99 yukon 5.7 vortec misfire HELP

[ccapehartusarmyINF.(ret)]

so cross injectors off the list
okay so what can cause multiple misfires across 3 different cylinders with proper working injectors and good compression? i think weve already covered the plugs and plugs wires right

 

[lifted_yukon22]

Yea they are all new could it possibly be sensor inside distributor or the gear but about 15k ago it was wore but not near enough to replace it. Could I have a weak coil possibly?

---------- Post added at 06:55 PM ---------- Previous post was at 06:49 PM ----------

Could the injectors be getting stuck open when the motor is in a strain? After I replace the #5 injector with a new one it still misfired on that cylinder....when it began it was almost very intermittently now of I have to give it hard throttle it's a daily thing...

 

[SunlitComet]

ignore the actual injectors and compression and concentrate on a possibly bad wire or dizzy cap. make sure wires are delco or high end brand like msd and such. make sure cap and rotor are delphi, delco or high end as before. the cam sensor itself would not likely do such a thing. dizzy gear not likely just effecting one cylinder so much.same goes with coil. those two items would effect all the cylinders badly. check for flash-over and arcing on the plug wire and dizzy.

---------- Post added at 05:28 PM ---------- Previous post was at 05:27 PM ----------

don't recall you mentioning the brand name of the new parts.

 

[ccapehartusarmyINF.(ret)]

start checking wires for resistance and check for proper voltage
i you should be getting 20k 100k volts at the plugs
you can check the input voltage at the coil wich should be 12 volts if im not mistaken but like he said if the coil was the issue i would affect all the cylinders

 

[SunlitComet]

100k volts is asking a lot. the msd 8231 coil max is 40k.

 

[lifted_yukon22]

All ac delco except wires because no one in town had them in stock but the old ones were ac delco just changed the to rule them out...

---------- Post added at 08:44 PM ---------- Previous post was at 08:40 PM ----------

The wires were the napa brand Belden max I think

---------- Post added at 09:07 PM ---------- Previous post was at 08:44 PM ----------

I've been reading on other forums and I found this thread that he was having same problem as me as it sounds. I think he is better than me at explaining the situation I'm going to link it in and read his description. http://www.gm-trucks.com/forums/topic/56103-57-vortec-missfire/

 

[ccapehartusarmyINF.(ret)]

yeah i know

100k volts is asking a lot. the msd 8231 coil max is 40k.

lol yes i realize 100k is alotta spark sorry its been awhile since ive taken advanced electronics

---------- Post added at 06:36 PM ---------- Previous post was at 06:29 PM ----------

you explained it just fine he just used a few less words no big deal

---------- Post added at 06:41 PM ---------- Previous post was at 06:36 PM ----------

and from those responses looks like there about 5 pages of posts behind us

 

[lifted_yukon22]

I use a regular multi meter to check wires restiance right? Ok I may sound like a idiot what do I use to check the spark?

 

[ccapehartusarmyINF.(ret)]

yes use a multi meter for both when you check resistance you switch yer multi meter to the ohms symbol for the plugs use a spark plug tester

did you buy pre gapped plugs?
okay its been along time since ive seen anyone get there plugs in the wrong firing order
but if the plugs were in the wrong order it wouldnt hardly run would it?

 

[SunlitComet]

at 215k the wear on the engine should have eliminated the valve guide issue that was made into a tsb. get another 41-933 plug for #5 and get rid of that wire set. never ever buy house brand parts. get ACDelco 9718Q wires. mail order from rock auto or amazon if needed for about $50. and make sure they are firmly in place. use a multimeter with ohms to check resistance of existing ones. no wire should be at more then 30k ohms tops.all platinum plugs for obs vortec should be pre-gapped at .060".