Car revs and sounds better cold?

[DMC Fanatic]

Hey guys,

I just had all my exhaust leaks fixed on the stock exhaust system. Both manifold gaskets were replaced as well as the gaskets for the crossover pipe. For some reason it seems like the car revs a lot better when the engine is cold(open loop) and has that nice VROOM sound. When the engine is hot, it almost sounds like it still has an exhaust leak and I can usually hear a little bit of popping from the exhaust. It does not do this cold though. The car has no vacuum leaks and the dwell swings from 30 to 40 degrees in closed loop. I was thinking about adjusting the mixture a tad rich to see if that helps but Im afraid to keep playing around with the mixture. Is what I'm describing normal? Can this even be a plugged catalytic converter? Any help is appreciated since I'm out of ideas at the moment.

Thanks!

-Sean

[Ron]

fyi- The manual calls for 35-45 (pulsating) for normal operation.

[Bitsyncmaster]

Just hold the wide open throttle switch on to test if a richer mixture will fix your problem.

[DMC Fanatic]

Can I rev the engine while pressing the switch to see if it sounds better at higher rpms?

[Bitsyncmaster]

Can I rev the engine while pressing the switch to see if it sounds better at higher rpms?

Yes. All the WOT switch does is set your lambda to open loop at 60% duty on the FV. Closed loop runs 30% to 40%. So your mixture goes to about 13 AFR.

[DMC Fanatic]

Here's a quick update: I pressed the WOT switch while the car was warm and the engine sounded good while revving it. So in that case, I adjusted the mixture for the dwell to swing from about 20 - 25 degrees. So far it seems okay and the engine has a little more pep now.To make the dwell higher though, I had to turn the mixture screw CCW which seemed wrong because thats supposed to lean it out. I'm using the Actron dwell meter from Sears. Is turning the screw CCW supposed to increase the dwell? Or maybe the meter is hooked up backwards? I have the green wire from the meter hooked up to the orange wire and black to ground.

[DMC Fanatic]

Sorry I meant between 40 to 50 degree swing on dwell meter^

[DMCMW Dave]

Sorry I meant between 40 to 50 degree swing on dwell meter^


A bit counterintuitive. You have to recall that the system is attempting to hit a certain mixture. When you lean out the base mix, it goes richer to hit that number. When you are completely out of the range of the system it will be stuck at the lowest number (if too rich) or the highest number (if too lean). When you are making the adjustment you are changing the mechanical relationship of the air flap to the fuel distributor. You are not directly changing what the computer does, the computer is reacting to the mechanical change.

You leaned it out. As you lean it the dwell reading gets higher as the system compensates for being too lean. If you set it to be (statically) richer the meter will read lower numbers..

[DMC Fanatic]

Thanks Dave! It makes more sense to me now. So do you think my dwell reading at the moment is good and within spec?

[DMCMW Dave]

Thanks Dave! It makes more sense to me now. So do you think my dwell reading at the moment is good and within spec?

Yes - that's within spec and you noted that it runs better.

[Bitsyncmaster]

You can't adjust the mixture unless you set it so far that it goes to the max or min dwell. If you do that you may as well disconnect the O2 sensor and run open loop.

You can put a wideband controller in the system with a wideband O2 sensor to make closed loop mixture adjustment. I have done that in my car.