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Misfire. Need help, dealer cant figure it out either

Need a VW Guru’s help before I pull my Glock and shoot 02 Jetta

Bad misfire P0301

a bit long, please bear with me. 02 jetta gls with 2.0 AVH engine auto trans. over summer my brother overheated it & blew head gasket & valves. All parts listed are new between aug and now. I repaired engine as follows

new head & bolts

head gasket

timing belt

water pump

coolant flange on drivers side

new fuel rail and injectors

car also has new coil pack, new VW plug wires and 1 week ago new iridium plugs

my brother didn?t want car, so i bought it from him. Ran great after I rebuilt top end. Car did 140 on the turnpike & ran great. once or twice while giving moderate to high throttle CEL would flash and I pulled P0300 as a pending code. Problem stopped after 2 days.

last week after 4 hrs of idling(don’t ask) started misfiring and CEL flashes constantly P0301 The misfire seems worse at idle and low speed. Car will get to highway speed but has bad pickup.

This is what I?ve done/checked

New iridium plugs

Plug wires 4.5 ohms

Coil pack is good and producing enough spark at each wire

MAF sensor cleaned

Cyl 1 compression good

all injectors are clicking and when disconnected cause appropriate CEL error code

Brought car to VW dealer for diagnosis

VAG COM shows multiple misfire on cyl 1

Mechanic confirmed all the steps I took and components tested ok. He tried new coil pack, new plug and wire for cyl 1 and no change. At this point the free 1 ? hr diagnostic time was up & I had to get about my day & didn?t have the $102/hr for him to continue.

What am I missing?


The VERY first thing I would be doing asap is a compression test…especially after having this engine apart the way you have and changing the items you have.

This is probably THE most important piece of info all of us need. If you dont have compression everything stops right there. I could go on and on on what to check outside that but we need a comp test done on ALL of the cylinders…THAT IS ABSOLUTELY STEP ONE. No point in going further until we have those results.

Try cleaning the EGR valve if you have one. Replacing the O2 sensor has also helped some folks for this kind of problem.

You state Cylinder 1 compression is good. People routinely come onto this forum and state the same thing when nothing could be further from the truth. Even shops routinely refer to bad readings as good ones.

So what is the actual number on that cylinder?

(Keep in mind that severe overheating often ruins the piston rings too.)

I would be utterly embarased to post I did all this to a car and had the nerve to tag at the end “Dealer can’t figure it out either” AND it was free work I was complaining about, you actually bailed on the mechanic when it came time to start paying? that was considerate of you.

What are you missing? one thing is for sure,any help from me.

This is a joke thread,right?

Forgot to post compression
Cyl 1 125 psi
Cyl 2 120 psi
Cyl 3 130 psi
Cyl 4 120 psi

Well, I did not have the time to wait at the dealer any longer, and having paid quite a bit of money recently to the shop for other things, I didn’t have the cash to spend right now.
You lack of help is noted, hope you feel better deciding I’m an idiot. You’re a real hero

Did the O2 sensors about a month ago. I will check & clean EGR. Thanks for the suggestion.

Could you have wiped out the cam lobe on either the intake or exhaust lobe for #1 cyl. by going 140mph with a brand new head not even broken in? They don’t have the extreme break-in additives in the oil anymore and a lot of hotrodders are losing new camshafts unless they buy special lubricants.

Well, your engine is crap. All of those compression readings flat suck.

I’d like to say that it amazes me that those readings would be passed off as tolerable but somehow I’m not surprised.

Go back and redo that compression test in the “wet” version and I think you will find that those readings will take a huge jump upwards. This means the piston rings are gone.

I have been that man that had a car the customer worked over like this dumped on. When you get something like this dispatched to you you get pulled out of the dispatch line up and it just flat ruins your day. Mechanics are not in the profession to make hourly wages, they have too much invested to accept “straight time”. I have to ask, did you tell them right from the beginning that you are only here until you have to start paying and then it is off to some other shop?

If you warned them that you were only in it for the free part but they still took it on then it is the manager that ruined the mechanics day. Typicaly managers do not do this to a good drivability man so I have to believe your car was not dispatched to the sharpest knife in the drawer.

"car also has new coil pack, . . . Coil pack is good and producing enough spark at each wire"
Enough Spark ?

Where did the coil pack come from ? This is a “pack” and not individual coils ? Generation II coils usually don’t cause problems, but earlier versions can.

Many of these Jettas were subjects of a Service Campaign and at least one 10 page Volkswagen Techcnical Service Bulletin that pertains to random misfire (PO300) and individual cylinder misfires, approved ignition coils, replacing ignition coils, etcetera.

You might want to see if your vehicle is one listed in the bulletin (looks like most are) and check it out. Did the dealer use the bulletin ?

I’d see if I could move wires and see if the misfire moves with it or try a different coil. Anyhow, besides the advice given by OK4450, the problems with coils on these cars and the DTCs make them suspects.


i didnt do that until i had about 500 miles on the engine. i really dont beat on my cars, my saturn that i semi retired has 275,000 miles on it and she started right up after sitting for 2 months.
i try not to do stupid things to the cars.

i asked them how much it was for them to use the VAG COM to pull codes and data because my OBD II scan tool only reads the generic codes. i was told i could get 90 min diagnostics free. I told them unless it was major and beyond what I thought i could do, that i would be doing repairs based on what the testing revealed.
i was asked into the shop to answer a few questions for the mechanic-he appeared competent and methodical for the few minutes i was back there.
they knew up front i was just looking for the info vag com could provide, and i did offer payment for that. i feel bad that the mechanic got screwed but they offered the service for free after i was willing to pay for what i wanted.

ok wet compression test.

new coil pack, not individual coils, purchased from VW dealer in July 2010. i used a spark gap tester that i hooked up to the spark plug side, adjusted the gap for a .40 gap, grounded the unit and then checked that the spark jumped the gap. each cyl had a good strong spark that jumped properly. each pin on the harness that goes to the coil pack has the proper voltage.
new wires, plugs and a new coil pack were used to test with no change.
my car is not part of the coil pack recall even though its the same pack that was recalled. the previous pack was cracked and faulty, thats why i had to buy the new one.
the plug wires are also from VW/audi dealer.

When you replaced the cylinder head, did you have the engine block deck checked to make sure it was level before you installed the new head and gasket?

If the block was warped, you might have rewarped the head.

Do a cooling system pressure test, while you are doing everything else.
Also, try switching the fuel injector over to another cylinder to see if the problem follows it, just for grins.


Yes I had the machine shop guy check the block. I shall do the cooling system check tomorrow (wed) afternoon as well as switch the injector to another cylinder. Someone just gave me that idea a little while ago-you must be on to something!
Thanks to all for the input!

You have new plugs in the engine but that does not mean those plugs (especially No. 1) are any good.

A new plug can be killed by what you could call an incomplete combustion process. The engine apparently has a serious problem and 125 PSI just won’t squash the fuel/air mix very well. It will run on that amount but not nearly at optimum and it’s anybody’s guess as to how long it will run at all.

You could try throwing another plug in that cylinder to see what happens. I’ve gotten plugs right out of the box that were no good so it’s entirely possible for one to fail within a few miles in a problematic engine.

ok i will try new plugs also. what do you recommend?