Engine running rough cannot set mixture

[Dhennick99]

Car was sputtering bad. Had it floored and it would barely go. I had an aftermarket Bosch idle motor installed previously. So I swapped back in the factory idle motor and it was still doing it. I had the factory ecu installed, but Dave Mckeen's updated version on hand. I jumped the ecu diode, backed out the throttle screw and installed Dave's ecu. I also set the curb idle using the on-board led on Dave's ecu. When I went to set the fuel mixture the dwell needle wouldn't swing at all. Frequency valve isn't buzzing either. Car starts and the dash rpm needle continually hunts. The rpm will drop so low that it stalls out while hunting. Attached is a photo of where the dwell meter sits.


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[Bitsyncmaster]

The RPM relay turns the lambda system on by powering the "main fuel relay" (lambda relay). First is make sure that lambda relay is the correct type. If you have no FV buzz still then you need to start checking for a bad RPM relay, connection to lambda relay and connections to FV and lambda ECU.

[Michael]

A little backstory or history would prove most helpful.

[dn010]

Check the condition of your bulkhead connectors.

[cis6409]

Get the frequency valve working first , car will never run right with it not functioning.
As Michael says, a little backstory info would help..

[Dhennick99]

Bulkhead connectors were solid. I don't know what else there is to tell as far as backstory. The car just started the spuddering without warning or anything leading up that would be identifiable as cause.

The hunting issue has been going on ever since the spark plugs were done. Perhaps something was disturbed. I checked vaccum lines and everything appears to be connected properly.

[David T]

Sometimes the non-functioning frequency valve can be as simple as a bad connection with the connector plug to the valve. Take the connector off and put it back on a few times and see if that helps. Another thing that can stop it from buzzing is if the mixture is WAY off. A stuck plunger in the mixture unit can do that. A bad Lambda relay can prevent power getting to the Lambda ECU and running the frequency valve. If you are getting a reading, any reading at all, on your dwell meter, it means the ECU is getting power and the relays are not the problem. Without the frequency valve buzzing, it is not adding any fuel to make the A/F ratio correct so you are running very lean, that's why you don't have any power and it won't idle. The mixture screw sets the base mixture and the frequency valve adds what is necessary to get the correct mixture. Do not try to adjust the mixture screw to "fix" this. Get the frequency valve to buzz. Is the muffler getting red hot? That means the mixture is WAY too rich and the plunger is stuck. If the muffler isn't red hot you are running too lean and the plunger isn't stuck but the frequency valve isn't working, it's probably an electrical problem. There is a small ground wire that goes to the intake manifold to ground the frequency valve. See if you knocked it loose.

[Dhennick99]

The muffler isn't getting red hot. Richening the mix won't engage the frequency valve? The ground is intact.

[David T]

OK, we're getting somewhere. We know the ECU is getting power and the mixture is lean. Try doing and undoing the plug on the frequency valve a couple of times. If that doesn't get the valve to buzz, next is to check the O2 sensor.

[dn010]

Correct me if I'm wrong (since I haven't messed with K-jet in many years since my swap), but can't you just trip the full throttle microswitch in order to force the FV on, to at least check it for operation to rule out electrical/connection problems?

[Dhennick99]

The o2 sensor was recently replaced in an effort to get a handle on the hunting.

[David T]

Tripping the WOT switch will cause the ECU to go to a higher duty cycle, the frequency valve should be buzzing anyway, it will just make it buzz a bit more. Make sure the O2 sensor is connected, the wire didn't get knocked loose. There are tests you can do to the ECU to force it into different duty cycles by grounding the O2 sensor wire or applying a voltage to it. That tests the ECU. You would still have to test the wiring from the ECU to the frequency valve. If you have power to the ECU and the frequency valve isn't buzzing, chances are you have a bad connection between the ECU and the frequency valve. Try plugging and unplugging the connector on the frequency valve several times.

[Ethan Rode]

Frequency valve should buzz regardless of O2 sensor.

If O2 sensor isn't connected, the Lambda ECU can't go into closed loop and will hold the frequency valve at a set duty cycle. You should still hear the frequency valve buzzing, and the dwell reading will be steady and high.

Test the coil of the frequency valve. With the connector unplugged, you should see a reading between 2-3 ohms between the two pins. Anything above or below indicates bad valve.

