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Danny
Danny, VW Mechanic
Category: VW
Satisfied Customers: 4004
Experience:  ASE Master Certified with L1 Certification, Volkswagen Certified, VW and Audi repair shop owner
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Jetta: 2.0L..misfires..P0303/P0304) when accelerating..highway speeds

Customer Question

98 2.0L Jetta (ABA) misfires (P0303/P0304) when accelerating up to highway speeds. Runs perfectly (no codes) if you stay below 45. New wires, plugs, coil, dist cap, rotor and MAF. Smooth idle. Suggestion?
Submitted: 8 years ago.
Category: VW
Expert:  Danny replied 8 years ago.
Dansmith,

Does the vehicle also lack power under heavy acceleration? Only 3 and 4 misfire never 2 or 1?

Danny
Customer: replied 8 years ago.
Yes, it lacks power under heavy acceleration -- I'd say that that's the primary cause of the misfire when getting up to highway speed. Once at speed it smoothes out. I just re-pulled the codes -- still just 3 & 4.
Expert:  Danny replied 8 years ago.
I think you have a plugged catalytic converter, this symptom is hard to diagnose, almost indistinguishable for even a dealer tech to diagnose from a faulty cap/rotor and often only misfires on a couple of cylinders.

Drop the exhaust pre cat, clear the codes, and take it for a drive. It'll be loud but my bet is you won't have the lack of power or misfires anymore. I'd say that's the problem.

Danny
Danny and 6 other VW Specialists are ready to help you
Customer: replied 8 years ago.

I'll give it a shot. Thanks.

Expert:  Danny replied 8 years ago.
Let me know how it turns out.

Danny
Customer: replied 8 years ago.
I replaced the catalytic converter -- there is a definite increase in power. Unfortunately, I am still getting a misfire in cylinders 3&4 (P0303/P0304) with heavy acceleration. Any other thoughts?
Customer: replied 8 years ago.
I eplaced the catalytic converter -- there is a definite increase in power. Unfortunately, I am still getting a misfire in cylinders 3&4 (P0303/P0304) with heavy acceleration/going up hills. Any other thoughts?
Expert:  Danny replied 8 years ago.
I think it's time to do a compression test on the engine to see if it lacks compression on those two cylinders. If that turns out ok I'd swap the number 3 and 4 injectors to cylinders 1 and 2 and see if the misfire follows the injectors to 1 and 2.
Customer: replied 8 years ago.
OK. I'll give it a try this weekend. Thanks!

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