When I start my car up after it's been sitting long enough to be completly cool, it feels like a racehorse that has to be held in check. Two or three minutes of warmup and it'a a nice little 305 smog motor with barely enough power to get out of it's own way. It isn't that the RPMs are high, they're sitting around 750-1000 and it still has more power than normal at 1000 rpm. Now, I'm thinking that the fuel flow is higher and the timing is probably different, because on a carbed vehicle, you'd run the choke for a while which either chokes off the air flow or enriches the fuel flow. In either case, it sends a very rich mixture until the engine warms up. Anyway, any insight is appretiated.

Dan

 

mine does the same thing. played with the timing but nothing worked. what gives??

 

A couple of things can cause that. I'd invest in a lifter valley oil deflector or an Air-Gap manifold to keep the intake mixture cool.

Next get a 180 degree thermostat and make a fan switch.

That is all i can think of at the moment

 

It is becasue your O2 sensor is not warmed up yet, and the veh is running richer. Once it warms up it starts reading the fuel mixture in the exhaust and will go from rich to lean and back and forth as it see's fit.

 

ti is also partially the illusion of fast idle. with the car pulling against the brakes and all teh extra fule around it feels like it takes off better, but at that point it is actually slower than once it is warmed up.

later
tim

 

anyone have any thoughts about whether cold motors run slightly higher compression or not?

 

a leak down on a cold engien woudl be worse than on a warm engine. once the engine has soem temperature in it teh metal will expand slightly and seal better.

later
tim

 

High revs before the car warms up isn't good for the motor either. Just a thought.

 

I've heard its also because the tranny fuild is very cold, so it thickens up a bit, and this tightens up your convertor. Mine feels "strong" off the line when its cold too, but theres no way its actually making more power. Plus I don't wanna rev a cold motor very hard, I've heard thats not a good thing to do. Like this BMW... it had LEDs in the tach, and the redline gets higher as the motor warms up... how trick is that :hail:

 

bmw are sweet machines , gonna get one for my old lady i think

 

Or that new Lexus with the rotating tach that raises the redline as it warms up.. :hail:

 

Mine does the same. The thottle response is unreal!!! So let's look at each of the comments and theories and put it all together.

1: We all know the during a cold start, it's not so much that the O2 sensor is cold, but the readings are totally ignored when the ECM is in open-loop mode. Thus, the rich mixture. With this is mind, it seems that our motors love the rich mixture (again, a proven fact about the TBI's) but it likes it on the lower side of the RPM scale as well. What to do? Richen the mixture up a bit (with more fuel press, I believe).

2: Engine temp: This one is probably gonna be beaten back and forth, but my guess is that the cool temps allow more timing throughout the RPM range due to lower combustion temps (less chance of engine knock). Install a lower thermostat.

3. Tranny fuild: I must admit, I never thought of that one, but it makes plenty of sense since the fluid it thicker when cold, the torque convertor is able to apply more torque to the input shaft on the trany, thus more torque to the rear wheels. Of course, this is only true on cars with auto tranys! Install a trans-cooler!

4: Fast idle: Sure, this engine is making more power as the RPM's raise, and since at idle the RPMs are upto 1000 more than warm idle, there's more power just waiting to be released instantly. How to fix this one? Raise the idle, right? Wrong. Install a higher stall converter. But make sure it's matched to the rest of your bolt-on parts (intake, cam, heads, etc...).

5: Temp of air coming into the engine. During a cold start, the temp of the air coming into the engine is the same temp of the air outside of the car. As the engine warms up, the air under the hood raises and so does the air coming in. Try to install a cold-air intake setup and/or a air-gap manifold.


These are just my ideas on these as I've spent a lot of time trying to figure it all out.

 

Uh yeah...the oil cannot properly coat the bearings when it's cold because of it's thickness. So basically it's almost metal on metal. Why do you think turbo cars aren't allowed boost til warm? Cause the oil cokes the turbine because it's too thick.

I think one of the biggest influences in the power making ability of the engine, is the cooler denser intake charge. And when the engine isn't warm, the heat isnt being transferred to the incoming air/fuel because there is no heat! Thus the combustion is a much more efficient one.