Need some rebuild advice for 4.0

[joepackersrock]

Well I was hoping to put it off until I got out of school...but the 4.0 is just getting weaker and weaker. This is going to be my first time tearing into an engine so if anybody knows of a good guide that would be extremely helpful.

So I my 4.0 has about 250,000 on it and only gets about 11 or 12 mpg. That may be largely due to the fact that my exhaust manifolds are so rotted out that have the exhaust exits at the y-pipe rather than the tailpipe. That issue will be taken care of following the rebuild. I checked the codes and it was throwing up o2 sensors (obviously) and something about the fuel system being lean at part throttle. When I pulled the plugs half of them were coated with that brownish ash which I hear means the valve guides seals need replacing. Other than that it has just a little bit of that tick from the lifters, but I've never heard one that didnt at this mileage. So what should I be replacing...valves? rods? lifters? How far down should I go?

 

[disciplerocks]

Why not pick up a lower mileage one from the junkyard? They are a dime a dozen around here.

 

[joepackersrock]

That is also a possibility, the other problem is I dont have very much in the way of tools, torque wrench and sockets is about it. Anything beyond that and its sledgehammer and crowbar

About how much you think I could pick one up for?

 

[Dancinci]

I'm casually shopping around for an engine also. Prices I'm getting here are $400-$500.

The trouble I run into is finding low miles. My truck is a 1997, 4.0 and the engine exchange book shows 1998 and newer is not a direct swap. Every engine I find (1997 and older) already has high miles, or has been laying in a junk yard for 10 years.

Any advice on this??

 

[disciplerocks]

I can get one here already pulled for under $300. And I just dropped a motor in my truck. Only used hand tools, except on the flywheel bolts.

 

[86rangerxlt]

the way i see it if your tearing into the motor might as well do a full rebuild. pick up a full kit new pistons new rings all new gaskets etc. by the time your done you'll have a brand new motor. pop the heads off and have them resurfaced and rebuilt. inspect the block for wear. especially look at the cylinders. find yourself a nice rebuild guide online. and be thorough. dont rush it take your time and do everything correctly and make sure everything is to spec. you may have to pick up some tools along the way that you dont have but hey cant ever have too many tools can you?

 

[disciplerocks]

If you want to keep yours, I'd check your compression. If its good, then your bottom end is probably fine.

 

[rusty70f100]

I think the situation would improve a lot if you fixed your exhaust! You see, in the exhaust there are a lot of things going on with reversion, etc. Especially up by the motor and the y-pipe! If it exits right after the y-pipe, with no catalytic converter or anything, the oxygen sensor is going to see some oxygen from the atmosphere, and report to the computer that the motor is running lean!

That would explain your brown plugs too.

If you put something on the exhaust after the y-pipe, anything, for about 2 feet or so at a minimum, and, so long as it's sealed, your mileage should improve. Ideally you'd want a muffler of some variety in the system though.

Now I didn't know if its your exhaust manifolds or the y-pipe that's rotted out. If it's the manifolds themselves, you've got more work to do. But still, fix the exhaust first. I'd almost take it to an exhaust shop and tell 'em to fix it at that point. I hate exhaust work.

As for the tick, the pushrods do seem to wear out on the rocker end. Eventually this does cause a little bit of a tick in these motors. I'd just pull the valve covers and change out the rockers and pushrods.

So, to summarize, fix the exhaust first, then get yourself some new rockers and pushrods. It'll be just fine.