warm up..what happens?

[techspy]

I have been noticing how much difference there is in performance/smoothness after my S4 has warmed up. I uderstand that such in the trans, the fluid needs to warm up to allow proper operation. But what about the engine? I understand that the fluids need to get up to the correct temp, but how does that effect the smoothness/performance? Until my S4 warms up, it is really rough (sputters, cuts out etc), and is generally very tempermental. Any comments suggestions?

John
94 S4

[autocross7]

This is typical and I would not be too worried. My Esprit (a 1988 Turbo/injected)runs the same way... as well as my Austin Healy, and RX-7. Add to that list a couple Ferraris and Porsches I'm more than familiar with.

You pretty much hit the nail...
The oil pressure when cold is typically very high so the motor has to work through it - Esprits run a pretty heavy oil so you know when it is cold.

The exauhst manifold also allows escaping gas to travel more freely when warm. If you get the chance to see a race car up close, some teams will rap this area. Although, this warms up pretty quik...

The lambda (or O2) sensor must also warm up a bit before it sends the proper signal to the engine management system.

Combustion also occurs better once the motor gets warm. Cold air is easy to compress, but the heat existing in the cylinder helps ignition. Top fuel engines actually shut electrical systems down about half way through the quarter mile (whats left of them anyway). Those engines continue to run due to the heat and compression they generate and can only be shut off by shutting down the fuel flow. Extreem yes, but same physics are in your Esprit to a smaller degree.

Newer cars and cars with more advanced computer control engine management systems have the same issues. However, they 'mask' the issues better by auto adjusting the timing advance and fuel mixture.

I'm sure others can add to the above, but you get the idea. Your idle speed should drop quite a bit as well once the motor runs up to temp... sorry for the length!!! but i hope I helped.

Drive topless!!!
Cameron

[techspy]

Very good points Cameron. I really didn't take into account the more power that it takes to pump cold thicker oil. That coupled with the o2 sensor needing to warm up before sending correct info probably explains the situation. I just wonder how there can be so much difference between my S4 and a newer car.
I have been thinking about wrapping my exhaust, mainly for keeping the heat down in the engine compartment. But maybe It will help reduce the warmup time too.

John
94 S4

[mikelr]

John,
I noticed this as well on my S4, but I don't believe it has that much to do with cold oil or lambda sensor.
The O2 sensor on our cars is heated so it should be up to temp pretty quickly. I feel that the rough running is due to a lack of fine tunning on Lotus's part. GM cars of the same vintage running the same injection gear run very well when cold due to the extensive programing that GM developed.
I think maybe Lotus was a little lax on the cold run progaming on purpose. It is definetly better for the engine to be run for a few moments before putting any substantial load on it and this little qurk forces you to do this.
Just my take on it anyway.

[karlfranz]

techspy said:

I have been noticing how much difference there is in performance/smoothness after my S4 has warmed up. I uderstand that such in the trans, the fluid needs to warm up to allow proper operation. But what about the engine? I understand that the fluids need to get up to the correct temp, but how does that effect the smoothness/performance? Until my S4 warms up, it is really rough (sputters, cuts out etc), and is generally very tempermental. Any comments suggestions? John 94 S4

When the Esprit is started with a cold engine the ECM is running in what is know as "Open Loop Mode". In this mode the ECM ignores the signal from the O2 (Lambda) sensor. Instead it uses a fuel map table along with inputs from the coolant temperature and MAP sensors. This is what causes your engine to run rough - the ECM is just doing its best to guess what the proper air/fuel ratio should be.

After 1) a specified amount of time has pased; 2) the coolant temp is above a certain value; and 3) the O2 sensor reports it is hot enough to operate properly, the ECM switches over to a "Closed Loop Mode". In this mode, the ECM uses the varying voltage output of the O2 sensor to calulate the proper fuel to air ratio. It uses this info to control how long to fire the fuel injectors in order to maintain the ideal 14.7:1 air/fuel ratio that makes your engine smooth out.

Cheers.

[mikelr]

karlfranz said:

When the Esprit is started with a cold engine the ECM is running in what is know as "Open Loop Mode". In this mode the ECM ignores the signal from the O2 (Lambda) sensor. Instead it uses a fuel map table along with inputs from the coolant temperature and MAP sensors. This is what causes your engine to run rough - the ECM is just doing its best to guess what the proper air/fuel ratio should be. After 1) a specified amount of time has pased; 2) the coolant temp is above a certain value; and 3) the O2 sensor reports it is hot enough to operate properly, the ECM switches over to a "Closed Loop Mode". In this mode, the ECM uses the varying voltage output of the O2 sensor to calulate the proper fuel to air ratio. It uses this info to control how long to fire the fuel injectors in order to maintain the ideal 14.7:1 air/fuel ratio that makes your engine smooth out. Cheers.

That's very true Karl,
But that does not stop older GM cars from running smooth when cold (in open loop).

[Dr.Hess]

Does the S4 still have the exhaust back pressure valve?

Dr.Hess

[karlfranz]

mikelr said:

That's very true Karl, But that does not stop older GM cars from running smooth when cold (in open loop).

Those smooth-running older GM cars weren't trying to pump well over 250HP out of a 2.2L I4 engine either.

[mikelr]

Dr.Hess said:

Does the S4 still have the exhaust back pressure valve? Dr.Hess

Yes

[techspy]

My S4 still has the backpressure valve and all electronics still installed, but the valve it fixed open. I don't think that is effecting it...is it?
And I wonder about the older gm vehicles with the same ecu (an old GMC pickup I believe) although different tables etc, but why would they run better cold? Just because of the tables?

John
94 S4

[benfell100]

Unless you are a diehard and want to keep it 'absolutely' bone stock I would rip that rusty bit of sooty junk (EBPV) off the exhaust and fit a spacer and plug the vacuum line (important) with a screw and some super glue or something. The damn thing weighs about 2kg, gets jammed open/shut when you least expect/need it and was only a means to getting the car emmissions compliant for the first 2 minutes of a cold start. When I took mine off I never wanted to see it again.
Dom