Hey guys. I'm moving over here to get more fuel system minded opinions. You can read the whole saga in the FE engine forum titled "Smoking 352". I will give a brief recap here.

The vehicle is a 1965 F100 with an FE 352, probably 30,000 miles on a great rebuild, .030 over, nice torquey cam, ported and polished C8AE heads, Edelbrock performer intake, Holley 4160 600 CFM Frankencarb, headers Flowmaster 40's, T19 trans, and 3.70 final drive.

Had the heads off for head gaskets and resurface. Ran great afterwards but was sucking oil from the valley on decel. Pulled intake and resealed it. The job went smoothly but I soon developed what I now believe to be a lean misfire at freeway cruising speed. 75-80, 3200-3500 RPM, throttle just past cracked open. It develops after maybe ten minutes of driving. Before that, I can take it through the gears full throttle, into the secondaries up over a hundred without a problem. No hesitation, no miss, no issues. But when I just get settled in at 75-80 after a while, ten miles or so, it will miss. You can feel it and hear a chuffing noise. If I don't back out of the throttle it will continue and the truck will be jerking and bucking with the misses. Can't acce4leraste through it, can only back off the throttle. If I pull over and open the hood and scratch my head for a minute it will be fine to merge into traffic at full throttle and another couple miles after that. Happens every time I drive far enough.

So far I have, in no particular order, replaced; fuel filter, cap and rotor, coil, spark plugs, fuel filter, rebuilt carburetor (It was clean inside) opened carb and increased main jets, idle bleeds, both primary and secondary by .006 at the instruction of a reputable carb guy. I have checked fuel pressure. It was high, like nine #'s, installed a regulator and tried different pressures. I have filled the tank a couple of times at three different stations, I have adjusted the timing. I'm at my wit's end and need help. Anyone got any ideas?
Thanks for reading, and any suggestions, Dan. TK65

 

There are 2 things that come to my mind....... the diaphrams in the fuel pumps are subject to pinholes because of all the "blended fuels today"... they start off very tiny enough to where they only slightly impact at high rpms and as time goes on and they become larger, the issues are now seen a much lower rpm's (progressively), yet, they will still pass the psi/volume test. IMHO, I would swap it out (even if it's new it could be defective) The 2nd thing is a vacuume leak.... very tiny caused by heat....time for a smoke test....

but I'm betting on the fuel pump!

Been there, seen that, done it before!

 

You may be on to something and it wont bother me to replace it. It has been clacking like a bad lifter since I got the truck, and the PSI is too high. Just need to find a quality pump now. Thanks!

 

I ordered the Carter M6509 street fuel pump. Made in America, high volume, carb pressure. An interesting development, stopped on the freeway to read a plug during failure mode and found that two plugs had worked loose and were missing the center electrode. Replaced them and have not had a miss since.

 

How did the rest of the plugs look?
Rich, lean, or just right? BTW it is hard to read plugs with today's fuel.


What I would worry about is why were the plugs missing the center electrode?
Were they running lean to burn it out?
You found the cause of the misfire but now to find the caused of the bad plugs?
Dave ----

 

Dave, sorry I took so long to reply. Honestly, I didn't look at the rest of the plugs, just torqued them down so they stay planted.
As for the missing electrode I attribute that to the plugs working loose. A loose plug would necessarily result in a lean cylinder I would think, with air leaking in at the plug and therefore not pulling as much of the air/fuel charge in. My theory might be full of holes too. At least my pistons aren't!
Since I last posted I got myself an A/F/R gauge setup and found that I was running super-rich after following the advice of my carburetor guru. I have been working my way down through jet sizes and am at 66's in the primary, which is I believe about what bI started at.
Thanks! Dan, TK65