C4 question/ stalling motor

[bax]

So the motor runs and idles fine, Pull the trans into gear and it stalls the engine. So I rase the idle, same problem. Raise it to 1200 rpm. Drop it into gear, motor almost will stall unless you let the truck roll. Could this be a Torque converter issue?I have lost a sprag in a TC and had no lock up but to have complete lock up and 700 rpm. Something is screwy ????

 

[DirtDonk]

This has come up many times over the years, but not for quite some time now. And now I don't remember what all was used to fix the issue.

What about ignition timing? Where is it set, and is it full manifold vacuum?
Just thinking out loud that if the vacuum signal goes down enough when you put it in gear, maybe the idle is simply getting knocked down enough to stall.

Is it a performance engine maybe, with low vacuum numbers in general?
If it's got high vacuum (like over 20" or so) then I don't see how this would be an issue. But still wondering out loud about it.

Paul

 

[bax]

bone stock 1974 351. i will check the vacuum tomorrow. Timing is set at 8

 

[DirtDonk]

Hmm, what kinds of things change when a transmission is shifted into gear, or the idle goes down a few hundred rpm?
You could be on to something with the converter locking up. How does it accelerate when you do manage to keep it running? Is it jumpy and ready to roll out, or does it have any give in it at all?
What about with your foot on the brake, but pushing the accelerator pedal? Any slippage that seems in the normal range? Or is it trying to jump forward no matter what?

Kickdown lever attached? Any chance that the lever pushes forward on the linkage when it's shifted into gear? I don't think that's how the kick-down mechanism works, but it is a mechanical connection to the carb from the transmission after all. Never seen one move without the carb linkage pushing it, but I don't know how it actually works either.

Hmm, what about trying to disconnect it from the drivetrain to determine if it's engine related, or lock-up related? Kick the transfer case into neutral and then shift the trans.
If it still dies, then you know it's not anything after the output shaft.
Won't tell you if it's engine related, or something binding up in the trans, but it will at least eliminate one area.

And if it works fine with the t-case in neutral, then you'll at least know that it's not the engine itself. I think....%)

Paul

 

[Slowleak]

My ‘76 had that problem. It was stock with ported vacuum. Turns out the timing was low, as it should be for a stock ‘76, but it also had a hole in the vacuum diaphragm.

Put it in gear and it sucked in air thru the vacuum diaphragm, ran lean, got no advance, and the idle dropped,. That retarded the timing even more if it was advancing, and it stalled unless I gave it gas and let it roll...

Might check your vacuum advance diaphragm.

 

[bax]

Driving, once rolling it shifts fine thru the gears. Come to a stop and it will stall. Shift into neutral to stop and them drop back into gear and try to catch it with the gas before it stalls. I am still thinking converter. But I have never seen one brake and have no stall?

 

[blubuckaroo]

Sounds like a vacuum leak.

 

[bax]

Sounds like a vacuum leak.

It does, but it's not. Going to go thru and do all the checks on the engine. I will see if I can find anything.
Thanks everyone.

 

[blubuckaroo]

It does, but it's not. Going to go thru and do all the checks on the engine. I will see if I can find anything.
Thanks everyone.

Vacuum leak can be internal.
Intake manifold gaskets can be a problem.

 

[pcf_mark]

As DirtDonk said - if you have the vacuum advance connected to manifold vacuum (vacuum at idle) when you put it into gear the vacuum drops the spark advance goes away and the engine dies. I do not think you have a converter problem but an ignition and carburetor problem. My C4 torque converter was bad and it had essentially no stall to it would pull the idle down to 500 rpm and you needed to use both feet to keep it running.

I would do a basic tune up check up. A quick health check would be to do a cylinder balance test by pulling off the plug wires one a time and watch the rpm drop. I bet you find a few week cylinders.

