cylinder 1 misfire, after putting in new coils and plugs
Asked by Carcissist Jun 27, 2023 at 09:11 PM about the 2009 Volkswagen Jetta SEL
Question type: Maintenance & Repair
i have a 2009 vw jetta 2.5. been sitting for about a year and a half. i just did
some maintenance to get it up and running- plugs, coils, oil, brakes etc. after
replacing the plugs and coils i have been getting a cylinder 1 misfire when
previously with the old plugs and coils there was no code. it only happens on
cold start but never during operation, any ideas?
8 Answers
Low compression on number 1. Vacuum leak number 1 intake runner. Weak spark on number 1, bad coil or plug, could also be a plugged injector. It's ok at operational temp but too lean during cold running. Whats the compression of the engine?
Carcissist answered 9 months ago
i havent been able to compression test it, but i have done a drop test on all cylinders and theyre all contributing so i know that its not plugs or coils, i have ordered a fuel filter and some injector cleaner, the exhaust smells like humid air and is pretty caustic on the eyes so its definitely running pretty lean, im hoping after working through the rpms at higher speed i can rule any stale gas/ water from the 1/4 tank that was sitting in it for the 1.5 years
Don't run it with less than 1/4 tank of fuel, your already in danger of fouling the fuel pump due to possible bad gas, add at least 5 gallons of high test fuel and a bottle of Techron, run that for at least 20 minutes then change the fuel filter. drive it around until you get to 1/4 tank and refill it with regular fuel and another bottle of Techron or just fill it up with Chevron fuel. and go from there. Hopefully it will clean up the varnished injectors.
Carcissist answered 9 months ago
i had filled it up all the way with a fuel system cleaner initially, but I have only been able to drive it a total of 20 miles after fill up but i think some gunk must have been floating around in the 1/4 tank of old and 3/4 of new with fuel system cleaner, but I'm gunna try what you said
How much fuel system cleaner did you put in the tank?
I would still add at least 3 gallons of high octane fuel.
Carcissist answered 9 months ago
hey so i solved the mysterious misfire on cylinder 1, after doing plugs, coils, injectors and cycling fuel cleaner and the misfire still persisted. i opted to check the fuel pump itself and found that that did the trick, the filter pouch inside the pump was fairly gunked up and the hoses were much darker then i was expecting, i suspect that to be the cause of the persistent misfire on cylinder 1, i drained the tank and added fresh 93 gas and havent had any check engine lights or pending codes! hope this helps someone chasing the same thing
