Cold Start for PV

[Les W.]

Can someone help me understand what the RPM's should be on a cold start for a 1972 LT-1 when the coolant temp is around 50 degrees? What happens with mine with the fast idle on the high step of the cam at start up, the RPM's go to about 1800 for around 30 to 45 sec. then a drop of 300 RPM's. Then it may take 3 minutes to climb to the 2350 RPM's without tapping the accelerator. Is this the norm? Thanks for any explaination.

[Duke W.]

Re: Cold Start for PV

What you report appears to be somewhat normal. The service manual should have a spec for the fast idle speed, but usually it's specified as hot. What does the CSM say?

For example, my '63 340 HP fast idle speed spec is 1750 hot, but on a cold start in mild temperatures the initial fast idle speed is about 1500.

If one were to allow the engine to warm up without tapping the accelerator the idle speed will increase to 1750 after a few minutes as the engine approaches normal operating temperature.

The only thing I don't understand about your situation is why the initial cold idle speed drops off 300 after 30-45 seconds.

Duke

[Tim E.]

Re: Cold Start for PV

Les - I would suggest 2 things....

First, if you haven't already purchased it, pick up a copy of the '72 PV manual. The expected fast and cold idle speeds will be listed there for all engines. With any luck, there will be a description of any expected RPM creep and a description of the kickdown process & timeframes.

Second, send a note to the 72 Team Leader (the Team Leader will perform your PV). He'll happily explain exactly what he'll be looking for.

This is for a '66 327/300hp but may be similar to how your car will need to behave. My PV judge expected to see the fast idle in the range, right now, with little to no RPM creep up or down, and regardless of outside air temperature. A pretty stiff standard, but that's the behavior he expected to see, explained it to me in advance, and any deviation would be a failure (which mine did in the past on a 95 degree ambient day).

Tim

[Duke W.]

Re: Cold Start for PV

This is for a '66 327/300hp but may be similar to how your car will need to behave. My PV judge expected to see the fast idle in the range, right now, with little to no RPM creep up or down, and regardless of outside air temperature. A pretty stiff standard, but that's the behavior he expected to see, explained it to me in advance, and any deviation would be a failure (which mine did in the past on a 95 degree ambient day).

Tim

What does the CSM say about setting the cold idle. If it is speced "hot" as on my '63, then the PV judge was dead wrong!

Duke

[Thad L.]

Re: Cold Start for PV

I think that drop in RPM's after 30-45 seconds is the TCS temp switch warming up and taking away the vac advance!

[Les W.]

Re: Cold Start for PV

Yes, the drop in RPM is do to the temp switch. I have the PV manual and it is not clear as to time to fast idle speed which in my case is to be 2350. I'll contact Stan Falenski to have him explain how it is suposed to work. Thanks all for your help. Les

[Edward J.]

Re: Cold Start for PV

Les, the fast idle will climb as the choke butterfly starts opening this is normal after the car starts to warm with out touching the gas. I believe the fast idle spec. is on the emisson label under hood.

The CEC sytem for 72 will be operational on cold start until the engine temp. reachs 82 degrees in which the vaccum supply is shut off to the vacuum advance and the rpm drop about 300 rpms on 4 speed cars. slightly less with automatic cars. Good luck with PV.

[Michael H.]

[Edward J.]

Re: Cold Start for PV

The cold idle spec. is set warm and as you say once the engine is started the actual spec. may change from car to car. But I think that this spec maybe what the PV judge will be looking at?

[Timothy B.]

Re: Cold Start for PV

The cold idle spec. is set warm and as you say once the engine is started the actual spec. may change from car to car. But I think that this spec maybe what the PV judge will be looking at?

Ed,

To add to the judging point on fast idle what if the air temp is say 75* and the fast idle does not set on the high step of the cam. Does the car fail under this condition.

Usually when the choke completely closes the high step is set and when the vacuum pull is applied after starting a touch of the throttle drops to the second step.

[Edward J.]

Re: Cold Start for PV

Tim, If started on cold start the choke butterfly sets on the highest set of fast idle. if you do not touch the throttle the rpms should be at the spec.when warm, Another way maybe if the PV judge set the fast idle cam, This may not be something he may know how to do.Then the question arises what if the car doesn't stay running as most carburators don't like to when cold. Thank god for fuel injection. Carburators always had to many drivibilty problems.

[Timothy B.]

Re: Cold Start for PV

Ed,

If it 75* the choke may not slap closed completely so the high step may not be set, what happens then?

[Edward J.]

Re: Cold Start for PV

Ed,

If it 75* the choke may not slap closed completely so the high step may not be set, what happens then?

Tim, I am not sure about what the PV judge would do on a warm day, but I have been to some events that by pass the cold start on warmer days. or when cars are being driven in at 7:00 am for an event.

[Jerome P.]

Re: Cold Start for PV

Yes, the drop in RPM is do to the temp switch. I have the PV manual and it is not clear as to time to fast idle speed which in my case is to be 2350. I'll contact Stan Falenski to have him explain how it is suposed to work. Thanks all for your help. Les

Les,

Please let us know what Stan had to say.

[Les W.]

Re: Cold Start for PV

I will speak to Stan sometime this weekend to verify that what I am experiencing on cold start is correct or not. I will let you know next week.

Les