My Suburban just started running rough, and misfiring on cylinder 1.
The problem is intermittent and seems to do it worse after its warmed up and is most noticeable when under a load and under 2000 rpm's. When it first started I thought the trans was slipping when I would move from a stop. Then I realized that it was just misfiring. It does not always do it. It sometimes seems to run fine but I can recreate it sometimes if I powerbrake in drive letting it first go to idle then goose it to 1500 rpm's it will often start and maintain the misfire. Doing this was the only way I could get the misfire to continue long enough to actually set a code so I had a clue as to the problem. But it only seems to do it just off idle under load.
WHAT I HAVE DONE
I replaced all the injectors, and the coil pack on cylinder 1. It has only been 1 day but it seems to be mostly gone after the coil pack replacement but still occasionally it will miss. I also replaced fuel filter about 8 months ago. I have also done seafoam and injector cleaner, neither of which made a difference. I have a computer scanner and checked the O2 sensors and they seem to be working correctly and I also checked the fuel pressure regulator for leaks and vacuum, they seem good. I can't check fuel pressure but the fact that it runs good are higher rpm's but just having problems off idle would seem to not point to a fuel pressure problem.
I'm stumped. Although it seems to be running much better I can still get the occassional miss by doing the powerbrake method. Any ideas?