Converting lambda fuel head to non-lambda

boosted79 · 06-29-2024, 06:23 AM

After studying the Bosch k-jet with lambda technical manual I think I have this figured out. The only difference between the non-lambda and lambda is the fixed orifice that supplies the lower chambers with fuel pressure and of course the FV that dumps fuel from the lower chambers back to the tank thus causing a larger differential across the fuel slits and opening the differential pressure valves more to richen the AF ratio. So simply drilling out that fixed orifice will allow the lower chambers to operate at system pressure just like a non-lambda head. And of course the FV would be removed and the supply port plugged or simply disconnect the FV and leave the lines in place. Then tune it just like a non-lambda system with an adjustable WUR.

I intend to do this when I rebuild this engine.

boosted79 · 07-01-2024, 06:22 AM

I was hoping to get some comments on this. I wish I would have looked at that orifice that supplies the lower chambers when I installed the new diaphram. But I'm not taking it apart again now, I just want to get the car running at this point. Under a steady state condition (no changes to airflow, ie. no change to the plunger position, the lower chamber pressure will equalize with the system pressure even with the orifice. This assumes the FV is inoperable, ie. closed. But I'm thinking that under an air flow increase, ie. more flow and pressure to the top chambers that orifice may not allow the diaphram to push the fuel out from the lower chambers quick enough and as a result cause a lean condition? At this point I'm just going to try reducing the control pressure and adjusting the idle mixture screw to try to get it to run w/o the FV operating. I don't want to get into troubleshooting the lambda wiring mess to figure out what the problem is. I'm eventually going to remove all of it.

mark houghton · 07-01-2024, 03:27 PM

Quote:

Originally Posted by boosted79

I was hoping to get some comments on this. I wish I would have looked at that orifice that supplies the lower chambers when I installed the new diaphram. But I'm not taking it apart again now, I just want to get the car running at this point. Under a steady state condition (no changes to airflow, ie. no change to the plunger position, the lower chamber pressure will equalize with the system pressure even with the orifice. This assumes the FV is inoperable, ie. closed. But I'm thinking that under an air flow increase, ie. more flow and pressure to the top chambers that orifice may not allow the diaphram to push the fuel out from the lower chambers quick enough and as a result cause a lean condition? At this point I'm just going to try reducing the control pressure and adjusting the idle mixture screw to try to get it to run w/o the FV operating. I don't want to get into troubleshooting the lambda wiring mess to figure out what the problem is. I'm eventually going to remove all of it.

There are CIS wizzards among us that know a boat load more than I, so all I can do is follow your thread because it seems to make logical sense. I for one would love to do entirely without the Lambda circuits...all I do now is run with the O2 sensor unplugged/open loop and tune around it. Of course the frequency valve is still buzzing away but my fear is what ifff that freak valve were to die?
For kicks many many moons ago I unplugged the freq valve and attempted to tune around it. Not happenin', she ran wayyy lean according to my AFR and I couldn't compensate with simply cranking down the idle mixture screw. I'm all for getting rid of anything that may eventually strand me.

RarlyL8 · RarlyL8's Garage

We stock converted -145 lambda delete modified fuel distributors and set them up to match the needs of the engine. Same goes for the WUR's.
As you know you cannot just delete the lambda system as the frequency valve is required to keep the AFRs within spec.

boosted79 · 07-03-2024, 03:18 AM

Yes, I know you can't run a Lambda head absent the FV without making adjustments but I'm trying to determine what the actual physical differences are between the Lambda and non-Lambda heads. The only thing I can come up with is the orifice that supplies fuel into the lower chambers. This is what the Bosch tech manual says:

"In order to be able to vary the pressure in the lower chambers, these are decoupled (in contrast to the conventional K-jetronic fuel distributor) from the primary pressure. Decoupling is by means of a fixed throttle. A further throttle connects the lower chambers with the fuel return. "

The "fixed throttle" is the orifice between the system pressure existing under the plunger and the lower chambers. The "further throttle" is the FV.

In order for the FV to drop the lower chamber pressure the fixed orifice has to be small enough to restrict the flow going into the lower chambers as the FV dumps fuel from the lower chambers into the return, otherwise the pressure in the lower chambers will not drop.

With the FV disabled, as the plunger moves up and down with changes in air flow the diaphram has to move up and down to force fuel into and out of the lower chambers. With the fixed orifice in place the flow entering and exiting the lower chambers will be restricted.

So simply opening up that orifice should allow the lambda head to operate just like a non-lambda head.

But adjustments to the spring pressure in the differential valves and or changes to the control pressure will still be necessary to get the correct AFR with the FV out of the picture.

9dreizig · 07-03-2024, 12:11 PM

Quote:

Originally Posted by RarlyL8

We stock converted -145 lambda delete modified fuel distributors and set them up to match the needs of the engine. Same goes for the WUR's.
As you know you cannot just delete the lambda system as the frequency valve is required to keep the AFRs within spec.

Brian, I was under the understanding that the Lambda was really just for idle AFR's ? Am I incorrect ?

flightlead404 · flightlead404's Garage

Quote:

Originally Posted by 9dreizig

Brian, I was under the understanding that the Lambda was really just for idle AFR's ? Am I incorrect ?

Correct, goes open loop above 1,500 rpm if I remember correctly.

That frequency valve has a lot of range however, and works wonderfully to control mixture with Franken CIS

Reanimotion · 07-08-2024, 11:37 PM

A couple of data points worth noting before deciding if the Drill-baby-Drill option is for you.

The frequency valve in open loop runs at 50% duty cycle, and doesn't deviate much from that when warm and in lambda control mode.

On the 964 Turbo the frequency valve is driven at 75% for 0.5 seconds to provide acceleration enrichment

For a properly running engine, modified or not, the Lambda Delete heads must be set at a point somewhere below the maximum flow possible if the frequency valve was still controlling things.

Flow and sharp edges do not play well together so inspect the existing restriction paths and consider shape and surface finish before allowing Harrison Ford near your fuel head.

boosted79 · 07-21-2024, 05:33 AM

I got this '88 running without the FV. After I rebuilt the fuel head I checked the pressures. System was 6.0 B, CCP was 2.7 at 25C, WCP was 4.0. I shimmed the system reg. spring to get 7 B, adjusted the WCP to 3.65 (Leask WUR). It would sputter and smoke with some pedal and run like crap, this is with the car sitting. I finally disconnected the power to the WUR so it sees CCP all the time. Voila, it runs and sounds great. I do not have my AEM WB installed so don't really know what the AFR is but all I want to do is drive it about 30 miles from storage to my shop. I will stay out of the boost.
What doesn't make sense to me is why it was running so rich with the WUR powered, it should run leaner with the higher CP. But that is not what I'm seeing just looking at the exhaust. Crazy. Anyway it's getting a rebuild with SC cams etc. so not going to worry about it now.