302 Stalls at Idle - Ford Mustang Forum
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post #1 of 39 (permalink) Old 06-25-2019 Thread Starter
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302 Stalls at Idle

I've own the car now for over 2 years and haven't been able to narrow down exactly why the car stalls at idle. When I'm waiting at a stop light for about a minute the car starts to hiccup and if I don't put it in neutral to raise the idle speed it will stall.

Here's what I've done so far:
1. Adjusted the floats in the Edlebrock 1406 carb, adjusted the air and fuel mixture
2. New spark plugs and wires
3. New distributor cap
4. Adjusted timing
5. New control module on Mallory Unilite distributor
6. Adjusted mechanical advance on distributor
7. Checked vacuum from intake manifold (vac 14-17 psi)
8. Checked for vacuum leaks around carb body using carb cleaner
9. New fuel filter
10. New fuel pump
11. Set fast idle to 1000 rpms while in drive

Here are some thoughts that I had that could potentially be the problem:
1. PCV hose plugged (I recall reading a post where this was a problem)
2. Vacuum advance distributor needed?
3. Aggressive cam requiring a higher idle speed?

I have no way to verify what the cam is in the car but it could a performance camshaft requiring an idle of 1200-1500 rpm. I want to avoid setting the idle speed any higher because the car will run-on after I shut it off and I often have to leave it in gear when I turn it off to avoid this from happening.

Where else should I look for or try?

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post #2 of 39 (permalink) Old 06-25-2019
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I'm in the same boat. Is it a automatic by chance

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post #3 of 39 (permalink) Old 06-25-2019
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Originally Posted by JoeKlo View Post
I've own the car now for over 2 years and haven't been able to narrow down exactly why the car stalls at idle. When I'm waiting at a stop light for about a minute the car starts to hiccup and if I don't put it in neutral to raise the idle speed it will stall.

Here's what I've done so far:
1. Adjusted the floats in the Edlebrock 1406 carb, adjusted the air and fuel mixture
2. New spark plugs and wires
3. New distributor cap
4. Adjusted timing
5. New control module on Mallory Unilite distributor
6. Adjusted mechanical advance on distributor
7. Checked vacuum from intake manifold (vac 14-17 psi)
8. Checked for vacuum leaks around carb body using carb cleaner
9. New fuel filter
10. New fuel pump
11. Set fast idle to 1000 rpms while in drive

Here are some thoughts that I had that could potentially be the problem:
1. PCV hose plugged (I recall reading a post where this was a problem)
2. Vacuum advance distributor needed?
3. Aggressive cam requiring a higher idle speed?

I have no way to verify what the cam is in the car but it could a performance camshaft requiring an idle of 1200-1500 rpm. I want to avoid setting the idle speed any higher because the car will run-on after I shut it off and I often have to leave it in gear when I turn it off to avoid this from happening.

Where else should I look for or try?
have you checked the actually fuel flow and pressure in the line? A stock fuel pump may not be giving you quite enough fuel at low RPM. Add an electric pump in line

Agressive cams sometimes do not have enough center line time to develop good vacuum at idle. raise idle to 950 RPM in drive with foot on brake (automatics cars of course)

sounds weird but is your current air cleaner air intake set up creating enough turbulence over the carb to get good fuel atomization at low speed?

Run on after the key is shut off or dieseling is can be caused by many other issues try retarding the timing a bit with the high idle setting.
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post #4 of 39 (permalink) Old 06-25-2019
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The fact that it does this at a stop 'after a few minutes' is making me wonder about heat soak. Are you using a phenolic spacer between your carb and manifold? If things get so hot the gas in your carb begins to boil, it will barf extra fuel into your engine, and at idle, that would definitely cause some hiccups.

A phenolic spacer will help insulate your carburetor from the manifold heat, and usually prevents this problem.

Additionally, YES, vacuum advance is a critical part for any street driven car. Mechanical advance only sets your timing for wide-open-throttle. When you are at idle, your cylinders are getting so little air and fuel, even at full compression, there's not much pressure. When it's ignited, it burns much more slowly than it does at WOT, with peak cylinder pressure chasing the falling piston on the power stroke. Without vacuum advance to light the mixture earlier, based on manifold vacuum, your engine is going to be spitting a lot of still-burning gas and air into the exhaust manifolds, and running rough. At idle, your exhaust manifolds will get HOT. The same holds true at cruise. Worse gas mileage, poor idle quality, high under-hood temps, and even a tendency to bog a little when you step on the gas are all to be expected without vac advance.


