Hello all,
Bought a 2003 XLT with the 3.0 V6 Vulcan engine paired to a five speed manual. The guy I bought it from said the check engine light was for a O2 sensor, but once I read it I have a misfire in cylinders 1 and 2. The misfire was not very noticeable at first but I feel like it is getting worse, I've already replaced plugs, wires, and the coil pack, and made sure everything was lined up correctly. Any advice on what to do next? I'm starting to worry I have a broken valve or something.

 

whats the mileage, O2 sensors need to be changed every 10yrs or 100k miles. what did the plugs look like in cylinder 1 n 2, were they different from the rest. the 3.0 V6 Vulcan are known to burn valves. compression test is the best way to check. cold motor all plugs out.

 

Thanks for your reply docm,
The engine has 205,000 miles on it. No idea when the O2 sensors were last replaced, do you think it could be a cause of the miss? Plugs in cylinders 1 and 2 are the same as the rest but I will double check proper installation today. I haven't done a compression test yet but I did put a dollar bill up to the exhaust and it didn't go in at all.

 

you should replace the O2 sensors, yes it is possible they are causing a misfire. the passengers side is not too hard, take the wheel off. drivers side is a little tricky, use bosch sensors. but i think the compression test will give you quick results, cold motor all plugs out.

 

Might also be worth if not changing but cleaning your fuel injectors, this was the main cause of my misfiring after replacing my original 3.0 with a remanufactured 3.0. I still am having major cold start issues but no misfiring after the shop changed out 3 of the original injectors for new ones.

 

Hello all,
Just ran a compression test on cylinders 1-3 (Cylinders 1 and 2 had the misfire)
Cylinder 1: 125 PSI
Cylinder 2: 155 PSI
Cylinder 3: 150 PSI
So because of this, I feel like I can put aside any fears of a blown engine. I noticed that the spark plugs in cylinders 1 and 2 especially were very goopy and smelled strongly of fuel. The plug from cylinder 3 was a little dirty as well, but not nearly to the extent that the first 2 were. I'm suspecting that fuel injectors are indeed the culprit here. I purchased a replacement set and plan to replace them all soon.
Is there anything else I should be considering? One thing worth noting is that the catalytic converters were tampered with by the previous owner. He said they were "clogged" and so he drilled holes in them. Could this potentially be aiding the misfire, and giving me an incorrect air-fuel mixture? Lots of questions. Thank you

 

id do the O2 sensors as well. im sure its not the problem but the motor will really like it... at 200k its time

 

You're definitely right!

 

May I ask where you purchased a replacement set from?

 

the cats, there is an O2 sensor behind the last cat. it has nothing to do with the motor performance, its just for emissions. being cloged up will make a motor run with less power or no power.

 

I purchased a pretty cheap replacement set from Partsgeek.. I believe it was around 90 dollars for the whole set. Should I return them and buy some nicer injectors just for cylinders 1 and 2?
Good point about the cats docm.

 

As long as they’re not Chinese knock offs I think you’ll be fine. I made the mistake of purchasing Chinese ones off of Amazon. My truck ran, but it was super lean and after watching videos on them, they don’t atomize fuel properly this video really steered me away from the Chinese ones but, I’ve also bought in a really expensive set from Napa and for whatever reason those didn’t work at all the only thing I can think is they were the 14 pound injectors for a system without flex fuel and my truck being a flex fuel vehicle didn’t like them?…

 

i got a set off ebay, tested and refurbished for $50, i didt think mine were bad and they worked. i felt i could always put the old ones in if needed. they have about 30k on them, no problem.

 

Understood. Thanks for the feedback!