Is this the famed "ignition module" problem? I have a Duraspark ignition, looks factory. Same one thats in my '85.

1981 Ranger/Lariat. Has had a 460 swapped in at somepoint in it's life, with C9VE heads and a 600cfm Holley w/ manual choke.

Also has a C6, and a GearVendors overdrive


Problem-
Truck drives fine empty. Very peppy. Put a full load in it, and it'll drive great a while, then suddenly it just "bogs down" and RPMs fall. If I let my foot off at this point, I can find a spot where I can continue to drive, but I can't push it farther than that.

I thought I fixed it with a new cap/rotor/wires/plugs and it ran great. Then I put the trailer on it, it ran great untill I hit a mild grade on the freeway. Then I could only maintain 30-35. And it isn't incline related I don't think, last time this happened, it occured on flat stretches too, only I could go a 45-50 instead of 35tops.

Plus, as I mentioned, it'll pull real good up a hill, then suddenly it'll bog. It's certainly not speed based, but more of "how far I can push it" because as I mentioned, the more load the lower the top speed.

I'll go out and grab the HEI disty of my '85 if that's the problem. But I don't want to if it isn't.

Oh, the truck had 2 modules bolted to the fender, plus one under the seat. And I pulled another from the '84 I just bought. No change, but perhaps they are all bad? Does the hall-effect setup go bad?

Does this sound ignition related at all? It still gets plenty of fuel!


 

Sounds more like a carb related issue, the typical bad ignition module will just suddenly shut the engine down.

 

Is it the stock Holley with vent tubes on the bowls? The stock 460 Holley's (a 4180) say the are rated at 600, but I believe Holley under estimates their emissions carbs, when you get an aftermarket one they aren't as peppy as the originals. I put a 600 Edelbrock on my Motorhome thinking wit would be up to the task, it was not.

Or you could just need a fuel filter because of reduced flow (or a carb rebuild).

 

I agree, it sounds like a fuel problem.
Possibilities (in no special order):

1. Dirty fuel filter
2. Weak/worn fuel pump
3. Crap in tank plugging fuel pickup screen
4. Crap/rust in fuel lines restricting flow

 

Sounds like fuel starvation, since it will keep running only at a reduced rate. Any time you demand a lot of fuel during a hard pull, it's giving out.

As was said, check the fuel filters. Since this engine was swapped in, check for any weird fuel line routing that could be too close to a custom exhaust pipe. If you have a lot of rubber line in the fuel system, see if it's collapsing or is routed too close to a heat source. People love to run a rubber line the whole way for the fuel system.

 

I had my head so stuck on the ignition, I don't know why. I have a list on my wall of reasons "Engine won't reach opperating RPM" that I never even looked at

Well guys, heres what I've got to update you on

First, I noticed while removing a mile of non-factor wiring that the PO had added (amongst other things) a inline electric fuel pump. I had scratched my head at that, wondering why it was there.

So you got me thinking, and I hooked it up. I only used it briefly, enough to hit 30 on my street (where I bogged down not 1 hour prior) and it worked fine. So I turned it off and tried again, and behold! It seemed to work with the e-pump off!

2nd thing I noticed-

Fuel is inline, between mechanical pump and carb. All the fuel drains out of it when it's off, and flow looks anemic when it's running. The fuel pump is BURIED under the PS and AC, so I see why the PO added the e-pump.

I'm thinking I'll replace the mechanical pump and all the hosing from the crossmember to the carb, and see how it goes.

Thanks guys for getting my head pointed in the right direction, I'll report back!

 

"Fuel is inline, between mechanical pump and carb. All the fuel drains out of it when it's off, and flow looks anemic when it's running."

This is your problem. The mechanical fuel pump has two check valves. One lets fuel into the inlet, but not back out again. The other lets fuel out of the outlet, but not back in again.

I had the same problem with my '82. My tank had rust plus 28 years of general crap in it. I used to have to replace my fuel filters every 1K miles (and I am talking about larger aftermarket filters, not the tiny little factory filter). This crud and rust also takes its toll on the check valves in the pump. Mine got to the point where it hardly pumped anything.

I would suggest that you clean the tank or replace it. Inspect the pickup tube in the tank - mine had a small rust hole about half-way up. Install a good fuel filter between the tank and the electric fuel pump (if you are going to use the electric pump).

If you just replace the fuel pump, it may run OK for a while, but sooner or later the crap will eat up the check valves and you will be right back where you are now. My fuel pump lasted about 5k miles before I replaced my tank.

 

I'll pull the tanks and clean them, that was actually in my plans (as well as replacing the hoses)

I think the e-pump will work for now just to help me drive, but I'll take it out after getting it all fixed.