Hi guys. It's been over a month since the last time I was on here when I was troubleshooting a "no start" issue. That problem was fixed thanks to y'alls help but in the last week it starting running bad again. I'll give you some details first to help rule out any possible problems.


It's a 2000 Blazer, 2wd, 2dr, 4.3L, Auto, @115K miles.


@ 9 months ago I put a new distributor cap, rotor, and fuel filter on it.


unrelated- @ 6 months ago I replaced the air filter and changed the oil. We only put about 4-5K miles on it a year now.


unrelated- @ 4 months ago- New tires


@4-6 weeks ago put new intake manifold gaskets and plenum gaskets on it. The leaks were fixed after I did that but the engine wouldn't start. It was a coincidence but I ended up having to replace the fuel pump as well(with a Delphi pump). While I had the tank off I cleaned out the tank but it was pretty clean as it was. After that it started right up and ran great. I went ahead and changed the fuel filter again just in case.


unrelated- @ 3 weeks ago I put a new battery in it.


Here's what happened. Conditions outside when it happened were in the 40's. My son was parked and idling at a Sonic Drive-in. He said it was running and idling great when he pulled in and parked. Just sitting there he said it just started running rough.


I ran a scan on it when he came home and got a P0307 code. That's a cylinder 7 misfire code on a 6 cylinder engine. Nice, right? So yesterday I checked for vacuum leaks and made sure all electrical connectors were plugged in tight. No luck.
Today I replaced the spark plugs and wires. No luck but now I have a P0300 code which is a Multiple cylinder misfire. I rechecked the wires, firing order, etc. It wasn't that. It starts right up but at times it will backfire when it starts and then it sits there and idles rough. Never rough enough to die. When accelerating the throttle it will cut out slightly and then rev up. When out driving it will accelerate but it definitely has a big loss of power.


OBD-II website gives me some other things to try but I just wanted to see if anyone has had any experience or suggestions before I moved on to O2 sensors, burnt valves, and so on?


If you have any other questions just let me know.


Thanks in advance for your help.

 

Keep in mind o2 sensors will only cause it to act up when it's warm!!& have u tried cleaning your maf sensor?

 

Try the cap & rotor. My 97 Blazer has a p0300 code right now and I was chasing my tail trying to figure it out. My cap, rotor, plugs, and wires are only about 5 months old. I narrowed it down to either a worn out ignition coil or a bad cap and rotor.
Easiest fix first right?
Took the cap and rotor off and noticed some white scoring on the contact poles of the cap and scoring on the end of the rotor and some nice build up on the rotor contact. Used some light sandpaper to clean it up and put it back on. It runs completely different now.

That would be my guess. Had it happen to both of my blazers already. And they don't like aftermarket caps or rotors. I'd stick to ACDelco.

 

THANK YOU for giving us good stats/results as half the people say "my car wont start wut do i do?" LOL anyways id try a can of "seafoam". pour half in the tank. half of it goes in the brake booster line while cars running. SLOWLY stick the line in it. When you do it. have a special friend hold the rpms to 2k or 3k, so the engine doesnt die. one you are down to 1/4 bottle let em get of it. dump it in. it'll stall. let it set for a hour. start it up. it'll run like ****. drive it around the block hard. should help. seafoam is the ****.

i gotta say,ac delco caps,YES rotors. no. Why? the few ive replaced they are a pita to put in. lil too much plastic. those bwd ones snap right on. so far,this is the only thing ac delco i dont like period. (sorry delco,i truely love you,but your rotors suck)

 

It possibly not being O2 sensor makes since. I haven't cleaned the MAF but I know when I unplug it and plug it back in there is no difference. I checked the vacuum and at idle it ran steady @18Hg. Since I have moved I can find my compression gauge that's not going to happen for a bit. I did take the cap and rotor off. The rotor looked good. The AC Delco cap had the same white residue built up that Chris015 had. I just cleaned it with a brass brush, checked continuity, and it checks out fine. There is still no change. Same cutting out and missing as before. I did notice that I haven't seen a strong blue arc when checking spark. No strong blue arc on any plug. Kind of of like when the voltage gets low. I was thinking maybe coil but I have always experienced the coil to work or not work. Never just a weak coil. Maybe it can? I guess if I don't figure it out in the next couple of days I think I'm going to have to give up and just take it to the mechanic. I just really, really have a hard time giving up. It's not the money as it is feeling like it beat me. Man I hate that! What ever I find out though I'll post my results. Thanks guys.


PS- If you can give me your opinion on the MAF(not making a difference when unplugging it) and the coil I'd appreciate it.

 

Not sure about unplugging the maf, but cleaning won't take long.....as far as the coil, get u a spray bottle full of water start trk and start spraying the coil and wires while it's running do this at night......if the wires are bad u will see the electricity traveling thru them.....and u will see the coil arc!!! The darker the better!!!! Lol

 

Posting my results. After all of that it trouble it ended up being the 9 month old distributor cap. It had a small crack on #1 and #2 right where the inside electrode meets the plastic. What a pain in the butt this was for it to only be the distributor cap. Oh well. At least it wasn't a head or valve or something bigger. Thanks for y'alls help with this.