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Old 10-20-2000, 02:45 PM
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What should the cold compression test readings be on an 83 380SEL.If compression comes back low, is it usually burned valves or maybe just adjustment. I can hear valves tapping on both sides. Engine runs very rough (like it is only firing on 5 or 6 cylinders) Have you ever heard of valves being so far out of adjustment that this would happen(skip, rough idle, loss of power)? What would cause this? Ignition parts(wires, plugs, cap, rotor) have been replaced. Also if I have to get a valve job, wht is it going to cost?(ballpark figure) I live in Northern Florida.
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Old 10-20-2000, 10:23 PM
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Join Date: Jul 2000
Posts: 638
You can do a 'quickie' compression test by cranking the engine with th eignition off and see if the cranking speed is uniform. A low cylinder will be obvious from increase in cranking speed. The 'vlave tapping' you hear is either from a timing chain flopping around (very expensive if you let it break), worn camshaft and followers, defective hydraulic lash adjusters, or valve adjuster shims to thin for the need. The valves would have to be WAY loose for it not to run. The missing--first pull th espark plug wires off the spark plugs one at a time with it running and see if that cylinder is firing. It helps to pull them off when its cold to unstick them. Pull on the boot, not the wire. You should get a spark that will jump to ground with the wire held close to metal. If waek or no spark check for spark at the distributor cap tower or measure wire resistance (12000 Ohms/ft) With spark to the cylinder confirmed, but no firing, time to pull the plug and check for fouling (assuming the cranking speed test was OK. If the plug is bad change them all and do a compression test while they are all out. should be >145#.

If compression is OK, plugs ok, spark to them ok, then it has to be fuel. Pull the injector and swap ot with a known good one (a cylinder that is firing ok.)If the dead cylinder now fires OK, and the formerly good one dies-proves a bad injector. If the formerly good one stil fires but dead one stays dead--it's either a big air leak or the fuel distributor. Air leaks can be found by running a small stream of water over the injector holders and intake manifold while its running sand listening for changes. Its common for injector holdr seals to leak they are cheap and easy to replace. Fuel distributor is easy to replace, but not cheap.
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