Chasing a Demon, long post

bingo2 · #1 (**permalink**) 09-10-2010, 08:48 AM

I recently purchased an RU car that was completed in 2004 with just short of 6000 miles on it from the second owner, who over the past couple of years had put about 800 miles on it. The car was out of state so I had a friend check it out for me and reported that everything seemed to be OK, he drove it and said all systems were go.

When I received the car and fired it up for the first time I could tell it was running extremely rich and had a slight off idle stumble and while listening to the exhaust note, the left side had a nice even tempo and the right side sounded as if it had an intermittent misfire, although the engine idled smoothly. After the engine cooled down, I pulled the plugs and of course they were black as coal, sooty, with no indication of oil fouling.

The engine is a SB 331 stroker, Brodix heads, Crane Powermax hydraulic roller, Crane roller lifters, Crane roller rockers, Edelbrock RPM Air Gap intake manifold with a Holley HP 4150, PN 0-80541-1 and MSD Pro Billet distributor and 6AL controller. The carb had been modified by Steve Zepeda in Houston, TX when the engine was built with billet metering blocks and throttle plate and jetting matched to the engine specs. I spoke with Steve and he said the engine ran great when he finished with it. He suggested doing the basics, pull the float bowls, check the PVs, fuel level and do a general clean up and reset the idle mixture, which I’ve done, but had some difficulty getting much reaction from the passenger side idle mixture screws and while doing so also noted that the engine has 13 inches of vacuum at idle, which would account for the 65 PVs, installed new plugs as well. That cured the off idle stumble and the richness, the PVs were shot. It didn’t cure the misfire issue.

Next was removing the distributor cap, nice and clean, no apparent issues and I did a continuity check on the plug wires (didn’t check the resistance though), all good. Pulled the plugs on the right side again and the plugs from cylinders 1, 3 and 4 looked OK, a little dark from idling while adjusting the idle screws but, the plug from cylinder 2 looked like new, dry, like no fuel was entering the cylinder.

I think I’ve done about all I can do with the diagnostic tools I have, I gave my timing light away about 10 years ago, thinking I’d never have a need for it again and I don’t have compression or leak down testing equipment.

Any thoughts or comments would be appreciated. I’ll probably end up taking the car to the local speed shop that has done some work on my Mustang for further diagnosis.

Curt C. · #2 (**permalink**) 09-10-2010, 01:25 PM

You say its misfiring because you can hear it? Does it misfire while driving? Can you feel it? Light load? Heavy load?

CobraEd · #3 (**permalink**) 09-10-2010, 01:33 PM

do a compression test. Are the plugs black due to fuel or oil?

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bingo2 · #4 (**permalink**) 09-10-2010, 01:36 PM

Thanks for the reply. The engine is not making full power. The No. 2 cylinder is dead, not receiving any fuel. I suspect it is a valve train issue, hopefully something as simple as a bad lifter. We'll see next week.

Rick Parker · #5 (**permalink**) 09-10-2010, 01:57 PM

A bad lifter would be audible, very much so.

tcrist · #6 (**permalink**) 09-10-2010, 02:00 PM

A quick check is to pull your coil wire (so it will not start) and valve covers. Crank your engine over and watch the rockers move. See if the rockers (especially on that cylinder) are moving and how far. If you pull your plugs also, your engine will crank over much easier.

Just a thought,

Gaz64 · #7 (**permalink**) 09-17-2010, 02:43 AM

Any news yet?

Have you done a compression test, ALL plugs out, Wide open throttle.

I'd bet you have a riding intake valve on NO.2.

bingo2 · #8 (**permalink**) 09-17-2010, 07:03 AM

Quote:

Originally Posted by Gaz64

Any news yet?

Have you done a compression test, ALL plugs out, Wide open throttle.

I'd bet you have a riding intake valve on NO.2.

We did the compression test, all cylinders are at 160-165. Checked the timing; good. Closed the shop doors and turned off the lights and noticed the plug wires arcing from the aluminum wire separators, which we discovered were too small in diameter for the plug wires and had cut through the insulator sleeve of many of the wires. Additionally, we pulled the rocker covers and found a couple of the rockers had somehow worked loose a bit; we reset the lifter preload on all of them and the engine responded positively. We are currently waiting for the new plug wires to arrive and are confident they will resolve any remaining misfire issue.

Then it's off to see the local carb guru.

Thanks for the concern and the suggestions. I'll follow up after we install the plug wires and get the carb sorted.