Ok so a little background of what I have and did recently to my truck. Its a 1980 F100 with the 5.0L 302, 4 speed manual with 4wheel drive and 2bbl carburetor. I recently put on a catalytic converter into the exhaust system since CO now has strict emissions requirements. I decided to go big on it so I ran both 2in pipes from manifolds down into a single 3in then the cat then straight back. Every since I did this the truck will not get going in gear but idles fine in neutral. Its like it has no power/torque. I did jack the rear end up so the tires were off the ground and it seemed to respond normally with power that way but not when the engine is under load, with tires on the ground. When the truck was up in the air I could spin the rear tires freely so I know its not a stuck E-brake.

Also I did replace the distributor cap and rotor but did not touch carb settings or plugs or fuel lines. Just popped off the old cap and put on a MSD cap and matching rotor from Summit. The reason I replaced it was because the old rotor in the old cap broke when I tried starting the truck right after exhaust was done. The contact on the rotor that connects the coil to the spark plug wires was snapped off. Simple fix replacing the cap and rotor but now I have this no power issue.

First thing I really don't think the exhaust has anything to do with the power issue, but I am not ruling that out yet.
Any advice or tips would be greatly appreciated, thanks.

 

This is a new CAT right, not a used (maybe clogged) part?

 

If the cat is new, Sounds like timing.

If the rotor cap broke,etc. Could have jumped time.

Distributor, Timing chain,etcl

I would check the timing first and go from there.

 

yea, the rotor "breaking" is mighty suspicious to me. Something bound up? Also, check your firing order. 1-5-4-2-6-3-7-8 for the non-HO 302.

Find TDC on the compression stroke, and make sure the rotor end is pointing right at the #1 post on the cap. Then check your firing order going counter-clockwise.

 

It is a new cat along with all the exhaust piping. i originally thought it was the 15426378 order bc that's what chiltons says, ran very bad and gave me popping sounds out carb. i switched over to 13726548 firing order and idles smooth as silk now and revs perfect. the dang no power thing under load is really stumping me. i will check timing once i get my hands on a timing light. thanks

 

Here is some sound advice my father gave me years ago...If it ran before you touched it and it doesn't run now, its something YOU did!

That said...what did you do to the pickup? Did you change the intake, pull the distributor, change wires, anything else but just the exhaust? Why would the rotor break if it ran before you changed the exhaust and you didn't touch it?

For that matter...have you ever had it running or was it your daily driver?

The no power issue...could easily be the firing order (15426378 should be right). The popping could be bad timing (as in the distributor moved when you did the cap). On blocks it only takes a few HP to make the tires spin...no corollary to running down the road.

We need the full story to help you.

Kenny

 

Original engine in the truck? Replacement HO cam with 351W firing order?

 

This is the order of events from start to finish that I did.

First the truck ran perfect before I started anything at all. It is just a weekend truck not a daily driver, but the engine is orginal as is the carb.

1. Cut off exhaust and installed new single 3" with a CAT.
2. Fired up engine and it would not run for anything or even stay idling.
3. Cut off 3" exhaust, same problem.
4. Pulled plug wires and plugs, found several with oil on contacts, then popped off distributor and found the rotor contact had broken off (the strip of metal that lays across the top of the rotor).
5. Put new cap and rotor on and installed plugs and wires with 15426378.
6. would not idle after that and gave small popping sounds out of carb.
7. Switched the firing order to 13726548, and will now idle perfect, rev nice and strong, and Also put 3" exhaust back on.
8. Took it out of garage for a quick test drive and here we are with the issue at hand.

I am stumped, but I will be checking timing soon once I get a timing light. I was also wondering if it could be the vacuum advance on the distributor that may not be working properly? Is there a way to test to see if that is functioning without just swapping in a new one?

 

It is the original engine but not sure what the original owner did to the cam. The guy I bought it from was the original owner, he bought it new in 1980 and now I have it.

 

Is the exhaust bolted after the manifold, or welded? Un bolt it and see if you can run well with the cat-back disconnected.


Sounds more likely that timing is FUBAR.

How does it turn over? Faster or slower than it did? Does it crank at an even speed or speed and slow?

 

The exhaust is botled from manifolds to the Y but then fully welded from Y back to muffler. It does crank a bit faster now, but does not fluctuate while cranking, it stays at an even speed while cranking, although it is a faster crank than it was originally.

 

I agree that you should look to the last thing that was done to find the problem, but in this case there were two things done: The exhaust and the dizzy work. So, to think through that...

I once was silly enough to ride motorcycles and had a Honda 750 with a 4-into-1 exhaust. I didn't like the noise so packed the muffler with stainless steel wool. Sure quieted things down and it seemed to run fine - until I was at speed and trying to pull a hill. It didn't hurt the low RPM power. In fact, it didn't hurt the high RPM power until you were in top gear and running pretty hard. So, unless your cat is totally and completely plugged I can't imagine the exhaust killing the power the way you say it has been killed. And, if it is plugged you wouldn't hear much, if any, exhaust out the tailpipe.

So, I'm leaning to whatever caused the rotor to break. And the only thing I can think would do that would be for the lower bearing to have gone bad in the dizzy, allowing the shaft to wobble and the rotor touch one of the terminals. But, I've never seen the lower bearing get that bad. Anyway, if the dizzy isn't nailed down pretty well that could have moved it and set the timing back significantly. And that would cut the power dramatically.

Forgot to say, if the bearing is bad the timing will be all over the map and that engine isn't going to run well at all.

 

It could also be the hold down Gary. From what I've seen at yards, the v8's share a similar distributor hold down to the 300's?

I had mine hand tight and was moving the truck this week. Stalling, with a stiff new dizzy in, was enough to move the distributor out of time.

Pull the entire distributor out to check the gear and shaft on it. Set the engine to TDC on the front cylinder, pass side, and go back 8deg.

Also, if you've been running far enough out of time to have no power, pull the plugs and make sure they aren't dirty.

 

That's kinda what i was saying about it moving. BUT, something serious had to happen to cause the rotor to break. I think that is our smoking gun.

 

cam was changed.
Is the distributor drive gear compatible with the new one?
Is the cam retainer tight and in place?