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Author Topic: Cylinder 7 misfire  (Read 19278 times)

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misanthrope

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Cylinder 7 misfire
« on: 11/17/11 01:27 PM »

2004 Avalanche 5.3 ~130k miles.

Engine began to run a little rough in town at about 25mph. After about 10 minutes of driving engine light came on. Turned onto 30mph road to head home and light starts flashing. Slowed down under 30 and it was solid again, stepped on gas and light would come on at 2000 rpm even if under 30mph. No power.

Ran code, random misfire. Used IR heat gun to check Cats, driver side upstream 390F/downstream 500+, passenger side upstream 410F/downstream 289F. Replaced with new catalytic converter assembly, all 4 o2 sensors(never been changed). Fired truck up and idle was still not smooth, when I let off brake in gear, engine is pretty rough. Ran code, random misfire and cylinder 7 misfire. Swapped all spark plugs with oem, checked for spark on all coil packs and wires, found good. Engine ran same. Swapped cylinder 7s coil pack and spark plug wire with cylinder 5 but code stayed on cylinder 7. Returned coil pack and spark plug wire to original position. Had a shop run fuel system on their machine, same symptoms. Engine began shutting off on its own, cleaned out throttle body with cleaner and engine stopped shutting off after start up. Pulled injector 7, had build up inside. Replaced injector, truck ran like a champ with no codes.

4 days later, engine started running rough very gradually the more I drove, code flashing at 25mph or any speed for that matter...Random misfire code again. Swapped fuel rails and injectors with oem (got em all for $200 new, couldn't pass it up:) Drove around and it ran great, could feel engine still felt like it was missing but very slightly if that makes sense, no codes. Drove down highway and it ran great, stepped on gas and it felt like something gave and the engine power went away again with the engine light blinking.Checked plugs, wires, coil packs(swapped again) to make sure it was all hooked up properly, found original plug wires on plugs a bit loose so I swapped out to MSDs since they were they same price, still no change. Code still flashing when I drive but at 25 now instead of 30mph, rough idle, no power, engine feels like it's pulsating from the misfire when I drive. Have not pulled injector 7 to see if it was clogged again.

Thinking back to when the engine felt like it gave way and the power disappeared and the clogged injector from the first time around, is it possible for it to have been charcoal? I only ask because I keep seeing the evap canister tsb whenever I search for my misfire on cylinder 7. Don't think it's fuel contamination, I ONLY run 90 octane(highest I can get from the 1 gas station in town) and as to the quality, your guess is as good as mine. Oil gets farmed out of Alaska yet we pay more than all you guys in the lower 48, how does that make sense?

Anyways, I THINK I may hear a vacuum leak but I can't be sure. I haven't checked the vacuum or sprayed it around where I hear the noise(it could just be me imagining the belt sound making a vacuum noise).

Any ideas are welcome, this is getting silly. Fortunately I had the intention of changing things out one at a time so I don't feel so bad, this just all came at once a little sooner than I wished :help:

Thanks in advance!
« Last Edit: 11/17/11 02:47 PM by misanthrope »
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Semper Gumby

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Re: Cylinder 7 misfire
« Reply #1 on: 11/17/11 01:32 PM »

What was the actual code P03XX
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misanthrope

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Re: Cylinder 7 misfire
« Reply #2 on: 11/17/11 02:05 PM »

What was the actual code P03XX

Thank you for your response.

I THINK random misfire was P0300, cylinder 7 misfire was P0307. The P0300 code is the only one that  comes up consistently. If I am driving and the light is flashing, SOMETIMES I will see the cylinder 7 misfire code.

I will have to verify tomorrow, at the moment it's 5F, 65mph(up to 70) winds, white and I'm in my boxers.
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Semper Gumby

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Re: Cylinder 7 misfire
« Reply #3 on: 11/17/11 02:15 PM »

Just so I know you had original plugs and wires at 130,000 miles.  ???
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misanthrope

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Re: Cylinder 7 misfire
« Reply #4 on: 11/17/11 02:37 PM »

Just so I know you had original plugs and wires at 130,000 miles.  ???

Plug wires were original, plugs were swapped at around 80,000 miles, o2 sensors were original as well. Cat started to rattle at a little over 100,000 miles and guess it finally gave. Lasted me 30,000 miles. Guess I need to consider myself lucky.

Sad thing, is that I spend more time maintaining the truck mechanically than electronically and I'm an electronics tech :E: Engine, cooling system, tranny, t case, diff, suspension, bushings, joints, etc get a pretty ran through with a fine tooth comb on a regular basis several times a year. In my experience working with anything from Loran, DGPS, radar, microwave to radios, electronics will fail when they fail. You can continue to monitor them and watch for degradation with all the nifty equipment, but ultimately, a lot of them will fail when they feel like they don't want to keep the magic smoke in anymore. I've seen megatrons fail after less than 4,000 hours while most have lasted WELL OVER 60,000 hours. The 3 most common occurances with electronics are that the tolerance gets out of whack at different rates, connection is broken(electrically or just covered in dust) or a component is physically damaged. Beyond that, in theory, electronics should continue to work.....or so they say.
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Semper Gumby

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Re: Cylinder 7 misfire
« Reply #5 on: 11/17/11 02:44 PM »

We all did, I think the cats are fried if I see the P0300 code. But I'm not there. Good luck
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Re: Cylinder 7 misfire
« Reply #6 on: 11/17/11 11:13 PM »

DO you have slight loss in coolant?

