Hello, I have owned a 99 Yukon for 12 months. An original owner w/ 125k on the clock. Now has 143k. PO installed wires/plugs/fuel pump/gasket prior to me purchasing it. The MPG has never been great. I developed a hard start problem after about 7 months. From some of the information I found on-line it appeared the gas gauge mis-reading was part of the problem. Added 5 gallons and it started right up. Fuel pressure has been checked and found within spec. After MORE reading I decided I would have the brother-in-law swap out the poppets for the conversion. Started fine after that as well. About 4 months ago I started to trip the SES light. I also noticed the misfire in the 40-50 mph range, the B-I-L brought home the high dollar diagnosis tool and it had 8k misfires on cyclinder 4. At idle it was stuttering as well. Cleaned MAF, swapped plugs and it still was having issues on #4. I have been pestering him to do a compression check on #4 and like everyones lives these days we haven't been able to get together to figure it out. I have read the post on here about swapping the scensor out. Wondering if that is the next step. I am unsure if PO replaced the distributor cap. I have heard of fuel pumps going bad, even after they were replaced recently (about 18 months on this one). I have replaced fuel filter (which wasn't bad). Anything I am missing? I am thinking of having an alternate mechanic take a look at it. I really like the truck, just want to feel confident she is not going to leave me stranded.
Appreciate any input you may have.

thank you.

I think i would check your poppet conversion. I assume you replaced the poopets with injectors? I would think it would be fairly easy to home the injector to another hole and see if the missfire follows.

I guess we also assume that you checked for spark on that wire and its good?

I suppose it wouldn't be a bad idea to check compression before you did anything else. If compression is low nothing else you can do will make a difference.

Thank you for the speedy reply. I think I also will double check distributor cap.



Thanks again for your reply.

had an alternate mechanic take a look at it. Distributor cap/rotor was toast. I picked it up tonight and could not believe what it sounded like at start up. A quick poke of the pedal and she actually felt like a normal 350. He replaced the plugs, cap/rotor and charged me $30 labor + parts. Best money I have spent in a long time. It also had misfires at other cylinders prior to this change. It's good to have a local that you can have faith in.