79 E350 fire rescue truck (ambulance) 460 C6, dually, low gears (? 4.88 or so) 80K miles. No cat or smog pump
Engine only tolerates about 30* total advance, 10 static +20 mechanical, still pings slightly at higher revs, >3000 i think (with vac advance disconnected). Really likes about 12* static at low RPM.
Ive rebuilt carb (4180), increased jet sizes from 61 to 70, replaced EGR, welded mechanical advance in dist to decrease from 32 to approx 20*. Also fresh plugs, wires, dist cap, fuel pump. Burns minimal oil, runs smoothly and makes decent power. Gas milage a little on the low side (5-6). I am using 87 octane fuel.
I know it is in fact pinging because when I retard it enough, it stops (but feels like a 6 banger). I do have a small leak from the right side manifold (from running it so retarded and heating it up).
Also the timing mark is stable when checked with the timing light.
I can weld up the distributor reluctor ( i think thats what they call it) to decrease mechanical advance further. RIght now the gap is .360" I think if I limited the total advance to 26 it would be Ok.
Is it normal for a heavy low geared truck to tolerate so little advance?

 

#1 Ditch the timing set and go with a straight up set. With 80K on the clock you'll soon need to do it anyway. No time like the present.

#2 Do an upper cylinder flush to get rid of carbon and go one step colder on the plugs.

#3 Switch to 89 octane.

I bet your preignition problems are mostly, if not all, cured. Plus, you'll make noticeably more power and get noticeably better economy.

30 deg total timing isn't a whole heck of a lot. I would expect mild preignition from a stocker with this much timing, but not so much you couldn't cure the problem by backing off the timing a degree or two. I suspect you have a problem with a lot of crap built up in the cylinder that's causing hot spots, or possibly a hot tip on a plug. The retarded timing set doesn't help.

Brad

 

Hi there, I run a 460 and had all sorts of problems with pinging, first check which heads are on the engine, mine are C9's comp. ratio 10.5 which does not help to stop pinging different heads have different CR's, I changed the after market Crane ignition system to an HEI Distributor, one wire only, changed plugs one step colder(6) and I am running on 98 octane fuel and on the border of retard. I am planning to take the heads off in the near future and have the bathtubs milled out so as to drop the CR because I cannot really afford the 10c /litre more than for regular unleaded plus some for the additive to stop valveseat burn, Lead replacement fuel is not an option for me, and at least here in Australia they stopped using high content of ethanol in the unleaded fuel. Luck
Henk from Oz

 

I was planning on doing the timing chain swap and replacing the manifold gasket at the same time, relatively soon i hope. I am also going to check the thermostat, could be a 220 for all i know. THe engine is a stock 1979 truck engine, low compression for sure. Thats a good idea on the colder plugs. I have driven the truck about 3K miles in the last 9 months including a recent 180 mile hiway trip, so I dont think there is too much carbon build up causing the problem, but ill flush it anyways. I cant believe this engine didnt ping from the factory, 32* mech advance, + vac advance + 8* static with 61 jets in the carb along with the retarded cam timing.

 

This may sound funny but, most of the times I have ever had any pinging problem it was from either valve train components or fuel. A little water in the tank goes a long way. Also, higher octane fuel will reduce ping. Ping is premature detonation, right? I run a 160 thermostat with great results. Do you purchase your gas at the same or different places? Find one you like and stick with it and at least rule the water out.

 

Hi ,I'm a new member to the forum. I have been reading through many posts pertaining to your problem. I've found many. I had the same problem as you do or you may have solved it by now. I have a 86' Ford Econoline 350 XL Ambulance Type III (that's a van cab with a box attached) with a 460/7.5 litre engine, C6 transmission, duallie Dana 70 rearend w/Limited slip carrier (used to be 4:10 ratio now is 3:55 ratio). It has about 106000 miles on it and weights in at about 9300lbs.
about 2000 miles ago I've rebuilt the engine,trans & rearend. The engine I freshend it up with new std. rings, bearings (mains & rods), a Melling high volume standard pressure oil pump, Edelbrock Performer cam, lifters, timing gear set (straight-up, older style pre-emissions),non-egr intake & valve springs, heads got a valve job (done myself), Holley 750 dual line vacum secondary carb (72 main jets & 65 power valve), older Jacobs computer ignition module, Jacobs magnetic core coil, Accel 8.5mm plug wires, Champion 4018 truck spark plugs.
My pinging problem was much like yours. You adjust timing to stop pinging at highway cruising and you have almost no power taking off from deadstop. I solved my problem by recurving the stock distributor. It turned out that the mechanical advance was giving to much advance, about 42 degrees at the crank.
By disassembling the distributor and rotating the advance cam 180 degrees (my distributor advance cam had 16 degree & 21 degree notches, you multiply these numbers by 2, and thats the amount of advance at the crank)(in other words I set mine in the 16 degree notch, was in the 21) and reinstalling the advance cam and using the lightest springs from an Accell distributor recurve kit (The kit will provide instructions on how to do this) then put it the rest of the way together. On the vacum advance I ended up having the screw (you adjust with an allen wrench through the end vacuum hose port) backed out all the way (counterclockwise) until you hear a click with each full turn (the screw doesn't fall out, you feel a lot of resistance turning it though) then turn it in about 3 to 4 turns. My timing advance at 3500 - 4000 rpm with vacuum unhooked and plugged, is 37 degrees. This is done with a dial back to zero timing light.
These settings in my application gave me very good results. The engine pulls strong from dead stop, good acceleration, and pulls well at highway speed (70mph), with no pinging or detonation at any time. All this with 87 octane gas.
I don't know my mpg at this time but I do know it's up from 5.5 mpg before recurving distributor. My exhaust at this time is stock (restrictive) my next project upgrade for near future.
I hope my long windedness may help you and/or others with pinging/detonation problems. Again these settings worked for my application (why I included details of my FORD) and will not work for all engines or most.
Every engine has it's own advance curve in which it runs at optimum. I found this link in this forum another member has provided (sorry I don't recall his name right now, he may remind me when reading my post ) http://www.reincarnation-automotive....ons_index.html
This page will provide great detail in recurving your distributor.

 

Your vacuum advance unit is pulling the timing around to far. Replace it with an adjustable unit preferable. To test this just dist connect the vacuum advanc hose from the dist and plug it. Make a run with it. No pinging then you know what to do. Changing the jets in the carb will not make pinging stop. Recurving the dist won't help either. Too much timing is the cause, almost always and in your discribed case it has to be the vacuum advance unit. Changing the timing set will not help either.