GMC safari

Hi All

Have a 1997 gmc Safari 70,000 km running rough at higher speeds 95 to 110 kmph eng light came on had plugs,wires,cap and rotor replaced. Was told that miss was gone, not so.( eng light started to flash then stayed on steady when out after 30 km ) Replaced fuel filter ran great until climbing a hill (95 to 110 kmph) The two time the light came on was just after a fill up 87 octane and once climbing a hill. Could this becaused by a weak gas cap. The only other thing tthat I have not replaced is pvc Valve and air filter.
Or anything else.

Thanks
Al Bendera :banghead:

To help you properly, we need to know what codes your truck is setting.

AutoZone will scan your vehicle for free, just don't let them fix your car!!! :nono:

Let us know - Hope we can help.

HI: GMCTECH

About the code for eng miss fire it was P0300 at two places and P0300B at another. They said that P0300b was jut the scaner. Only seems to run bad at higher speeds or up hills. Also seems to be running fine last couple of daysbut haven't tried to
going up a hill faster than 90kmph

Mine ran like shit when I used 87octane did not like hills
try 89 instead..also It say in the manual that if you change from the stock tires to something else it will make the check engine light come on under load or stress like a hill..very strange but who knows