Replaced my cap, coil and rotor chasing a random, intermittent misfire. Plenty of carbon and wear on the cap and rotor, and I believe the drivability has improved a little, but I still have that random misfire. Next up is a compression test. I have some questions about the procedure, but I'll start my own thread.

 

I had a horrible miss at idle - shook the truck so badly that I shifted into neutral at stop lights. A compression test said 7 cylinders were excellent and 1 was lower but still within the acceptable range. But, a leakdown test said I had both a burned intake and exhaust valve on one cylinder a a burned intake on another. And, when I pulled the heads that was the case.

So, don't just rely on a compression test. That is one tool and it has its place. But, if it doesn't point out a problem you should go the next step.

A leak-down tester puts compressed air through a regulator to get a repeatable pressure, witnessed by a gauge at that point, runs the air through an orifice to introduce resistance, with the resulting pressure shown on another gauge, and puts that into the cylinder through the sparkplug hole. Any leakage shows up as a pressure drop across the oriface and is directly read on the 2nd gauge. If the leakage is through the exhaust valve you'll hear it in the tailpipe. If it is the intake valve you'll hear it in the carb.

I made my tester from info found on the web, but you may need to do a fair bit of reading the get good info as there are many who say they know but don't - just like on everything.

 

Thanks for the advice. I'll definitely do a leakdown if necessary, though I already know the engine is tired and has considerable blowby.

I just can't wrap my head around why it will just randomly misfire every few seconds. It's definitely drivable, and in fact drives better than ever after setting my timing and idle, and replacing the above components, but the misfire just aggravates me.

 

Does it have a minor exhaust leak? You'd be surprised how a tiny exhaust leak can make an engine seem to misfire.

 

I considered that, and checked it out last night. There is no audible leak, and when I covered the pipe with a rag, the idle began falling, and there was considerable pressure trying to push my hand off, so I don't think there's a leak, but if there's a better method for testing, I'm all ears.

 

Just have a good listen with the engine idling, hood up. If you hear a little spit/sputter sound everytime the engine seems to misfire, then you likely have either an exhaust leak or plug wire crossfiring.

Mine does this. It leaks slightly between the head and exhaust manifold. I just haven't talked myself into dropping that intake/exhaust assembly and replacing the gasket, for such a minor leak. I keep hoping I'll run across a killer deal on an offy DP to make it more worthwhile to drop that monster assembly.......

 

Go out at night and start it with the hood open, I have found many bad plug wires this way. Have you changed plugs lately, sure can make a difference in how it runs.

okiepc1

 

today i went the junkyard and found a factory brush gaurd on a 1982 f100, for my 1982 f100, it was a pain in the butt to get off, i ended up bringing a wireless grinder, and ground the heads off the bolts. i love that grinder. brought it home and painted it black, and it fit perfect, but mines the lariat so i had to take the pads off the bumper.

 

replaced wheel bearings, I don't believe the PO ever serviced them. The races where all chewed up and the grease that was in them was all grimey and clumped. rolls along much smoother and quieter now.

 

I did wheel bearings, brakes, and new Mile Marker hubs. I think your PO must of owned my truck also. What a mess...

 

Yep, new plugs and wires a few weeks ago.

 

Installed new striker bolts for the doors - now they close tight with no rattling, amazing!

 

tightened down the rear cab mounts, no more bouncing and thumping when I brake hard.

 

Mine does this too, and I'm in the same boat. I'm waiting to get ahold of an Offy Intake, Headers, and a mini-starter before I replace the gasket with a Mr. Gasket 260.

 

Pictures? The factory brush guard is extremely rare!