Unbelievably frustrated! So I decided to take a compression test on my perfectly running 350 small block in my 34 Ford. No particular reason. Well I pull off the wires, pull out the plugs, and do the test. Very good numbers all at 120. I put the plus back in, connect the wires, and the engine now runs like crap. It won't even idle. I figured maybe I reverse a couple of wires by accident. Checked the firing order and all is well. Maybe I cracked the insulator on the plugs. Bought a new set of plugs. No different. I'm racking my frigging brains out.
Im guessing you ruined a wire pulling them off the plugs. check the exhaust for cool cylinders and start from there.
Check your distributor hold-down bolt to make sure it's snug and didn't permit the distributor to rotate ever so slightly while you were moving wires about.
If it ain't broke, somethin somethin....Did the terminals positively snap onto the plugs? All other suggestions are on the money.
120 - that's really shitty for a SBC. 120 and even across all 8 cyl ? I'd be looking and I Wouldn't expect it to run well or try to get it there. I've seen engines jump time and loose compression in the blink of an eye right in my own bay. Trouble shooting 101- when a new problem appears, go back to the last thing you did, touched, changed or fixed.
Depends on if he did the test properly. I have watched people get bad readings when they did a compression test with the carburetor shut.
I got a label maker, I love that thing, I always label my plug wires at plugs and dist. great for wiring before pulling motor or doing repairs. Makes life more stress free. I think 120 sounds good to me unless you got some big dome pistons Maybe a smog motor. Anyway my two cents worth.
How many miles on your 350? Check the timing if possible (distributor could have moved or timing chain might be stretched and jumped a tooth or two or your points may be bad or could have worked loose.). Make certain the high tension wire from the coil to the center of the distributor cap is pushed all the way in at each end, and that all wired connections to the coil are tight. Also make certain all plug wires are pushed all the way in at the distributor cap and onto each plug. A bad ignition condenser can make an engine run badly by shorting much of the spark to ground. Check you ignition resistor; it should have 12 volts at one end and a little less on the other end when your points are open (a broken or bad resistor would affect the voltage going to the primary side of your ignition.). Check for any vacuum leaks (cracked or loose hoses, etc. Ruptured diaphragm at distributor or modulator at auto transmission (a ruptured modulator will have your engine sucking down transmission fluid.) or power brake booster. If you own an ohmmeter, and know how to use it, mark/ number the plug wires with blue masking tape, leave them attached to the distributor cap, remove the plug wires from each plug, leave the wires attached to the cap, remove the cap from the distributor. Now use the ohmmeter to measure each plug wire from each terminal inside the cap to the plug end. They should all measure close to the same; it will be obvious which ones are broken or have a much higher resistance. Best of luck. Sent from my iPad using The H.A.M.B. mobile app
I always start out by thinking what I did last. Maybe the wires are in the proper firing order but you did not start from the correct #1 spot on the Dist. Just a thought.
More info , is this a points setup or electronic . If points you may have burnt the pints while doing your Compression test .
Based on your description, it's almost guaranteed that the issue is being caused by something you did. Runs perfectly, pulled plugs, did compression test, put back together and it's turned to shit. Did you drop any of the plugs and bend the gap closed? If not, then there's a good chance that you messed up some plug wires, don't have them seated properly, or have a couple crossed. Vacuum canister hose on the distributor still connected? 1-8-4-3-6-5-7-2, with 1-3-5-7 on the drivers side and 2-4-6-8 on the passenger side. Note that the distributor positioning may not be the same on your car, as you can drop a distributor in pretty much anywhere, and as long as you know where #1 is the rest will follow suit.
And, check the plugs for a cracked porcelain. Rare in the old days, but with the present off-shore junk, I've run into it several times. Even rigorously removing/installing a plug wire can crack 'em. Used to be you could drop-kick 'em across the garage floor and they's be fine, not now.
You hit it right on the nose. After doing the compression test and replacing the plugs, I decided to change my valve covers. I had some old finned aluminum covers without breathers or pcv hole. While I had the tools out, I put on some finned aluminum M/T covers.THAT WAS THE LAST THING I DID. WELL, the rocker arms were rubbing against the side of the covers causing the valve movement to be restricted. A little Dremel work in 16 spots and I'm back to normal. ( I think )
I want to thank everybody for all the great suggestions. I should keep this entire thread as a work check list for whenever there's any other issues.
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