A buddy's 420SEL has been sitting in the road for 5 months.... He's been experiencing performance issues for a while. Seems to have been suffering from poor power. Someone did some work to try to improve it, but made it worse. Technicians gave him the runaround, but told him to get rid of it and just drive it starting in L, then 2, then D, to make sure the RPM's get high enough before it would pick up.

His battery died, so I took one from my 300SD (which seems larger, but still fit), turned the ingition, heard it catch/ignite and run for about 1 second, and then it stalled. It sounded weird and definitely jumped around a bit more than would seem normal. It's been sitting around for 5 months. Tried several more times to turn it on and all I hear is clicking. The engine won't crank over any more.

The starter is new-ish, and so he doubts it's a bad starter. How might I test the starter and rule that out? Where is it? Can I use a multimeter to somehow test it? I can jack the car onto ramps if I need to get underneath.

I definitely hear a loud clicking when I turn the ignition on. Not sure if that's the starter, or just the spark plugs. I haven't disconnected the spark plug wires to see if it still makes the clicking noise, but I can try that if it makes sense.

There's just no engine cranking at all! I took a wrench that fit the power steering pump and turned it from inward of the vehicle to outward (clockwise if you look at the vehicle from the front). I'm pretty sure that's the right way. Unfortunately, I DID NOT see the crankshaft turn AT ALL. The radiator fan (and something else accessory) turned, but not the crankshaft.

Is it possible that the battery from my diesel could have been too strong and caused something problematic?

My friend thinks the engine is seized, and I'm wondering how I can check that for sure, and if that's fixable in a short period of time without towing the vehicle? I noticed that there is nothing on the crankshaft to rotate it directly, it seems to be just a hole that goes into nowhere. My diesel at least had a bolt to use a ratchet to grab onto.

He's ready to get it towed for scrap if it can get started pretty soon. If I can at least start it up and drive it away, I would consider taking it off his hands, to see if it's repairable, but I can't even get it started, and I can't check the engine health via a compression test, when the engine won't crank over.

Any ideas? I'm thinking it may be worth at least getting as many common parts/devices off the vehicle as possible, either for my own use (I have a 300SD/TD), or for selling as parts.

Also, he says the transmission was replaced, but it has been leaking like crazy and nothing anybody could do to reseal it would work. He says it's leaking from the pan, but I didn't get it up on ramps to see myself. He had driven it at least 8 months beautifully with the new transmission before the performance completely died out one evening as he was entering the freeway. It chugged along, but he had to manually shift/rev the engine up (L->2->D) before it would pick up and consider shifting. Not sure if this is even relevant to it not cranking over, which is my bigger concern.

I checked the fuses and all look okay. Unless perhaps one blew somewhere (not under the fuse box). Should I try using a remote starter to at least eliminate the starter or electrical from possibly being the culprit? I just can't find the starter on this thing!

Am I correct in thinking it's best to bypass the ingition/fuse box and use the remote starter, and then if that still fails, somehow test the starter's operation (not sure how), and if that passes, then consider it as an engine issue? Anything else it could be other than a seized engine, if it were still mechanical?

Am I doing it wrong in turning the engine over at the power steering pump? (again, the crankshaft is not budging)

If I get the valve covers taken off, will there be anything noticeable there that's wrong? ie chain, etc