misfire wont go away the shop is stumped

I have a 98 GMC its a 6 cyl dont remember the size what ever is standard 2wd any way about 8months ago it started running rough took it in and it got a tune up ran great then 4 months later started running rough took it back replaned all plugs,wires distrubiter,cap and roter.Again ran great about 3 months later same problem this time with a check engine light. took it back mis fire code checked all wires ,ect. all good ,no arcing replaced main coil and wire. problem never went away took it to another shop they said egr valve ok 300$( got ripped off), no fix so took it back to my orginal mechanic (they dont rip me off), checked all again now thay are stumped can't figure it out, sometime it runs great sometims idles rough and misses sometimes runs rough till you smash the gas,now it dosent want to start and when it does thick black smoke check engine light still says misfire.They say its not a fuel problem i disagree have an apointment again next week.any help would be greatly helpful this is costing me a fortune.im afraid to take it to the dealer just to have them say its something i already fixed and CHARGE ME TRIPLE for info I already know we all know how dealers dont listen to what you said you had check and replaced already

im afraid to take it to the dealer just to have them say its something i already fixed and CHARGE ME TRIPLE for info I already know we all know how dealers dont listen to what you said you had check and replaced already

OK you have taken your vehicle to someone who claims to know how to fix your vehicle and they have cost you 3X what the repair would have cost you at the dealer.
I know the answer to your problem (and the fix is quite simple)..but since you are so down on dealers, I'll keep the repair to your problem my secret.

OK you have taken your vehicle to someone who claims to know how to fix your vehicle and they have cost you 3X what the repair would have cost you at the dealer.
I know the answer to your problem (and the fix is quite simple)..but since you are so down on dealers, I'll keep the repair to your problem my secret.


No thats not what the post said try again i never said this "you have taken your vehicle to someone who claims to know how to fix your vehicle and they have cost you 3X" if they knew how to fix it they would they tried everything they know and the last time i took a diffrent car to the dealer they wanted to replace a bunch of expencive parts that did not need replaceing. I fixed that car myself and drive it everyday.so i am lery of dealers..but thanks for your upbeat positive attuide and sleep well knowing you helped you fellow man out and they wonder why the county is in trouble I remember when people were nice and kind.

I first started reading this and started thinking Valve is going bad. But that would not cause the no start and black smoke. Now I'm thinking Mass air flow sensor. Good luck and keep us updated.

I will started fine today and ran ok thats whats so strange some days it runs perfect some days not very strange

I'm still thinking Mass air flow sensor.

problem solved....distrubetor cap again 3ed one this year this one has lasted the longest so far.

I would question the quality of the parts installed by the mechanic that "doesn't rip you off". One cap should last three years, not three caps in one year!

yes the shop says they see alot of the same problem with that model van whan ever it gets warm outside or a few days of ran i acts up i think its getting moisture in their and the contacts get corroded.

yes the shop says they see alot of the same problem with that model van whan ever it gets warm outside or a few days of ran i acts up i think its getting moisture in their and the contacts get corroded.

As long as they don't change the brand of parts that they install, they're going to continue seeing the same problems! You paid for two cheapies and one good one, (if it is in fact a good one), plus all that labor...time to find a TECHNICIAN, and broom that parts replacer.

THe distribitor has to be pulled out,probally a worn out distribitor gear.Look for shiney spots and mark the distribitor before pulling out,timing is not adjustableIt is a common problem.I have seen this happen,but a GMC truck with a 350.It ran bad,the distribitor gear was worn out put another distribitor gear in it and ran really good after the distribitor gear was replaced.