I have a 1990 gmc sierra with a 6 cylinder engine. It always starts on the second try. What should I look for? Maybe replace the map sensor?
I also drop to 1/4 mark at idle on the oil pressure gauge. What can cause this issue?
Check the Frequently Asked Questions. There's a whole page of videos on this common problem.
First I would do a fuel pressure leak down check to see if you have a leaking injector dripping fuel into the engine after shutting it off... This not only depletes the pressure in the fuel system so it takes longer to get the system back up when restarting, that raw fuel can foul the spark plug temporarily and it needs to be cleared out before the engine can start. As for the oil pressure, since the oil pump capacity is linked directly to the engine RPM, it will be lowest at idle. 1/4 of the oil pressure range is perfectly fine at idle.