 

[bax]

going to check vacuum. Good idea to check the advance diaphragm in the distributor. I have checked for other vacuum leaks. It has a 670 truck avenger holly carb on it. I can stall the motor by turning in the idle mixture screws. So if there is a vacuum leak it is a small one. Do a compression test. If all this checks out I may pull the intake and re gasket it just to be sure it's sealed. Wondering about a worn camshaft? It has a but of a miss going down the road. We will see I guess. Thanks for the suggestions. I was trying to rule out transmission and none of us think that is the problem so I will go with shit engine for the time being.

 

[DirtDonk]

I think if you can shift the t-case into neutral and it still does it, you've ruled out the transmission. But if the problem goes away, you've pretty much proven it's in the transmission I would think.

Paul

 

[jedblake]

My 347 had this issue and was caused by low vaccum. I ended up installing a higher stall converter.
You state that the engine and trans is original. Perhaps the engine has suffered internal wear or damage causing low or inconsistent vaccum? This could easily be checked with a gauge. Below is a great article on vaccum testing and related scenarios.
https://acbs.org/engine-health-vacuum-gauge/

 

[pcf_mark]

Also to rule out the converter if you get it into drive by using both feet (one brake one gas) and can rev the engine against the brake your converter has stall. A broken converter generally locks hard core. You should be able to gently rev it and see the rpm rise with limited pushing through the brakes.

I would do the basics of a tune up first taking the intake off sucks and may solve nothing.

 

[68ford]

I dont think it's your issue, but I would make sure you're on a poeted vacuum location so the vacuum advance is not doing anything at idle like designed. Then I would set the timing to at least 12 degrees.

 

[Justafordguy]

I dont think it's your issue, but I would make sure you're on a poeted vacuum location so the vacuum advance is not doing anything at idle like designed. Then I would set the timing to at least 12 degrees.

I agree 100%, check for ported vac for distributor, verify the diaphragm isn't bad, and bump up the timing to at least 12 degrees. Even stock they really run better with at least 12 degrees.

 

[Viperwolf1]

It does, but it's not. Going to go thru and do all the checks on the engine. I will see if I can find anything.
Thanks everyone.

Could still be a vac leak at the bottom of the intake ports, pulling air from the crankcase. Felpro 1250 gaskets are good for causing that.

 

[MarsChariot]

Yes, I agree that this sounds more like a vacuum leak than a transmission issue. In fact, I have been fighting this same problem the past 10 months…after very carefully re-installing the intake ( a cast iron Ford 4V intake, too) in an effort to solve this very lower port leak scenario. Apparently I failed.

My wild guess is that in some cases the angle of the intake seal surface on the head side is slightly larger than the intake side, so there is slightly wider gap near the bottom of the intake-head join.

In my case, I spent a lot of time cleaning the sealing surfaces, got a beautiful quarter inch bead of RTV along the front and rear sealing surfaces, was very careful to apply a thin bead of sealant around the water ports, and a thin skim around the intake ports. Next time I will pay particular attention to applying sealant along the bottom of the intake ports. Very frustrating when you know there is a vacuum leak and no matter what you do, you can’t find it, and there is nothing you can do to detect it and you did your very best to eliminate the very problem.

 

[DJs74]

It does, but it's not. Going to go thru and do all the checks on the engine. I will see if I can find anything.
Thanks everyone.

I've run into 2 different scenarios as you describe, both ended up being vacuum problems in my cases
One was BB 429, C6 in an F150... one day fine, the next day as you describe. Ended up being two bent valves - because they were not seating properly, a vacuum leak was occurring.
Second was 289, C4 in a '67 Mustang... not mine. Friend built it and ran great at idle in 'N' and Ok after moving but would not idle in gear. This one turned out to be intake gasket / torque sequence problem. Had internal port to port vacuum leak. New gasket set and torqued in proper sequence cured the problem.

DJs74

 

[welndmn]

Build your own smoke machine to look for vacuum leaks.
https://www.youtube.com/watch?v=EhNQiIRsCCk