I've never seen such a thing on a light-duty modern truck

[WConley]

Hi guys -

Lately I've been struggling with an issue on my 1997 4.0L Ranger.  It's been misfiring at idle (hot only) and of course throwing codes 301 and 306.  FYI it has 155K easy miles on it.  I've never towed anything and most of the miles have been at highway speeds.  The truck is in such good shape that it's worth keeping.

The collective wisdom on the internet all points to intake manifold leaks.  I've torn the upper and lower intake down twice to be sure it wasn't an issue.  I even built a smoke machine to try and pinpoint a leak!  Nada.  The fuel trims were a bit lean, so I replaced the HEGO sensors and even rebuilt the EGR system.

Finally I had enough and pulled the heads off.  Here's what I found:



Can you believe it??  This is the worst one - Cylinder #6, but some others were nearly as bad.

You'd think I was pulling fifth wheel trailers up inclines for 155K miles 

Clearly the Krauts in Cologne were not minding the induction hardening machine the day that engine went through.  Just goes to show the "obvious" is not always the answer.

I've just received a new set of heads - $685.00 delivered ready to bolt on.  For that money plus some gaskets it's worth keeping the old girl around a while longer.

[jayb]

MAN, Bill, I've never seen a valve sunk that bad before!  It is remarkable the engine ran even somewhat normally in that condition.  It ought to feel like a new truck with the replacement heads.

[WConley]

Jay - the most surprising thing is that compression on all cylinders was 155 - 165 psi  

I measured it cold though.  If I had gone ahead and measured it hot, I would have seen evidence of a couple of valves hanging open.

Yeah I'm impressed the thing ran as well as it did.  It will feel like a new truck, since I'm probably picking up a full point of compression in at least half the cylinders.  Dare I hope for decent fuel economy too???

The short block is in excellent shape, with the cylinders showing good cross-hatch everywhere.  Mobil-1 really is excellent oil 

[machoneman]

Wow Bill, and I've seen many a pic of bad valve seat recession and a few in person but this one takes the cake. Lucky too it didn't pop off the valve's head or drop the whole valve. And I'll admit that I've advised many to skip the hardened valve seat replacement with unleaded fuel unless one is driving a heavily loaded truck. I wonder as well how the factory missed the induction hardening step on only one cylinder???.....weird indeed!

On re-read, I missed the fact that you said a few others looked almost as bad. Yep, the pair of heads somehow either missed the hardening step or something went wrong with that step when the heads were heated or later cool quenched.

[aarons428]

I also have a 97 ford ranger with a 4.0l and will have to do head gaskets soon. One question did you have to replace the head bolts or did you reuse the old ones?

[WConley]

I'm putting the new heads on in the morning.  I'm also re-using the head bolts.  These are not "torque-to-yield" fasteners that you have to throw away after one use.  I feel comfortable with them going back on.

If it was newer and would be seeing a lot of heavy use, I might think differently.  The truck is lucky to see 3,000 miles a year now.

- Bill

[Qikbbstang]

Hope you post a picture of the seat -- just like to see how it managed to maintain a seal w/o torching a section.  I actually have a 390GT head that has just about the same valve head porting job as your does.

[WConley]

Ask and ye shall receive!



The valve looks surprisingly good, though it clearly was only acting as a loose plug for a long time.


BTW I just finished installing the new heads yesterday.  The truck is all buttoned up and runs sweet  

To aarons428 - The original head bolts went back on just fine and felt good torquing up to spec.  Make sure you have a good T-55 1/2" drive Torx tool for these, because they need quite a bit of Ooomph.

[jayb]

Sheesh!  Kiss the first .200" of lift goodbye LOL!

[machoneman]

Good pic. Amazing too as it almost looks like it was made that way! Usually one side of the seat or valve is burned up but not in this case. Odd indeed. 

[WConley]

Yeah I'm very surprised.  It almost looks like a freshly machined pocket for a new valve seat. 

You can't see it in the pic, but the short side of the port is razor thin under the seat.  The lifter just ran out of lash adjustment before the thing could sink any more!

[WConley]

Sheesh!  Kiss the first .200" of lift goodbye LOL!

I just measured it.  .270"    That's over half the lift!


I just finished installing a new A/C compressor and charging the system.  For the first time in a couple of years I have cold air and no Check Engine light    It was worth the effort!

[babybolt]

One thing I've noticed about these "late model" fuel injection engines is they still seem to run acceptably even with some major problems.  I had a 5.0L F150 with a bad intake leak that drove me nuts, but it ran - most of the time.  And just this spring my 351W F350 was running a little hot and the fuel mileage was up a couple of mpg's.  After about 4 days of fooling with it I found a vacuum leak in a small rubber hose near the EGR.  All of the sensors and parts at the front of the engine seemed to go bad, one after the other; my theory is the hot/cold cycle does them in.  At over 230K miles it still has the original coolant hoses/radiator/water pump/alternator/AC compressor, can't complain.

[Barry_R]

Wow indeed!
I've never seen one that bad!
Wonder how the head itself brinnels?
Cast from peanut butter?

[WConley]

Wow indeed!
I've never seen one that bad!
Wonder how the head itself brinnels?
Cast from peanut butter?

Hi Barry.  Nice to hear from you  

Unfortunately the head is now probably part of an ingot headed to China.  I didn't see anything untoward though.  The head bolt bosses weren't deformed at all and the rocker shaft bolts were holding good torque.  There was also no evidence of leakage through the fire rings of the head gaskets.

Maybe it's this communist California gasoline the poor thing has had to drink its whole life  

Driving the truck with the new heads has been an epiphany!  It actually generates lbs-feet for overtaking at freeway speeds now, instead of kicking down two gears, wheezing, and throwing misfire codes.  I can also see evidence of substantial fuel economy improvement after half a tank.

I was so impressed that I spent Sunday afternoon applying polishing compound and paste wax to the old girl.  She dun shined up real good!