Pinging on 351M when warm

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Apr 30, 2001 | 09:22 AM

brents

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Pinging on 351M when warm

Hi,

I normally drive my truck less than 5 minutes to work, but this weekend I took it for a long drive (~40 mins) and the engine started to ping really bad once it was warm. It runs really good when it is cold and the choke is on, but once it gets "hot" (about at the "o" in "normal" on my temp gauge) it really starts to ping, so bad it sounds like a diesel.

I have the vac advance going through a thermal vac switch that cuts off the vacumme when hot, so I am not sure what else would make it ping so bad. I only run 92 octane gas, but it doesn't seem to make a difference if I go to a higher grade.

I had the carb totally rebulit, and paid a old time ford mechanic where I live to "tune it" and set the engine timing. I think it is set to about 8 degrees BTDC.

Why does it run so good when cold, but so bad when it gets hot? When I back the timing off when hot so it doesn't ping, it runs like crap when cold. Is there a way to have the best of both worlds?

Also, are there any centrifical weights in my distributor, I could not see any centrifical advance?

Sorry for all the questions, any tips are very appreciated!
Thanks,
-Brents

Apr 30, 2001 | 02:40 PM

Bill_Beyer

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From: PacNW

Pinging on 351M when warm

Just off the top of my head I'd say that your EGR valve is bad. Either the diaphragm is shot or more likely the constant short runs where the engine doesn't warm up has caused carbon to build up and blocked the passage. I'd pull it off and take a look to see whether or not it's functioning.

Apr 30, 2001 | 02:51 PM

brents

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Pinging on 351M when warm

Hi Bill,

Thanks for the info, I don't have the EGR hooked up right now. Perhaps this is why it runs so bad. The EGR is there, but not hooked up, it hasn't been ever since I have owned the truck.

I will try looking at it tonight, and if it doesn't look carboned up I will hook it up.

Thanks again,
-Brents

Apr 30, 2001 | 04:40 PM

Bill_Beyer

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From: PacNW

Pinging on 351M when warm

It could also be carbon build up on the pistons. I just have the feeling it's related to the multiple short trips and the engine spending so much of the time running rich.

May 10, 2001 | 02:17 PM

yellow banna

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Pinging on 351M when warm

Hi My truck seems to have that very same problum. It only does it when it is at 2000 or higher Rpm's And I know that there is no carbon build up so it's ether worn out or the EGR.
But thanks for the clue on the EGR!

May 16, 2001 | 11:16 AM

brents

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Pinging on 351M when warm

Hi,

Looks like I have solved the pinging problem. Like most problems, there are several layers to them.

The first problem was the EGR was plugged. I cleaned the carbon out of it and that made an improvement.

The second problem was the flap in the breather was stuck "on" all the time, even when no vacuum was applied! This caused the motor to suck very hot air from the exhaust manifold stove box all the time (not just when cold). I discovered that this flap should open when the temp gets above about 100 degrees. I loosened the flap by hand (it was almost siezed), sprayed it with WD-40, and it seems to open and close now.

Thanks for the help,
-Brents