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Old 10-02-2017, 12:07 PM   #1
Bricktothefuture
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Default K-jet Lamda AFR

Ok - here's the latest on the rebuilt 245. '79 B21f w/kjet lamda, RSI Stage II NA cam.

Got my timing more or less worked out - got one of the adjustable cam gears on sale and set it about 4 degrees advanced, ignition timing at 12 degrees. Power band around 2500-3000RPM, drives really well.

Added a wideband sensor w/analog output for my k-jet ECU. Here's where I'm getting stuck. I'm not sure where it's most important to be near 14.7 (or 14.3 as I was advised the RSI cam would appreciated a little more fuel.) I'm aware that having the aftermarket cam changes everything so I know I need to compromise somewhere since k-jet can't really compensate.

Right now I'm around 13.2 at idle, but hit at lean as 15.4 under load (3000RPM going up a hill, full throttle, etc) Steady cruise is around 14.2-14.8.

Is it worth being really rich at lean to add more fuel so I'm at stoich at full throttle? Or should I lean things out a bit and not worry about the occasional stretch where I'm running lean? Don't want to toast any valves, but don't like spitting extra gas out of the tailpipe either...
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Old 10-02-2017, 03:14 PM   #2
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Would be helpful to see what the actual CO% is at idle. Cam with overlap can throw off the O2 readings a lot at low RPM.
I ended up modifying ECU inputs on the K-Jet to switch into open loop whan at idle running a K-cam because it wanted to go too rich.
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Old 10-02-2017, 03:42 PM   #3
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Would be helpful to see what the actual CO% is at idle. Cam with overlap can throw off the O2 readings a lot at low RPM.
I ended up modifying ECU inputs on the K-Jet to switch into open loop whan at idle running a K-cam because it wanted to go too rich.
Huh. If only I had an EGA... Might ask if the shop in town would let me hook up to theirs for a few min.
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Old 10-02-2017, 06:53 PM   #4
dl242gt
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On a kjet ecu there is a pin 7 for enrichment under certain engine conditions. If your version isn't one with pin 7 enrichment you could use a never lambda controller and have terminal 7 for enrichment. The turbo ones have pin 7, and 11 for even more fuel. You can use a throttle switch and have it ground terminal 7 at full throttle to help with the fueling under load.

I would also suggest adjust the basic dwell at idle of the lambda to about 39-42 degrees dwell. My kjet turbo uses a enem V15 and it likes the idle a bit richer. I set it for 39 degrees dwell. Nowadays it is probably more important to keep it to the rich side since we have at least 10% alcohol along with the gas. The stock setting is from 41-44 degrees dwell. Lower dwell more fuel at idle, more dwell means you are leaning it out at idle. Be sure to only adjust with the 02 good and hot. Rev at 1500 for about 30 seconds before checking the dwell setting.
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Old 10-03-2017, 09:10 PM   #5
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Hmmm, I think my '85 turbo K-jet lambda works differently than what's being described.

- Until the O2 sensor is up to operating temperature, idle and cruise use a fixed "open loop" frequency valve dwell of 43° The "open loop" idle mixture CO/AFR is adjusted with O2 sensor disconnected using the hex screw on the pie plate. Normally, it's set for slightly rich (1% CO / 14.3 AFR).

- Once the O2 sensor is up to temperature, the lambda controller takes over and continuously swings the mixture back and forth to center the AFR around 14.7. This applies for idle, cruise, and any other time that the enrichment switches aren't activated. If the average AFR is high (lean), the lambda controller increases the frequency valve dwell to add more fuel, and similarly decreases dwell when rich. Unless you unplug the O2 sensor, lambda will stay around 14.7 (needed to keep the cat happy and exhaust clean).

- Under acceleration, boost, or cold weather startup, one or more enrichment switches closes and the lambda controller goes to higher dwell values for enrichment.

- You can lookup the "terminal 11 trick" on the home turbobricks.com page under articles. I have no idea how well it works. These days, most folks go to LH2.4 or MegaSquirt to provide proper fueling with non-factory setups.
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Old 10-04-2017, 07:07 AM   #6
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I'm on early k-jet lamda - no enrichment or thermal sensor. All I've got is the O2 sensor, ECU, and frequency valve. My wideband outputs an analog signal for the lamda ECU.
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Old 10-04-2017, 03:17 PM   #7
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Ideally the mixture is adjusted with a fresh oil change and air filter. Then with the o2 disconnected, engine fully warm you set the basic idle mixture using a CO meter. You also check to see that with the o2 disconnected you get 45 degrees default dwell. Then you reconnect the sensor and keeping the o2 hot by revving the engine a bit. You now check the id,e dwell setting and use the same mixture screw to get an idle dwell as I described above. Slightly richer for you with the cam in there.
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Old 10-04-2017, 04:56 PM   #8
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In place of a CO meter can I use the wideband with analog output disconnected to set basic idle mix? Would that be at 14.7?
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Old 10-04-2017, 05:37 PM   #9
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I second what Dave said.