If you advance your initial mechanical timing to the point where you get a reasonable idle, then when you step on the gas you've got way too much timing, resulting in detonation and excessive cylinder temps. (that would lead to dieseling on shutoff, because parts inside the combustion chamber are glowing, giving your engine a new source of ignition even without the spark)


Adding vac advance will allow you to idle at a much more reasonable RPM too, so you can shift into gear (with an automatic?) and not bark the tires.
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post #5 of 39 (permalink) Old 06-25-2019
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Vacuum advance is not required for the engine to function, it is not a performance device its a fuel saving device. While I agree the extra advance will help the engine run a bit cooler and may aide a bit if properly set up at idle, its not required.

A PCV is not a requirement either, the only time it will give trouble is if it does not close when its supposed.

Are you running a higher stall torque converter, cam changes may require that. What is your timing set to, both initial and total? Did you modify the bottom end so that all your parts and cam are working in harmony?

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post #6 of 39 (permalink) Old 06-25-2019
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Having run straight mechanical timing on an original dual-point Autolite distributor for years, let me put it this way:


Vacuum advance is much better in every way. I will never run another street-driven car without it.


You can also do without PCV stuff, but it does help prevent a greasy mess where your blowby comes out the vents in your valve covers.

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post #7 of 39 (permalink) Old 06-26-2019 Thread Starter
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Originally Posted by jwthompson200 View Post
I'm in the same boat. Is it a automatic by chance

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Its a C4 automatic tranny. If it were a manual tranny I wouldn't have an issue. Once the clutch is engaged at a stop light it would idle higher and wouldn't stall. I wish it were a manual as it would be a lot more fun to drive.
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post #8 of 39 (permalink) Old 06-26-2019 Thread Starter
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Originally Posted by baylensmanfl View Post
have you checked the actually fuel flow and pressure in the line? A stock fuel pump may not be giving you quite enough fuel at low RPM. Add an electric pump in line

Agressive cams sometimes do not have enough center line time to develop good vacuum at idle. raise idle to 950 RPM in drive with foot on brake (automatics cars of course)

sounds weird but is your current air cleaner air intake set up creating enough turbulence over the carb to get good fuel atomization at low speed?

Run on after the key is shut off or dieseling is can be caused by many other issues try retarding the timing a bit with the high idle setting.
How would l check the fuel line pressure? Idle is at about 1000 RPM now. It would need to be set higher to prevent stalling. I don't think this is an option because it's idling high already. Not sure how to check the air intake effectiveness either.
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post #9 of 39 (permalink) Old 06-26-2019 Thread Starter
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The fact that it does this at a stop 'after a few minutes' is making me wonder about heat soak. Are you using a phenolic spacer between your carb and manifold? If things get so hot the gas in your carb begins to boil, it will barf extra fuel into your engine, and at idle, that would definitely cause some hiccups.

A phenolic spacer will help insulate your carburetor from the manifold heat, and usually prevents this problem.

Additionally, YES, vacuum advance is a critical part for any street driven car. Mechanical advance only sets your timing for wide-open-throttle. When you are at idle, your cylinders are getting so little air and fuel, even at full compression, there's not much pressure. When it's ignited, it burns much more slowly than it does at WOT, with peak cylinder pressure chasing the falling piston on the power stroke. Without vacuum advance to light the mixture earlier, based on manifold vacuum, your engine is going to be spitting a lot of still-burning gas and air into the exhaust manifolds, and running rough. At idle, your exhaust manifolds will get HOT. The same holds true at cruise. Worse gas mileage, poor idle quality, high under-hood temps, and even a tendency to bog a little when you step on the gas are all to be expected without vac advance.


If you advance your initial mechanical timing to the point where you get a reasonable idle, then when you step on the gas you've got way too much timing, resulting in detonation and excessive cylinder temps. (that would lead to dieseling on shutoff, because parts inside the combustion chamber are glowing, giving your engine a new source of ignition even without the spark)


Adding vac advance will allow you to idle at a much more reasonable RPM too, so you can shift into gear (with an automatic?) and not bark the tires.
I did add a wooden carb spacer. The phenolic type was a tad too high to allow the carb to fit under the hood. Starting to get fuel boil off in the summer time heat as it's hard to start in the morning because the fuel most likely evaporated overnight due to a hot engine. The engine does run hot. I'm changing the oil every 1000-2000 miles most likely because of that. New radiator and the engine temp is typically below 200 so I never had it overheat. Gas mileage sucks - about 6 mpg. Maybe that's typical for that year, make and model - LOL. And yes it does bog a little when stepping on the gas. Any recommendations for a vac advance ford 302 distributor?
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Quote:
Originally Posted by JoeKlo View Post
Its a C4 automatic tranny. If it were a manual tranny I wouldn't have an issue. Once the clutch is engaged at a stop light it would idle higher and wouldn't stall. I wish it were a manual as it would be a lot more fun to drive.
I think it may be too low of stall on you torque converter

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post #11 of 39 (permalink) Old 06-26-2019 Thread Starter
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Originally Posted by 07redstang View Post
Vacuum advance is not required for the engine to function, it is not a performance device its a fuel saving device. While I agree the extra advance will help the engine run a bit cooler and may aide a bit if properly set up at idle, its not required.

