ChevyDave007

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?

73shark

How about the #1 plug?

dh1

If so, clean one of them thoroughly and install it in #1. You might have gotten a bad injector.

ChevyDave007

Sorry I forgot to mention that about 3 months ago I replaced all spark plugs with Autolite Iridium XP's.

I also need to clarify that the misfire was happened before replacing injectors. That was the reason I changed them, but still getting miss and code from cylinder #1.

ChevyDave007

I am considering changing plug wires but I have changed them around in relation on the engine and still get the same cylinder misfiring, so I don't think it the problem.

73shark

Change #1 plug. Next time use AC Delco plugs.

ChevyDave007

Well it has been two days since it last missed. didn't do anything that would have stopped it. (I did change water pump but not relevant to misfire).

All I can guess is this was all caused by a tank of bad gas. I have filled up twice since it started and it hasn't done it since the second fill up (on Saturday).

I'll have to check and see if its still doing it over the next week, but fingers are crossed that it was just some water in fuel.

sheldon 97suburban

iv had this problem check the distributor rotor for play if there is play, your distributor gear needs to be replaced they just get wore over time, and causes the timing to get thrown off at random

tlavergne

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.

ChevyDave007

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.

I got it off ebay
http://cgi.ebay.com/ebaymotors/ws/eB...=160537423813:)