MKC1962, I reread the thread again this morning and I had been assuming you have already done what Toby is suggesting here. This part is a circuit board like item that sits under the rotor on the Dist. It is called the switch plate, or Cam sensor, or pickup plate.

Thanks for the continued input.


I cut out the cat yesterday and its clean as a whistle. ran it straight piped with it out and it still does the same thing. Cranks and idles great, but little to know revving up ability.

The distributor cap was part of the initial tuneup as were all the rest of the basic ignition parts. Coil was tested against FSM test specs and showed a primary and secondary coil resistance in the range specicifed in the FSM. Since then have yes inspected the cap as well as the pickup coil. Pickup coil was also tested against the FSM specs and passed said test. Yesterday went as far as to remove the new plugs to check and see if maybe one was was cracked or damaged during install. All were ok from that perspective but did notice that all were sooty as though running too rich. 02 was previously checked during up to temp running conditions as fluxuated nicely from 0 - .9 vdc. Not to include does not kick a code unless I force it to.


Any and all sensors changed to date, I can disconnect and will in fact trip associated codes, otherwise no codes trip.


Compression was tested on a warm engine some time back and found to be around 145 on all cylinders with little if any variance between. From what i read this is about middle of the road on the good side PSi for an engine with 121k.


Oil pressure has not been checked with an actual oil pressure test guage but the dash guage does go from nothing up to about 3/4 when running. As the engien runs incredibly smoothly with no obviuos chatter fo any type, have no reason to suspect oil presure as a cause for a non rev ability.


Timing set was replaced when I did the plenum Hughes kit as was the tensioner. Timing set was set to dot to dot gear spec, and rotated several times to make sure it stayed the same as to ensure no slipping of teeth or mistiming. Prior to buckling up put the crank pulley back on to get it to TDC and confirmed that the Rotor button did in fact point at #1 position and it did. Also reconfimred proper plug wiring orientation. 165432


As for the pickup coil, it was tested against the FSM specs and did pass. Was closelly inspected for any and all damage and saw none.


As for the cam fuel sync. from what I see in the FSM the cam sensor mounted in the base of the pickup coil interacts with the half moon shield at the base of the distributor, that if the half moon plate is locked into it approriate spot and the pickup coil in its spot all that is synced. But I'll dig into that topic a bit more to see if maybe its got somethin to do with that. But Ive not in any way removed or moved the half moon plate, the pickup coil only mounts one way, and the same with the rotor and dist cap.


Now as for this Reset of PCM, have no idea how to go about doing that. Ive connected the code reader to it several times as I would intentionally trip sensors to see if I would get PCM OBD feedback and after doing so reset it back to norm.

Now...could maybe the pickup coil CAM sensor part being losing some of its ability to send the proper signal for the fuel distributionn part? maybe...dunno. There is no test data available to imply its working either half or all the way, only that it works and sends a pulse.

To reset the computer disconnect the neg battery cable for 5 minutes. Some guys say to turn the key on after to make sure the juice drains out of the system. ?
I had to fix my fuel sync. It was -6 to -15 Its at zero and jumps up some now.
If it turns out your cam sensor is OK and your fuel sync is good (as in my post #24, Zero is dealer spec but the guy who wrote that up swears by +3) I am unsure of what might be next. Possibly the torque converter? or as has been suggested the PCM.

This is bugging me. I opened my 95 FSM and in the engine chapter the diagnosis section starts with checking for a leak in the intake. It suggests spraying water at the suspected leak to see if RPM's change. I usually use carb cleaner to check for vacuum leaks. It will change RPM's if it sucks any in. Then it goes to checking cylinder compression test. I think you said you have 145+/-? in all 6. Next is Head gasket failure diagnosis.:
A leaking engine cylinder head gasket usually results
in loss of power, loss of coolant and engine misfiring.
An engine cylinder head gasket leak can be located
between adjacent cylinders or between a cylinder and
the adjacent water jacket.
² An engine cylinder head gasket leaking between
adjacent cylinders is indicated by a loss of power
and/or engine misfire.
² An engine cylinder head gasket leaking between a
cylinder and an adjacent water jacket is indicated by
coolant foaming or overheating and loss of coolant.