A PCV is not a requirement either, the only time it will give trouble is if it does not close when its supposed.

Are you running a higher stall torque converter, cam changes may require that. What is your timing set to, both initial and total? Did you modify the bottom end so that all your parts and cam are working in harmony?
I played around with the timing a lot so I may need professional help to figure it out any further (God forbid). Pretty sure it's the original torque converter. You would have thought that if the previous owner put in a performance cam he would have also considered replacing the torque converter. Going off remember but I believe the initial timing was set to 18 or 20 and the total was 34. The only work I've done on the bottom end is replace the bearings. The top end was modified by the previous owner with 351 Edlebrock heads, Edlebrock Performance Intake manifold and Edlebrock 1406 4 barrel carb. Again the performance cam is only speculation on my part. It could be original as far as I know. Everything else on the bottom end looks like the original small block 302 Ford Windsor.
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Its a C4 automatic tranny. If it were a manual tranny I wouldn't have an issue. Once the clutch is engaged at a stop light it would idle higher and wouldn't stall. I wish it were a manual as it would be a lot more fun to drive.
Back when I was in college I had a little business tuning up cars for my fellow students. A guy brought me a early Ford Maverick with an I6 and a C4 and the same symptoms as yours. I rebuilt the carb, changed plugs, new points, etc. Had it running and idling perfectly and it would still stall out. It turned out to be the transmission.

When was the last time the transmission was serviced? A complete fluid change (including the torque converter) and new filter might solve the problem.
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Back when I was in college I had a little business tuning up cars for my fellow students. A guy brought me a early Ford Maverick with an I6 and a C4 and the same symptoms as yours. I rebuilt the carb, changed plugs, new points, etc. Had it running and idling perfectly and it would still stall out. It turned out to be the transmission.

When was the last time the transmission was serviced? A complete fluid change (including the torque converter) and new filter might solve the problem.
yes the new term is "STICTION" or sticky friction from older fluid break down leaving deposits on various peices. Can even cause the power steering to act funny. While a good C4 will only require about 20 psi internal pressure to shift and lock up the bands as needed, most of the release are spring driven and subject to the STICTION problem.

Draining the trans and torque convertor isn't hard just messy! A new sump screen will really help also!
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Quote:
Originally Posted by JoeKlo View Post
I did add a wooden carb spacer. The phenolic type was a tad too high to allow the carb to fit under the hood. Starting to get fuel boil off in the summer time heat as it's hard to start in the morning because the fuel most likely evaporated overnight due to a hot engine. The engine does run hot. I'm changing the oil every 1000-2000 miles most likely because of that. New radiator and the engine temp is typically below 200 so I never had it overheat. Gas mileage sucks - about 6 mpg. Maybe that's typical for that year, make and model - LOL. And yes it does bog a little when stepping on the gas. Any recommendations for a vac advance ford 302 distributor?
Most any Autolite distributor would be fantastic, if it's in good shape. Whatever you get, you'll want to check the total mechanical advance in degrees, and set everything up yourself. If it's pre-70s, it's probably already in the ballpark. If it's 72+, you will have to make adjustments to the timing curve, vac advance, and total timing. They used some weird settings for smog engines. I prefer the stock type distributors, both because they look correct for a Ford, but also because they fit with monte carlo bars and don't cause air cleaner interference.

Honestly, I think this is the crux of your problem. Even with a performance cam, it's not uncommon to see these cars getting more like 15-20 mpg. I think once you get your timing right, you'll be astounded at how much power you've got, and a lot of your other problems will go away.
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I've had my car for over 7 years and I've stalled badly once. I blamed the stalling on 3 things, timing, carb and distributor. A lot have changed since then and I no longer have the 289. I was able to sort all of these problems with my 347 stroker. Though I've learned alot through the years by asking questions around here and yet I'm still a rookie. From what I've experienced my advice to you is, get yourself a VA distributor and start from scratch looking for timing and the right advance curve. I could recommend you my HEI Flamethrower but given is a GM style dizzy I know alot of Ford guys believe is a travesty to put one in. I've been more than pleased with it ever since I dialed in with the right spring weights. I still have my 1406 Eddy, it's been jetted to handle the 347, best fuel economy about 11 mpg this is city. On highway I go more much more on a 100 mile trip I did last month. The 1406 is an easy carb to work on so dont throw it away just learn how to adjust it with your vacuum gauge. I idle at 950 rpm with engine fully warmed up at around 198 degrees. Rpm drops once I engage the transmission.


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