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Isn't this replacing parts time? You have replaced everything else. What about replacing whatever WUR is in there. I know Mark has some. The 79 I gave him had a good one on there. Isn't the WUR like the brain of the whole thing?
Hi Pete,
There are some real K-jet experts here, and I am the opposite. Please listen to them, as I know you will. I would need to have confidence in the basics of hooking up the gauge set, then knowing what the pressure readings indicate. I am not certain exactly what pressure you are reading; control pressure or system pressure. People who tune these systems all the time could probably narrow down your search. I agree that your problem is probably somewhere in the fueling system, and although it ran fine before, something has knocked it off its game. I wonder if there are rubber fragments anywhere else?
Good luck,
Dave
The videos I posted earlier are reading pressures in one on the input supply line and in the other the return line. The one on the output of the WUR shows the pressure gradually decreasing as the temperature increases so that kind of seems to be working.
If I have to replace the WUR, I may go with one of the electronically mappable ones, like that from Unwired Tools.
Seems like the FD might be the problem though.
I don't think there's much of a fuel wash problem since the engine is going lean most of the time and not rich, no?
I'm now wondering if I somehow I mislabeled the 4 virtually identical electrical plugs - WUR, air control valve, cold start injector, and what looks like a coolant temp sensor since unplugging them doesn't seem to have much of an effect.
Could someone explain to me how the air metering plate and fuel distributor work together to control the amount of fuel being sent to the injectors relative to the amount of air coming in through the plate.
Is it difficult to rebuild a fuel distributor properly and what kits have people had success with?
Anyone have a New or Remanufactured fuel distributor they want to sell that they won't need any longer but haven't gotten around to selling yet?
The pancake plate moves based on air flowing through to the engine intake. The lever that the plate connects to has an adjustment screw that changes the relationship between the plate and lever slightly. This is the idle mixture screw. Know that it makes a measurable difference at idle and low speeds, but has virtually no effect on mixture past about 25% load (horsepower) on the engine.
Control pressure, managed by the WUR, is king of mixture control under load.
There are (were) little brass screens in the ports to limit the size of crud that might move around the system. Absent fuel and in the presence of air, the brass deteriorates. That's main reason we hear that CIS cars need to be driven regularly. Folks are about the habit of taking those screens out when they start corroding to the point of restricting fuel flow. They really need to be in there. I used to keep a supply of spares when I had CIS cars, but three moves and thirty years since, the parts are long gone.
Carl may have guidance to share on a proper WUR for the supercharged car. There are certain WUR versions specified for "high altitude" service, where atmospheric pressure is used to actively bias the control pressure up when it detects low ambient pressure (higher altitude). That effectively leans out the mixture to compensate for the less dense air coming in. The metering unit is, after all, volumetric rather than mass flow sensing.
Rebuilding the fuel metering unit ("distributor") isn't difficult, but like many things it needs some serious care. The springs and pistons are carefully matched, so they need to be carefully captured and their original positions in the body preserved.
The head is sealed to the body with a gasket that was originally installed with no sealant. I used to test the head for flat with a sheet of 800 wet-or-dry floating in oil in a granite surface plate. Many used a piece of glass for this. Installing the head is an exercise in progressive torque tightening of the screws, so the head stays flat as the screws are tightened. Like a cylinder head but minus the soft gasket. If the head or body sealing surface is damaged at all (prying the head off with a screwdriver is enough), it needs to be repaired flat again. Some use Indian Head Shellac gasket sealer to manage fuel seepage when the parts or technique are less than perfect.
There are certainly some YouTube videos showing a lot of this. There are also some very good books that teach the theory of operation plus some service and component building techniques. I think the go-to is the Randy Probst book if you can find one.
