Engine misfire - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tbrown5079 · 01-07-2016, 10:02 PM

I've had my 4.8 running for a while now after solving a ground issue. I haven't had it on the street yet, but getting anxious. Sometimes when I start it to move it or just let it sit in the driveway and run for 10 or 15 minutes it will be running on 7 cylinders. If I take the plugs out and find the one that is misfiring and dry it, it will run on all 8 cylinders. It has been a different cylinder every time. I'm hoping when I get it on the street that will stop happening. Anyone else have this problem? Could the trouble be in the tune?

aknovaman · 01-07-2016, 10:05 PM

Could be the tune but unlikely. Is your MAF clean? Any way for you to data log what the engine is doing?

tbrown5079 · 01-07-2016, 10:38 PM

Not at this point. The MAF should be clean. I have had a check engine light but I unhook the battery every time for safety reasons so it goes away. I will get my scanner out and see what the codes are. I'm the eternal optimist so I keep thinking it will go away when I start to run it this spring. If not I will start by changing the plugs. Thanks.

BR3W CITY · 01-08-2016, 02:38 AM

Hard to know if we aren't sure which codes its putting out. Misfire, multiple Misfire, etc.

Its possible that you have random injectors sticking and wetting your plug causing a non-fire instead of an actual misfire. Its possible you have low system voltage, its possible you still have a grounding issue (always look back at the last thing you worked on).

Does it go from running fine, to all of a sudden running on 7...or does it just start and run on 7 from the jump?

What plugs @ what gap (measured, not what the box said)?
What wires are being run.

Need more info in general. And FWIW, problems don't just go away.

tbrown5079 · 01-08-2016, 08:38 PM

All good advice, thanks. Yes, it is a non fire not a misfire. Once I take the plugs out and clean them it will run fine the next few times I run it Then all of a sudden when I start it it will non fire on one cylinder. Always a different one.. The sticking injector sounds like a possibility. Again, once I start running it this will give me something to work on. Thanks for your time.
Tbrown

BR3W CITY · 01-09-2016, 12:43 AM

You can soak the injectors in some seafoam for a bit, doesn't take much.

01-07-2016, 10:02 PM	#1
tbrown5079 Registered User Join Date: Feb 2007 Location: Blairsville, PA Posts: 301	Engine misfire I've had my 4.8 running for a while now after solving a ground issue. I haven't had it on the street yet, but getting anxious. Sometimes when I start it to move it or just let it sit in the driveway and run for 10 or 15 minutes it will be running on 7 cylinders. If I take the plugs out and find the one that is misfiring and dry it, it will run on all 8 cylinders. It has been a different cylinder every time. I'm hoping when I get it on the street that will stop happening. Anyone else have this problem? Could the trouble be in the tune? __________________ tbrown's 56 Cameo Build

01-07-2016, 10:05 PM	#2
aknovaman Registered User Join Date: Aug 2013 Location: Tecumseh Posts: 355	Re: Engine misfire Could be the tune but unlikely. Is your MAF clean? Any way for you to data log what the engine is doing? __________________ Current project 1959 Willys = GEZR TRUK Geezer is a Latin compound word made up of two roots. Gee meaning Urine Stain and Zer meaning your pants are open! FMCDH GBU and GBA http://www.youtube.com/user/aknovaman/videos

01-07-2016, 10:38 PM	#3
tbrown5079 Registered User Join Date: Feb 2007 Location: Blairsville, PA Posts: 301	Re: Engine misfire Not at this point. The MAF should be clean. I have had a check engine light but I unhook the battery every time for safety reasons so it goes away. I will get my scanner out and see what the codes are. I'm the eternal optimist so I keep thinking it will go away when I start to run it this spring. If not I will start by changing the plugs. Thanks. __________________ tbrown's 56 Cameo Build

01-08-2016, 02:38 AM	#4
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	Re: Engine misfire Hard to know if we aren't sure which codes its putting out. Misfire, multiple Misfire, etc. Its possible that you have random injectors sticking and wetting your plug causing a non-fire instead of an actual misfire. Its possible you have low system voltage, its possible you still have a grounding issue (always look back at the last thing you worked on). Does it go from running fine, to all of a sudden running on 7...or does it just start and run on 7 from the jump? What plugs @ what gap (measured, not what the box said)? What wires are being run. Need more info in general. And FWIW, problems don't just go away. __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

01-08-2016, 08:38 PM	#5
tbrown5079 Registered User Join Date: Feb 2007 Location: Blairsville, PA Posts: 301	Re: Engine misfire All good advice, thanks. Yes, it is a non fire not a misfire. Once I take the plugs out and clean them it will run fine the next few times I run it Then all of a sudden when I start it it will non fire on one cylinder. Always a different one.. The sticking injector sounds like a possibility. Again, once I start running it this will give me something to work on. Thanks for your time. Tbrown __________________ tbrown's 56 Cameo Build

01-09-2016, 12:43 AM	#6
BR3W CITY meowMEOWmeowMEOW Join Date: Sep 2009 Location: MKE WI Posts: 7,128	Re: Engine misfire You can soak the injectors in some seafoam for a bit, doesn't take much. __________________ *'66 Short Step / SD Tuned / Big Cam LQ4 / Backhalfed /Built 4l80e / #REBUILDEVERYTHING* MY BUILD THE H8RDCPTR //\\ MY YOUTUBE CHANNEL REV J HD

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