How to Adjust Mixture on a Fuel-Injected 1800


May 27, 2007

Glenn,

I have a 1971 which is fuel injected. Changed all the injectors, lines, and "o" rings. Car runs good but very rich mixture and plenty of blue smoke. How do I check and adjust the mixture properly? Thanks.

Dennis Watkins


Dennis - There is no proper way to adjust the mixture, but it can be done. The fuel injection components are supposed to work together to provide the correct mixture for all conditions. Before you try to adjust the mixture using an undocumented procedure, you should first go down the entire troubleshooting list of fuel injection components in the Haynes manual or another workshop manual. Apart from the things you mentioned fixing already, there are several more components that may affect the mixture, especially vacuum lines and connections, manifold air pressure sensor and the fuel pressure regulator.

If everything checks out alright and it's still too rich, you can try adjusting the manifold air pressure sensor. Remove the plastic plug from the sensor and use a small screwdriver to adjust the underlying screw. Change only a half turn before testing. Sorry, I don't remember which way to turn to make the mixture leaner. Note that the manifold air pressure sensor has a diaphragm. If it is ruptured, your adjustments will not help. I haven't ever tried to test this diaphragm, but I imagine you could try sucking gently on the vacuum tube. If air passes through the diaphragm, it's toast.

I haven't owned a fuel-injected Volvo for many years, so you might get better information on the 1800 e-mail list:

http://autos.groups.yahoo.com/group/1800list

Good luck. -Glenn.


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