Engine Dies When Shifting to Drive

[Razzle ‘73]

Car starts and idles but as soon as I shift to drive or reverse the engine dies. I have a new carb, engine tunes and new points. Any suggestions what to do next?

 

[giantpune]

What is the idle speed while its in park?

 

[Razzle ‘73]

No tach, so not sure

 

[giantpune]

Thats my first guess. When you put an automatic car in gear, the engine gets load and the RPMs drop. If you already have your idle set low, then putting it in gear makes the engine try to idle too low and it wont stay running. Even without a tach on the dash, you can connect a temporary tach under the hood. My timing light has one build in. You just put on 3 clamps and it tells your the idle speed.

One thing you could try is giving it a little bit of throttle as you shift out of P. Not like wide open, engine screaming throttle. Just try to raise the RPMs up a couple hundred like a quick idle.

Hopefully nothing inside the transmission or torque converter are locked up. That could cause this.
Does the engine stop violently or does it just kinda die off and sputter out?

 

[Ron Tanzi]

Do you have a regular 3 speed automatic or is it an AOD? If it was converted to an AOD you could have a stuck torque converter lock up solenoid.

 

[Razzle ‘73]

Thats my first guess. When you put an automatic car in gear, the engine gets load and the RPMs drop. If you already have your idle set low, then putting it in gear makes the engine try to idle too low and it wont stay running. Even without a tach on the dash, you can connect a temporary tach under the hood. My timing light has one build in. You just put on 3 clamps and it tells your the idle speed.

One thing you could try is giving it a little bit of throttle as you shift out of P. Not like wide open, engine screaming throttle. Just try to raise the RPMs up a couple hundred like a quick idle.

Hopefully nothing inside the transmission or torque converter are locked up. That could cause this.
Does the engine stop violently or does it just kinda die off and sputter out?

Engine just dies off not violently. When I come up to stop signs, I have to put it in neutral and keep giving it gas or else it just dies off

 

[Razzle ‘73]

Do you have a regular 3 speed automatic or is it an AOD? If it was converted to an AOD you could have a stuck torque converter lock up solenoid.

Regular 3 speed auto, original engine.

 

[mrgmhale]

Engine just dies off not violently. When I come up to stop signs, I have to put it in neutral and keep giving it gas or else it just dies off

I would check dwell and engine timing, then idle speed and idle air/fuel adjustment. With an auto tranny in drive you are shooting for an idle speed of 650 RPM. A/C will cause it to drop a bit, but 650 in Park or Neutral is a good place to be - assuming the air fuel ration adjustment screws are set properly.

 

[giantpune]

I would check dwell and engine timing, then idle speed and idle air/fuel adjustment. With an auto tranny in drive you are shooting for an idle speed of 650 RPM. A/C will cause it to drop a bit, but 650 in Park or Neutral is a good place to be - assuming the air fuel ration adjustment screws are set properly.

Is it 650 in P or N? I was thinking it was supposed to be 650 while in gear, which would put it around 800-850 while in park or neutral.

 

[jpaz]

Ok, so new carb and other things done. Sounds like you don’t have it tuned correct, float level not correct, hot idle not correct or possible vacuum leaks, but I have to agree with giantprune, not enough idle in gear. Hot idle should be checked with all accessories on and in gear, including turning on the headlights.

 

[Sheriff41]

Also check your hose to the trans vacuum modulator hasn't come off.

 

[Bill73Ragtop]

Vacuum leak would cause same behavior so might be worth checking. You mention new carb so checking around base gasket would be a start.

 

[73inNH]

OP do you know how to increase the idle on the carb? If so increase it a bit (you'll hear the engine run faster) and see if it's any better. There still may be an underlying issue, but let's at least determine if raising the idle stop the engine from dying.

If you don't know how to do so, let us know which carburetor it is and we will explain how to raise the idle.

 

[mrgmhale]

Is it 650 in P or N? I was thinking it was supposed to be 650 while in gear, which would put it around 800-850 while in park or neutral.

My bad, I misstated. The tiny iPhone screen caused me to overlook the error. 650 in Drive, yes. With A/C off in our case. I have found 750 in Neutral or Park lets our engine run at nearly 650 RPM in Drive, so depending on if Lynda is available to help keep the car in Drive and the brake on, r if I am working alone,I use either idle speed (650D, or 750 N/P) Some later vehicles 74 (and later) had an idle spec with A/C on, sometimes two idle speeds specified, one for A/C off, and the other for A/C on when a Throttle Position Solenoid (TPS) was used to bump idle speed a little when the A/C is on.

An aside, be sure to set your dwell and ignition timing to spec before adjusting the carburetor. While you are at it test the distributor vacuum advance diaphragm to make sure it is not leaking or ruptured. It won't impact your idle speed or quality (unless it is incorrectly connected), but a ruptured or leaking diaphragm will adversely impact your off idle performance and your MPG.

For our 71-73 Mustangs those Throttle Position Solenoids were used to adjust the idle in Drive when the TPS actuating rod/pin is extended, as opposed to using them top increase idle speed with the A/C turned on. And, of course, I have a YouTube videos showing how the TPS works, and how the base and TPS On & Off idle speeds are adjusted on our 73 Mustang Convertible (302 2v):

https://youtu.be/ljJ1uNy86wI

https://youtu.be/mwLwwUtI1cE

Here is another video where video where closer to the end I show how I adjust the idle air fuel mixture screws. There are a few ways to set the A/F idle screws, using a tachometer, using a vacuum gauge, using both tach anf gauge, and of course setting it "by ear." Later on in more concisely controll emission control environments we get into setting by "Lean Roll," using "Propane Enrichment," and/or using a CO/HC exhaust gas analyzer. For me, on these older Mustangs, I tend to "go by ear," although at times I will use a vacuum gauge and/or tachometer - depending on how I feel at the moment, heh heh... In the video description I provide the mm:ss into the video you can find idle or solenoid related info:

https://youtu.be/U-ETjhRqUwQ

 

[basstrix]

You said you have a new carb and new points. Was the timing re-set after the dwell/point gap was set? If not, you need to do this as changing dwell changes timing. With the new carb, could you have possibly changed the type of vacuum from a ported/timed vacuum to manifold vacuum (for the vacuum advance) on the new carb? Having vacuum advance connected to manifold vacuum will cause a bigger swing in idle speed between neutral and drive where timed vacuum wont have any affect.