The WUR is somewhat specific to the application. It modulates control pressure based on coolant temperature, plus it has an electric heating element that leans out the mixture as the engine is warming up. The temperature vs pressure curve is important. You can build a test fixture to verify this function, and there are MINOR but DANGEROUS adjustments you can make to the bimetallic strip and spring that actually manage the pressure. Sounds like you have the gauges already, so you are well on your way. The pressure/temperature curves in the WSM are good. Dinking with the WUR thermo spring is not recommended for amateurs, as very tiny changes have a big effect on pressure and mixture.
So, do we think my high pressure and rhythmic mixture and running fluctuations or issues are being caused by a bad WUR, a bad FD, or both? I was trying to understand how the system works in theory to try and determine what to buy to try next as I'm about out of ideas.
Even if the pressure coming into the WUR were high, as long as I could knock it down to the right range, the engine then wouldn't care, right? This makes me think that the WUR is the place to start.
I have the filter screens in my FD and during the last fuel line change removed them and cleaned them out. They weren't gunked up and you can see from the picture of the FD pressure screw that it doesn't look like there's much junk in there. That screw came out spotless and the photo I posted is how it looked upon removal - I didn't wipe it or spray it with anything to make it look like that.
I'm still stuck on how a running engine with a known good WUR and FD, those parts removed and then put back on, that they would suddenly become defective. Not impossible, true, but improbable.
About your connectors, the Aux air valve and the WUR get 12v power all the time, the connector has one Pos and on Neg. If you had inadvertently connected one of these to the cold start injector, you'd be firing the cold start injector constantly and the result would be a constant rich condition. The 4th AMP connector is a water temp sensor. I dont think this is the issue, but you could start the motor and while its running, disconnect all 4 of the connectors and see if it makes any difference in the tune.
At the FD, there is a filter screen sometimes at the OUTLET line of the FD that connects to the WUR on the other end. Make sure this is not blocked, or the line from FD to WUR kinked or plugged. That would cause your Very High system pressures.
Last edited by Carl Fausett; 06-18-2019 at 12:12 PM.
For what its worth, I like K-Jetronic. Its brilliant and an absolute anvil once its set up. Just feed it fresh fuel and its happy. It Achilles heal is old gas and varnish. We topped out at 460 WHP/541 BHP on our 16v K-jet race car before we changed to race a 32v motor instead. It ran well for us, although in my video for Pikes Peak you can hear the fuel/air ratio was all wrong in the last few turns at 14,000 feet. But then, every fuel delivery system had that issue then.
Looking at the record - no other Fuel Injection system spanned as many years as K-Jet, and through many Government regs and changes. And remember that in the case of the 1989 Porsche 911 Turbo (the 930) - the car that Porsche used to get back the moniker of "worlds fastest production car" from Ferrari - they chose K-Jet. Think about that. The year was 1988/89, and Porsche certainly had access to the Bosch LH-Jetronic system, but they opted for K-Jetronic for their Ferrari beater. I like it.
Wasn't that a 930 in the movie Bad Boys II? Worlds fastest production car. A K-Jet was in that car.
I'm still stuck on how a running engine with a known good WUR and FD, those parts removed and then put back on, that they would suddenly become defective. Not impossible, true, but improbable.
About your connectors, the Aux air valve and the WUR get 12v power all the time, the connector has one Pos and on Neg. If you had inadvertently connected one of these to the cold start injector, you'd be firing the cold start injector constantly and the result would be a constant rich condition. The 4th AMP connector is a water tekp sensor. I dont think this is the issue, but you could start the motor and while its running, disconnect all 4 of the connectors and see if it makes any difference in the tune.
At the FD, there is a filter screen sometimes at the OUTLET line of the FD that connects to the WUR on the other end. Make sure this is not blocked, or the line from FD to WUR kinked or plugged. That would cause your Very High system pressures.
This is why I've been very hesitant to make any changes to either of those things and then lose the baseline of what had been working.
