how to diagnose a vehicle has unknown problem?

I inherited 2005 Mercury Mariner with unknown problem. besides that its been sitting about 3 yrs.

where do I start after I check to see if engine is not frozen? it was abandoned in his yard after a problem I don't know about. I assume it wouldn't run.

I'm getting a battery, gonna squirt marvel oil in the plugs. my bet is electrical or brain issue but I have nothing to go on. its high mileage I'm sure so ill guess over 250,000.

any help appreciated.

rr

You need 4 things. Compression, fuel, spark and spark at the right time.

Edit: I wouldn't use the battery the 1st time to try and turn it over. Pull all the plugs, squirt some penetrating oil and let it sit. Then I would turn it over by hand.

. I wouldn't use the battery the 1st time to try and turn it over. Pull all the plugs, squirt some penetrating oil and let it sit. Then I would turn it over by hand.

engine turns over by hand ok. gonna try a battery next, but can't use one in my primary vehicle. I'll have to get one.

the reason I asked about the brain or timing was bcause if that is the problem will I be beating my head against the wall? I can check the timing marks at least by removing the timing cover this has a 3.0 V6 in it.

thx,
rr

You have already assumed what is wrong. Without proper diagnosis you're just guessing. All good mechanics I have known start with the "what is working" and do a process of elimination to determine what is not. Have you considered the engine is good and the tranny is toast?

understand. I'm just trying to anticipate things that will hinder the normal diagnosis process.

just trying to find out what maybe have checked first if possible. I just want to start the engine. I will worry about tranny after that.

update.
Just today (now) I found out from a relative that the vehicle started running erratically then kept stalling. eventually, they couldn't start it at all.

rr

Then I would check for spark 1st, the simplest.

sorry, will update once I get a battery. hopefully, this week.

Listen to the engine's noise carefully and if you still cannot diagnose the problem then I suggest that you should head to the nearest service station.

Thanks

Listen to the engine's noise carefully and if you still cannot diagnose the problem then I suggest that you should head to the nearest service station.

He hasn't got it started yet.

ok, had minor issues like a hurricane (Irma) basically hit me dead on with the eye where I live. I managed without power for 9 days and now have a battery to start diagnosing the Mariner.

I will post what happens when I turn the key, if it turns over at all - ill check for spark.

we can go from there. still doin some clean-up. I'll do the start test in the next few days.

Glad to hear you are okay. The car can wait...