I think you mentioned you have an FSM maybe a look at the engine section is in order? This is really odd to me that nothing has improved the ability to increase RPM's even temporarily. I had the same issue. I also had the trans rebuilt after I did all the sensors and the TC/tensioner (not worth it the guy was a charlatan and he exchanged my matching number tranny after telling me he would rebuild it!). Fixing the exhaust leaks on both sides was the thing that eliminated wierd issues. Now I'm just trying to improve mileage.

on the cam/fuel sync how does one go about determing the + or - setting? Ive searched the FSM for a procedure but yet to find it.

From what i read the timing is not adjustable on the 3.9. But Just for the heck of it today I hooked up a timing light the old fashion way and showed the crank timing mark to be about 40-60 ATDC at idle. That sure doesnt seem quite right. I figure if the timing cover has an actual timing gauge built into it, it must be used for something. If an engine were actually that far A or Btdc it would also act the same as I am seeing....maybe this is where the cam/fuel sync comes into play?

This made me think of the condition that the timing chain was in before I replaced it. the old one had So much slack you could nearly touch the chain in the middle and clearly based on gear dots not perfectly timed at all. Makes me wonder if some previous owner may have attempted to alter the distributor rotation not knowing that this would not accomplish much.

As for checking for vac leaks I always use a propane torch, unlit of course!!....if you find one it will rev as well.

As for the comment about a torque converter this is a manual.

I do have the test kit for checking for exhaust gasses in the coolant and may try that. But, I am loosing no coolant, no coolant in oil or oil in coolant. No overheating or cooling issues at all. Though 145+ is a bit below the recommeded 160 for a new engine, for it to have that consistent across all 6 cylinders doesnt really point at a blown gasket, id expect to see a variance or loss on a few.

Not exactly the case, it does rev up at times and when it does it acts just perfectly but its only occasionally, not consistent at all.

did some searching on the topic of sync, will check this tomorrow.

"Not exactly the case, it does rev up at times and when it does it acts just perfectly but its only occasionally, not consistent at all." OK

You can set the fuel sync with a scanner that has the ability. I have a MT 2500. It revs the motor up to 2K rpms and you turn the dist until you get it at the place you want. The readout gives you the +/- numbers. Or you can use that method on Post #24. That guy claims he went back and checked his work after he got a scanner for his shop and he was never more than 2 off on the ones he did with that manual method of setting it with the motor off looking down over the Dist. I did it and when I checked after I got the SnapOn MT2500 it was -6 and jumped to -15 a lot. I have it at +1 which is as close to zero as it would stay. They are on Ebay usually around $300.
Here is another procedure for doing it. http://www.bionicdodge.com/Download/...uel%20Sync.pdf

Ive got just about every tool imaginable, but dont think I Have one of those. However, I did recently also inherit an entire shop full of tools from an old freind who enherited them himself but he never used them. Thousands of $ worth of snap on diagnostic stuff was just some of it. I have yet to make time to go through everything he brought me, so maybe? but in the mean time I will try to do the manual approach. I did find the procedure under Dakota.net forum late last night.


here is another thing that crossed my mind on the way to work this morning. For the most part I work on classic cars, but do work on just about any make. I dont do transmission work often, but on this truck did have to replace the clutch and flywheel due to extreme wear and gouging. I did compare the old flywheel to the new and they appeared identical. Both had the 1 nub, 2 nub pattern around the other edge for the cranksensor pickup. Most manuals that i have worked on, the flywheel can only go on one way based on bolt hole orientation. And in the case of this one also appeared that there was only one way. But is there maybe two ways. The proper and 180? and in doing so does maybe the section that passes the Crank sensor 1 nub vs 2 get out of sync? If I think back to when I first started working on this truck (3 months now), aside from the fact it was about 60k overdue for maint, and its clutch totally gone, I just never recall it having this little amount of backfire, it did rev from what one could tell with the worn clutch, but by no means acting the way it does right now.

I do not know enough to answer your question about the flywheel. My new crank sensor was much shorter than the old one. It is supposed to be a new design. It sure made the truck run better.