Random misfire - no codes - what to look for?

[dmperfection]

I've been experiencing some random misfire lately on my '02 5.3L, 223k miles, no codes. I suspect I might have a coil that acting up. I'm somewhat capable of performing most routine maintenance, but chasing misfires isn't my something I do everyday. Can someone share some advise on how to test coils?

I've done the following over the last year. I've cleaned up the throttle body. Also, thinking it was idle only, I pulled of IAC and cleaned that up well and throttle body hole. OEM plugs and wires dropped in about 10 to 12 months ago. At about the same time, ran the GM fuel injection cleaner with pressurized cleaning tool at fuel rail.

I'd appreciate any guidance.

Thanks.

 

[digitalfiend]

This isn't a guaranteed solution, but have you looked into replacing intake manifold gaskets? I was getting lean codes P171 and P174 and I think I was getting misfire codes too, but it's been too long for me to remember for certain. I started having this problem somewhere between 130k and 150k...so if you're at 223k then it couldn't hurt to replace your intake gaskets and anything else as you're taking the intake off.

 

[John03Z71]

I've been experiencing some random misfire lately on my '02 5.3L, 223k miles, no codes. I suspect I might have a coil that acting up. I'm somewhat capable of performing most routine maintenance, but chasing misfires isn't my something I do everyday. Can someone share some advise on how to test coils?

I've done the following over the last year. I've cleaned up the throttle body. Also, thinking it was idle only, I pulled of IAC and cleaned that up well and throttle body hole. OEM plugs and wires dropped in about 10 to 12 months ago. At about the same time, ran the GM fuel injection cleaner with pressurized cleaning tool at fuel rail.

I'd appreciate any guidance.

Thanks.

What brand/type plugs and wires did you put in? I did my plugs and wires a little over 12 months ago and just experienced a severe misfire issue, turns out since I didn't use genuine AC Delco plugs and wires at the time the engine decided to not like them anymore. Switched to genuine plugs/wires and haven't had the issue since. Just something to think about.

 

[dmperfection101]

What brand/type plugs and wires did you put in?

I go Delco OEM, die-hard all the way with my Tahoe. However, you do bring up a good point. I've definitely heard of Delco plugs going bad prematurely. Looking for a good way to test coils and at the same time rule out wires. The misfire isn't causing any drivability problems, just annoying to feel a stumble.

---------- Post added at 11:11 PM ---------- Previous post was at 10:27 PM ----------

This isn't a guaranteed solution, but have you looked into replacing intake manifold gaskets? I was getting lean codes P171 and P174 and I think I was getting misfire codes too, but it's been too long for me to remember for certain. I started having this problem somewhere between 130k and 150k...so if you're at 223k then it couldn't hurt to replace your intake gaskets and anything else as you're taking the intake off.

I experienced the infamous intake gaskets issue around 80k miles and had the codes to go along with rough idle.

I just may consider doing intake gaskets again, since mine have since been updated to newer design.May our may not solve my issue.

 

[FrankU]

Take the truck to a dark place at night and pop the hood with the engine running. Look for any secondary ignition arching.

 

[Mudfrog]

Which AC Deloco's did you guys use? I used Denso Platinums that I keep here at work and I'm not happy with them. At idle it always feels like there is a slight miss. I looked several places and I do not see an AC Delco Iridium listed for a 2002 5.3 Flex.

Also, the AC Delco wires that I bought seem to long, they were about 2" longer than the ones I replaced (they were aftermarket), my main concern is one of the wires will rub the steering linkage where the bolt is. Per application look up they were supposed to be the correct wires.

 

[John03Z71]

Which AC Deloco's did you guys use? I used Denso Platinums that I keep here at work and I'm not happy with them. At idle it always feels like there is a slight miss. I looked several places and I do not see an AC Delco Iridium listed for a 2002 5.3 Flex.

Also, the AC Delco wires that I bought seem to long, they were about 2" longer than the ones I replaced (they were aftermarket), my main concern is one of the wires will rub the steering linkage where the bolt is. Per application look up they were supposed to be the correct wires.

I used AC Delco #41-962's with 9748GG wires when I replaced mine about a month ago (2003 5.3 flex), and as mentioned so far so good. AC Delco has a rebate promo going on right now too, I got the plugs via Amazon Prime for $5.58/plug and Delco has a $1.50/plug rebate.

Another thing to consider is the condition of the wires in case you've pulled them to check your plugs; when I was trying to diagnose my problem I removed/replaced the plug wires a few different times and the last time I did it I must have pulled something loose inside one of the wires because it ran HORRIBLE and I didn't change anything. It still felt like it was making a good connection but apparently not. Just another .02.

 

[Mudfrog]

I used AC Delco #41-962's with 9748GG wires when I replaced mine about a month ago (2003 5.3 flex), and as mentioned so far so good. AC Delco has a rebate promo going on right now too, I got the plugs via Amazon Prime for $5.58/plug and Delco has a $1.50/plug rebate.

Another thing to consider is the condition of the wires in case you've pulled them to check your plugs; when I was trying to diagnose my problem I removed/replaced the plug wires a few different times and the last time I did it I must have pulled something loose inside one of the wires because it ran HORRIBLE and I didn't change anything. It still felt like it was making a good connection but apparently not. Just another .02.

I used the 748HH wires, this is the only set that Amazon stated would work with my engine.

 

[John03Z71]

I used the 748HH wires, this is the only set that Amazon stated would work with my engine.

As per AC Delco's site use 748GG wires if you have the round Delphi coils and use 748HH wires if you have the square Melco coils. Amazon is great but I would not trust their part finder to be 100% accurate.

 

[Mudfrog]

When I looked them up I verified the number on the coils, that might have been through Advance's site though.

Surely the wires wouldn't be my issue would it? I assumed the main difference was the length.