Fuel injected ford 302 miss under light acceleration

ford

#1

Help!!! I’ve tried almost everything imaginable. Spark is very strong at plugs. One inch spark. Under Wide open throttle, engine pulls strong, No missfire. Replaced the TPS twice. No change. Replaced distributor. Any suggestions appreciated. Former Auto mechanics instructor baffled.


#2

Give us a little help here… What year? What car model? Transmission? Mileage? Modifications?


#3

Former Auto mechanics instructor baffled. I think we know why the word former was used.


#4

Try a mustang gt forum. They have more detailed input. Intake leak? Vacuum line?


#5

I’d like to see that one inch spark.

The Ford 302 has been built with every stage of technical innovation in fuel injection and ignition so it’s difficult to know where to start guessing.


#6

I think it isn’t a Mustang… his profile has Crown Victoria in it. So is this a Crown Vickie??


#7

Surely you still have some of the tools and equipment left over from your teaching days. I would like to see a screen capture of the labscope trace of the oxygen sensor at idle, WOT, and at part throttle during the misfire event. Fuel pressure at idle and WOT, and the BARO reading from scan data. This will get us in the right direction. I assume you’ve done basic ignition testing and compared firing kV and burn time?


#8

There hasn’t been a lot of info provided but I would run a compression test. One cylinder going down a bit can cause a miss on light acceleration that will disappear under WOT. Maybe a vacuum test would also be a good idea to precede any compression test.

I’ve seen corrosion on a coil wire end do the same thing. Assuming this is a TFI or Dura Spark model.

These older Fords are pretty simple so it should not be difficult to sort out.


#9

86 crown Vic. AOD. 10,000 on 18 month old rebuild. Completely stock. Tried all the suggested fixes. NO change in this “stutter”. WOT runs great.


#10

Any spark plug other than the factory recommended Motorcraft part gives questionable performance.

Ford’s original ignition rotor on that car had “cat whiskers” that were eventually found to be causing a great many driveability problems and phased out by Ford but after market suppliers continued to sell their stock using the old design.

The Intake Air Temperature sensor can be the cause and difficult to diagnose.

This book

https://books.google.com/books/about/Ford_EEC_IV_Systems_Manual_1983_1992.html?id=AUoTAAAACAAJ

is the most helpful that I have found in diagnosing EEC IV Fords. A Breakout box is very helpfull.


#11

Yes, Rear wheel drive, full size


#12

I’m guessing you have some slightly clogged fuel injectors. Try an injector cleaning treatment, see if that offers some help. This is especially true if you notice the engine seems to not work flawlessly when slowing down and turn corners in the 15 mph range in neighborhood driving. Any signs of stumbling, surging when doing that would be a clue you may have slightly clogged injectors.


#13

Maybe a compression test would verify whether or not it’s related to a mechanical fault.

The fact that it was rebuilt 18 monts ago does not necessarily mean that everything is in order.


#14

Are you sure this “stutter” is engine related? AOD torque converters have a tendency to develop a “shudder” at lower rpms, part-throttle, light acceleration.

But please provide us with a little info to help us in the right direction. What’s the firing kV through the ignition system under load? Any fault codes? 86 will not give us any live data, but sensor outputs on a graphing meter will help us. Can we see O2 sensor please? MAP frequency with KOEO and at idle? It’s easy to test fuel pressure on these, what’s the pressure?


#15

I wonder how many shops ever tested MAP frequency @asemaster?


#16

Not enough. In the past every mechanic had a “known good” Ford MAP sensor in his toolbox. I wonder where they came from?


#17

I recall that Ford factory shop manuals always fell back on the tactic “install a known good part and test” @asemaster. Those early EEC Fords could be a nightmare even with a breakout box and a sack full of meters and test lights. Can you recall where your “known good” MAP sensor came from? I sure don’t. But there are Ford, Mopar and GM sensors in my ingition box tool box . And I had a Fluke meter and a digital lab scope to test Hertz but trying a good part was just too quick and easy. And the Ford BARO sensor was such a ridiculous, useless piece. Maybe driving non stop from Death Valley to Pikes Peak would make one worthwhile. I’m surprised that so many mid 80s Fords are still daily drivers.