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Idling problem


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so I changed my fuel sending unit and some how the idling on the car messed up and it now idles around about 400-250 rpm but before I had it set at 575rpm. I believe its the timing because all the vacuum lines are good 

the distributor was stuck and wouldn't turn at all but the hold down was not tight  (I fixed it it will turn now

When I used a timing light it was off by about 30-40 degrees with the distibutor vac plugged. 

My dad thinks it skipped a peice on the timing chain could that be the cause? And if so how would I fix it?

 

Thank you in advance sorry for all my dumb questions I don't know alot about these classic mustangs

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You never know what the timing was set at before you got it. If you turned the distributor back to reduce the timing that also lowers RPMs. Readjust the engine speed to specs, you'll also likely need to readjust the idle mixture.

 

The timing chain has to be extremely loose to jump teeth, and if it happened once it'll likely keep doing it due to the loads from lifting the valves and turning the oil pump. You can check it by manually turning the engine in one direction until the rotor begins to turn, mark the location of the crankshaft, and then manually turn the engine in the opposite direction until the rotor starts turning again. It helps if you use the timing marks on the harmonic balancer as a reference. If the crankshaft turns more than 10° before the rotor begins to turn your timing chain is likely too loose. If you use the timing marks for a reference, 5° of timing equals 10° of crankshaft rotation.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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I'm kinda worried about your Idle speed.  575 seems low to me.  I think you should be at least at 800 to get the correct lubrication and oil splash for your cam.

 

Just a thought.

 

kcmash

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First off. What are we dealing with? What year, what engine. Any mods?

 

Its a 1971 351c with a mild cam

 

I set the rpm to 575 in drive cause thats what this engine bay sticker said it should be at

In park its about 800 or so 

 I know for sure the harmonic balancer is off pretty bad at TDC its about 30-40 degrees off

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How did you determine that the harmonic balancer is that far off? It's not uncommon for an original to get off, as the elastomeric material dries out and the outer ring gets twisted around on the inner hub that's connected to the crankshaft. If yours is off by that far you should be noticing some vibrations.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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First off. What are we dealing with? What year, what engine. Any mods?

 

Its a 1971 351c with a mild cam

 

I set the rpm to 575 in drive cause thats what this engine bay sticker said it should be at

In park its about 800 or so 

 I know for sure the harmonic balancer is off pretty bad at TDC its about 30-40 degrees off

 

Well once you change cam or other stock components, the factory settings mean nothing.

John - 72 Q Code

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I agree with the need to speed up your idle rpm. The cam does not get much lube unless the idle is up. I actually put my car out of gear when I stop at a light to keep the rpm up. Too many people love to hear them lope an it eats the cam and lifters. 

On the timing you need to check deeper on if it has jumped time. This pic is a piston out of my Dad's car that he loaned out. It jumped time and the person that borrowed just turned the distributor and tried to drive home. Valves hit pistons and broke one off and boom junk engine.

If it has jumped and valves have hit pistons you need to do a valve job and might have to replace bent valves / bent push rods. DSC-2097.jpg

 

DSC-2098.jpg

 

DSC-2099.jpg

When a man is in the woods and talks and no women are there is he still wrong??:P

David

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I agree with the need to speed up your idle rpm. The cam does not get much lube unless the idle is up. I actually put my car out of gear when I stop at a light to keep the rpm up. Too many people love to hear them lope an it eats the cam and lifters. 

On the timing you need to check deeper on if it has jumped time. This pic is a piston out of my Dad's car that he loaned out. It jumped time and the person that borrowed just turned the distributor and tried to drive home. Valves hit pistons and broke one off and boom junk engine.

If it has jumped and valves have hit pistons you need to do a valve job and might have to replace bent valves / bent push rods. DSC-2097.jpg

 

DSC-2098.jpg

 

DSC-2099.jpg

Awesome thank you for the info. I pulled the engine (it needs a new oil pan) ill check out the timing chain when I tested to see how much slop was in the chain it took about 8 degrees of the balancer before the distributor turned. The valve being bent is something im scared of im gonna take off the valve covers/heads to see if that might be the problem.

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