Detonation

Reply Subscribe

Thread Tools

Search this Thread

Jul 22, 2004 | 12:09 PM

kevinspann

Thread Starter

New User

Joined: Jul 2004

Posts: 10

Likes: 0

Detonation

The 351M in our '79 F-250 seems to be detonating and i dont know why. Teh motor is stock and has i guess around 8:1 compression so why does it detonate on 91 octane gas? I am going to check plugs and ignition to make sure that is not the problem and then maybe fix the coolant gauge to see if it runs hot. I dont really know what to do to it....

Jul 22, 2004 | 12:11 PM

68torino

Posting Guru

Joined: May 2003

Posts: 1,011

Likes: 0

From: South Dakota

Also check the timing. But when does it detonate? And what sound....marbles in a tin can....or major explosions?

Jul 22, 2004 | 12:13 PM

monsterbaby

Hotshot

Joined: Dec 2003

Posts: 18,423

Likes: 9

From: iowa

you might also check your fuel filter, and the carb for dirt lean condition can also cause detonation.

Jul 23, 2004 | 10:20 AM

kevinspann

Thread Starter

New User

Joined: Jul 2004

Posts: 10

Likes: 0

It detonates at low speeds, or when getting off the highway. I guess it sounds more like marbles in a tin can than explosions. It couldbe running lean, have bad timing, or both....definately in need of a tune up though

Jul 23, 2004 | 01:53 PM

monsterbaby

Hotshot

Joined: Dec 2003

Posts: 18,423

Likes: 9

From: iowa

Quote:

Originally Posted by kevinspann

when you say getting off the hiway do you mean when you are deaccerating because if that is what you mean you are not having detonation you have major engine trouble

Jul 23, 2004 | 07:29 PM

danlee

Postmaster

Joined: Aug 2001

Posts: 4,270

Likes: 5

From: Delaware

Check your EGR valve. If that is disconnected or stuck closed, you will have a lean mixture. This can produce pinging at light throttle, but never while decelerating.