CIS: Adjust mixture for new elevation?

[j_green]

Hi all, I just recently bought a'74 911 coupe with a previously swapped in 3.0 from an '83 SC. The car was owned and sold in Colorado, I've brought it back to Arizona with me. The car was great in CO and ran with no issues, unfortunately the first time I went for a drive after getting it down here I had a couple large backfires and have been getting smaller ones each time I've taken it out.

The car had a pop off valve installed previously and the airbox seems fine, I think it's just running lean due to the lower altitude. I was under the impression the lambda system would control for that, so not sure if I'm expecting too much of it and should adjust it myself (or at a shop if needed) or if I should start troubleshooting more seriously. Let me know what you all think, thanks!

[icarp]

for 5000 ft in CO to ? in AZ put the 3mm allen in the sensor plate adjuster and turn the grub screw about 5 min clockwise , remember rich-in lean-out turn about 5 min per test forAZyou should not need more that two tries . If your idle or back to idle pulses then it is too rich , lean out 2 min on the clock
Ian
I live at 6000ft and make adjustments regularly , sea level to mountains

[Flat6pac]

Disconnect the oxygen sensor and turn the enrichment slightly to enrich. Turn slightly clockwise to enrich. Don’t over do the turn, keep it to less than a 1/4 turn. Know where you started from.
Reconnect the ox sensor.
Bruce

[j_green]

Awesome, I'll give that a shot. Thank you both!

[boyt911sc]

Test for unmetered air before attempting to tinker your fuel mixture. This is the most blatant mistakes committed by people trying to fix their CIS problem. Confirm the absence of sources of unmetered air first, then do the fuel mixture adjustment. Not the other way around.

Tony

[j_green]

Thanks for your input Tony, I did a quick smoke test this morning and didn't see anything obvious which is good. I think for my own peace of mind I'll go through as many of the diagnostics as I can on the fuel system and do a valve adjustment. Having just bought the car, it's probably best to know everything is working as it should.

[boyt911sc]

Originally Posted by j_green

Thanks for your input Tony, I did a quick smoke test this morning and didn't see anything obvious which is good. I think for my own peace of mind I'll go through as many of the diagnostics as I can on the fuel system and do a valve adjustment. Having just bought the car, it's probably best to know everything is working as it should.

JG,

How did you do the smoke test? Have you isolated the air box from atmosphere during the test? Many times, people failed to isolate the air box during a smoke test and erroneously find no visible leak. Keep us posted.

Tony

[j_green]

I mostly followed the steps here:
https://www.pelicanparts.com/techarticles/Porsche_911/07-ENGINE-Smoke_Pro_Vacuum_Leak_Test/07-ENGINE-Smoke_Pro_Vacuum_Leak_Test.htm

In through the pop-off valve and covered the metering plate up top with a bag/tape.

Went back to take a look and noticed an open port on the airbox, pictured below. That would be sucking in dirty air which isn't great but it's still before the metering plate.. but what should be connected there?

[j_green]

After some more poking around my next discovery was that there is in fact no O2 sensor

[Reiver]

J....is this a US '83 930-16 or a ROW 930-10...the ROW model does not have an 02 sensor and the fuel AFR is set by vacuum from the WUR.
I have a ROW '83 in Wickenburg and drive in Phx and the mountains often to 6k enroute to Prescott.
I set my CO/AFR to 3.4/13.2 and that works well at the dif elevations.
The 930-10 has a higher comp ratio than the US model so running a bit fat is also a safety measure.
I have a wideband AFR gauge in place of the clock....a good idea with CIS.
If you have a US model they are set lean and if the 02 has been disconnected they go to a pre set fault condition that may not be ideal....I ran my US model about 2.8 which is much fatter than the lambda would set it.
This of course will not pass smog but with collector insurance you don't need to.

[j_green]

Thanks Reiver, I've tracked down the engine number and it is a 930-16
So seems like my best bet will be to take it to a shop and have them dial in the CO until I can get an O2 sensor put in. AFR gauge definitely sounds like a good investment, and fortunately my clock is already broken so I won't lose any functionality if I go that route!
Do you have a shop in the valley you'd recommend? My google search lead me to Patrick Motorsports, which is nearby me and seems to have a good reputation.

[Reiver]

Stuttgart SW....480 968 6764...the owner Jack has been in the indy Porsche biz for decades and is knowledgeable and very, very honest. Great guy.
If you call ahead he'll warm up the CO machine for you and adjust it...that'll take just a few minutes. He is nearby too just prior to the 202 off of University.
Drive in and out.

[eastbay]

Originally Posted by j_green

I mostly followed the steps here:
https://www.pelicanparts.com/techarticles/Porsche_911/07-ENGINE-Smoke_Pro_Vacuum_Leak_Test/07-ENGINE-Smoke_Pro_Vacuum_Leak_Test.htm

In through the pop-off valve and covered the metering plate up top with a bag/tape.

Went back to take a look and noticed an open port on the airbox, pictured below. That would be sucking in dirty air which isn't great but it's still before the metering plate.. but what should be connected there?

That is the nipple for the charcoal canister hose

[stlrj]

Originally Posted by boyt911sc

Test for unmetered air before attempting to tinker your fuel mixture. This is the most blatant mistakes committed by people trying to fix their CIS problem. Confirm the absence of sources of unmetered air first, then do the fuel mixture adjustment. Not the other way around.

Tony

Mixture adjustments compensate for unmetered air since most engines come that way.

[Reiver]

Lots of folks disconnected the cannister hose (charcoal element on the right side fender wall) as if it fails charcoal can be sucked into the airbox.
Block off that opening though.

[j_green]

Thanks for the recommendation Reiver, I'll give him a call this afternoon.
Also good to know on the charcoal cannister. Looks like most of my evap system is gone, so at least it was intentional. I plugged it already as well.

If you'll all indulge me one more question, I found this connector without a mate as I was looking for vac leaks and I can't figure out what it's for. Anyone know?

[Reiver]

When you see Jack at Stuttgart ask him and he'll tell you where that connection goes.... my Row operates dif than the US so can't get a fix on that...Jack will know.

[Reiver]

One of the best mods for anyone running CIS injection is a wideband AFR gauge...you know exactly what is going on with fuel delivery at all times....idle/cruise/wot...and if there is an issue you know it asap....and can adjust at will.
I got the analog as it matched (kinda) the reg gauges but some like the other route.

[dhanl82]

I agree on the importance of having a wide band air fuel air/fuel ratio. I have had one for 5 years, and would not own a cis car without one - takes all the unknowns away and makes tuning so much easier and accurate for all driving conditions.

[stlrj]

Originally Posted by j_green

... had a couple large backfires and have been getting smaller ones each time I've taken it out.

Unfortunately, you will need a new airbox and no amount of AFR gizmos will fix that.