whats normal acceleration for a 351M?

[delco1946]

Thanks for all the suggestions! i'll try to look at these tomorrow or this weekend.

So I’m not sure what you meant by a 335 firing order - I looked up the firing order for a 351 and my engine seems to match that. I then hooked up a vacuum gauge based on the cat being suspect or a clog of some sort. Ive watched several YouTube videos and I guess I’m still not sure how to interpret my results.

At idle I measured approx 22 psi to 24ish. When I accelerated and raced the engine and steadied it ( no tach) the vacuum dropped to 17-18 ish and the needle was bouncing a lot within a narrow range, but if I held it steady it would stay in that general range. I can’t tell from the vids if it’s supposed to keep dropping or if the bouncing needle is more important. Either way it seems like a maybe have a clog.

Adding to this, starting late last summer, when I come to a stop, with the fan blowing, I can sometimes smell a stink. Never have been able to figure it out. Doesn’t smell like what comes out of my tailpipe ( after cat and muffler) but when I stick my head under the hood the closest I’ve ever been able to pin point it is somewhere near the passenger exhaust manifold. A blockage would make a lot of sense in that the back pressure is causing exhaust to escape into the bay and get sucked up by the blower motor.

I crawled under the truck and I don’t see any obvious easy way to disconnect the cat. Saw a couple of u bolts that looked liked they’ll be a pain to get off.

[ArdWrknTrk]

So I’m not sure what you meant by a 335 firing order - I looked up the firing order for a 351 and my engine seems to match that. I then hooked up a vacuum gauge based on the cat being suspect or a clog of some sort. Ive watched several YouTube videos and I guess I’m still not sure how to interpret my results.

At idle I measured approx 22 psi to 24ish. When I accelerated and raced the engine and steadied it ( no tach) the vacuum dropped to 17-18 ish and the needle was bouncing a lot within a narrow range, but if I held it steady it would stay in that general range. I can’t tell from the vids if it’s supposed to keep dropping or if the bouncing needle is more important. Either way it seems like a maybe have a clog.

Adding to this, starting late last summer, when I come to a stop, with the fan blowing, I can sometimes smell a stink. Never have been able to figure it out. Doesn’t smell like what comes out of my tailpipe ( after cat and muffler) but when I stick my head under the hood the closest I’ve ever been able to pin point it is somewhere near the passenger exhaust manifold. A blockage would make a lot of sense in that the back pressure is causing exhaust to escape into the bay and get sucked up by the blower motor.

I crawled under the truck and I don’t see any obvious easy way to disconnect the cat. Saw a couple of u bolts that looked liked they’ll be a pain to get off.

Christopher, can't you loosen the head pipe to manifold connections?

 

[delco1946]

Christopher, can't you loosen the head pipe to manifold connections?

I’ll take a look Jim. I’ve never done that but I guess there’s a first time for everything.

Do my symptoms and read outs sound like a clog to someone more familiar with this than me?

[ArdWrknTrk]

Is there an easy way to check for exhaust blockage? I have a cat so i'm guessing it would all need to come off upstream of that...?

https://www.bing.com/videos/search?q=checking+exhaust+blockage+with+cvacuum+gauge&docid=607993629045621911&mid=EF77EC6467A280BFD885EF77EC6467A280BFD885&view=detail&FORM=VIRE

David,

This is the same guy Reamer (Ron) referenced when he swore up and down that he didn't have an exhaust blockage.

We all know that turned into a two month, $2,000 adventure when my advice in the third post of that thread was to disconnect the head pipe.

Of course YMMV, but I'm not listening to Eric's poorly thought out internet advice -at all- anymore.

[1986F150Six]

David,

This is the same guy Reamer (Ron) referenced when he swore up and down that he didn't have an exhaust blockage.

We all know that turned into a two month, $2,000 adventure when my advice in the third post of that thread was to disconnect the head pipe.

Of course YMMV, but I'm not listening to Eric's poorly thought out internet advice -at all- anymore.

Thank you, Jim.

[ArdWrknTrk]

Thank you, Jim.

David,

I don't mean to pee in anyone's Cornflakes.

But I will go grab a link to that thread, and we can relive all the twists and turns (including, but not limited to: a new timing set, carburetor, distributor and Ignition box)

Edit: ironically it was almost exactly a year ago... http://forum.garysgaragemahal.com/Hmmm-loss-of-power-won-t-hold-speed-tp33697.html

Then this thread spawned "My timing chain adventure begins"

Which did net a replacement for Ron's sloppy timing chain, but that thread went on for 12 pages still didn't fix the problem..

 

[old55pete]

Thank you, Jim.

Does it smell like rotten eggs? With those readings, I would spray down the nuts that hold the Y pipe to the mianfolds with some PB blaster and let it soak, spray it down several times, then hit the nuts with some heat from a propain torch. Do what ever you have to do to NOT break the studs as they are a pain to drill out. Then take it for a test drive and see if the performance returns. If it does, eather the cat is plugged or the whole system is plugged.....If not, it's back to square one.

[delco1946]

Does it smell like rotten eggs? With those readings, I would spray down the nuts that hold the Y pipe to the mianfolds with some PB blaster and let it soak, spray it down several times, then hit the nuts with some heat from a propain torch. Do what ever you have to do to NOT break the studs as they are a pain to drill out. Then take it for a test drive and see if the performance returns. If it does, eather the cat is plugged or the whole system is plugged.....If not, it's back to square one.

Hey Steve - the smell ive gotten isnt quite rotten eggs, but is certainly unpleasant. I guess if i had to pick "a smell" it reminds me more of burning dirty electrical stuff, old crud/rubber etc. But i've never been able to see anything being damaged. I seems to be focused at the back of the passenger manifold and near the heater.

I've removed the heater, cleaned it, and vaccumed all the crud out so nothing related the dropping resistor or heater should be "burning" etc. I wonder if something has plugged up the pipe between the manifold and cat that may just be slowly burning. I dont recall having this acceleration problem when i first got the truck (i didn't have the smell either )

I'm not really following some of the last posts to "David" but regardless I think this has been very helpful. Confirming a plugged exhaust is at the top of that list with installing a new harmonic balancer shortly after!

[ArdWrknTrk]

I'm not really following some of the last posts to "David" but regardless I think this has been very helpful. Confirming a plugged exhaust is at the top of that list.....

Go read for yourself what a clogged cat seems like, Christopher.

Given the smell you say you have I'd consider dragging brakes, because we don't have much sulphur in any fuels anymore.

The acid rain was a big problem back in the '70's and early '80's before sulphur was regulated.

 

[1986F150Six]

Hey Steve - the smell ive gotten isnt quite rotten eggs, but is certainly unpleasant. I guess if i had to pick "a smell" it reminds me more of burning dirty electrical stuff, old crud/rubber etc. But i've never been able to see anything being damaged. I seems to be focused at the back of the passenger manifold and near the heater.

I am likely way off base, but could the engine be running very lean? This condition has a distinctive odor and would explain difficult starts and being low on power.