Of course it doesn’t change the timing. A lean enough mix can burn so slowly that it’s still burning when the intake valve opens.
What’s sort of weird about your problem OP is how it seemed to all happen at once. It had been running fine for you for some time, then your buddy borrows it, and it stalls out/lost all power just a block or two down the road from where he borrowed it. If you were having compression problems or timing chain slack problems, the symptom would gradually worsen over a number of months and miles, & wouldn’t usually come on all at once – unless the timing snapped, but in that case it wouldn’t run at all. One important clue you got in your favor, when you set the base (idle) timing back to where it is supposed to be it runs much better. That’s a good sign that ignition timing is the key here. Still, I have no idea what’s causing your problem… But I have some ideas…
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The retarded ignition timing may have damaged the cat. Sometimes failing cats, the insides will break apart all at once and immediately clog the exhaust system. Like if your buddy drove a little too fast over a big bump in the road. A clogged cat would be consistent the symptoms. Intake manifold vacuum would be considerably lower (closer to zero) if this happened. Normally warm engine idle intake manifold vacuum is in the range of 15 to 22 in hg. If the cat is plugged up it might measure more like 10-12. Easy enough to test anyway. If you reach an ambiguous result, you can always just temporarily disconnect the cat and see if that returns the vehicle to full power.
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The crankshaft ignition timing signal from what I can tell is done w/ a hall effect sensor inside the distributor. So that sensor could be bad. Or the distributor shaft might not be properly sync’s with the crankshaft. I couldn’t see where your distributor gear hooks into on your engine. Usually it is either the oil pump or the camshaft. If it is at the camshaft, then the timing chain looseness might be the cause of the ignition timing problem. You’d need to come up with an explanation how the timing chain would go loose all at once though. It’s possible I suppose, maybe some part that routes the timing chain path broke.
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failed distributor or distributor octane rod
After that you’d have to go through these one by one: ignition coil, dist cap, dist rotor, spark plugs, spark plug wires, ign or sensor grounding problems, air filter, fuel filter, injector problem, water in fuel, fuel filter, intake manifold gasket, fuel pressure, coolant temperature problem.
There’s a tsb and a customer interest bulletin you might want to take a look at. Your dealership should be able to make you a copy, or you might can find them just googling. Best of luck. I’m always a fan a Ford trucks. 
edit: starting to think you’re soon going to removing the timing chain cover for a visual inspection
TSB: 91-12-11 , lack of power, no start
Customer Interest: 87610, stalling, no start, caused by water intrusion into tfi housing
With the SPOUT reconnected did you think to keep the light on the timing mark and verify whether or not it’s advancing when the engine is revved?
Those TFI ignition modules have been very prone to heat related failures and can cause all kinds of problems. Ford was even sued in a class action once over them and ponied up about 230 million dollars I think it was. They even sent me a letter stating that if I had any receipts for replacement modules or repairs (not an issue) they would reimburse me. So I sent a few copies in and 7 or 8 months later I received a check in the mail. The wheels of justice turn slowly…
You would not believe how hot those modules get even on a non-running cold engine. With the module off and the key on, the metal plate on the back will fry an egg in a matter of minutes. I discovered this the hard way…
With 20 degrees retarded timing I’m surprised it even started at all.
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It looks I will be pulling that timing cover. Any advice on the crank bolt? Can I use a breaker bar and bump starter? Anything else I should be aware of? I have the Haynes manual but it makes everything look so easy. Thanks
Crank bolt removal would be no problem if the engine didn’t rotate to thwart your efforts. But alas. Pro’s use impact wrenches for that job, which makes it easier. Works b/c the rapid acceleration of an impact wrench takes advantage of the rotational inertia of the engine, allowing the bolt to break free without the engine turning. Others here, if you don’t have a hefty impact wrench, have recommended to remove the starter motor and wedge some kind of stop between the flywheel teeth and the engine. I’ve never had the need to remove the crank bolt on my own 302 equipped truck, but I did that job on my Corolla a few times as part of timing belt jobs. Toyota provided a couple of holes in the crank pulley, so I made a tool out of piece of lumber with screws positioned at the correct distance to fit in those holes, then I just figured out a place to fit that piece of wood in between some sturdy looking car parts where it wouldn’t be able to move. Then I just used a breaker bar to remove the crank bolt. I’d be reluctant myself to use the starter, for fear of damaging something in the process, such as snapping off the head of the crank bolt. That wouldn’t be a fun thing.
To remove the crank bolt. take any cylinder and put the piston at the bottom of that cylinder.
Thru the spark plug hole, fill the cylinder with nylon rope.
Make sure you leave rope out the spark plug hole so it can be removed.
Now when crank bolt is removed, the piston will move up until the rope stops it without doing damage to the piston/valves.
Tester
I think that I’ll just bow out of this one. You’re going to rip the front of the engine apart to check for a worn timing chain when a previously mentioned inspection of the timing mark dancing can do the same thing. Best of luck.
