What have I over looked

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   Customer brings in a 2004 chevy avalanche 5.3 liter  said check engine light is in.  I scan it and get a random misfire along with a mass air flow sensor under reporting. I also took it for a drive. During the drive I notice the check engine light to flash.

Told the customer my feelings.  He wants to do plugs and wires seeing as it has 180k on the vehicle.  And he wanted the mass air flow. 

I do the work.  Start it ag still misses. This time no flashing light and no mass air flow code.  

Look farther into this random miss and my monitor on the scanner is going nuts for cylinder 2 and 7. Quick easy and no cost I move cylinder 2 coil to number 3 I belive. No help.  

Doing some thinking what can cause this. Intake gaskets-- but long and short fuel show nearly prefect.  Injectors-- again trims show good and during a balance test the 2 that missed performed just as good as ones that were not suspect. 

Last before I gave up tonight I did a cam crank relearn. Tomorrow I'll go drive it. 

Have I over looked anything or does anything come to your guys mind. 

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bobkyllo Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 14 Sep 2009 Location: minnesota Points: 1547	Post Options Post Reply Quote bobkyllo Report Post Thanks(0) Quote Reply Topic: What have I over looked Posted: Yesterday at 12:58am
	Customer brings in a 2004 chevy avalanche 5.3 liter said check engine light is in. I scan it and get a random misfire along with a mass air flow sensor under reporting. I also took it for a drive. During the drive I notice the check engine light to flash. Told the customer my feelings. He wants to do plugs and wires seeing as it has 180k on the vehicle. And he wanted the mass air flow. I do the work. Start it ag still misses. This time no flashing light and no mass air flow code. Look farther into this random miss and my monitor on the scanner is going nuts for cylinder 2 and 7. Quick easy and no cost I move cylinder 2 coil to number 3 I belive. No help. Doing some thinking what can cause this. Intake gaskets-- but long and short fuel show nearly prefect. Injectors-- again trims show good and during a balance test the 2 that missed performed just as good as ones that were not suspect. Last before I gave up tonight I did a cam crank relearn. Tomorrow I'll go drive it. Have I over looked anything or does anything come to your guys mind.

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jaybmiller Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 12 Sep 2009 Location: Greensville,Ont Points: 22440	Post Options Post Reply Quote jaybmiller Report Post Thanks(0) Quote Reply Posted: Yesterday at 6:30am
	off the top of my head.... hmm. 20 year old.. disconnect 'computer' connectors ,clean and reseat at least 3-4 times inspect(remove/clean/reattach) ALL possible ground wires between engine and 'computer' check wires on the 'coils' for chews,almost breaks,cuts. have no idea HOW the computer decides 'misfire on #2'.... but I suspect 'bad' wires/connectors OR maybe the injector ? Coil could be fine, but inj not spraying right ??
	3 D-14s,A-C forklift, B-112 Kubota BX23S lil' TOOT( The Other Orange Tractor) Never burn your bridges, unless you can walk on water

Lars(wi) Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 14 Sep 2009 Location: Permian Basin Points: 7183	Post Options Post Reply Quote Lars(wi) Report Post Thanks(0) Quote Reply Posted: Yesterday at 6:50am
	Hydraulic lifters? Maybe a couple getting weak/worn out. Lobe or two worn down on camshaft. Owner probably was not diligent enough on oil changes.
	I tried to follow the science, but it was not there. I then followed the money, and that’s where I found the science.

Les Kerf Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 08 May 2020 Location: Idaho Points: 771	Post Options Post Reply Quote Les Kerf Report Post Thanks(0) Quote Reply Posted: Yesterday at 7:33am
	My 98 Isuzu Trooper did a similar missfire due to a bad intake manifold gasket. Replacing spark plugs didn't help.

steve(ill) Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 11 Sep 2009 Location: illinois Points: 81020	Post Options Post Reply Quote steve(ill) Report Post Thanks(0) Quote Reply Posted: Yesterday at 7:53am
	never had a chevy.. but 2001 and 2002 F150 with 5.4 and 2006 with 4.6 .... EVERY missfire i had was due to a COIL, bad INJECTOR , or the electrical plug/ bent wire on them..
	Like them all, but love the "B"s.

steve(ill) Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Access Joined: 11 Sep 2009 Location: illinois Points: 81020	Post Options Post Reply Quote steve(ill) Report Post Thanks(0) Quote Reply Posted: Yesterday at 8:01am
	i did an ON LINE SEARCH for "2004 chevy 5.3 missfire" ... and normally its coils or injectors... when those are changed and no help, it seems the problem goes to the Lifters wearing out.. Several posts on that Known problem .
	Like them all, but love the "B"s.

Alberta Phil Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 13 Sep 2009 Location: Alberta, Canada Points: 3769	Post Options Post Reply Quote Alberta Phil Report Post Thanks(0) Quote Reply Posted: Yesterday at 9:24am
	I have an '05 Saturn Vue and had a similar problem with the V6. My mechanic buddy checked it out and it was showing a miss on #5 and intermittent on #2. He swapped plugs and coils around and no difference. He said it had probably never had a valve adjustment, so got my OK to do it. That fixed it, but with a $1000 bill as half the engine has to be taken apart and re-assembled. 6 hours labor!

Hubert (Ga)engine7 Members Profile Send Private Message Find Members Posts Add to Buddy List Orange Level Joined: 12 Sep 2009 Location: Jackson Cnty,GA Points: 6288	Post Options Post Reply Quote Hubert (Ga)engine7 Report Post Thanks(0) Quote Reply Posted: Yesterday at 3:34pm
	Presently I have a similar problem with my 99 F150 with 5.4, check engine light illuminating then later intermittently flashing, showing misfiring on #3. I’m thinking bad computer/connection or grounding issues. Let us know what you find.
	Just an old country boy saved by the grace of God.