Well I've been lurking on this forum for a while to gain some insight. It's getting to be time for specific questions. I know there are experienced people here that can help me.
I have a `91 F-250 4x2, 460, AODE which I use for hauling/towing but not as a daily driver(certainly not with 87 octane at $3.00 gal.!).
This is the part where the old pro's roll their eyes- the smog pump is gone but the EGR remains. The cats are gone and it has stock manifolds going to a 3" two into one pipe.
I've fiddled with the timing and running 89 octane to keep the pinging to a minimum but, as you guys know, these things are not enough to eliminate the pinging.
I'm sure someone will suggest that I just get a pump and hook it back up. If that seems like the cheapest easiest way to you guys I'll have a look at that.
However, I'm trying to do this as cheaply as possible as it's a secondary vehicle and getting up there in years (like it's owner).
I'm looking for advice on changing out the distributor, headers, computer mods etc. (via junk yards) for improving it's pulling capability.
Sorry for the length of this post.

Thanks,
SKE

 

I doubt that not having a smog pump is causing the engine to ping. Have you checked for trouble codes in the computer?

 

start by replacing plugs, checking wires, cap/rotor, air filter.

it is probably not the smog pump.

codes?

 

This is exactly the same problem I had with my '89.. no smog pump and it runs so lean it pings under even moderate load. Put the smog pump back on and all is fine. Everybody here told me the pump makes no difference.. but it did on my '89.. there were no codes at all and no other problems with the engine before or after.

Long tube headers will be the best upgrade for that motor. Changing out the computer or distributor for other factory units will have no affect on the engine performance.

 

Nothing about the smog pump has anything to do with the air/fuel mixture in the engine, so I'm not sure why it made such a big difference. It may be worth a try, but I can't see how it would matter.

 

Yeah... I know we have been through all this before.. but it made a pretty dramatic difference with my truck. In my case all associated air injection plumbing was intact and working properly, with no leaks, and as soon as the system went closed loop it would ping under any load at all. I removed the air pump because one of the thermactor valves died and I didn't think the system was necessary for good engine function.
For the sake of argument, I can see how injecting air upstream of the O2 sensor would make a difference. This would tend to lean out the mixture and the computer would try to compensate by richening the mixture. Looking at it the other way, if this extra air was missing the computer would think it's running rich and then lean out the mix... which leads to detonation.
This assumes that this injected air is factored into the computer mapping somehow, which I can't confirm, and of course the factory mapping changes with each release so it's possible this may only affect earlier years.

 

It's my understanding that the introduction of semi burnt gases into the combustion process has a huge effect on the needs of the engine. I've read posts on this and in the 460 section about recurving the distributor and changing the cam position just to name two. These changes I would consider if convinced that they would eliminate the problem. I'm not really interested in changing heads or the cam shaft if it's avoidable.
Long tube headers make sense to me and I would consider that change, especially if I could find some used in good condition.

When time permits I will scan the engine and check the codes. The tune-up parts are about 1.5 years old with approx. 10,000 miles on them.

Thanks for the input guys and keep it coming!
SKE

 

The smog pump and EGR aren't the same thing. EGR does have a big effect on the fuel and spark requirements of the engine. The smog pump should be entirely after combustion.

 

I'd buy that. It makes sense to me - but is the O2 sensor's band wide enough to alter the fuel/air ratio enough to cause pinging?

 

To truly know if that would cause a problem we'd need to know the strategy of the computer, which would tell us when it routes the injected air to the ports upstream of the O2 sensors.