Greetings, wise folks!

I've been trying to puzzle through the problems which cropped up about a month ago on my K-jet equipped '81 B21 with 190k miles. Here are the symptoms:

Intial startup is quick and smooth. After about 15 seconds, it gets *really* lumpy, and takeoff bogs down and missing is frequent, particularly at low rpm and heavy applications of throttle. When the car gets warmed up, idle is only mildly lumpy, and takeoff is satisfactory with no missing unless I hit it with a heavy throttle. Going up grades warmed up, the engine misses at low rpm. Downshifting into the 3000+ rpm helps a lot to smooth things out.

I was initially suspicious of a significant vacuum leak. I'm not sure that's the problem -- the intake manifold gasket is only 36 months old, and the bolts are down tight. I've isolated the charcoal canister and the interior heater control vacuum lines, with no change. All other vacuum lines are fresh and tight. The injectors, injector holders and o-rings are only 18 months old. I've sprayed all around the engine with propane and carb cleaner on multiple occasions (I had the injector holders 'swimming' in carb cleaner) with no effect. The big rubber bellows from the distributor to the intake manifold is on tight.

In the elctrics department, the spark plugs are 6 months old, cables are 6 months old; I've sprayed them and the harness down with water mist and I see no sparking. The coil is 36 months old, the engine harness I rebuilt 36 months ago. I resoldered the fuel pump relay circuit board 4 weeks ago. The control pressure regulator (warm up regulator) was rebuilt 3 weeks ago. I replaced the oxygen sensor 3 weeks ago. On the suggestion of a colleague that the temp. sensor for the fifth injector may be malfunctioning and the injector is spraying all the time, I unplugged the injector, and there's no change in engine performance.

Last summer, my '83 LH-jet equipped B23 displayed similar symptoms for several days before its Hall effect sensor pickup died. Might the reluctor coil in the distributor of my K-jet be similarly ready to give up the ghost?

I'm stumped and am about ready to take it to a $$$ Bosch specialist. Any last suggestions on where to turn next before I take that plunge?

Thanks a million in advance.

Rob

I don't think you have a O2 or frequency valve problem. That system isn't suppose to be able to cause enough difference to be noticeable by the driver. It's strictly a fine tuning system.

I do agree that it sounds like a lean problem. Have you looked at the injector spray patterns. It should be a very fine spray at idle and increase with movement of the air meter. A technique for doing this is to pull out one injector and slip a 3 ft. piece of clear vinyl tubing over the end. Stick the other end into a 20 oz. plastic soda bottle. Then you must plug the hole in the head. I use a black rubber plug I found at the hardware store where I bought the tubing. Start the engine and observe the spray. Try revving the engine a little also.

Alternately, you can test all 4 injectors at once by pulling them all and installing tubing and bottle on each. Instead of running the engine, pull the main fuel pump relay and jumper the two connections to the pump on the socket ( I forget the pin numbers ). You can then vary the flow by moving the air meter by hand. The advantage here is you can tell if the injectors are flowing the same volume by comparing the fuel in the bottles. You can also check that there is no leakage from the injectors when the air meter is at rest.

If you find a problem here, try some fuel system or injector cleaner. I use a 5 gal. gas can by disconnecting the fuel pump inlet and running a hose to the can. This concentrates the cleaner into only 5 gals. instead of the hole tank. I also let the system sit over night with the clearner in it before putting fresh gas in the can and flushing the system. I did this with the "alternate" setup above and you could really see the dirt in the bottles. My car had 280 kmiles.

Hi, John!

Back again...

"I don't think you have a O2 or frequency valve problem. That system isn't suppose to be able to cause

enough difference to be noticeable by the driver. It's strictly a fine tuning system. "

Just thought I'd let you know directly that I followed up on the suggestion of Jim's to look into the frequency valve. You can read more about it in my reply to him, but when I pulled the harness connection off to measure voltage in the harness to ensure that it was getting juice, the motor really bogged down and stalled. Maybe it's that the Lambda adjustments made by the O2 sensor and ECU are indiscernable by the driver; but when the frequency valve was rendered inoperable, the motor really pigged out.

I'll get some Techron and run two bottles through and see if the problem goes away. (Cross your fingers for me...)

Thanks again for your help!

Rob

I'm wrong, Jim is right. The freq. valve can make a big differance if the valve itself is full on or full off. I was thinking of the "limp home" mode which the system goes into if the O2 sensor fails.

