Re:Re:Re:Re:Re:Re:Re:Re:Re:99 Explorer violent intermittent shaking

Does this work?
Ah, it does. Long post then "session has expired" and it's gone.

TC 10-15 degrees, fine.
Compression 157-172, what I expected with 190K on the clock and a fuel/vacuum issue.

Plugs perfect and exactly the same.

Symptoms changing a bit. Lead in to bucking and jerking now gives surging.

Next couple of days, I'll pull upper plenum, check each injector plug for firing, make sure nothing was pinched between upper and lower parts.

Here is what has transpired:

After compression test, the vehicle has run perfectly. 3+ days now. Cool and damp days, warm and dry days.

Since I have experience with garbage in cylinders or valves and a compression test with all plugs out that expelled garbage out plug holes, I suspect that is what occurred, garbage from shop work when they changed the injector. Last one I did that ejected garbage was a V-12 Lincoln. Seriously.

I went ahead and started doing service work I have put off while this issue was prevalent, oil and filter yesterday.

Need to drain and flush Power Steering next week, but car runs good now.

I've actually experienced something similar to some of your symptoms. The surging and not going anywhere issue in particular. Same thing with the fuel trim numbers not being suspect. Both hovered 0% and gave no indication there was an issue.

What it ended up being was the MAF. Your engines MAF may be different but I suspect its the same or very similar. Mine was a 2001 Ford taurus with the 3.0 OHV vulcan engine. The MAF essentially controls the duty cycle of the fuel injectors. I was lucky enough to have two used MAF sensors to swap and thats what helped me find the problem. With one of them, the car wouldn't even idle and you would see black smoke out of the exhaust. Basically the MAF told the computer I was at WOT and it was pulsing the injectors on max duty cycle.

The other MAF sensor is what reminds me of your condition. The car would run fine, shift through the gears on light throttle, but it felt sort of bogged down either way. However, when I would go WOT the rpms would just surge and the car would not move. It would slowly start gaining speed till it slammed into its gear change.

The nice things about Ford is that the computer has substitute data if the MAF went bad, and the car will drive. Try unplugging the MAF and go drive it around. See if your issue improves. For me and the car I was dealing with, it would shift through all gears harsh, but the obvious change in symptom condemned the MAF as far as I was concerned. I of course checked all circuit integrity first. Had good 5V reference, power side and grounds were good. I replaced the MAF and everything was fixed. Other symptoms this caused me was rough idle. You could hear it surge at bit at idle, and the idle would hover higher than normal to where I would have to noticeably press harder on the brake at a stop to keep the car from moving because it idled around 1200 rpm. All symptoms went away with the MAF replacement.

It is worth noting that the MAF I was dealing with was the six wire kind. So it has the intake air temp sensor integrated into the MAF sensor. Yours may be the three wire one indicating that the IAT is separate from the MAF. In that case try to test both. I will say though that I do not have a nice automotive scope. But with a bluetooth OBDII scanner and a good phone app, I was able to see live data fine. No weird readings on the MAF rate, no weird spikes in the voltage on the signal wire, and the MAF rate changed linearly with respect to throttle. It was a tough one to figure out. Best I can conclude as to why my data looked good was that the MAF rate changed too slowly. So it acted "lazy". That's the best explanation I have.

Don't rule out vacuum leaks you might not have found either. On this car I had some that would be very hard to find without a smoke machine. I made a diy smoke machine based on a guys build on youtube for around 20 bucks. It's not perfect but its been invaluable to diagnosing these problems. May want to look into making one. I used the design by the youtuber "martinbuilt" only I put my air hose fittings on the top of the cap and I bought my tiki torch wick and nichrome wire off amazon (he used stainless steel welding wire instead of nichrome wire which is the type of wire used in toasters and would be appropriate for this build). Just wrap as much wire around the wick as tightly as you can without having it touch each loop and you should be fine.

Hope it helps.