Mondial runs lean on Acceleration

As you know, on accelleration you should be at 12 or a little less, although I have seen dynos where early K-jet accellerate at an A/F of 14. If you truly are that lean at 17, the engine will hesitate and sputter. I have found that the Ferrari V-8 QV will start to miss at A/F s over 16. And, if they are very lean under load, BAD BAD things can happen. Just ensure that what you are seeing is accurate and not an effect of something else (air leak, etc).

If you indeed are lean on accelleration and it is symptomatic with missing, based on what you have said the likely problem is the control pressure on your fuel injection. If you haven't, read a little bit on K-jetronic control pressure on-line. Culprits that springs to mind is the warm-up regulator, and/or the O2 sensor-mediated frequency valve, if your car has one.

Good luck, and hope to hear what was up.

 

This is a good question. There is no official info out there other than where the mixture should be set at idle. My understanding is that you can move the curve up and down by changing the idle mixture, but you cannot change the shape of the curve (at least not without expert help and physically altering the air sensor and/or the metering unit).

What I have found is that when I set my idle mixture (CO in the exhaust) to the specification in the manual, it is fairly lean under acceleration. In my case it was around 15. There was no detonation, and the engine made great power but it still makes me a little nervous.

I adjusted the idle screw richer buy a 1/4 turn and it dropped the AFR under power to around 13.5. If you think you are seriously lean I would start there. You should also check for air leaks in vacuum lines.

 

I have a very similar problem on an 85 Mondial that was brought to my garage last week. The engine has strong acceleration from idle to 5000rpms or more when first started in the morning and immediately driven. After about 90 seconds, (when it switches from open to closed loop?) the throttle response and power are greatly reduced, and the sound of the exhaust gains an odd burbling. The engine will have this problem until about 3200rpms and then it accelerates much stronger and the exhaust sounds wonderful. If engine speed is constant above about 3200, again, all is good. It will keep this pattern of driveability until it cools overnight. I made all of the usual checks, spark plugs (a little lean looking), ignition wires, vac hoses, grounds, etc all good. Monitoring the O2 voltage output using a Snap-On Vantage, I found the signal wave at idle to be good, voltage cycling from .4v to .5 to .6 then back again. If you tip in the throttle, the wave becomes a flat line at the bottom of the scale and the voltage drops below .2 and it takes several seconds for it to begin to pick back up. Adjusting the mixture screw in the CIS distributer did not fix it. Dying to throw a part at the problem, I chose the O2 sensor. Got a new Bosch from World Pac for $62. I thought that maybe the old one was responding too slowly. Nope, same problem. Although, it did improve throttle response and power ABOVE 3200rpms, slightly. My next step was going to be to begin with a more basic approach, testing fuel pump pressure, and all of the other CIS basic mechanical/electronic components. I checked the O2 monitoring relay, mine doesn't have an external or internal fuse, the diode checked ok. I can hear the frequency valve buzzing. I read some where on line to try jumping the wires on the Bosch sensor in the bottom of the coolant reservoir. Might try that tomorrow after I put the wheels back on her.