Stumble/Power Loss at Higher RPM

So....in the continuing saga of disliking early fuel injection, I have an odd stumble/intermittent loss of power I'm working to track down. Truck has no issues when it is cold, but if it sits in the sun all day and temp is above 70* or so, it will act like it is losing fuel pressure at higher RPM and is worse under load vs cruising.  No real noticeable issues in the lower half of the RPM range.  I hooked up a fuel pressure gauge and confirmed pressure is good and stable, no issue there.  Because of the heat related symptoms it certainly seemed like it could be a TFI/stator issue, so I went ahead and threw those parts at it.....Didn't change anything.  I now have the breakout box installed so I can start checking signals on the fly when it happens.  Wish me luck.  Any thoughts you might have, I'd love to hear.

Stop changing parts that aren't due on the maintenance schedule.  Diagnose the symptoms.  Do you have a Haynes?



BTW
Your truck's EFI isn't substantially different from a '93 5.0L.  The ICM is in a different location, and its function is very slightly different; yours has 1 more fuel pump; and its fuel switching valve is a separate assembly...  But they're equally-reliable when properly maintained, and vastly superior to carbs.

I wonder if you are losing fuel pressure at higher RPM and temps.  If you have an iPhone and an Apple watch you could tape the phone where it can see the fuel pressure gauge, turn the camera on, and see it on the watch.  Or just start a video and watch it later.

I agree on swapping parts, but intermittent issues are a PITA and the TFI module and stator were fairly inexpensive.  This is also my daily driver so reliability is critical vs. getting stranded.  No Haynes, but do have the EVTM.  Again, biggest issue with the diagnostic side is being able to diagnose when it happens, which is while driving and under load in high RPMs.  That usually means getting onto the freeway and diagnosing while doing 75mph and driving.....  At this point, everything on the truck is 33 years old except for a few things, so not too concerned about replacing things here and there anyway.  

I guess it's always a possibility that fuel pressure is still an issue, I ran with a gauge on it and watched it while driving, rock solid.  I wouldn't think it would be intermittent either based on temperature.  I've had a few fuel pumps fail on other vehicles and none of them have ever had intermittent issues, they have all been good or bad and nothing in between.  

**I should also add that I don't see any issues in 1st or 2nd gear, even running into the higher RPMs.  This only seems to happen with the greater loads in 3rd and 4th.  Truck is a manual too and does not feel like clutch issues at all.

Of course, we had a cold front move in so not sure I'll be able to look at anything on the drive home in the next day or two, but will leave the breakout box installed.

FYI..it was 30* on the ride to work this morning and she ran great!

hit the Hall-Effect device in your dizzy with some high pressure air to remove any debri hanging around.

Sorry I missed your reply.  I just replaced the stator and ignition module so I don't think it's a debris issue.

It was finally warm enough for the truck to have the issue again.  I check the TPS and MAP signals while driving down the road and they were both rock steady during the stumble events.

As I was looking through the EVTM, it did dawn on me that I had broken the knock sensor awhile back, but never noticed any issues with the truck and since I can't find one, I left it be.  Now I'm wondering if it might be part of the issue.

Anyone have any idea where to get one?  All of the part numbers I can find for newer versions are all obsolete.

I wonder if that might do it.  But I sure don't know.

And, while I don't know the calibration code for your truck, all of the 302's seem to use:
E3AZ 12A699-A Sensor assy, (engine spark knock intensity)

The Motorcraft # is DY-304, and the part should be marked #E1AF 12A697-AA.

I found several hits when searching for that part number, including these:

Ebay: https://www.ebay.com/itm/Ford-Products-Knock-Sensor-SHIPS-FROM-USA-For-E3AZ-12A699-A-Replaces-KS13-/292036700381

Amazon: https://www.amazon.com/Products-Knock-SensorSHIPS-E3AZ-12A699-Replaces/dp/B07KNBL5KW

That's the first time I have seen that part # listed for sale in a long time.  I hope it has the right frequency.

I don't think the KS worked very well in the 85-86 302 EFI, in 87' they moved the KS to the back of the engine, where it stayed for many years.

KS97 vs KS13 ?

I have had a electric fuel pump fail when it got hot.
Now this was on a John Deere garden tractor with a 22 hp water cooled motor that had FI with the pump in tank.

I on cool days cutting the grass, 3 hours just riding to do grass, it was ok.
When the temp got warmer I would get about half done and the tractor would start to surging when under power but idled just fine. If you kept cutting it would just cut out.

forums kept pointing to bad spark but with my rude testing both coils would fire so that point to a fuel issue. The only test port on this tractor is at the TB, read after the fuel regulator so how do you know if pump or regulator? Remove the filter the is before the regulator, cut the quick release ends off filter to use on the fuel psi gauge, mount gauge to hood and go out cutting till it happens.
Yep half way thru the surging started and the gauge started jumping till it went to 0 and motor stopped.
Let it cool off about half hour and it would start and run till it heated up again.

That was a first for me too so I would check the fuel psi when this happens.
Good luck
Dave ----

Guess I'll have to borrow the parts store fuel pressure setup again.  Just looks a bit hokey driving around with it takes to the hood so I can see it.... Lol.... Don't really want to spend the money on a pressure gauge.

Gary - I did see those sensors, but I've had bag luck with Chinese knockoff sensors on other projects.  Just not sure I can trust them.  

I tried searching for the DY 304, but I get the air charger temp sensor popping up.

I don't know any more than what the master parts catalog tells me, but it is possible that DY-304 is the wrong #.

I have a spare original KS sent to me by Rembrant/Cory. If you would like to try it out, I will send it to you. Send me your address; vjsimone@hotmail.com.

Thanks Vinny!  I'll shoot you an email.

Nathan