Thermo-vacuum switch operation

[Horsebox]

Quick question that I'm trying to get my head around.

My thermo-vac switch is jammed in the "warm engine" position. So the control pressure regulator never sees the engine vacuum during warm-up. But the ignition advance diaphragm gets the vacuum once the engine is warm and the throttle is off the idlespeed microswitch, via the solenoid. Cold operation is wrong because no vac to the CPR but warm operation is correct with vac applied to the ignition distributor once the the throttle is off-idle.

So the question is: is the the mixture rich or lean during warm-up?

My brain is a bit messed up trying to figure it out!

Thanks! :banghead:

Mark

[PJ Grady Inc.]

Quick question that I'm trying to get my head around.

My thermo-vac switch is jammed in the "warm engine" position. So the control pressure regulator never sees the engine vacuum during warm-up. But the ignition advance diaphragm gets the vacuum once the engine is warm and the throttle is off the idlespeed microswitch, via the solenoid. Cold operation is wrong because no vac to the CPR but warm operation is correct with vac applied to the ignition distributor once the the throttle is off-idle.

So the question is: is the the mixture rich or lean during warm-up?

My brain is a bit messed up trying to figure it out!

Thanks! :banghead:

Mark

Stop banging your head as you could cause damage to the wall:)! Without the vacuum feed the pressure would be higher causing the fuel mixture to be leaner.
Rob

[David T]

Stop banging your head as you could cause damage to the wall:)! Without the vacuum feed the pressure would be higher causing the fuel mixture to be leaner.
Rob

It may be that the thermo switch is OK but the hoses are connected wrong or they are leaking. The CPR should still control the warm-up cycle but the main purpose of the vacuum on the CPR is to give a little extra enrichment during acceleration when cold, kind of like an acceleration pump on a carburetor. There were some service bulletins. Refer to D:01:11-12 and ST-18-10/81 and ST-32-12/81 Make sure the delay valve is oriented correctly.

[Horsebox]

Thanks, I'd forgotten all about the service bulletins!

I'd actually got it the other way around in my head. I figured since no vacuum was getting to my CPR during warm-up, that would be the same as say, accelerating up a hill with the throttle wide open. Very little vacuum in that case either, and that's when the system is meant to enricher the mixture when the engine is cold.

I suppose it boils down to whether you think engine manifold vacuum (depression) is highest at idle under no load or at full chat trying to accelerate uphill.

Mark

[Ron]

I suppose it boils down to whether you think engine manifold vacuum (depression) is highest at idle under no load or at full chat trying to accelerate uphill.(At further the risk of your poor head ;-):
There is no vacuum at the WUR/CPR at idle when cold (because the port feeding it is upstream of the throttle plate) and as you know, virtually absent when at "full chat". So, ~same difference here...

Just in case, for clarity...
If WUR/CPR vacuum is missing, while the engine is cold, it would run lean during the first part of accelerating ONLY -- It would not matter at idle, etc...

[PJ Grady Inc.]

(At further the risk of your poor head ;-):
There is no vacuum at the WUR/CPR at idle when cold (because the port feeding it is upstream of the throttle plate) and as you know, virtually absent when at "full chat". So, ~same difference here...

Just in case, for clarity...
If WUR/CPR vacuum is missing, while the engine is cold, it would run lean during the first part of accelerating ONLY -- It would not matter at idle, etc...

"There is no vacuum at the WUR/CPR at idle when cold (because the port feeding it is upstream of the throttle plate)"(Quote-Ron).

I disagree Ron...there IS vacuum when cold because it takes it directly through the vacuum switch under the intake manifold.
The port at the throttle valve leads to the charcoal canister in the L/H body pontoon. Your car's vacuum routing is apparently incorrect.
In all cases the stock DMC PVR should be routed as per the vacuum hose routing label that should be affixed to the inner engine cover.
Rob

[Ron]

"There is no vacuum at the WUR/CPR at idle when cold (because the port feeding it is upstream of the throttle plate)"(Quote-Ron).

