ke jetronic mixture screws

High idle could be caused by a vacuum leak or similar - any unmetered air getting into the system.

 

why you open a new thread? this is getting confusing when you look in 2 or 3 years and have then problem to find what you look for.

 

I would think the plunger is in contact with the air sensor plate at all times with a correctly adjusted CIS unit. Slight turning of the adjustment screw (Few degrees, not turns) will then alter the ratio between air and fuel just as per your description. The ratio is adjusted at the factory (Bosch, most likely) and the screw is then locked with some sort of an anti tamper mechanism. The setting should be life long. If you have no evidence of the adjustment screw being tampered with, i.e. anti tamper mechanism still in place and not damaged, then you need to look for other problems that can cause a fuel air mixture issues (If that's what you have).

Best, Peter

 

The setting is not life long. Bosch has gone to great lengths to publish materials, train people and offer equipment for the proper adjustment and tuning of all of the earlier systems including CIS. The adjustment was not sealed except on later US versions and then only to comply with US law. Were were given very specific information on how to remove those seals.
We were required by Ferrari to remove those seals and complete all adjustments including fuel mixture during new car preparation prior to delivery to the buyer. I cannot remember a single case of a car being delivered by the factory that was in specification. There are far too many variable that the system is incapable of coping with on its own for it to remain in proper tune on its own.

 

Pretty familiar with it already thanks. No, when there is fuel pressure the screw is in constant contact.

 

Many years ago when I had a TR, I ended up buying a 4-Gas Analyzer so I could adjust the fuel mixture. As I recall when adjusting the mixture, I had to put a rubber plug into the adjuster screw access hole after each adjustment - otherwise the vacuum leak would throw the readings way off. Once I got things right, I would thread bolt into the hole (with a rubber o-ring).

 

IIRC, on K-Jet, the plunger is in contact with airflow plate mechanism when fuel pressure is present, but KE-Jet has a specified "play" distance.

Are both of your banks exhibiting the identical (bad) behavior? If so, I'd be more suspicious of a measurement or O2 sensor problem. Are you measuring the unplugged O2 sensor voltage when it is warm/hot? An O2 sensor's output is meaningless until it is fairly hot (like running the engine until the water temp gauge is at least 155 deg F).

 

If a US car it had a blank, pressed in aluminum plug sealing the hole preventing access to the screw that covered the adjustment. By law when we removed that plug it was supposed to be replaced. The factory screw had a tapered seat and no O ring. The V8s had the blank aluminum plug and no screw. They were not even threaded.

 

Thanks for the information. One could maybe argue that if the fuel is unchanged over the lifespan of the system then no adjustments should be necessary. What I basically try to say is that if you turn that adjustment screw you need to have the right competence and tools (Or experience) and not least you need to be able to determine that all other systems are working as intended before you change the air / fuel ratio.

Best, Peter

 

Many more variables than just fuel composition. Until electronic systems were able to monitor and adjust themselves which came well after CIS, all systems gave us adjustments and they were needed.

I will agree adjusting it by ear or any method mot accurately measuring exhaust gasses is not only a waste of time but potentially hazardous to the car.

 

The factory screws on the Testarossa KE airflow meters have a square seat with no o-ring. The head of the screw is a smaller diameter than a regular 5mm allen or flat-head machine screw. When I come across a car that is missing these screws (it has happened more than once, and the cars ran like crap), I machine down the head of a 5mm allen screw to the same diameter as the original Bosch and it works great.

When this screw is not in place is causes the car to have an unmetered air leak which causes the injection system to go lean. When I am adjusting them on a car, I have a pair of factory Bosch rubber plugs on a wire with a loop in it (they were the factory Bosch plugs on VW Rabbit and BMW 320I CIS injection units, before they had to be sealed) that I use to plug the units while I am making adjustments
Image Unavailable, Please Login

 

My first Testarossa was a real mess, it would run, but it was a project car. Some previous idiot had removed the access plugs to adjust the fuel mixture and never put them back in. When I adjusted the air-bypass screws they had no effect, that's when I found the massive air leak. Since I didn't even know what the original bolts looked like, I just used a bolt & o-ring to seal things up. Great pictures Motob....really clears things up!

Many great folks on this fantastic forum helped me get that old TR running right. I learned so much from Steve Magnusson and Rifledriver...and others too. At times I was pulling my hair out, but in the end that TR ran and drove great. It's been quite a few years now, but looking back....I really miss those days.

 

Both Steve Magnusson and Rifledriver are a great source of knowledge!!

 

when you use a wide band O2 sensor then you see how sensitive this screw change the mixture.

right