Have a Ranger with 4.0 and 75,000 miles.

Suddenly lost power while driving. Could barely get up even the slightest grade. No codes. No engine light. Had a strong rattle noise and very low compression readings - less than 50 psi. From these forums learned that this was likely a timing chain issue.

Pulled the engine, bought the special tools, pulled the heads, found a broken right side cassette, had a machine shop replace the bent valves.

Very carefully followed the shop manual and these forums while I replaced both cassettes and the front timing chain and tensioner. Did a differential compression test on the stand and everything looked good.

Put the engine back in, fired it up and it still had no power. Again no codes. No engine light.

Checked fuel pressure. That is in spec. Checked coil output - all good.

Only abnormal indications is that a conventional compression gauge shows 150 psi on Cylinders 4 & 5 while cylinders 1&2 show only 100 psi at idle. Just to make things more interesting, a differential compression test on 1&2 looks very good 48 out of 50 psi.

Is there anyone out there with any ideas? Thanks in advance.

 

Did you reset the PCM after? There is a limp home mode that it will go into to prevent damage when it senses something out of whack and it may still be in that mode. Although it usually sets a CEL it is possible that it won't id try pulling the battery for an hour and then test drive it again.

 

Reset the computer several times. It did not make any difference.

 

Though I am no expert, I ask two questions.... Could it be possible cracked pistons or rings (from the shock of hitting the vales)? Or, if I understand the SOHC, you did the front chain, but there is also a shaft that feeds the rear cam chain. Did this shaft or chain get damaged in any way? I also suggest doing a code clearing (not a pcm reset) just to be sure.

Just me pondering the many eccentricities of a elec/mech device.

 

Thanks for the reply.

Replaced all the chains, tensioners and sprockets.

Also in the calmness of a new day, rechecked the compressions. They are all between 145 and 155 psi. This is leading me away from any valve timing problem.

Ignition is good. Fuel pressure is good. Beginning to think it may be the computer.

 

Did you line the cams and crank up properly.

 

Bought the special tools and lined them up as described in the shop manual. If they were not lined up, I don't think the compressions would look good.

 

I would double check all your sensors and hoses, being motor was out. If nothing obvious i would probably say cam was timed wrong. It is possible to have cam 180 degrees off and it will still run

 

Timing casette broke causing it to slip time bend valves and run like ****. Its likely its doing the same thing because the cam is still out of time. Just my 2cents.
Two 4.0 sohc rebuilds under my belt