I disagree Ron...there IS vacuum when cold because it takes it directly through the vacuum switch under the intake manifold.
That's right -- Thanks Rob!!
I don't know what I was thinking...I just put a new vacuum switch in the day before...(Routing is correct...I think I got turned around at the "W" pipe when thinking of the source/port ;-) :banghead:

Anyway, although I had the reason wrong, it would act as I said, I.E. During "warm-up", "Without the vacuum feed the pressure would be higher causing the fuel mixture to be leaner" (than it should be), is true for acceleration, but not while idling.
Agree?

[PJ Grady Inc.]

That's right -- Thanks Rob!!
I don't know what I was thinking...I just put a new vacuum switch in the day before...(Routing is correct...I think I got turned around at the "W" pipe when thinking of the source/port ;-) :banghead:

Anyway, although I had the reason wrong, it would act as I said, I.E. During "warm-up", "Without the vacuum feed the pressure would be higher causing the fuel mixture to be leaner" (than it should be), is true for acceleration, but not while idling.
Agree?

Yes that sounds about right but I don't we're helping Mark with a diagnosis by pursueing our line of thought here so I'll readdress his post.
Rob

[PJ Grady Inc.]

Quick question that I'm trying to get my head around.

My thermo-vac switch is jammed in the "warm engine" position. So the control pressure regulator never sees the engine vacuum during warm-up. But the ignition advance diaphragm gets the vacuum once the engine is warm and the throttle is off the idlespeed microswitch, via the solenoid. Cold operation is wrong because no vac to the CPR but warm operation is correct with vac applied to the ignition distributor once the the throttle is off-idle.

So the question is: is the the mixture rich or lean during warm-up?

My brain is a bit messed up trying to figure it out!

Thanks! :banghead:

Mark
All automotive fuel systems are designed to run richer in the cold warmup phase so that's a given. Bad solenoid switches (NOS style that is) are quite rare so check your hose routing carefully before looking elsewhere Mark. Have you found out anything more?
Rob

[Ron]

...but I don't we're helping Mark with a diagnosis by pursueing our line of thought here so I'll readdress his post.
RobThis leaves one wondering why you didn't just say "yes" and leave it at that then...

I really don't think Mark minds me making sure he is not left with the impression that the answer to his question is simply "lean", as is implied in your original reply, and your resulting correction of my explanation of why that is a "half truth". If you don't see that that was my intent, maybe you should try getting up from the other side of the bed...

Whatever!

[PJ Grady Inc.]

This leaves one wondering why you didn't just say "yes" and leave it at that then...

I really don't think Mark minds me making sure he is not left with the impression that the answer to his question is simply "lean", as is implied in your original reply, and your resulting correction of my explanation of why that is a "half truth". If you don't see that that was my intent, maybe you should try getting up from the other side of the bed...

Whatever!

I was trying to get back to his original question. I think you are being a bit oversensitive as I'm not having a bad day as you implied and was not trying to slight you. Why are people so touchy on these forums? I'll leave this thread under your care from here on. My apologies for the bruised ego.
Rob

[Ron]

I was trying to get back to his original question. I think you are being a bit oversensitive as I'm not having a bad day as you implied and was not trying to slight you. Why are people so touchy on these forums? I'll leave this thread under your care from here on. My apologies for the bruised ego.
RobYou took me wrong (and it seems you were and are being touchy to me). I don't get a bruised ego over someone correcting me, especially when I'm trying to help someone else -- I sure wouldn't thank them if I did!?!
Actually, that's what I thought I was doing -- Your answer to his only question, given the absence of WUR vacuum, "...is the the mixture rich or lean during warm-up?" was asked and answered. So, I guess the problem was I didn't see a question to "get back to"??
Granted, why no WUR vacuum and why vacuum is always at the solenoid valve obviously comes to mind, but he seemed to be sure a bad thermal vacuum switch was causing that. (Which makes sense IF that vacuum is actually routed through the vacuum switch, at all....)
Why you seem to think it all doesn't relate to "the question" directly (and at least the the irony in the last part of your reply) is beyond me.
:dunno:

I was only trying to cover pitfalls, Rob. E.G. With the given information, it could be running rich/lean at idle and he is trying to determine if he has more than one problem (and thinking either is over missing WUR vacuum at cold idle, isn't going to help...).
Sorry if I stepped on your toes in the process -- Again , that was not my intent.

