MISFIRE madness continues...2000 VW jetta mk4 12v 190K miles

[gbagby]

I'm back

Someone suggested that a worn timing chain/tensioner/guide rail could cause a misfire, is this correct?

most recent codes P0300 random misfires
P0305 cly 5 misfire
P0303 cly 3 misfire
P0420 bank 1: efficiency below threshold (pre O2 sensor...right?)

Last week I replaced plugs, wires, coilpack...NO CHANGE
then I checked all fuel injectors for resistance(all good-14-16 Ohms)

Today I bought a preO2 sensor and put it on. Drove it 12 miles after clearing P0420 code. AND got the same code again!!! what gives? Still misfiring!!!

Rear O2 sensor? (nvr got a rear code)
Cat. converter? (nvr got a cat code)
Timing chain issue? (is there such a code?)

I'm planning on buying a compression gauge today.
Someone suggested checking cylinders for compression...is this worthwile?
will indicate what? valve damage, head gasket damage? is it specific?
that's another $35 for the gauge is why I ask

Should I take it in to have someone scan it more in depth? For a precise and definitive answer?
Or will they just do the same thing? replace parts one by one until they find the cause? I can do that AND save $$$ on labor. with the exception of an in depth diagnosis.


Btw, I looked at the Ross website...quite a few VAG setups. AND very costly for the "professional" series $1200
Will the "enthusiast" series $99-$299 give a definitive diagnosis?
What kind does Gary have?

[GTIVRon]

The "professional" one comes with a laptop. If you have a laptop you can drag out to the car and use then you don't need that.

Just get the HEX+CAN interface with USB. It's $350. You can find them used for cheaper in classifieds from time to time.

[Taznmich]

I replaced my guide this past week end. Kinda of a big job, but possible. Here are a couple of things that helped me a lot. I only changed the top guide. You have to pull the trans to do the lower. Hope it helps.

http://forums.vwvortex.com/showthrea...k-on-a-12V-VR6

http://forums.vwvortex.com/showthrea...s-on-a-12v-VR6

It needed to be done but it didn't help my mis firing. Still trying to figure it out.