I had a problem on my 86 EFI 302. The canister filter in the tank selector was bad. Not the high pressure filter on the frame, the one between the high and low pressure pumps back by the front tank. The bottom spins off and there's a filter in there. I don't know if they still use a filter in there on your truck.

But that'll show up if you check FP with a gauge while road testing.

 

Low engine vacuum can also show catalytic converter piugging. Easiest test is to put the truck next to another one with the same engine but stock exhaust - if your exhaust pressure at the tailpipe is a lot lower, then your cat is plugged.

Thing is, with that many miles you might as well go ahead and replace the cats. If they haven't failed by now, they will soon.

Check fuel pressure first, though, as that's a bit easier and less cumbersome.

 

If you have your foot to the floor and the engine won't rev any higher under load, its usually due to a clogged cat. I'd also check fuel pressure, compression, and the ignition system. Make sure the plugs are gapped properly, the cap and rotor aren't worn, and the coil hasn't given up the ghost. Timing will play a huge role here too.

Also check for seized wheel cylinders, dragging calipers, or other mechanical problems. Every little bit counts.

Warm the truck to operating temperature, then hold at 2500 for 3 minutes. Have someone observe to see if the convertor and piping before it begin to change color. Also, an infrared temp gun is useful for this, if the temperatures are crazy high then you know you have a melted down cat.

 

EEC-IV was one of the most capable EFI systems of its time, especially the MAF Mustang systems....but that's beside the point.

But yes, you'll want to check the fuel pressure for sure. Full filters are another thing as well. A partially plugged filter will still show good fuel pressure at idle/low load, but pressure will tank as soon as you make the engine do something.

At 197k, the cats are getting on in age, and there is a possibility that they are plugged.

 

delete... ..

 

But it's a simple system and still works pretty well even when there are lots of other things wrong.

Not trying to dis the EEC-IV. Most of the cars/trucks I've owned have been EEC-IV.

Anyway, yes, this truck should be able to pull 4500 easy.

 

When in nuetral and you floor it. Does it rev quick or is it slow responding and a gradual increase of RPMs?


It will rev quickly but the truck will not "take off" quickly from flooring it. I floor it frequently because of the horrible acceleration. Also will not rev when on hills. For example in a 55mph zone on a hill I am in 4th gear 2500 rpm foot to the floor and it will not rev higher.

 

Timing is good. I as well as my mechanic checked it and it showed as it should be. (I think 10 degrees or something like that)

 

Where are you located, one of the members here may be able to help you.
302s generally seem lacking in torque, but I'm with the rest of the choir and saying check the cat. A stock 302 should just be starting to pull at 2k, and should pull hard through 5k, at least all mine did. No where near as hard as my 7.3 does but it should be noticeable acceleration.

Check the back pressure.
Check the compression.
Check the vacuum.
Check the fuel pressure.
And post results.

 

What happens if you drop down a gear?

 

Sounds like you've solved your own mystery. This will probably spark debate from people talking about valves, etc. But it's a simple test. Even more basic than checking vacuums and pressures. Unbolt the exhaust after the header. If it's clogged so badly you're unsafe driving you can probably leave it hanging in place. Just having that gap at the flange at the back of the header should show you a different truck. Sounds like they had some issues that were ignored and ended up replacing the engine. Cat probably looks like toxic sludge inside. Really, that's what it is anyway.

And at $61, I'd replace it anyway. I come from cars where the muffler is 3-500. One car I gutted because replacement cats were 1600. You say 'it's only a 5.0', but remember that these trucks can handle themselves with a 300. A 5.0 should at leave have throttle response.

 

I will be replacing my EGR because it is not seating correctly and is faulty in that it will not hold vacuum pressure. So I have a vac leak there. Crappy Advance Auto China Part. But even with the old egr, the truck was even slower.

 

Will rev higher but will not go above a certain rpm, usually around 2500. But if I am on flat ground. The truck drives normal. I can rev the truck high but my acceleration really stops and forces me to change gears before 3000 rpm. After that, its really useless reving

 

And at $61, I'd replace it anyway.



Where can I get a $61 cat. And I don't weld. Can most shops weld in one you bring it?

 

Ok, so timing checks out. Did you get a chance to check fuel pressure?

As for the EGR, it's a good idea to fix it if it's not working but since the truck was slow before it's not likely the cause.

As for the torque of a 5.0, it's all relative. No it doesn't pull like a 7.3 but I've ruined a few rear tires in my youth doing burnouts in my Bronco...

On a flat road, you should easily be able to bury that speedo...

Edit: Talk to a muffler shop about welding in a new cat. The alternative is a whole new Y pipe with cat. Catco makes one that's about $250. Talk to the muffler shop and make your decision