I have a 66 El C that I bought several years back. It has a late style (~'90 model) 350 motor with factory alum heads (center bolt covers), alum. intake, HEI, supercomp headers, 600 AFB (rebuilt about 5 months ago), and a light hydraulic cam. It has suppression wires (no sparks at night, doesn't screw up electronic tach rpm like bad wires do, so I assume they are O.K.), and cap and rotor are new. It doesn't have vacuum advance on the distributor, and I haven't messed with the timing in years. It has about 135K on it, and has been a problem free daily driver until now. I run premium gas to avoid knock, and it runs O.K. I noticed the engine was starting to missfire a little on a one hour trip last week, not backfiring out tail pipe, not out carb either. I then noticed the oil pressure (at 70 mph, about 2900 rpm) was amazingly high, like 90 psi. Normally it runs at maybe 50 psi at this speed, and barely 30 psi at idle. At idle it was 40 to 45 psi. I changed the oil filter, and put new plugs in, and while underneath noticed I had a header leak near the primary / collector tube interface (haven't sealed it up yet). I also put in some new spark plugs, although the old ones really didn't look bad (a little larger gap, had at least 80K on them). The oil pressure came down
to 55 to 60 at 3000 rpm, and 35 at idle, still higher than what I am used to seeing. The engine has gotten lower and lower on power as the days go by. I pulled one valve cover, on right side where noise seems to come from, and nothing was loose, except one rocker is set low, looks like one cam lobe (no. 6 intake) is apparently worn down some, it sits about 1/8 in. lower, but has been that way since at least 80K miles. It idles O.K., with a little lower than normal vacuum (12 inches, needle seems steady at all rpm's), but when driving, it won't pull under any load without a popping sound, like hitting on a valve cover or oil pan (it is an irregular / intermittant sound, from up front, even under light throttle maintaining speed, that becomes more regular and scarey sounding as more throttle is applied), and a little pinging now too. Valve train sounds fairly tight at idle, not really any ticking from excess clearance. Some of the "popping" noise is probably from the header leak, but I don't think that a header leak would make power go away or cause pinging. The engine seems to be getting weaker every day, today I could barely keep it going at 45 mph on way home. The oil is clean, water / coolant is clean. Coolant runs at 170 deg F, same as normal, engine is not running hot (today was a 36 degree day, yesterday an 85 degree day). I have burned 2 tanks of gas from my normal source, don't run any additives. PCV valves on both sides are clear also (was a problem over the summer, they were plugged, had oil leaking everywhere).

I still don't understand why the oil pressure would stay fairly high, even after the filter was changed (Baldwin B-7 - large capacity, 10W30 oil). I'm afraid maybe the high oil pressure has caused some valve train damage or something. Any ideas on where I should start looking? I'm not looking forward to teardown outside in the ice storms we'll have here the next couple of days, but I would appreciate any ideas out there to think about in the mean time. Thanks in advance.

J.B.

Well, this is a lot of speculation but...

1) I would definitely start with a new set of wires. Just seeing no sparks at night doesn't mean that there is not some internal breakdown of the conductor which is giving you no or very weak spark. Most everything else on the ignition you said is new, so that should be OK.

2) I think the exhaust header leak is trivial...not really a cause of any trouble or the result of anything. Would ne nice to have it fixed, though.

3) I can't, for the life of me figure out why the oil pressure would go high. You say you changed the filter and plugs and the oil pressure came down? Equally strange, since the plugs should have no effect and I would think a dirty filter would lower the pressure (if it did anything), not raise it. The only possible thing that I can think of is if a piston/rings/headgasket somehow failed and the crankcase was pressurized...but 90 PSI, I would think that would blow out many things before you ever got that high. Is there any chance that this is a defective gauge?

4) The valve cover "tapping" Could this be a sign that more of your cam lobes are going flat and the rockers are out of adjustment?

I think in this instance, a good compression check across all cylinders will help you see what the engine is doing, or at least be a good starting point.

Thanks for the reply. I finally put on the new plug wires in the rain tonight, didn't make the misfire go away. I agree on the header leak, I don't think that is a part of the problem. I think the oil pressure went high because of the old filter, it had been on a little too long. I don't know how oil pressure could still stay pretty high even after I changed the filter though. I don't have a reason to suspect the gauge, it goes to zero, and it fluctuates with RPM, and seems to react normally but it still runs well above 60 psig now even when warm. My concern was that when the oil pressure was really high, could I have bent something in the valve train. Incidentally, I had changed the plugs to see if missfire was from bad plug, not due to oil pressure. I have had loose rockers before on this engine (the stock type rocker nuts loosened on me from prior owner, they kept backing off and I replaced them with new nuts, end of problem). I notice that the missfire is under load, with low vacuum conditions, but not when coasting under no throttle, it is very smooth - it does seem like it could be just one cylinder involved. If I had a burnt intake valve, I'd expect a big intake backfire, or if an exhaust valve, maybe a big exhaust backfire especially when coasting down from high rpm under no throttle. Anybody else have any ideas? I guess next weekend I will break out the compression tester and see what I can find with it. Thanks,
J.B.