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?
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That was a chronic problem on my 1999 7.3. I had put in plugs other than AC Delco in a tune up. A GM mechanic told me to go back to AC Delco...I did and the misfire went away. I agree with 73shark...go back to OE AC Delco plugs.
If it was older suburban I would look at the distributor but the 02 has a distributorless system with individual coil packs for each cylinder run off crankshaft sensor.
the good news is that since my last post no more misfires. So either the coil pack I replaced on cylinder #1 was actually bad or I had a bad tank of gas and it took awhile to get it all out.
I appreciate everyone's response's.
On a side note I replaced the shroud, clutch fan with an aftermarket dual 16" setup, and its works great! I am very pleased with it. The engine is much quieter and it only comes on when needed, plus my fuel economy is improved and it just feels peppier. I won't know exactly how much better for several tanks but I am very pleased.