The crank position sensor is usually fastened to its mount with bolts and locating dowels, so it should hold its position very well. If it is contacting the crank pulley, then something has gone wrong. Did anything fall into that area to knock it out of position, or bend its bracket?

One other thing I've seen is when someone services the thermostat housing, they don't realize that the wires for the CKP sensor go right past that area, and inadvertently damage it. Then the engine runs like crap, or won't start.

 

There should be an small air gap between the toothed wheel & the Crank sensor, check it out , this could be a problem, it could have come loose or as mentioned the bracket could be damaged. Are the teeth on the wheel in good shape?

If the CKP sensor has failed you will get no spark at all & no RPM reading (from EEC). If the Cam position ( CMP) sensor has failed the engine will still run, however you will get a CEL with a code. The CKP may not throw a code ( dont know why but it happened to my Son & no cel).

 

Hmm. Maybe I'm on to something then. I'll take a close look at that. Is replacing the crank angle sensor plug and play, or does it require proper adjustment like a TPS might?

 

I was just poking around under the van's hood. Nothing that I can get my hands on is loose or disconnected.

I can verify, though, my previous thought that the crank angle sensor is touching the tone wheel on the balancer pulley. There are two parallel witness marks that line up perfectly with the sensor portion of the unit, and the plastic encasing the end of the sensor appears to be rubbed/curled off to one side. The wheel doesn't look damaged - the marks are two stripes where the surface rust has rubbed off, nothing more than that.

So I'll order up a new sensor from the autopart store and hopefully change it out this weekend. With luck, I can get in there without pulling too much part, and with a little more luck, maybe that's the solution to my problem...

 

It's plug ,n, play. Compare the readings with an Ohmeter (digital) before you fit it. If they are the same -+ 20% it's probably O.K. You may be able to get a return on it. The unit should not be touching the toothed wheel at any point. If it does it could eventually break the magnet loose.

 

So I take it you have no spark?

 

OK, it runs again. Still not sure if its cured, but at least its drivable. I replaced the crank angle sensor and the valve thingie on the charcoal canister that I previously broke. Started right up.

The OEM crank angle sensor was different from the replacement, and lacked the dowel pin for locating. Not only that, but both bolt holes were slots, so there really was nothing to positively locate it. It may well have drifted down over time and eventually hit the crank. It had a molded tab on either side of the magnet, which appeared to serve as a "brush guard" to protect the magnet in that eventuality. Both had worn away and the signs of slight abrasion on the bottom of the magnet casing. Whether it was failed or not I can't say.

I also retried the other PCM that I have. It started and ran on that as well, but I did notice differences in idle levels. With the original one, it was idling between 800-850 RPM in park/neutral, and 650-700 RPM when in gear. The replacement PCM seemed to maintain a 750-800 RPM idle regardless, maybe slightly higher without a load. The numbers on the scanner were bouncing around a bit, so it was tough to get a real consistant speed. Where should it idle when in gear, stopped, with the brake applied?

Next step is to drive it around a bit and see what codes pop back up, if any. So we'll see...

 

congradulations
must have been a piece of rock landed and beat around on the toothed wheel and sensor pickup of the crank sensor. seen them all beat up and full of mud and still run perfectly on mudders before. tore one out on my Aero log roading years ago with a chunk of limb that flew up.

must have damaged the tooth associated with cyl 5 fire position the most.

be careful with the 97 Aero PCMs. it's the only year of lean burn combustion heads in the Aero 4L. too lean a mixture from the PCM and exhaust valves disappear.

 

The replacement PCM was actually from a '97 Explorer with OHV 4.0L and 5-R55 trans. IIRC, it should also have had the lean burn heads. Anyway, I only substituted it for a few minutes as an experiment before pulling the OEM unit back in.

BTW, the plastic tabs on the old crank sensor actually appeared to be in contact with the crank wheel. I think the abrasion I saw was from direct contact, not from debris. I didn't see any real damage on the crank shaft. So this may well not have impact on the misfire issue. I'm going for a test run now.

 

Well, I drove it about 100 miles over the weekend. Clearly, the misfire issue still exists. At about 90 miles, it popped up a code - this time only for #5 again. So, I'm back to that. I'm trying to figure out how to approach this; now I'm back to thinking about how the #5 plug looked leaner than the others. Maybe it still is fuel related, even though I should be able to rule out the inject itself. If its running and the other cylinders are firing properly, then I can probably also rule out fuel pressure. So what drives the signal to open the injectors? Is there anything else in the system besides the PCM and cam angle sensor?

 

any damage to the crank wheel teeth?
just an edge rolled over or worn off may be enough to affect the crank position sensor sending correct cyl fire info to the PCM.

do you actually feel the miss?
does the tranny drop out of TC lockup and or OD?

injectors ruled out since you had them serviced and they more than likely went back in different holes.

intermittent short or open on #5 injector wiring, possibility

my money is still on leaking valves, will cause lean cylinder, leakdown test will find those.
one lean cylinder usually won't cause strong enough cyl knock to hear.
could also be damaged push rod, the 4Ls wear badly on the ends, or damaged lifter causing low air/fuel mixture flow in that cyl.
or worn cam lob, have seen cams with only one lobe gone bad. failed induction hard surfacing from factory or just a bad metal casting.

 

So the mis-fire is now occurring at speed (instead of just idle)?

I'll take another SWAG based on plug number 5 looking leaner than others: When you had the intake manifold off, you had to disconnect the harness that is dressed around the lower intake manifold, where the two large connectors are hanging down from the cowl. Were there signs of corrosion on any of the wires or pins? These are the wires that connect to the injectors (and a couple of the temp sensors).

 

I guess the misfire must be happening under load. It isn't nearly as noticeable at speed, but I am starting to think that the slight shudder isn't tire balance related (I took the snow tires off over the weekend). It's barely preceivable, at least compared to all the noise and vibration in my other car (but that's a prepared stage rally car and not exactly a good reference). And I do think that it's somewhat down on power too.

I am not seeing any impact on transmission operation. I did not see any damage to the crank tone wheel or corrosion on the injector harness connector. Doesn't mean it isn't there, I just didn't see any. Regarding the injectors, I sent them out in individually numbered bags and received them in individually numbered bags. I can't guarantee that they stayed the same numbers, though, so they may have been switched around.

At this point, I'm going to try working with the "simple" possibilities. If none of that fixes it and signs point conclusively to a head/valve issue then I'll drive it as-is until I can come up with something to replace it. I've got until December on it's NY State Inspection (which it won't pass with codes thrown), so as long as I sort something out by then I can get away with it.

 

any update on this? I've got misfire issues also started with #6, now have it on #5 also.

 

No, no resolution on my part. I've just been driving the thing as-is until I can phase in the '98 Mountaineer I just picked up to replace the van. At this point, it isn't worth pursuing any further to me.