Hiya, Dave! This reminds me when I came to the board back in '04 with the same question(s) about K-Jet and you helped me out with this exact same advice. I was rebuilding and fine-tuning the system and knew zip about K-Jet. I was completely in the dark. Good stuff to see you still in here helping the fellas out. Hats off!

For the OP: Once you get it set up, no vacuum leaks, the system basically stays that way. Mine has been bone stable. For maintenance, my .02 worth of advice is to run a fuel system cleaner with PEA (Chevron Techron or Redline) which is what Bosch recommended just before your oil change. Keeps the fuel system and especially the injectors nice and clean.
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Old 10-04-2017, 05:53 PM   #10
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Yes, use the wide band to get the basic co adjustment. Then reconnect and use the dwell meter to setup the lambda cycle.

Thank you so much. It's good to still be here. I appreciate the long term friends I've made here over the years.
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Old 10-04-2017, 06:15 PM   #11
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Quote:
Originally Posted by keesue View Post
I second what Dave said.

Hiya, Dave! This reminds me when I came to the board back in '04 with the same question(s) about K-Jet and you helped me out with this exact same advice. I was rebuilding and fine-tuning the system and knew zip about K-Jet. I was completely in the dark. Good stuff to see you still in here helping the fellas out. Hats off!

For the OP: Once you get it set up, no vacuum leaks, the system basically stays that way. Mine has been bone stable. For maintenance, my .02 worth of advice is to run a fuel system cleaner with PEA (Chevron Techron or Redline) which is what Bosch recommended just before your oil change. Keeps the fuel system and especially the injectors nice and clean.
Rebuilt engine. Before I reassembled it I cleaned EVERYTHING - lines, dizzy, WUR, etc. As close to new as I could get on a budget!
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Old 10-04-2017, 07:43 PM   #12
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Quote:
Originally Posted by Bricktothefuture View Post
I'm on early k-jet lamda - no enrichment or thermal sensor. All I've got is the O2 sensor, ECU, and frequency valve. My wideband outputs an analog signal for the lamda ECU.
Does your wideband have 2 output wires - one for dash gauge and one connected to K-Jet Lambda? If so, is the K-Jet output configured for Narrow Band O2 Sensor emulation? K-Jet is expecting a narrow band O2 sensor with a ~0.1volt output when leaner than 14.7, and a ~1.1volt output when richer than 14.7. If you're connecting the dashboard 0volt to 5volt output to K-Jet, it will confuse the lambda controller.

The K-jet lambda controller is pure 1970s analog electronics - opamps, transistors, resistors, capacitors; not a single logic gate and no CPU. (See this beautiful writeup: http://cleanflametrap.com/kjetControlller.htm).

By reprogramming the Narrow Band O2 emulation chart using the software from the wideband manufacturer, you should be able to adjust AFR for idle and cruise -- instead of the normal narrowband switch point of 14.7 AFR, you can move the 0.1volt and 1.1volt AFRs to be centered around a richer AFR (such as 14.3). The lamba controller will adjust the frequency valve so that the "narrowband" O2 signal is at ~1.1v 50% of the time and at ~0.1v 50% of the time.

Assuming steady flow and no lumpy cam effects, an AFR of 14.3 is about the same as a 1.0% CO reading - adjust the pie plate screw with O2 wire disconnected (and taped off so the sensor won't short to ground).

A more "modern" lambda controller with enrichment inputs would be a good investment to prevent going extra lean during boost.
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Old 10-04-2017, 08:20 PM   #13
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Wideband outputs an analog signal to match what lamda is expecting, but isn’t controllable or programmable. I’ll put up a link to the one I bought in the AM in case I’m missing something.

Edit - no need for boost enrichment, I’m N/A...
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Old 10-04-2017, 08:30 PM   #14
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With a cam in there you may want more top end fuel. You will see with your gauge. If you do need more fuel. An affordable way to increase fueling is to up the overall system pressure. Raising the system pressure is one of the 240 turbo performance mods and it will work well with a n/a engine, too.
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Old 10-05-2017, 11:46 AM   #15
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I went with modifying a WUR to make it adjustable to lower the control pressure instead of raising the system.
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Old 10-05-2017, 02:40 PM   #16
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That's a good way to go. What we discussed in the past was using a warmup regulator that had an enrichment circuit built into it. The one I was gonna try was the Audi turbo version. I think this is also how the B21ET got it's enrichment and that made a lot more power than a us lambda version B21FT.
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