======

Back to waiting on our regularly scheduled program...

[PJ Grady Inc.]

You took me wrong (and it seems you were and are being touchy to me). I don't get a bruised ego over someone correcting me, especially when I'm trying to help someone else -- I sure wouldn't thank them if I did!?!
Actually, that's what I thought I was doing -- Your answer to his only question, given the absence of WUR vacuum, "...is the the mixture rich or lean during warm-up?" was asked and answered. So, I guess the problem was I didn't see a question to "get back to"??
Granted, why no WUR vacuum and why vacuum is always at the solenoid valve obviously comes to mind, but he seemed to be sure a bad thermal vacuum switch was causing that. (Which makes sense IF that vacuum is actually routed through the vacuum switch, at all....)
Why you seem to think it all doesn't relate to "the question" directly (and at least the the irony in the last part of your reply) is beyond me.
:dunno:

I was only trying to cover pitfalls, Rob. E.G. With the given information, it could be running rich/lean at idle and he is trying to determine if he has more than one problem (and thinking either is over missing WUR vacuum at cold idle, isn't going to help...).
Sorry if I stepped on your toes in the process -- Again , that was not my intent.

======

Back to waiting on our regularly scheduled program...

Perhaps we were both being touchy? Anyhow as you say let's move on as it seems Mark has already done. Another case closed good buddy!
Rob

[Ron]

Perhaps we were both being touchy? Anyhow as you say let's move on as it seems Mark has already done. Another case closed good buddy!
Rob
Agreed - Works for me!
:cheers1:

[Horsebox]

Still here! Thanks for the interesting replies. I was more interested for the sake of it to be honest, rather than trying to fix something.

I get the impression the cars fueling was designed by a miser who wanted it to run lean to within an inch of its life. After replacing the injectors over the summer I accidentally drove it around at 4% CO and it was like a different car - could almost describe it as fast! :-). Might keep it that way!

I wonder if the performance would benefit from plumbing the CPR so that it gets vacuum all the time, and not just when cold. I've removed all the evaporative plumbing that serves no purpose except vacuum leaks, so I have the barb underneath the throttle body doing nothing at the moment - that would do for the vac source.

Bad plan? Just feels like the engine would benefit from more fuel most of the time!

[David T]

Still here! Thanks for the interesting replies. I was more interested for the sake of it to be honest, rather than trying to fix something.

I get the impression the cars fueling was designed by a miser who wanted it to run lean to within an inch of its life. After replacing the injectors over the summer I accidentally drove it around at 4% CO and it was like a different car - could almost describe it as fast! :-). Might keep it that way!

I wonder if the performance would benefit from plumbing the CPR so that it gets vacuum all the time, and not just when cold. I've removed all the evaporative plumbing that serves no purpose except vacuum leaks, so I have the barb underneath the throttle body doing nothing at the moment - that would do for the vac source.

Bad plan? Just feels like the engine would benefit from more fuel most of the time!

The fuel system was designed to run as close to optimum stochiometric ratio as possible. You would get a little more power if you ran rich but your emissions would go way up and you would burn out your catalytic converter. The best advice is to get your system running the best you can as it was intended to operate. As for the evap system, it does not use up any power and is very simple. Again, the best advice is to try to keep it working as it was intended. A side effect, you won't notice any gasoline fumes, they get stored and then burned up.

[Ron]

I wonder if the performance would benefit from plumbing the CPR so that it gets vacuum all the time, and not just when cold. I've removed all the evaporative plumbing that serves no purpose except vacuum leaks, so I have the barb underneath the throttle body doing nothing at the moment - that would do for the vac source.
Bad plan?
I doubt it would do any good at all since the CPR will go to its maximum pressure as soon as it hits 104F, which wouldn't take long even with the electrical unplugged.

I'm with David. ...Your best bet, across the board, is to set it up stock. (I run mine a tad rich, but it has no cat.)