t show all the codes that Vagcom does though.

When I drive the car it doesn’t immediately throw a code, but always has no power over 4k (and doesn’t seem great below that either, but I’ve never driven it running right so I don’t know what to expect). It doesn’t always do the flashing CEL, but the light comes on every time I’ve driven it.

#6

If you can keep putting of the codes that come back. If you see consistent codes that should help point to exactly what’s going on. The faults are located on the same side of the motor (bank 2) that’s good but due to the low numbers you quoted that might be bad. With the cat code low comp numbers and the loss of power there might be a chance you actually have a bad cat. You want to gut the precats anyway. That might be a good weekend project for you. And please do post the compression numbers per cylinder. There is actually a tech section of the website that has a big on going list. Adding to that will help you and others.

#7

I second the idea of a bad cat. I had my precat go out on bank 2 and throw misfire codes on three of the four cylinders, as well as the car just not sounding right or having any power. The indy shop I took it to just swapped coil packs around and couldn’t find anything, but when I took it to the dealership they said that they could tap the precat and hear the substrate inside rattling around. And as justincredible mentioned, you want to gut the precats anyways. I used it as an opportunity to get a set of JHM piggies and it changed the way the car responds to the throttle as well as a better exhaust note.

#8

How would the bad cat cause low compression?

#9

you can’t edit till 150 posts, so you’re 145 away…

#10

The bad cat increases the back pressure on that bank of cylinders, which can cause the misfire. And I think the added back pressure increases the stress on the piston rings as well. My car has lower compression than I would like all around, but it is lower on the cylinders that I had the high back pressure on.

#11

If a cat is bad, it becomes a mega restriction, and the engine can’t expel gas efficiently. You can liken it to going from a 2.25" downpipe to an effective 0.6" downpipe…and when you’re revving that engine up to 7000 RPMs…or 116 exhaust pulses per each of the 4 0.525 liter cylinders on that bank every second, and that bank of 4 cylinders is struggling to expel spent gas (and thus struggling to bring in fresh air on the intake side) you have problems. It’s like one of those crammed trains in china and everyone’s trying to get off through 1 door…in 10 seconds. Mayhem.

It’s amazing what a brutal exhaust problem will do to the whole system.

#12

I put the car up on the lift last night and tried to pull the exhaust at the header so I could examine the cats, but there seems to be no way to get to that top left bolt on the drivers side. Since it seems to be running unrestricted from idle to 4000ish, but still misfiring at idle, does a cat seem likely?

My thought process says the cat code is a result of the misfire, not a cause. It would seem to me that improper timing would cause low compression and misfire. Clogged cat could only cause low compression if the engine had been running bad for a while and had basically “worn out” the rings or cylinders on that bank, but only 2 of the 4 cylinders are misfiring, so I wouldn’t think all 4 would be low on compression if that were the case.

#13

In a lot of these cases the symptoms you mentioned are forum a clogged cat. Coil packs and plugs would be top on the list but you said they are fine. To get to the top bolt go through the wheel well. It’s blind but toy can feel and get to the bolts

#14

Hi, I hope I can shed some light, I have the same problem on a rs4 all misfires on bank 2, in my case the dealer has been awesome on helping out even with myself completing all repairs, heres some thoughts, check fuel pressure drop after the engine is off, you might have a pressure valve like the rs4, when you perform a readiness procedure that will tell you if the cats are good, i.e. ( temp on either side of oxygen sensors) now keep in mind your knock sensors for bank 2 goes as follows, cyl 5/6 has its own and 7/8 has its own sensor, if these are shot then it will send a misfire,fyi (dealer said these sensors are not an issue in many cases ), yes the timing chain could be an issue and i hope not in your case but i think you already ruled that out, bottom line, check all fuel related items including filter/switch banks fuel injectors/, since you already have new packs and plugs, check all connections, while the IM is off check torque on knock sensors 20 newton pounds. Anyways as I think your heading to the cats as the issues I would get a readiness done first. that will tell you the condition of the cats. good luck

#15

Rock those are all great things to look for. The S4 has a much different fuel system so some of the issues your seeing won’t be the same on his car as you have FSI and he has SI.

#16

Well gentlemen, I’m thrilled to report that I third the idea of a bad cat!
Not quite a weekend project, knocked it out in about 3hrs tonight (but only did the drivers side). Hardest part was getting the rusted bolts off the exhaust clamps where the cat meets the muffler. I pulled the downpipe/cats off, and took a look at it. To my untrained eye, it didn’t look terrible, but it didn’t look great. So I figured while it was off, I might was well gut the precat. Got that done and put everything back together, and gently went out for a test drive like I’ve done 10 times already. Only this time, once the car got over 4k rpms, it took off instead of falling on its face! ;D Thats probably the happiest I’ve been in years! All the anxiety of pulling the motor and spending a couple grand on the timing chain components disappeared!

Here are a couple pics of the clogged precat:

https://lh6.googleusercontent.com/-qNh_YKUgyeA/VGFwz3fw3FI/AAAAAAAACjo/HiXx23acbss/w331-h588-no/1110142016b.jpg

https://lh5.googleusercontent.com/-fmDcgX4c2_U/VGFxIwFfOzI/AAAAAAAACjw/Bmjp6d3bF0k/w331-h588-no/1110142016a.jpg

https://lh5.googleusercontent.com/-a1yV7Vx2HpA/VGFxmAZccUI/AAAAAAAACkA/ZbMwHGSKQAE/w331-h588-no/1110142016.jpg

And now that the car is fixed, I can be proud of it again, so heres a couple pics of an 8 year old car with 180k miles:

https://lh5.googleusercontent.com/-MIqzrY8St-k/VGGZ7VNbuGI/AAAAAAAACk8/Zoc9viuJIII/w785-h589-no/P1050946%2B(Large).JPG

https://lh5.googleusercontent.com/-CseZOJRLvmo/VGGaWCV03CI/AAAAAAAACmk/bmrmdKPsF4w/w785-h589-no/P1050962%2B(Large).JPG

https://lh3.googleusercontent.com/-MDE6337PT_Q/VGGasvfU-6I/AAAAAAAACok/3KSZ_a3qFd8/w785-h589-no/P1050978%2B(Large).JPG

#17

Holy shit 180,000 miles? Awesome

#18

180,000 miles?!?! Wow. Glad to see a car that actually gets driven. I sold my B5 S4 with 190k+ on it.

Glad to hear that it’s fixed. How do you like the feel of the car now with the piggie pipes? Does it feel more responsive to the throttle? And it must sound even better, right?

#19

Honestly I have no idea. It was running bad when I bought it a month or two ago. It definitely sounds good though!

#20

Jeepinmatt glad to hear you got it fixed. I saw you were skeptical for a second. Now just pay it forward if you see someone struggling for help just send them here.

#21

awesome, Ive have been thinking on doing the same thing, in fact its the only thing last to do on my rs4 for the misfire…thanks for the news

#22

Start A new thread misfires on FSI cars are very common. There are several fixes but it’s best to take each fix one at a time.