A idea hear, if the valve's duty cycle is so far off that it is affecting drivability perhaps disconnecting the O2 sensor's lead would help. This should put the system into the 50% duty cycle limp home mode. In this mode it should not affect driveability. To verify the duty cycle, check the voltage at the system test point. This is located near the system relay on the left fender. It is just a single wire hanging out of the harness with a single pin connector on it but nothing pluged in. If the valve is operating at full on or full off you will see 12V. or 1V. approx. respectively.

John -- thanks for your tip. I'll get the VOM out this afternoon and give it a try.

Rob

Thanks, John!

I am about due to run a bottle of Techron through -- I usually do that every 6 months, but it's been about a year now... However, the injectors are pretty new, 18 months -- would they crud up that fast?

Rob

Can you hear the frequency valve?

Your symptoms are of general leanness, which could well be caused by the frequency valve and/or the lambda box not getting power. Their power comes from a relay on the drivers side front fender, which is energised by one set of contacts in the fuel pump relay.

Jim -- I appreciate your input. Is there another name for the frequency valve? I've got a Bentley manual, and K-jets for the turbos are covered in that. What is the frequency valve, what is its function, and where does it live? ...and it's powered by that relay on the driver's fender near the battery?

I'll look into the Bentley fuel injection book as well and see what I can see.

Thanks!

Rob

It's sometimes called a chopper valve; it bypasses the control pressure past the fuel distributor, under the control of the lambda box. The lower the control pressure, the richer the mixture; if the valve isn't operating(it buzzes, you should be able to hear it with the hood open), the mixture will be lean. The valve is a small cylinder(~1"dia. X 2 1/2" long) clamped behind the fuel distributor with a fuel line on each end and a 2-pin electrical connector in the middle. +12 volts is fed to one pin and it's grounded by the lambda box through the other. If it isn't working, the O2 sensor voltage will be fixed and low, ~.1-.2 volts. See http://www.swedishbricks.net/faq/fio2.html

My '78 245 would intermittantly lose power to the FI relay(on the fender); sometimes I'd be idling in traffic and the idle would go from normal to lumpy and wierd and back randomly. Once on a long trip(just before I fixed the problem) the relay continuously lost power; the engine ran hotter than usual, idled strangely, had even less power than usual, but got ~30 mpg. The culprit turned out to be the fuel pump relay, where one set of contacts(not the fuel pump ones, obviously) wasn't closing, so the FI relay wasn't pulling in.

There are obviously other possibilities, but your problem sounded familiar.

Hi, again, Jim!

Thanks for getting back to me so promptly. I didn't find an entry for the 'frequency valve' in the Bentley 240 book index, nor was it depicted in the CI fuel injection section. So I went to the Bentley Bosch fuel injection book, and there was something depicted called a 'lambda valve'. In the text, it read "lambda valve, also called a 'frequency valve'..." Voila! So I went back to the Bentley 240 book under lambda systems, and they said go to 'emissions controls'. So...under the emissions controls index, there's a reference to frequency valve. Pretty byzantine...

Because I use a direct drive flex fan on this B21, rather than the clutch fan, the whoosh of air drowns out most noises. I used a vinyl hose, however, to hear that the frequency valve was indeed buzzing (I found it in direct view, right in front of the big bellows). The Bentley manual has a procedure to determine if it's receiving voltage, so I pulled off the harness connector to perform this test, and the engine immediately bogged down and stalled. I measured resistance between the terminals on the valve, and it was 2.3 ohms -- Bentley says it should be between 2 and 3. So...it seems that it's functioning, (and indeed has a huge impact on driveability) and the valve itself is within resistance specs.

Rats...struck out there, it seems... That would have been an easy fix.

Thanks again for your input!

Rob

I had an erratic idle problem on my '82 k-jet, and the O2 sensor and frequency valve were OK. My car is old enough to be emissions exempt, so I just played around with the mixture adjustment (3mm allen wrench in the hole on top of the fuel distributor) until it ran smoothly. No problems for over a year, gets 25 mpg highway, and starts and idles great. Try it if you have ruled everything else out.

Colin

Hi, Colin!

Thanks for your input. I can't really mess with that adjustment around here as compensation for other systems probably being on the fritz -- We've got pretty severe exhaust emissions inspections here in SE Penna.

I'm running some Techron through right now. However I have noticed something odd. A cold front passed through yesterday, and the air is now much less humid. Car's been running almost perfect yesterday and today; just an occasional miss... I'm wondering if it's a wiring problem, and humid air/condensation is fouling up something in the harness... I'm going to go over the wires again and clean connections and check for bad insulation.

Rob