Poor engine performance when hot

[skx762]

I’m trying to figure out an issue I have with the v8 in my Ranger.

Short version: I bought a Ranger with a v8 conversion already done, more out of pity and with the hopes I could fix what the original owner did to it and make things right in the world.

It’s a ’86 Ranger with a ’79 Cougar 302 v8 and c4 transmission.

The engine was knocking when I got it so I bought another engine for it but before I swap the carb/distributor/fuel pump and front engine pieces I would like to try and cure an issue it has.

It runs like crap after the thermostat opens, the rpm’s drop about 100 rpms and it also has an inconsistent miss through out all ranges (may be two separate issues).

The carb is like new, rebuilt 2 bbl Ford. I don’t see anywhere that it could be screwed up. The electric choke opens fine and stays open. It doesn’t hesitate when I accelerate or anything unusual.

The distributor is a GM HEI and when I tore it apart all the pieces looked new (I thought it might be a bad coil that didn’t want to work when it got hot). The timing seems ok and consistent.

The plugs are white to light gray and the PVC valve rattles when I shake it. Although it has several unused vacuum hose and EGR connections I can’t seem to find any that aren’t sealed.

I don’t want to transfer any of these issues over to the new engine but like wise I don’t want to buy a new distributor/intake manifold/carb/fuel pump either.

Any other ideas?

 

[baddad457]

Check to see that the head gaskets are on correctly. On most gaskets, there's a tab that pokes out covering the lower front corner of the block where the head doesn't overlap the deck. If that tab isn't there, the gasket is on backwards. Aside from that, I'd suspect that timing is the culprit, although I've never had any luck with Autolite 2 bbl carbs either. I would completely disconnect the choke to completely eliminate that as a cause, chokes have a wave of opening when you least expect them to.

 

[originalnitro]

It's to late to diagnose the miss in the 79 302. You said it had a knock,that alone could feel like a miss not to mention the 79 302 was a low compression, low performance engine.

I would clean and inspect the parts going on the new engine. If all looks good assemble it.

 

[skx762]

The knock is only noticeable above 2500 rpms but gets worse when you let off the gas / disappears under acceleration. The miss on the other hand is very irregular, not in “rhythm” but I agree and will start tear down of the old engine hopefully this week. Still awaiting some parts from Summit but nothing that will stop me from kicking the “rebuild” off.

The guy that sold me the engine has most of a serpentine belt set up on it that I will be taking off to install the regular v-belt system. I don’t want to buy the parts he said were necessary to eliminate the smog and A/C.

I think I will stick with the 2-barrel manifold/carb set up GM ignition and the fuel pump that is on the Cougar engine. I am going to be very critical of any dubious engineering and make sure that all the vacuum/fuel/electrical lines are run correctly.

I may do an autopsy on the Cougar engine to confirm it was a rod bearing and I am pondering a rebuild for it if it’s salvageable. Everything I read though tells me my money and time would be better invested in another roller motor though.

The plan was to have a spare engine and transmission in the garage for my Ranger. Something I could slowly rebuild through this upcoming winter. We will see.

I would have liked to cleared up that engine miss.