Here's the run down on what I've done since buying this truck at the end of Sept. Being an old Motor Head am sure this will be fixed but need some pointers if anyone has been through this before.
1986 Ford F 250, 460 CI V-8, 46K miles (original), non catylitic converter, Duraspark II, non-computer
Symptoms: Runs rough at idle, back fires slightly through carb when give it gas.
Plugs, appeared dark, electrode eroded, replaced plugs.
Plug Wires, couldn't get resistance value with tester, replaced wires. Cylinders 5 and 6 wires were crossed.
Replaced cap and rotor. Noticed weak spark on test plug. Tested coil, within stock values; replaced with MSD coil 40K volts, still weak spark.
Replace electronic pick up in Distributor, no change in spark or running.
Siphoned 15 gallons of suspect gas from both tanks, replaced with fresh non-ethanol gas.
Replaced Holley 4160 with Edelbrock 1406 4 bbl. Rejetted for altitude, jets, metering rods. Now idles without backfire, within 25 RPM on test meter. Re-check timing.
Tested Duraspark II unit, not within value. Replaced with Checkers Auto brand. Spark much improved.
Compression test, all 100-103 #'s. Re-check timing, reset idle tuning with vacuum guage.
Pulled right side valve cover, cycled engine with remote starter, all rock arms and push rods appear okay.
Verified rotor pointing at #1 plug @ TDC, re-checked wires, okay.
Point: starts with hesitation, then turns over and fires. Feels like distributor off a tooth. Timing is where it should be, vacuum hose on Timed Port on carb not full vacuum. Vacuum is 14-15 Lbs. Needle fluctuates, jumps in that range. Standard should be 17 Lbs. There are miles of vacuum lines.
Note: Have not checked cam lift yet. Friend remembered Ford had a run of bad cams in the mid-eighties (news to me). Was told when I bought the truck it had a "bad lifter". Did remove oil filter and put in half a quart or more of Marvel Mystery Oil.
No valve lifter noise can be heard in the engine compartment but you can hear a similar noise in the cab of the truck, fairly pronounced.
Next step, going to pull the left hand valve cover and check rocker arms and push rods for function.
Any shortcuts anyone know of??
1986 Ford F 250, 460 CI V-8, 46K miles (original), non catylitic converter, Duraspark II, non-computer
Symptoms: Runs rough at idle, back fires slightly through carb when give it gas.
Plugs, appeared dark, electrode eroded, replaced plugs.
Plug Wires, couldn't get resistance value with tester, replaced wires. Cylinders 5 and 6 wires were crossed.
Replaced cap and rotor. Noticed weak spark on test plug. Tested coil, within stock values; replaced with MSD coil 40K volts, still weak spark.
Replace electronic pick up in Distributor, no change in spark or running.
Siphoned 15 gallons of suspect gas from both tanks, replaced with fresh non-ethanol gas.
Replaced Holley 4160 with Edelbrock 1406 4 bbl. Rejetted for altitude, jets, metering rods. Now idles without backfire, within 25 RPM on test meter. Re-check timing.
Tested Duraspark II unit, not within value. Replaced with Checkers Auto brand. Spark much improved.
Compression test, all 100-103 #'s. Re-check timing, reset idle tuning with vacuum guage.
Pulled right side valve cover, cycled engine with remote starter, all rock arms and push rods appear okay.
Verified rotor pointing at #1 plug @ TDC, re-checked wires, okay.
Point: starts with hesitation, then turns over and fires. Feels like distributor off a tooth. Timing is where it should be, vacuum hose on Timed Port on carb not full vacuum. Vacuum is 14-15 Lbs. Needle fluctuates, jumps in that range. Standard should be 17 Lbs. There are miles of vacuum lines.
Note: Have not checked cam lift yet. Friend remembered Ford had a run of bad cams in the mid-eighties (news to me). Was told when I bought the truck it had a "bad lifter". Did remove oil filter and put in half a quart or more of Marvel Mystery Oil.
No valve lifter noise can be heard in the engine compartment but you can hear a similar noise in the cab of the truck, fairly pronounced.
Next step, going to pull the left hand valve cover and check rocker arms and push rods for function.
Any shortcuts anyone know of??