very odd problem with 351 cleveland

kalli · 01-23-2009, 11:57 AM

Hi all,

friend of mine bought a crashed 70s mustang and he is nearly finished. He asked me if I could call over for checking on carb and ignition.
The carb was rebuilt according to previous owner. The distributor is stock, new rotor, cap and breaker

The engine is clearly cleveland as the water outlet is on block and not on intake manifold as in my windsor. The fuel pump bolts are vertical instead of horizontal aligned. that were the most obvious differences.

Now the car sounded unhappy. not really misfiring but rumbly. couldn't hold low idle. Was going up and down. No vacuum leaks, i checked for that.

I wanted to know what cyilinder might give problems and so I pulled on spark plug lead while running. Idle went down. This way I made it through a few cylinders where I dodn't hear an obvious change in revs.
But cylinder #3 (or #2?) was very odd. The revs actually picked up by at least 200rpm once I pulled the cable. about 2 seconds later.
I plugged the cable back and the revs went down by that 200 again.
I could reproduce it as often as I wanted. So I said it must be the firing order.
But the book he had matched the firing order he had. As well the intake manifold (seems stock as well: D0AE .....) had the same sequence posted:
1-3-8-2-6-5-4-8

The have the TDC mark on the balancer verified using piston stop bolt. it is exact. I timed the car to 8 degrees in idle on #1 cylinder. Assuming hat #1 cylinder is the same as in the one in the windsor. (passenger side front of engine near radiator)
The balancer matching out TDC seems to verify this.

Anyone any explanation to this problem?
Is there an alternate firing oder we don't know about? any other explanations?
It is af plugging that cable in brings rounds down by 200 as if it would fire too early or something ...

Kalli

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dcohen · 01-23-2009, 12:28 PM

you sure its not a 351M?

i doubt it is but anything is possible, but the firing order is the same for both of them

MIL1ION · 01-23-2009, 12:35 PM

Check this page out.

http://www.boxwrench.net/specs/ford_351C.htm

Remember.... there are 2 TDC position to every cylinder.

You need to verify TDC a little after the intake valve closes.

dcohen · 01-23-2009, 12:46 PM

the way i do it is i put my thumb of the spark plug hole and have somebody turn the engine, you will be able to feel when the cylinder starts coming up on a compression stroke

once you verify that #1 is coming up on compression then just go by the marks on the harmomic balancer

get her up on TDC then turn the distributor gear until the #1 plug fires and put it back down in the engine, then you can put the timing light on it and get the timing spot on

one thing to remember is that you always adjust timing with the vacuum advance disconnected

kalli · 01-23-2009, 01:03 PM

Hiya,

you are correct. I didn't check when it's compression stroke or not. But that doesn't bother me in the slightest as when the distributor is out by 180 degrees it will not run at all as every single spark on all cylinders will end up at exhaust stroke

The only other idea I have is that he doesn't have the rotor aligned to the cap properly when putting the distributor in. With turning of the rotor I can still change timing measured on #1, but the spark might jump to a different cylinder inside the cap if there is distance between cap and rotor.

Kalli

vescotech · 01-23-2009, 04:10 PM

Kalli you could have a dist cap that has a crack or carbon track between two cylinders. When it is shorted between two cly they cancel eash other out. when you remove one it lets the other one fire. Also did you completely remove the wire from the cap or let it arch to the cap. A gas fouled plug will start firing sometimes if you pull the wire away and let it arch to the cap.

kalli · 01-23-2009, 06:24 PM

Hi Vescotech
the cap and rotor seem new. i removed the wire completely. that is the odd. thing runs without that one better thene with it. The spark plugs are new as well. but i believe you're on to something. It's the only explanation that makes sense to me if it's crossfiring in the cap "when you remove one it lets the other one fire". kinda really the only thing that makes sense. The rotor too far from cap contaxct would be similar issue. I'll doublecheck all that with him. maybe I'll pull the others while I have this one off and then again while I have it on. Maybe i can see a difference this causing to free a cylinder when unplugged

Kalli