Chasing Ghosts
Thread Starter
Instructor
Joined: Feb 2014
Posts: 104
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Chasing Ghosts
To start, my car is a 1978 L82, but the engine is a "hecho an mexico" lm1 (working on the fix for that now)
About a month and a half ago the car began running extremely rough anywhere past idle, & backfiring (confirmed through exhaust only & not carb)
I've replaced:
Plugs
Plug wires
Distributor cap & rotor
Coil
Fuel filter
I'm still running the original quadrajet on the engine, & it's done fine until now if it were the problem, no definable flat spots through the curve.. I'd also like to point out the timing has been reset to 10 past tdc w/o vacuum & I've resorted to filling with real gas instead of gasahol because there's still a few stations selling the good stuff out here, I'm at a loss, & I was looking for any input or ideas as to what could be causing the problem, any HELPFUL input would be greatly appreciated.. I'm not trying to drop $300+ on a carburetor for this engine when I've got the bottom end for a 383 on a stand in the living room (much to the frustration of my girlfriend)
About a month and a half ago the car began running extremely rough anywhere past idle, & backfiring (confirmed through exhaust only & not carb)
I've replaced:
Plugs
Plug wires
Distributor cap & rotor
Coil
Fuel filter
I'm still running the original quadrajet on the engine, & it's done fine until now if it were the problem, no definable flat spots through the curve.. I'd also like to point out the timing has been reset to 10 past tdc w/o vacuum & I've resorted to filling with real gas instead of gasahol because there's still a few stations selling the good stuff out here, I'm at a loss, & I was looking for any input or ideas as to what could be causing the problem, any HELPFUL input would be greatly appreciated.. I'm not trying to drop $300+ on a carburetor for this engine when I've got the bottom end for a 383 on a stand in the living room (much to the frustration of my girlfriend)
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Sounds like the cam has a bad lobe, not opening one of the valves or something wrong in the valve train. I would remove plug wires to see what cylinder is causing the problem, then remove that valve cover and investigate to see whether all valves and rockers are moving correctly. Also 10 deg after tdc is way too retarded, should be timed well before tdc.
Last edited by '75; Feb 7, 2016 at 05:28 PM. Reason: spelling
Team Owner
Joined: May 2001
Posts: 87,294
Likes: 1,579
From: Western NY
Sounds like the cam has a bad lobe, not opening one of the valves or something wrong in the valve train. I would remove plug wires to see what cylinder is causing the problem, then remove that valve cover and investigate to see whether all valves and rockers are moving correctly. Also 10 deg after tdc is way too retarded, should be timed well before tdc.
Just for the sake of information, what kind of motor oil have you been using in the car? Is it oil suited for flat tappet cams (ie, oil with a high ZDPP content)?
Thread Starter
Instructor
Joined: Feb 2014
Posts: 104
Likes: 1
I meant to say 10 degrees adv, at idle without vacuum, I've used royal purple for the last 2 years, & still added zinc addatives for peace of mind trying to be nice to the cam & lifters, between 2000-2500 rpm it rears it's head, but if I back off to barely maintaining speed at those rpms it mellows out to being much less defined, under load it sounds exactly like a full on miss, 10° was what they rolled off the assembly line stock with, & considering the stock cam would be an upgrade I don't see any need for further advance
Last edited by DBez93; Feb 7, 2016 at 06:12 PM.
Thread Starter
Instructor
Joined: Feb 2014
Posts: 104
Likes: 1
So today I tried to start the car & it was unusually difficult to start, but after finally getting it running it was running normal, perfectly through the rev range, right up until I reached 3k rpm, then almost like someone flicked a switch, it began backfiring every combustion stroke, I let out of it, & it was giving me the same misfire I'd had the entire time before today since the problem reared it's head, when it did start it was clouds of blue smoke..
Last edited by DBez93; Feb 8, 2016 at 11:16 PM.
Racer
Joined: Apr 2008
Posts: 406
Likes: 46
From: Lebanon OH
So today I tried to start the car & it was unusually difficult to start, but after finally getting it running it was running normal, perfectly through the rev range, right up until I reached 3k rpm, then almost like someone flicked a switch, it began backfiring every combustion stroke, I let out of it, & it was giving me the same misfire I'd had the entire time before today since the problem reared it's head, when it did start it was clouds of blue smoke..
I'm not sure pulling the plug wire will help isolate the problem if the fuel is igniting in the exhaust system. If the valve is not sealing, the cylinder should fail a compression test. I wouldn't run the car anymore as you could rupture the exhaust system. Just my thoughts...
Last edited by MajD; Feb 9, 2016 at 11:03 PM. Reason: Added better information
