RoWDyWS6

hello, ive been having a problem with my car misfiring at times.. this is the best way i can describe it. When i turn on the car the car is fine, nearly idleing perfect, but then i step on the brake and hold it there, shifting to drive (A4) still holding the brake not going anywhere, the engine starts shaking!
i notice at when coming up to a red light or stop ,its misfiring..

okay i already paid 400 bucks tryin to find out/fix the problem,

we checked plugs&wires
checked for vaccum leaks
checkd MAF sensor
checked coil packs
checked Injectors
switched out knock sensors
changed fuel rail system or whatever
sent the heads out to check if they were warped


when they do that compression test it reads out low compression, cylinder 5 &cylinder7..

Do you guys think the piston rings need to be replaced??? cus thats what thier recommendin for me to do next!! What do yall think??
Thanks -Rey

NAAllTheWay

iv always been told that when somethings wrong and you need to troubleshoot to do the cheap things first, rings....expensive if your not doing your own work, real expensive...so ME personally, i cannot think of anything else it could be, but you should see if anyone else does.....if worst comes to worst.....low compression would either be from a head gasket/warped heads, or rings......so if your heads arent warped, and your car doesnt puff some white smoke(head gasket)....that would leave the rings.

LS1Silverado05

iTrader: (41)

Are you certain that its an engine misfire, and not a vibration of some kind? You saying it happens in gear holding the brake but not at idle in P, tells me that something may be hitting or something that's giving you a perceived miss do to the harmonics. Just a thought......

RoWDyWS6

i believe its a misfire, the car has turned off before while waiting at a light.. but who knows

RPM WS6

iTrader: (3)

So compression is low on #5 and #7. First, how low is low? And second, have you done a leak down test? You can't just assume it's rings unless you're sure that both the intake and exhaust valves are fully closing on those cylinders. You could have bent valves or carbon build-up not allowing a valve to fully close when it's supposed to.

Also, are you burning large amounts of oil? If it was the rings, I would suspect this to be the case.

MrEddie

Could it be brake booster related (pulling too much vacuum) since it occurs primarily when you're using the brakes? What if you're in neutral and hit the brakes?

LS1Silverado05

iTrader: (41)

Ever verify the coolant temp sensor connection is nice and tight. My 01 SS had a random situation where it would die idling and we thought it was a tuning issue, but turned out if you unplugged the coolant temp sensor it would kill the car and I had a loose connector... Just something quick to check...

RoWDyWS6

umm sorry, whats a leak down test?? not sure what u meant by the vaulves.. they sent the heads to check if they were warped, but they were good! and ive had a oil leak for the longest time, never fixed it cus i hardly drove the car!

RoWDyWS6

they were also saying possibly with the way i describing the problem, that it could just be an o2 sensor! WTF! sorry i sound unintellegent.. im a newbie with this whole mechanics shiit... i just want this car fixed already! havnt drove it around in over 4 months.. just been turning it on, on the driveway..

RoWDyWS6

starts missing on Drive and Reverse, not on park or neutral

LS6427

iTrader: (2)

Do yourself a favor and get a scan using a real OBDII scanner, the ones the dealerships use.

See if the 02 sensors are switching properly after you're warmed up. When 02 sensors are "failing" but have not yet failed....you won't usually get a code or an SES light. Our PCM's are like the old style idiot lights for some issues. And a bad 02 sensor will cause the problems you're having.

.

DarkJuggalo

iTrader: (6)

i was having serious issues with mine when the 02's were going. replaced both and havent had a problem since... with a situation like yours and 02's only bein like 10$ each and u can do it your self easily that would have been my first step

RoWDyWS6

i've always had that SES light, for about 2-3 years but car ran smooth.. SES started flashing every now and then. (that started a less than a yr ago) thats when i noticed small misfiring! Noticed the small misfiring at a fast food drive thru..i know the flashing SES means multiple misfire but im not sure what the problems is.. I hope it is a o2 sensor, that would save me a shiit load of money rather than payin 800 to get the piston rings!

LS6427

iTrader: (2)

Piston rings do not cause misfires....so drop that as a cause. If you had bad enough rings or a broken ring...misfires would be the least of your worries and problems.

Go out to your car, see if any of the spark plug wires are touching your exhaust manifold pipes...AT ALL. That causes misfires.

I know you said you checked your injectors...don't know what/how you checked them........but fuel injector(s) leaking will cause misfires at low rpm's and at idle. Only way to really make sure they're not leaking is to have them installed in the rails...then turn your key to "on" and let the fuel pump prime the system. Then see if any start to drip.

Get it on a scanner................

.

LS6427

iTrader: (2)

$10 for an 02 sensor.............

Cheapest place I've ever seen is www.rockauto.com

$40.00 for Denso sensors with the wiring harnesses and plugs built in.

.

MiniTransAm

iTrader: (3)

I had the rings go on cylinders 5 and 7 and it would misfire in the higher gears if I lugged the engine too much. Shifter would shake also but yours may not since it's a A4. I ended up going with a used bottom end.

fleetmgr

Another thing you can try since you say this happens when you step on the brakes. Disconnect the vacuum line from the master cylinder and plug it so you don't have a massive vacuum leak. Then, start the car, step on the brakes and put it in gear and see what it does. If it doesn't start missing, replace the power brake booster.