possible bad flex plate? rpm cutting out.

[prelude]

Hello there brains of the interwebs.

Recently I had the 4.6 gems in my P38 have a mighty hiccup when I was overtaking. At first I though, my gearbox is finally up for a rebuild after all those k's but eventually I noticed the engine cutting out more often, accompanied by a distinct drop of the rev meter. Recently I had to overtake a tractor again and this time the hiccup resulted in the engine cutting out and I had to park it by the side of the road, looked around, started her up again and away we went. The interruptions grew over time and my first instinct was: it must be the Crank Position Sensor since the RPM on the dash is as erratic as the engine and that can only be because the measurement of the RPM is borked.

So I ordered a new sensor and took the old one out. Loe and behold, there are two groves worn into the sensor which can only mean the reluctor ring that is fixed to the flywheel has eaten into the sensor. I fitted the new one with a bit of trouble, cranked 'er over and presto, no more problems.

I have been driving around for about a week without any trouble but as that goes on our roads, I had to overtake a tractor and bam, again, a hiccup. By now the engine has trouble around the 2krpm mark and I'll bet when I pull the sensor again I'll find it worn again as well.

I did not have the chance to check the entire reluctor ring or anything since I am in the middle of a very stressful time working 16+ hrs a day to reach a deadline. I can really not afford to loose the only vehicle with a tow hook right now and I can still coax the old bus along but I fear something is wrong.

Some thinkin and googling would suggest perhaps the flex-plate, but I can't see how that would cause this kind of a problem.

Does Anyone have any suggestions or ideas what this could possibly be before I set of on a wild goose chase?

Cheers!
-P

[Scouse]

Remove the inspection cover and check if the reluctor ring is loose. Mine was moving on the rivets.

[prelude]

So I finally got around to separating the box from the engine and... Nothing. No broken flexplate, no loose reluctor ring. What I did find was that I can move the crank (with a prybar) back and forth which would explain the worn in sensor... More on that on a separate topic since this sucks big time. :(

-P

[prelude]

I finally got around to pulling the autobox from underneath the vehicle (note to self, if ever I need to go that far whilst not in a workshop, just pull the engine since the gearbox:transfercase is WAY heavier...). Turns out that the plate holding the crank position sensor was loose. (ERR3639) Turns out this was welded but the welds at some point had let go (which i find rather odd, how could that happen? Are the vibrations down there THAT heavy?) and it was glued back in place. That glue, whatever the type was, had let go by now and the whole assembly had started to rub against the reluctor ring. Bugger.

So I intend to find myself an alli welder who can tack that thing back into place PROPERLY and let's hope that is the end of it.

Still, much rather down here in a nice workshop than on the cannning or wherever :)

-P

[prelude]

And also down here it's time for an update:

It has been a while since I also did a lot of other work on the car in the mean time, including an engine flush which resulted in leaking freeze plugs (see other topic on here) but here goes! In the end welding the cast ali was not an easy job that we could perform or find someone to do. I removed the small pin that is used to fix the plate in the exact right place and drilled out the hole and tapped a thread in there. Using a small bolt with a dot of locktite the plate is now fixed in place this way. Sure, it is only secured on one end since it was very hard to do the same at the opposite side due to insufficient metal thickness but it should not be able to move at all. For now that seems to have solved the problem of the sensor eating itself.

Another "small" issue has arisen though. Since I had the autobox out anyway I decided to have it replaced by a new one, the old one had done 250k at that point so it seemed like a good idea. I also replaced the flexplate with a HD one since the whole thing was apart anyway. It seems reluctor ring is now a tad bit to far away from the sensor, which should not be. Also the shifting is rather harsh but I guess that is because of the tougher flex plate.

Anyway, this update is for anyone who finds himself in a similar situation; check the crankshaft sensor plate :)

Cheers,
-P