I have been working on my 78 bronco, it has a 351M and it failed emmissions. Well I found some problems which I fixed. EGR felt like it was sticking, couple broken vacume lines, and carb gaskets were cracked up.

It is running fine and dandy now, but ever since I put in a 195F thermistat it has been pinging. I filled up last night with 91 octane, and dumped in a 108 octane boot bottle to see if that helped the ping any. It did not.

1. It does not ping below 2000 rpms.

2. Base timing is 10 degrees now. I have to double check it since I fixed the vacume leaks. it may have changed the timng on it.

3. It does it in gear but it is hard to hear it. I can hear it better not driving. and reving the engine to 2k-2.5k rpms.

4. It will do this even if I pull the vacume advance off.

5. I bought a new coil, and new plugs. I just done a tune up on it not even 2 weeks ago. but I think I am going to replace these items. What is the possibility that the new wires are cross sparking and causing a cyclinder to fire when it is not supposed to?

 

Are you shure int's pinging? Maybe something else. An engine wont normally do that unless you have some load on it.
1977 Ford F-100
400m/c6/4:11/Gear Vender O.D.
Crane hydralic roller, forged, ported polished,Deamon,Edlebrock, yada, yada, yada
280,000 miles
Stock on the outside
modified/rebuilt everything

 

If it is not pinging what else could it be?

I do not hear it before 2k rpm's

 

[font size="1" color="#FF0000"]LAST EDITED ON 17-Aug-01 AT 05:10 PM (EST)[/font][p][font size="1" color="#FF0000"]LAST EDITED ON 17-Aug-01 AT 05:09 PM (EST)[/font]

Well pinging normal is worst when laying into the throttle going up a hill for instance. Low rpm and heavy load accentuate it. It sounds like you were shaking a coffee can with a few pieces of gravel in it. Sort of a rattle. Can you describe the sound in more detail? Is it constant when it starts?
How many miles on the engine? Any other work done lately to it. When did it start? So many questions!

1977 Ford F-100
400m/c6/4:11/Gear Vender O.D.
Crane hydralic roller, forged, ported polished,Deamon,Edlebrock, yada, yada, yada
280,000 miles
Stock on the outside
modified/rebuilt everything

 

No noises below 2k rpms

it seemed to start when I put in a 195F thermistat.

Not very auduable under 2k. It seems when the advance kicks in you hear the noise.

I threw my timing light on it. and around 2k rpms it was way past 30 degrees. more like 40 degrees, When the timing went right up I start to hear the noises. Even with the vacume hose off of the vacume advance I hear the noise as well.

the sound? I would say the best way to describe it would be kind of high pitch. not the low knock noise of a rod or main bearing.


Miles on engine are unknown.
Just done a complete tune up 2 weeks ago.

 

40 Degrees advanced is too much, back off the intial to zero degrees advanced. Then see if the noise goes away, it is not pinging, but back firing. If it goes away at zero, then advance it two degrees at a time until it starts again. I think that you have some vacuum lines connected wrong.

Dan Lee
'53 F100
400C-4V

 

I will try that tommarrow.

I even ran it with the vacume advance off it still makes the noise. could the springs in the distributor be shot and not making the correct mechanical advance?

 

Well check those springs. Maybe one of them broke. 40 degrees total is probably more than enough.

1977 Ford F-100
400m/c6/4:11/Gear Vender O.D.
Crane hydralic roller, forged, ported polished,Deamon,Edlebrock, yada, yada, yada
280,000 miles
Stock on the outside
modified/rebuilt everything

 

i'll tell ya alittle trick to do that will take care of all the spark knock or pinging what ever you want to call it. i had a 1976 mercury marquis with a 351 long long time ago and i had the same problem could not figure out why and tried everything to fix but couldn't. at the time i was going to tech school for diesel mech. and i told one of my instructor's what was going on and he told me the fix... now, leave you timing where it is for now, first take off the vacuum hose at the distributor off,, now take a 1/8 inch allen wrench and stick it into the hole where the hose plugs into.. if it's a true 351 distributor there will be an allen head screw in the hole, take the allen wrench and turn the screw counter clockwise about 1/2 to about 3/4 of a turn, now recheck your timing and install the vac hose and take for a test drive. you might have to repeat this process a couple of times to get it right, but it does work it worked for me. i had problems in the past with spark knock in my 460 and the best thing i did was put a 351M distributor in it and do this process and it works. what it does is tighten up vacuum advance so it doesn't pull so easy. you won't lose any performance either. try it and let us know what happens.. C.J.

 

Thanks. I do however know about that trick.

but it does it without the Vacume advance hooked up.

It starts at 2k rpm's. With the advance hooked up it is louder. without it the knock is just a tad quieter.

 

You might take a close look at your harmonic balancer. If it has spun your timing marks will be way off. If you can get #1 cylinder at tdc on the compression stoke you can compare that to the balnacer mark.

1977 Ford F-100
400m/c6/4:11/Gear Vender O.D.
Crane hydralic roller, forged, ported polished,Deamon,Edlebrock, yada, yada, yada
280,000 miles
Stock on the outside
modified/rebuilt everything

 

Ya know I never thougth about that one.

I will have to have a peek tonight when I replace some expensive smog parts I had top order!

 

A buddy of mine I just finaly got ahold of said I most likely have carbon buildup on the heads and piston tops. Effectivaly increasing the CR to cause pre igniton.

Any ideas how to remove this stuff?

 

You could run small amount of water or Marvel Myster Oil trough it at fast idle. (not too much at once!) Im thinking of a water injection system myself for long term carbon elimination.

1977 Ford F-100
400m/c6/4:11/Gear Vender O.D.
Crane hydralic roller, forged, ported polished,Deamon,Edlebrock, yada, yada, yada
280,000 miles
Stock on the outside
modified/rebuilt everything

 

Talk to me.

Just dump small amounts of water down the carb?

how much is needed to complete the job?