Could be intake gasket leak or cracked head this causes random misfire and sometimes specific cylinder depending on leak
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misanthrope

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Re: Cylinder 7 misfire
« Reply #7 on: 11/18/11 08:37 AM »

DO you have slight loss in coolant?

Could be intake gasket leak or cracked head this causes random misfire and sometimes specific cylinder depending on leak

Coolant level is good. Not wet spots around engine.

Confirmed code is P0307.

Now when I first start truck up there is o code, give it about 5 minutes of idle or driving and it throws a code a starts flashing. When I run the code while driving or idle, it continues to flash and won't steady up. My read tells me that P0307 is pending.
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avalonandl

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Re: Cylinder 7 misfire
« Reply #8 on: 11/18/11 08:56 AM »

Sounds like a coil pak. Unusual but not unheard of. Try a new coil for 7 cylinder, should be easy sits right on top.

Avalon
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misanthrope

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Re: Cylinder 7 misfire
« Reply #9 on: 11/18/11 08:58 AM »

Sounds like a coil pak. Unusual but not unheard of. Try a new coil for 7 cylinder, should be easy sits right on top.

Avalon

Swapped coil pack 7 with coil pack 5, cleared code and it keeps coming back on 7.
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avalonandl

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Re: Cylinder 7 misfire
« Reply #10 on: 11/18/11 09:03 AM »

OK, is the plug wet? Like its not firing? Could be a wiring harness issue, friend had the same issue on an Aurora. The harness may not be making cosistent contact to tell the coil to fire.

Avalon
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misanthrope

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Re: Cylinder 7 misfire
« Reply #11 on: 11/18/11 09:06 AM »

OK, is the plug wet? Like its not firing? Could be a wiring harness issue, friend had the same issue on an Aurora. The harness may not be making cosistent contact to tell the coil to fire.

Avalon

I'll go pull it. I did notice there was a slight fuel odor from 7 when I swapped the plugs(sniff all my plugs when I pull em). Didn't check to see if it's wet through.
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misanthrope

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Re: Cylinder 7 misfire
« Reply #12 on: 11/18/11 10:29 AM »

Sounds like a coil pak. Unusual but not unheard of. Try a new coil for 7 cylinder, should be easy sits right on top.

Avalon

You sir are the winner! How you ask? Checked plug as you suggested, found it to be wet and black. Cleaned it up and reinstalled. So no spark but brand new plug. Swapped pack 5 with 7 again, code stayed with cylinder 7. Swapped them back to original positions, pulled plug wire off 5 to check spark, good spark, engine misfired 5 and 7. Reinstalled plug wire on 5, code on 5 disappeared. Pulled plug wire off 7, have spark but intermittent. Checked harness plug for coil pack 7, found crack in wire insulation. Figured it must have been arcing some and thought that was all it was. Reinstalled plug onto coil pack, still error on cylinder 7(this clearing codes is getting old when it's 5F outside). Pulled plug off coil pack 5, finger tested, painful. Pulled plug wire off coil pack 7, finger test, painful...after a several cycles the spark got weaker and then stopped entirely. Turned off truck, restarted, pulled plug wire off coil pack 7 again and the spark was back then got weaker and was gone again.

New coil pack on order, be here in the morning.

Thanks everyone for all your help. Hopefully, my next response is that it's fixed. I'll update tomorrow when the part comes in. Time for a beer. Avalon you deserve a cookie, thanks again.
« Last Edit: 11/18/11 10:32 AM by misanthrope »
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misanthrope

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Re: Cylinder 7 misfire
« Reply #13 on: 11/19/11 05:57 AM »

Replaced coil, cleared code, still missing just no as bad. No code has come up since but I can feel it miss when I accelerate<sigh>, vacuum?
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misanthrope

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Re: Cylinder 7 misfire
« Reply #14 on: 11/19/11 08:49 AM »

Drove around for a bit, engine light started flashing, random misfire P0300 code pending. Seems like when the random misfire code is pending, it ends up being a P0307 but I don't feel like driving around for it to settle out and tell me that.

I did notice that when I put my ear up to the driver side, I hear very slight taps (like coil packs sparking away or injectors, I don't know, I know something is working), when I move over to the passenger side without leaning towards the engine, The sound is 3 times as loud. Thought maybe it's more than just cylinder 7 so I checked the other 3 coil packs on the driver side and they all have strong spark.

Anyone?
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avalonandl

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Re: Cylinder 7 misfire
« Reply #15 on: 11/19/11 11:39 PM »

The old way of checking for misfires is to do this in the dark, see if there are flashes from arcing. Did you fix the wiring insulaotrs? Arcing sounds like ticks.

Avalon
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misanthrope

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Re: Cylinder 7 misfire
« Reply #16 on: 12/01/11 05:31 PM »

Contaminated fuel. Water in tank rusted fuel pump, rust sucked up and clogged injectors. New pump/seal, tank cleaned, 3 clogged injector replaced(3,5 and 7. Explains the louder ticks on the passenger side since the driver side wasn't working:), fixed. For now.

Thanks everyone for your help :thumbsup:
« Last Edit: 12/02/11 03:35 AM by misanthrope »
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ohiobellboy

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Re: Cylinder 7 misfire
« Reply #17 on: 12/01/11 08:26 PM »

Contaminated fuel. Water in tank rusted fuel pump, rust sucked up and clogged injectors. New pump/seal, tank cleaned, clogged injector replace, fixed. For now.

OUCH!
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