YACT: Adjusting AFM without a gas analyzer?

[DurocShark]

I know this is a long shot, but thought I'd see if anybody has a trick for adjusting the mixture on a Jetronic Fuel Injection rig without a gas analyzer.

I can do it with the exhaust sniff test, but it comes out too lean. Not a problem on a water cooled car, but with my air cooled bus the higher temps caused by lean running are dangerous.

On the VW board all I got was, "introduce a vacuum leak. If the idle goes up it's too rich." I'm hoping for something more precise than that.

(Yeah, I know. I should just take it to a shop. But I hate other people touching my cars...)

 

[Rogeee]

Pick up one of these, warm up Gauc, fire up the propane torch, set the torch to a medium flame, blow out torch (leave the gas on), now introduce the propane to each carb, if the idle goes up, it's lean, if it goes down, it's rich, now adjust your fuel mixture screws no more than 1/4 turn (either rich or lean), keep doing this until until you get a slight stumble when appying the propane.

Now turn the propane down to it's minimum setting and do the above procedure once again, this will get you very very close to the optimal air/fuel ratio.

 

[DurocShark]

Oops.

78 Bus... Fuel Injected.

But that's a good idea. I like that better than the vacuum leak method. Thanks.

 

[Rogeee]

The procedure is slightly different when adjusting the mix on fuel injection.

Fully warm up the bus, this means that your oil temp must be at normal operating temp (take it for a good 20 minute ride on the highway), make absolutely sure your fuel injectors are throughly cleaned before starting this procedure, the vehicle has had a recent tune up (spark plugs, wires, cap & rotor, air filter, fuel filter).

When using this procedure do not under any circumstance turn the CO screw more than 3/8 of a turn in either direction, always mark it's original position by scribing a mark next to the screw.

Let thye bus idle for exactly 2 minutes, no less,no more, aplly the propane on it's lowest setting and watch for either s stumble or a increase/decrease in idle speed (you are going to need an accurate tach), if the vehicle stumbles and dies immediately, turn the CO screw inward 1/8 of a turn, if it stumbles and immediately recovers, leave the adjustent alone, if the idlegoes up, turn the CO screw outward 1/8 of a trun and repeat the test.

Once you have this adjustment to the point where the engine stumbles and then recovers on it's own, go drive the bus once again and watch for stumbling, pinging.
If either of these are present, turn the CO screw back to where it was and check for leaks at the EGR valve and piping along with the Auxilary air valve and it's associated plumbing.

If you find you cannot adjust it correctly,PM me and I will guide you over the phone.

 

[DurocShark]

Thanks man.

The reason this came up was: The bus was tuned 2 years ago. Passed smog, etc. Last year I helped the then owner do a top end refresh (new heads, re-ringed, etc). We replaced all the rubber on the FI and the fuel tank vent lines and fuel lines too.

This week I bought it off him. When I took it to smog it on Monday it got 3.16% CO. Failed. Limit is 3.00%. I swung around to the parking lot and using the sniff test I leaned it out and re-smogged it. 2 full turns out got 1.01% CO. I swung back into the parking lot and turned the screw in one turn figuring to split the difference. But I'm not comfortable with this seat-of-the-pants adjustment.

On my Volvo I can adjust to the sniff test because cooked heads aren't much of a risk. But on a Type 4 engine, the heads are much more sensitive to the heat from a lean burn.

I'll try the propane this weekend. I have a bottle right here...

 

[Rogeee]

Two full turns ?

Jeebus, ignore my adjustment procedure then, set the CO lean so it will pass, then richen it back up for driveability and engine longevity