cdg

Ok first, I think I can offer a junkyard distributor unit minus the vacuum advance to anybody who might need it for the costs of shipping. It was a pull from a celica but appears to be identical to my 1980 20r pickup. Sometimes they rust up inside in spite of the vacuum unit being OK...

Moving on, my 1980 pickup 20R with approx 160,000 miles is still having problems.

When the truck is warmed up, you can drive it very gently and it will run pretty good. Drive it hard and it will stop idling and really smoke black soot. It will idle below 500 RPM and gradually get lower and rouger till it dies (almost as if it was running on only 2 or 3 cylinders). Let it sit for a bit, and you can restart it, at which point the crappy idle will gradually straighten out and return to its proper smooth setting.

I plugged off the EGR valve (and physically blocked it with some steel plate and high temp gasket material). I replaced the notorious AAP diaphragm (it was leaking). I tried unhooking and rehooking various smog devices on the truck.

Another piece to the puzzle was recently uncovered as the truck lacks what the manuals call a Fast Idle Cam Breaker (FICB). The fast idle never worked, even when it was cold out. I am not sure if the FICB has something to do with the problem or not, but it is definitely missing from the vacuum circuits.

The truck always runs a little on the rich side and smokes a little black under heavy acceleration (and seems to be a little down in the power department). I am hoping most of this will go away with the vacuum advance. However I do not think that the new vacuum advance will fix the intermittent problem described above, because when the truck was running like crap, I have put a timing light on it and verified that the base timing is always in adjustment.


I used an inline spark checker to make sure the distributor wasn't missing a cylinder itermittently - it wasn't. It does have a new distributor cap, rotor, wires, and recent spark plugs too.

The Throttle Positioner system it uses is supposed to be hooked into the speedometer somehow, but the speedo is still dead on this truck.. - probably a broken cable but I have not diagnosed it yet.

The spark plugs show up as universally black, carbon fouled from running rich.

I am not sure now if it is an internal carb issue or a sticking valve. There is no sign that the timing chain is old, worn, or skipping teeth on the camshaft sprocket.


Your thoughts are appreciated. The truck is 6 years older than I am and some of these 80s emissions control issues are really obscure by any standards. I am hoping to run the truck with fewer smog controls than originally used.

cdg

A quick update, I installed the new vacuum advance. They were slightly different in appearance and had different numbers from Nippon Denso but the new one fit and appears to work fine (can't comment if this will give a more/less aggressive advance than the stock one).

Anyway as I first believed, the truck runs much better in general and you can feel all 90 horses thundering under the hood now.

I warmed it up and then ran it around the block and even ran it hard through the gears once or twice but couldn't get it to misbehave yet. I doubt the intermittent problem is fixed but 20 bucks says it will fix most of the lousy fuel econemy and black smoking off idle.

cdg

So I got the truck to misbehave again, this time, based on some forum archive research I grounded the idle cut solenoid. This had a twofold effect. It almost immediately blew the main engine fuse (forgot that the solenoid is hot on this one). It also almost immediately made the truck straighten out and idle really nice for a while (but it refused to restart until I replaced the engine fuse) . So what I will be trying is first just disconnecting the idle cut solenoid. Then I will be tracing the wires to make sure they are correct (looks like some frayed insulation might be present). Then I would say the truck will need a new solenoid. Not 100% if the problem will be fixed now or not but we will see. I've heard of some people just putting an interrupter switch in the fuel cut solenoid so I might try that too.