Timing / CO

[timc]

1986 930, All smog removed, Euro muffler w/o cat. Right now my CO is approx 2% and timing is stock. How much advance over stock timing can I safely run without getting into detonation? And is 2% good for CO? I always run prem fuel.

[timc]

Any opinions on the above?

Is it common for these cars to have a bit of poping in the exhaust at idle and when backing off the gas? What causes this?

[odog]

too lean. what sparkplugs are you using? W3DPO's? Have you mapped your distributor to check the advance curve? How are your plug wires? Valve adjustment good? What are the HC's? Why do you want to get more advance?


off throttle...think of CIS- still squirting fuel + heat in exhaust=that magical burble!

[timc]

Thanks for the reponse. I think you are correct, the lean would explain the poping at idle. The poping at idle was apparently due to the cold weather. We just had a cold spell right after I set the CO and the poping was occurring when the temp was below 50. Yesterday no poping at all, temp was above 50 all day. I guess the cold compressed air leaned out the mixture at idle.

Is 2% ok for CO?

I just did a major at my friends P shop. Valve adjust, plugs, cap, rotor, removed smog, removed cat, added euro muffler, set CO and timing.

[NathanUK]

Increase your CO to the max you are allowed or approx 4-5%

[javadog]

I run 3% CO and stock timing (25 to 26) on 91 octane. I can run 28 to 29 on 93 octane but there isn't much of a noticeable difference.

JR

[timc]

Mine is an 86 "catalyst" car, so my CO spec's are .6% +- 2%. I have the cat removed, so should I still follow spec's (fat would be 2.6%) or go with the 4-5%?

[javadog]

I'd re-check that CO spec for your car. The spec on an '86 is 0.6, plus or minus 0.2, not plus or minus 2.0.

Like I said, mine is happy at 3.0. Having said that, these cars differ a little from one to the next, and some are modified. I have another 930 that is happiest at a diffferent CO. I'd suggest you find a good shop to adjust yours and let them play with it a little. You want the leanest mixture that is still acceptable at full throttle under load and doesn't give you driveability problems at lower speeds and loads.

Or, you could talk to someone at a shop that specializes in the 930, like Imagine Auto.

JR

[timc]

Thankyou, you are correct, it is .6% +- .2%. It is currently set at 2%. I'll tweek from there to see where it runs best. What effect will leaving the O2 sensor permanently disconnected (other than poor gas mileage) be on setting the CO outside of spec? I no longer have the cat so I am wondering if I can leave the O2 disconnected.

[NathanUK]

Yes, leave it disconnected and set your CO to 4% or 5% if you are allowed. This will help you from leaning out under full boost.

Of course you should really have a high quality wideband AFR meter fitted and check your AFR's throught the whole range (rpm, load, boost etc). These can be adjusted by having your WUR modified by Brian Leask.