'04 XK8. The "mate-less" connector was for the fuel temp A sensor - it tripped the check engine light and the code said exactly what it was. For some reason those sensors are very easy to overlook. (Why do we need to know fuel temp? Is it a mixture fine point?)

After only 5 days of down time a lifter was so flat that cranking sounded like a missing valve - you know that sound when cranking when the pitch suddenly jumps up as the cranking speed momentarily increases on one cylinder? When it started, it whacked a good bit for several seconds, but quieted down to a mild tic within a minute or so. But this all makes no sense: it cranked as though a valve were stuck open, yet the whacking sound was obviously a collapsed (leaked-down) lifter ... which would indicate a valve that's more closed than normal, not more open than normal. Where is my logic going wrong? I've never heard of a lifter "pumping up" after days of sitting. I never would have thought a lifter had any sort of problem - except for some uneven running immediately after start-up, the engine runs flawlessly. I red-line it at least a couple of times a week (OK, maybe 10 or 30) - how concerned should I be?

 

You should be very concerned. There are no lifters. The cam lobes act directly on the caps on top of the valves. There have been a couple of reports of the 3rd gen tensioners failing, but I'm not sure how accurate that is.

 

Can you record the sound on your cell phone and post it? You may get some more accurate feedback that way.

 

The solid lifter or TAPPET has a shim that sets the cam to valve clearance or LASH.

No hydraulics are involved here.

Perhaps the valve seat is loose????????????

Could be a chain or tensioner as RJ237 stated???

bob gauff

 

I had a colossal failure of logic. I figured it out while trying to drift off to sleep last night (not real conducive to sleep). Here's what I am now sure happened: all of the plastic locking tabs on the fuel injector connectors broke; most stayed in the connector shells but a few fell off. I vacuumed up a couple, but in retrospect I'm sure one of them fell into an intake port where a valve was partially open (this is an assumption, not an observation). It jammed the valve open while cranking, making the low-compression-on-one-cylinder sound. Once the engine started, it fell into the cylinder and started getting banged around between piston crown and combustion chamber/valves. Within several seconds it got pulverized into smaller pieces, eventually getting digested, burned and spat out the exhaust port. Once it was completely gone, everything was back to normal - I'm just real lucky that it was plastic and not very substantial. I had vacuumed the valley and ports after disassembly and before reassembly - I remember sucking up a couple of locking tabs from the valley and an awful lot of shredded loom-wrap material, a good bit of which had fallen into the ports. I worked the ports over as much as I could, but due to fuel rails and such I couldn't get the vacuum attachment very far down into the ports, I had to just work on the port openings. I imagine the tab was wedged between the valve and seat anyway, and wasn't going to get sucked up. I'm sure it wasn't metal - the only metal bits involved in the job were a few nuts and a couple of small hose clamps and they all were accounted for. Had it been a metal bit, it would have been a lot more dramatic, would not have gone away and probably would have resulted in failure. If I ever remove the intake manifold again I'll vacuum a lot more diligently before pulling the manifold up and i'll have a bunch of old socks handy to stuff into the ports as soon as they're accessible. I won't have to worry about plastic connector retainer tabs though - every damned one of them broke off this time!