I know the timing chain is worn beyond spec with the backwards rotation test that showed 9 degrees of slop
Your skepticism got to me so I checked the truck with the timing light again and the timing was advancing on acceleration but it was also jumping back and forth at idle. So worn timing chain with confidence? I hope so I ordered the parts today.
I contacted the former owner through their ex and she said he had replaced the distributor while they owned it. I’m in the process of getting additional info. Maybe the CMP sensor in the distributor failed before and has again? Is that a common occurrence?
No experience w/the distributor shaft position sensors used in Ford’s electronic ignition systems, but if it failed it could definitely cause this symptom. My own Ford truck just uses conventional points, no electronic sensor. But my Corolla has electronic ignition & uses a couple of hall-effect (electronic) distributor shaft position sensors. One idea, there’s probably a spec on your engine for the proper distance between the dist shaft position sensor and the thing that it senses. Try measuring that gap with a feeler gauge, maybe it has jiggled loose and the sensor gap is too wide. That could cause this symptom.
With electronic ignition systems that sometimes is what is supposed to happen. It jiggles around at idle on my Corolla. To get a steady timing light reading in order to set the base timing, I have to insert a jumper in a connector to set the computer in a special diagnostic mode. Without doing that, the timing light aimed at the harmonic balancer jumps around at idle.
When it jumps around on your truck, is it still more or less centered on where it should be?
I expect you already know this, but bringing in a good diagnostic shop to help might be money well spent. They’ll have a Ford scan tool and an o’scope, so they can visually display the timing and ignition waveforms, including the amplitude, ring down times, and the relation in time of one to another. For an hours diagnostic time they might well be able to tell you exactly what’s wrong, then you can choose to fix it yourself if you like.
It does sound like the timing chain is worn. Based on the abnormally low compression and worn chain I’d say either the engine has a million miles on it or the oil was not changed as often as it should have been.
A note about doing a chain job on this engine and this is in regard to the timing chain cover. Note that on the inner surface of the cover where it mates against the engine block there are 2 round coolant passages; one on each side.
Over time and especially with aged engine coolant the mating surface of the aluminum timing chain cover can rot out around the coolant ports.
Clean the cover thoroughly and if pitting or erosion is bad enough I would suggest a new cover. It’s enough of a problem that a local salvage yard of all places sells new covers at about 40 bucks each.
The distributor was replaced but many replacement distributors do not come with the TFI module installed. At this point I’d say do the timing chain job and go from there.
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Well I’m back at square one with a new timing chain installed and a poorly running truck. I called a ford guy who sold me an engine a while back and he offered to loan me some diagnostic equipment. So that’s my next step. The cooling ports looked great on the cover so I put it back on.
I finally rapped my head around the obd 1 code concept and rigged up a trouble light came out with a 95 fuel pump secondary circuit failure. Is this the in tank or the pressure pump. I still hear the relay click when I turn the ignition to the run position.
I realized when running I longer hear the extremely loud fuel pump humming away. I pulled the in tank plug and it is getting voltage also if I press my ear to the tank it is running. I then moved up and feel a vibration in the pressure pump and if I unplug it the engine stalls. If I unplug the in tank pump the engine continues to run although I think there is a reservoir near the pump? So it seems that one pump is running slower than it should? Any advice would be appreciated. I should mention this truck has dual tanks although the switch that chooses between them does not work.
Tested the fuel pressure and it started at 10 and very slowly crept up to 30 so I swapped out the pump and the power has returned. It won’t idie and runs the best with the timing advanced quite a bit. Maybe I’ll swap back to the original tfi module and see what happens
30 psi seems pretty low fuel pressure for a modern fuel injected engine. I forget how your 302 engine is configured? Carb? Throttle body injection? Port injection? What fuel pressure is spec’d?
It’s good to hear you’ve eliminated valve timing as a cause. That’s something to go on. I have a 302 in my older Ford truck, but it is a carb configuration. I’ve never had a backfire out the intake or out the tailpipe, never had a single backfire in over 40 years, so can’t offer any experienced advice. But it is pretty common to hear of folks spraying starter fluid into the intake and getting a backfire out the intake. So a very rich mixture seems like it could cause that symptom, leaking injectors pooling gasoline in the intake, something like that.
Thirty PSI of fuel pressure is about normal on these engines.
I don’t know what’s being overlooked here but this should not be difficult to sort out as the engine management and so on is pretty simple on these engines.
A clogged converter can cause poor running but it would be highly unusual to happen as quickly as it did. Maybe a vacuum gauge connected to an intake manifold nipple would show something.
Someone isn’t by chance putting E85 in the tank, are they?
OP might try this easy-to-do experiment. When the engine is idling hold a $1 bill in the exhaust stream. It should only either hang straight down or move away from the tailpipe, and never move in a direction angled toward the tailpipe. Does it ever move toward the tailpipe?
Well I had everything working as good as before this incident so I went out to get buy some craiglist crap and drove about 20 miles and the thing stopped running. I pulled the distributor and the drive gear is gone! I can’t see the the gear in the hole. So is it ok to just ignore that? Would the gear make its way down to the oil pan or is going to cause havoc in the engine. And is it pain to replace that gear? Rock has it for 35 or the whole distributor for 55.