Topic: 88' head on a 98' block?

[dustjunkie]

First post, and I searched! 

I recently bought a 98' cherokee with the 2.5 and a blown head gasket for $250.  The previous owner told me that it was a 4.0 so I drove the 100 miles to pick it up and found the 4 popper.  It was very clean inside and out and I bought it for my 15 year old son, so the 2.5 fits the bill just fine.

After further inspection, the head had 2 mushroomed valves, one burnt one and 2-3 loose valve seats.  It got hot.  We went to the local pick-a-part and the only 2.5 was an 88' comanche.  The casting numbers were not the same, but they 'looked' identical.  I couldn't go wrong for $50.  I slapped it on and have two issues that may or may not be related. 

There is a noticeable valve train tick.  It comes and goes, so may be an unhappy lifter.  Are the heads compatible, mainly the rocker post?  I did use the 98' pushrods and rockers.  Everything was bolt on and way too easy to work on.

The second issue is an off idle stumble.  It pops in the intake once in a while.  It's almost like a carbed vehicle with a bad accelerator pump.  Kind of have to feather it until it gets to about 1500-2000 rpm's.  I'm wondering if it's a lean condition that may have created the over heating problem in the first place.  The intake was loose when I took it down so I assumed it was that.  The O2 sensors don't like heat, so it could be that as well.  Any ideas?

thanks!

[FourbangerYJ]

Welcome to the board 
The 2.5 does have some piston slap which comes and goes. More noticeable on start up. Mine goes away after it warms up.
The stumbling could be in the fuel delivery, clogged filter, pressure regulator,fuel pump. A clogged cat converter might be a problem too.

Since you swapped heads and it runs I would imagine it's doable. The biggest concern's I would have is if the oil galley's line up and if they are chambered in the same CC's.

[dustjunkie]

Oil get's to the head via the pushrods, so that works.  The water jackets ligned up fine.

I'll replace the fuel filter and check the pressure first, those are both easy.

[Jeffy]

There are two heads for the 2.5L.  I forget what's different.  IIRC it's very minor.  There were pics of the two in a thread from years ago.

Search the cast number and I'm sure you'll find it.

[dustjunkie]

I worked on it a little last night, the tick is going away, it may be as simple as some water got down in the lifter valley and caused some rust on a lifter or two.  A heat cycle or two and it will stop ticking.


The stumble is still there.  It has to be vacuum.  The A/C turns on and off but all the flow from the blower is stuck on defrost mode.  I tried carb cleaner all around the motor to see where it is sucking air, but found nothing.

[sharpxmen]

I worked on it a little last night, the tick is going away, it may be as simple as some water got down in the lifter valley and caused some rust on a lifter or two.  A heat cycle or two and it will stop ticking.


The stumble is still there.  It has to be vacuum.  The A/C turns on and off but all the flow from the blower is stuck on defrost mode.  I tried carb cleaner all around the motor to see where it is sucking air, but found nothing.

if you had a vacuum leak the idle would be high, if it's normal then most likely there's no leak.

EDIT: could be a leak at the rubber elbow on the MAP sensor and in that case the above doesn't apply (won't go higher in rpm).

[dustjunkie]

It has to be a significant leak or plugged vacuum port somewhere, A/C still doesn't work right and the stumble is still there.  There is no check engine light on.  There is also pressure in the valve cover blowing into the air box,....shouldn't that have vacuum?

[sharpxmen]

It has to be a significant leak or plugged vacuum port somewhere, A/C still doesn't work right and the stumble is still there.  There is no check engine light on.  There is also pressure in the valve cover blowing into the air box,....shouldn't that have vacuum?

what i am saying is that if there was a significant leak your idle will increase significantly - you can unplug the valve cover line that goes in the intake manifold (at the manifold fitting) and you will see the idle going up about 500rpm or so (not the line that goes to the airbox). Any significant vac leak will result in rpm increase - unlike the MAF based EFI systems where a vac leak will bypass the MAF sensor, the speed-density EFI that uses a MAP will detect a vac leak and increase the rpm due to a lower vacuum reading. what is your rpm at idle?

there is a fitting at the valve cove on this line that i mentioned, make sure is not plugged (you can clean it with a thin screwdriver or something similar) and also check the fitting in the manifold and the line itself so it is no plugged with gunk - so like you said, the airflow would be from the airbox thru the valve cover, out of the cover thru the brass fitting and from there into the intake manifold below the throttle body

did you check the rubber elbow on the MAP sensor? also, can't remember if you looked at the TPS or not (throttle position sensor) - a bad TPS can cause a stumble but so would a bad MAP sensor (these are most obvious but not the only ones so don't take this as a for sure thing)

hope this helps

[dustjunkie]

Ok, I figured it out.  The fuel pressure regulator on the rail, where the vacuum line goes in was bent a little bit, kinda at a 45 degree angle.  I also cleaned out the port on the manifold where the main vacuum line goes in.  Runs perfect, no stumble and it passed emissions testing without a problem.


The A/C issue was the check valve at the manifold.  The guy that had it before me turned the chack valve around backwards.  Flipped it around and the A/C cranks!


I also grabbed a dash pod from a wrecked 4.0 cherokee sport, plugged it in and all the guages worked without doing anything extra.  Low fuel light, tach and everything else works!  Best $30 bucks ever.  I wanted temp and oil pressure guages mostly, the other stuff was just a bonus.

[Jeffy]

The tach are supposed to be engine specific.

[dustjunkie]

So, do you think it's not reading correctly?  I can temporarily mount an aftermarket tach and see if they are close.

[dustjunkie]

I checked out the tach last night.  It runs through the stock computer and has to either be the cam, dizzy or crank sensor that runs it.  How can it be engine specific?  Every revolution of the crank whether you have 4 or 14 cylinders it get's a trigger.  It works and is accurate.

[sharpxmen]

I checked out the tach last night.  It runs through the stock computer and has to either be the cam, dizzy or crank sensor that runs it.  How can it be engine specific?  Every revolution of the crank whether you have 4 or 14 cylinders it get's a trigger.  It works and is accurate.

it is based on the way the signal is captured or more specifically the way the tach reads/receives impulses - it will not be 1 impulse per revolution, most tachs use ignition coil signal so they are specific for 4, 6, 8 or whatever number of cylinders (some/most a/m tachs have a switch to select the number of cylinders as 4/6/8). other tachs or gauge clusters use computer controlled signals so those would be incompatible with other manufacturers.

[Jeffy]

it is based on the way the signal is captured or more specifically the way the tach reads/receives impulses - it will not be 1 impulse per revolution, most tachs use ignition coil signal so they are specific for 4, 6, 8 or whatever number of cylinders (some/most a/m tachs have a switch to select the number of cylinders as 4/6/8). other tachs or gauge clusters use computer controlled signals so those would be incompatible with other manufacturers.

Some gauges do have jumpers so you can switch but I don't believe the Jeep does.

But hey if it's accurate against a test tach then it just go with it.

[dustjunkie]

Thanks again for your help.  This forum rocks.  We dropped a 4.0 TB on it and it was a noticable change.  I had to open up the manifold with a dremel and at first I changed all the sensors but not the IAC housing, it idled way fast, so I looked at the difference in the two and figured it out.  It needs the housing!

Here is the $600 car.......