'99 Ranger XLT needs help, bucking

[jhknight56072@yahoo.com]

1999 RAnger 4.0 v6 auto, 4x4; Has been acting up lately when cold will start shaking like the wheels are falling off as soon as it shifts into overdrive, intermittent problem. Persistent now, will not "clear". It has an intermittent habit of bucking and shaking when put in gear. the engine has 90k miles, the rest of the truck 155k miles. We replaced the engine a few years back as the original 4.0 had some coolant leaking into the engine somewhere which eventually ruined a main bearing and developed a knock. This engine is much stronger but someone suggested that it too may have a cracked head. Here is what I notice because my ear isn't good enough to be sure that all 6 cylinders are working; I pulled plug wires while idling and #3 made no difference. Pulled that spark plug and it looks normal. Tranny shift normal mostly up until overdrive when it starts shaking badly. One question I have is if one cylinder is weak or not firing would I not get a check engine light? and would a 5 cylinder condition cause the bucking? Most importantly wtf is going on with this old girl and what's it going to cost? If simple fix would like to avoid the mechanic. Help and ideas appreciated, thank you.

 

[RonD]

A cracked head would cause excessive pressure in cooling system, you would see this as a full or bubbling overflow tank.
You would also notice more white "smoke" from tail pipe in most cases.
Spark plug in that cylinder would look very very clean, steam cleaned, pull near by plug and compare.

You have a Waste spark system, this means the spark plugs are hooked up in series wiring, and if you unplug a spark plug wire you are really stopping spark in 2 cylinders, so not a good way to test system.
Paired cylinders are
3 4
2 6
1 5
Front of coil pack
So when spark plug 1 fires so does 5
when 2 fires so does 6
when 3 fires so does 4
And visa versa

Make sure the 5, 6, 4 side is correct, on the coil pack and at the cylinders, very very easy to mix this side up, and costs nothing to double check it
I know you know it is right, so do I every time I get it wrong, lol.

You can test coil pack with an OHM Meter, it can tell you if coil is bad but not if it is good, lol, yes I know, odd thing, but coils are low OHMs and high voltage so can be bad and test OK.

Clean the MAF sensor: http://www.therangerstation.com/tech_library/CleanMAF.shtml
This is free and not hard to do, and is a source of bucking with 4.0l


Does the CEL work?
It should come on with the key

Yes you will often get misfire codes but these are time related, misfires must be persistent, reads like yours are so if CEL is working I would start engine then unplug MAF sensor, you should get CEL right away, if not then you could have a computer problem.

 

[Big Jim M]

I would start by checking the coolant and the oil. If Ok then I would put a NEW PLUG and a NEW wire on #3 to see if the problem is lectric. If that don't help then I would pull all the plugs and do a compression test!
Big Jim

 

[RonD]

Good call Big Jim, I know my older 4.0l eats spark plugs, motorcraft or autolite seem to last longest, other brands are hit and MISS, and never last as long.

 

[jhknight56072@yahoo.com]

Thanks! There isn't a whole lot that I can check. I cannot get any spark plugs out with the hand tools that I have, just the #3 was the only one that I was able to bust loose. I think the coil is fine, when I pulled the wires off they all arced a good 3 inches! The MAF looks good. The CEL works, I know this 'cause after I got done pulling half the hoses and accessories off to change a leaky valve cover gasket I plugged something in the wrong place. But the bucking was happening before I messed with all that, it just won't clear this time.. thought; would oil from the leaking valve cover gasket foul the plugs externally perhaps causing permanent failure? I'm probably going to have to limp her over to a real mechanic but you know times are tough, had to try. Anyway, assuming the head isn't cracked or anything serious I at least accomplished the fix on the oil leak.
Thanks for all help.