Hi. I hope im in the right place. Anyway I have a 99 tahoe 5.7 liter vortec. I have a misfire code p0303. It only misfires when I'm going up a hill and I'm at 3000 rpms for to long. The check engine light flashes then goes solid. It will go off on it's own usually by the next day. Other than that I only feel a misfire when I'm at a steady 40 to 60 mph and that doesnt trigger the check engine light. If I'm accelerating there is no misfire. I've replaced plugs and wires, cap and rotor. I'm told to check the ecm ground. I think I have found it on the passenger side behind the cylinder head but not sure. Does anyone have a picture or have had this problem? If so how did you get to that wire or how did you resolve the problem? Thank you.

 

If you are only getting a misfire code on cylinder 3, it's not going to be ground issue. Check the compression in your cylinders and see how #3 compares to the rest of them.

 

I'll add if compression checks out OK it's that crappy stock plastic housing distributor.
I had under load misfires being set on my old '99 Yukon around 90k miles and compression was fine with all new cap, rotor, wires, plugs and pull a hill getting into the gas and it would misfire setting the CEL. After running a while code would clear.
Same thing, light throttle and idle it ran fine.
New distributor fixed mine, I did a aftermarket metal housing one not the crappy original one. Plastic housing ones are famous for the cap screws stripping out also.

 

Kchevy75 and repairman54. Thank you for your replies. I do believe the actual distributor is metal only cap and rotor are plastic. Is the what you are referring too?

 

I've heard of plastic distributor bases, but never have seen one yet. They likely mean aluminum distributors, which can strip out if the cap screws are not placed correctly and tightened down right Your cylinder compression testing should be no more the 15 percent from cylinder to cylinder.

 

My '99 Yukon 5.7 definitely had the plastic distrib. housing. Ears where the cap screws go into like to crack or break off and being in the back of the motor up against the firewall it's hard to see the distrib. housing.
Great motor in those years except for the distributor and the spider injectors. I had to change both, did the updated spider kit as I had a injector leaking through on shut down flooding the motor IE the hard start hold down the gas pedal on hot restarts.
Bought it used w/30k miles on it and sold it with 190k miles on it and guy who bought it ran it 2 more years until frame rust killed it.

 

I bought mine 7 years ago with 130k. It now has 307k. Runs like a champ other than the misfire. I'll look into the distributor. Thank you for your input

 

Sometimes I wonder why GM saves a few bucks on garbage like a plastic distributor housing. Then I look, or work, on a *ucked up beyond repair Ford or a Damn offell design Generally extrement Dodge, and I know why I stick with GM products.

I suppose one could get cheap and use JB weld to repair it, but who wants to do that, unless you have to? Not me. Steel and plastic don't make a good threaded combination.

 

Yep you could JB the screw ears it but you would have to pull it to do it right so replace it, once and done unless you have free time or want to risk the cap popping off on the road.
2x no Furd turbos or any makers turbo stuff for me for that matter. No diesels either. NA gas motors only.
Dodge (Fiat , fix it again tony or tom) are out of the question also. Only old school Mopar pre '80's if any Mopar's for me.

 

Same here.

No frakking turbos or diesels for me. I got the last year 2015 Chevy used the 2.5 liter non-turbo motor in a light vehicle as my sweet Malibu. It's been a great car with few defects. I'll keep her until one of us dies. Also, have a 1998 K-1500 that has been great. Had to replace the water pump as it was seeping, five years ago. I'll be swapping out the coolant this week. in fact 5 years since I did that, as I used a coolant additive, so that extended the life of the coolant. Had to change the Schrader valve on the low-side A/C last year, but she puts out a solid 42 F degrees. You can't beat that on a 23-year-old pickup truck. She's simple enough but tough as nails.