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Rich warm up for K jet

t8fanning

t8fanning

8v are still cool, right?
Joined
Oct 10, 2010
Location
Vancouver, WA
I've been doing a ton of reading trying to figure this out, but haven't found anything yet. If you know an applicable thread, please point me to it.

My problem is that on cold start my engine runs very rich (~10), and sometimes chugs like it is only running on 3 cylinders or something. After a minute or so, the chugging stops and it idles fine, but still rich (maybe 10-11). The car runs rich until the coolant is fully heated, and then it runs what I think is normal on light throttle (~14-15) and richens up on WOT (~11). So it seems my only problem is when the car is warming up.

Last weekend I took apart the control pressure regulator. Everything seemed clean and fine, but I cleaned it anyway. I thought it might be an issue with the lambda system, so I just measured my O2 voltage this morning after everything had warmed up and it was 0.87 V. That seems high from what I've read, but isn't it just indicating a rich condition?

I'm new to K-jet, so bear with me as I probably don't know anything. I haven't yet taken any fuel pressures, so I am trying to piece together a fuel pressure testing setup.
 
Sometimes the screens get clogged up, sometimes they just wear out from years of dutiful use. I'm chasing a similar issue in my '83 turbo, but the CPR checks out OK according to the test instructions on cleanflametrap.
 
I read through most of that thread the other day, and am meaning to build a pressure test setup like that. Do you have any extra banjo bolts you would sell? K-jet junkyard cars are few and far between here. I'm sure I can source the gauge, valve, and fuel lines locally.

The frequency valve does typically buzz, yesterday for the first time I noticed, it was intermittently on and off while the car was idling. It's supposed to buzz right?

My understanding was that the frequency valve is tied to the lambda system, but does the lambda system have the capability to adjust the A/F ratio that much?
 
The O2 sensor 'reads' the oxygen content of the exhaust gasses and converts that to a voltage that varies from 0.1v to 0.9v as andysbeta stated. That is input to the Lambda unit that translates that voltage to a variable duration voltage to the frequency valve. The valve opens and closes (dwell) to release the control pressure back to the fuel tank. More control pressure leans the fuel mixture, less control pressure enriches the mixture.

The CPR does the same thing varying the mixture by the operation of the heated element to enrich mixture when the engine is cold. Observing the control pressure compared to the graft slope of your specific CPR will tell you if it is functioning correctly.

The CPR, O2 sensor/Lambda control unit and frequency valve work in a circle to manage the fuel mixture as an antiquated mechanical/electrical computer.

Then there is the air/fuel adjustment screw. Don't touch it unless you have a dwell meter.

I forgot, here is a much better description than the above:

http://forums.turbobricks.com/showpost.php?p=5004662&postcount=35

Just think, a year ago I couldn't even spell Lambda.

I have plenty of 8mm banjo connectors but not the 10mm. Send me a PM with your address and I will send one of the small ones. Sorry, you are on your own for the 10mm. Mercedes, BMW, VW, Volvo and many others used the K-jet system. Surly you can find some car with a 10mm left on it.
 
Yes. The valve will buzz with varied intensity as it does it's job adjusting the air fuel mixture. It is a kind of pressure valve - which is what keeps the air fuel ratio at the 14.7 range. And yes, it will switch the fuel ratio in closed loop operation in conjunction with the o2 sensor. If it is not doing this then the fuel distributor fuel adjustment is either off, or the operating fuel pressure is either too high, or too low - which is all governed by the CPR (control pressure regulator). Also another factor is vacuum leaks , bad injector seals.
 
TestPoint said:
Then there is the air/fuel adjustment screw. Don't touch it unless you have a dwell meter.
Click to expand...

Crap. I've adjusted it a few times to try to make my warm idle stoichiometric. I've followed the bentley manual when they say to remove a line from the fuel distributor and richen the mixture until fuel just starts to flow out, then lean it a half turn. Is this poor practice? Do I need to find a dwell meter and adjust it properly now?

I just ordered another used CPR to test. It may not be the problem, but it'll be good to have a backup.

I've also recently replaced my injector O rings and checked for vacuum leaks by using carb cleaner and listening for idle changes, but I haven't found any leaks yet.
 
t8fanning said:
Crap. I've adjusted it a few times to try to make my warm idle stoichiometric. I've followed the bentley manual when they say to remove a line from the fuel distributor and richen the mixture until fuel just starts to flow out, then lean it a half turn. Is this poor practice? Do I need to find a dwell meter and adjust it properly now?

I just ordered another used CPR to test. It may not be the problem, but it'll be good to have a backup.

I've also recently replaced my injector O rings and checked for vacuum leaks by using carb cleaner and listening for idle changes, but I haven't found any leaks yet.
Click to expand...

Uh oh. Careful on that screw. Most of the time, that isn't the problem at all. You will need a dwell meter to get it set correctly again.

As far as vac leaks, carb cleaner is ok, but see if you can get ahold of that spray aerosol electronic/contact cleaner. Works much better in my experience.
 
Will I be ok in the meantime? Will having my dwell off run anything above its capacity and burn it out or something?

What about this tool?

http://www.harborfreight.com/lcd-automotive-multimeter-with-tachometer-kit-95670.html

Also, the Bentley manual says to check the dwell there is a hookup on the driver's (US) side fender by the power distribution board. Is it just a free wire around there? Any ideas what color it is? I've seen a free wire with a connector under the strut tower by the firewall, and I don't want to plug into the wrong wire.
 
The lead at the rear of the engine is for attachment of a starter button. The dwell lead is at the front left and yes, it is just hanging there with a black plastic connector on the end.

The HF digital meter will work just fine and do lots of other things also.
 
Great. My local HF has one, so I'll get it tonight and adjust my dwell to spec and report back. Thanks for the help and input.
 
Update. Got a dwell meter from HF and set my idle CO mixture. It now has a median value of ~43* in closed loop.

I have a question though. The Bentley manual says to first check the dwell in open loop, mine was 45*, which is in the specified range. But no matter how much I adjusted the screw in open loop, the dwell didn't change. When I grounded the green wire attached to the O2 sensor, the dwell increased to over 68*, another expected result. When I reconnected the O2 sensor and adjusted the screw, the dwell changed fine. Additionally, my wideband is showing stoichiometric, so I think everything is set right. I just want to confirm everything sounds ok.

I also sprayed aerosol electronic cleaner all over the place, focusing on the injectors. There was no change in idle, so I think I don't have any vacuum leaks.
 
Update 2. I replaced the CPR and re-checked the dwell, but still had an issue with strange idle for the first minute the car was running this morning. As soon as it warmed up though, everything seemed perfect.

I have a new fuel filter coming in case the current one is clogged and messing up line pressure, and I am in the middle of building a pressure tester, but what else can I do diagnostically?
 
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