I think I may have had the coolant sensor and the cold start injector plugs reversed as you say. I had a texting round table last night with the Carolina 928s guys (Peter, Scott, Ron, Seth, Chris, etc) and we started looking at that. Two of those plugs have the same wire colors and I'm assuming and believe these are the 12v and ground ones you mention that go to the Air Control valve and the WUR. They are different lengths and I don't think the plug that goes to the air control valve will reach any of the other plugs. Do they get 12v with the key on or only when the engine is running and where do they get their voltage from (the 14 pin connector and that harness)?
One of the two remaining plugs has 3 wires going into the plug even though it only has two contacts and it was decided last night that this one is the one for the cold start injector. Can you confirm this is correct? The other (yellow and brown 2 wire) is for the thermo sensor and from my pictures with the colored wire ties on each plug, it looks like I may have somehow labeled / wire tied these incorrectly where I had the 3 wire plug on the thermo switch and the other on the cold start injector.
I was trying different combinations of the plugs on the devices last night and with one combination, the car would fire up then die immediately. Further inspection revealed that my fuse pump fuse was blown so one of the combinations I tried must have shorted that circuit and blew the fuse. Replacing the fuse had the car fire up quickly like it always had before, but it was totally lean and then died and I was unable to get it to restart.
So I think we may be onto something. If the cold start injector was running all the time and I was adjusting the mixture screw leaner to compensate for this extra fuel that would explain why once I moved the connectors that the car started properly but was full lean immediately.
It would also explain why the mixture screw was so out of whack that at idle it was rich, but with any pedal or load would go full lean as I don't think the surplus fuel from the cold start injector is enough to handle that much plate movement.
The last thing I did last night was to rebaseline the mixture screw going fully CCW then with the fuel pump jumpered going CW until the injectors squealed and then CCW again about a half turn. Also closed the idle screw CW all the way and then CCW 2 turns. By the time I had made all three changes I think I had flooded the motor and it was too late to run it again in the garage anyway. I'm now out of town until tomorrow evening but will get back into it then.
I will also check the screens in the FD positions for the lines that run to and from the WUR to see if that's the cause of my pressure issue. I've tried both the OEM lines from the WUR to the FD and Greg Browns lines without any difference so I'm confident it's not a line issue but could be a filter screen issue to the line.
Thanks to everyone for sticking with me through this.
So I think we may be onto something. If the cold start injector was running all the time and I was adjusting the mixture screw leaner to compensate for this extra fuel that would explain why once I moved the connectors that the car started properly but was full lean immediately.
Sounds like it. Using a common voltmeter, the connectors for the Aux air valve and the WUR will have 12v when the ignition is in the ON or RUN position and that power will stay on as long as the key is in that position.
The cold start injector receives its power from the starter solinoid when cranking. When you stop cranking, the power to the CS Injector is meant to be shut off. To test that you have the right connector to the cold start injector, use the voltmeter to find that it only has power during cranking. The 2-wire connector with three wires going to it sounds right, as one of the ground wires also runs to the lower water temp sensor, I believe to prevent the CS injector from firing when the motor is already warm.
Last edited by Carl Fausett; 06-18-2019 at 12:10 PM.
Sounds like it. Using a common voltmeter, the connectors for the Aux air valve and the WUR will have 12v when the ignition is in the ON or RUN position and that power will stay on as long as the key is in that position.
The cold start injector receives its power from the starter solinoid when cranking. When you stop cranking, the power to the CS Injector is meant to be shut off. To test that you have the right connector to the cold start injector, use the voltmeter to find that it only has power during cranking. The 2-wire connector with three wires going to it sounds right, as one of the ground wires also runs to the lower water temp sensor, I bevel to prevent the CS injector from firing when the motor is already warm.
Does the plug for the thermo switch have 12v all the time on its opposing wire where if that was the one connected to the cold start valve would explain the theory. It would make even more sense if the 12v on that wire pulsed about every 5 seconds or so as that would also explain the rhythmic swinging of the AFR gauge between rich and lean as well.
I'll be really mad at myself if I've spent all this time chasing major mechanical issues and it turns out that I had 2 plugs reversed.
06-17-2019, 10:15 PM