If your valve passes the test, verify the connections are good. Then, with the car on, backprobe the frequency valve, test and verify
-Battery voltage on Red/Purple wire
-Pulses on Red/Brown Wire

you may need a logic probe to see the pulses. DVOM or test light may not work. Harbor Freight has one for $10


If you're missing battery voltage, issue is with the Lambda relay, or the wiring to/from Lambda Relay
If you're missing pulses, or pulses are weak, issue is with the Lambda ECU

If you need to check the ECU, remove the shell on the ECU connector and verify with car running:
-Battery Voltage at PIN 8, Grn/Yellow. No Voltage? Lambda Relay or wiring
-Ground at PINS 5 and 16, Black. No Ground? wiring
-Pulses at PIN 15, Rd/Brown. No Pulse, or weak pulses? Bad ECU
-You can also test feedback from 02 sensor at PIN 2. Should be between 0-1VDC between PIN 2 and Ground with the engine at operating temp

Good Luck!

[Dhennick99]

So I got the frequency valve to buzz and it's working. I was able to set the fuel mixture using a dwell. I have it right in the sweet spot, but the idle is still super high in neutral and park (I have an automatic). I followed a step by step procedure for setting the throttle and curb adjustment screws, but it's proving to be troublesome.

I'm able to get it set nicely at rest but the bracket that the adjustment screws are mounted into moves slightly when you hit the gas and it throws the idle off. If that bracket would stay put, I think I might be out of the woods and have this issue resolved.

[Ethan Rode]

So I got the frequency valve to buzz and it's working. I was able to set the fuel mixture using a dwell. I have it right in the sweet spot, but the idle is still super high in neutral and park (I have an automatic). I followed a step by step procedure for setting the throttle and curb adjustment screws, but it's proving to be troublesome.

I'm able to get it set nicely at rest but the bracket that the adjustment screws are mounted into moves slightly when you hit the gas and it throws the idle off. If that bracket would stay put, I think I might be out of the woods and have this issue resolved.

That's great. What did the issue turn out to be?

So, to set mixture properly, the idle issue needs to be solved. Service manual tells us that idle needs to be raised to 950ish to check mixture using a dwell meter. You can back the idle down to spec after mixture is set. The accuracy of the mixture setting is contingent upon everything else being right, and having a good O2 sensor, if we're using a dwell meter.

if you're using Dave McKeen's idle ecu, you won't set idle speed with the screws anymore, FYI. You will need to get the throttle linkage issue sorted out, however. Sounds like you might need to pull the throttle body, and check that the ball stud is tight on the crank. There's a spring retaining plate behind the crank that gets wallowed out on the throttle shaft, too. Make sure all these parts are tight, a ball peen hammer will help. You can't have any slop in that linkage if you want a predictable idle. You may also want to verify that your idle speed thermistor is good.

[David T]

As Ethan said, you want to eliminate any play in the throttle linkage. That includes checking the ball ends of the quadrant link. You might have to disassemble, clean and lubricate the throttle spool and lube the throttle cable as per the recall. I am also curious what you did to get the frequency valve to buzz. Get that bracket tight too. Your idle motor may need to be cleaned. Make sure the air bleed screws are lightly seated.

[Dhennick99]

I think I may have gotten a handle on it. There was a vacuum leak, one of the lines connected to the T right in front of the idle motor was disconnected. The car was running very lean, once I got that sorted I was able to get a dwell reading. It was trial and error with the throttle and curb idle screws. Once I found the sweet spot, I locked down the nuts and set the mixture. Went on a short drive and the car seemed to be performing as normal. I also went back to the stock ecu.

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[David T]

You don't just twiddle those screws. There is a procedure. If you don't have them right you can damage the throttle shaft, the stop screw is supposed to prevent you from overforcing the throttle shaft once the butterfly plates are closed. Then you set the idle switch so it just trips and not depress it any further or you damage the microswitch. There is a nice write up of the procedure somewhere.

[cis6409]

Glad to see your getting the issue sorted.

What fixed the frequency valve? It would help other owners when similar issues come up.. Was it a wiring issue or was the valve itself bad?

Shane

[Dhennick99]

There is a nice write up of the procedure somewhere.

If you find it, let me know.

As far as the frequency valve is concerned, once I reattached the vacuum line and richened the fuel mixture I started to get a reading from the dwell.

[dn010]

Did you check to be sure the three brass screws are fully seated/closed?

[Dhennick99]

Did you check to be sure the three brass screws are fully seated/closed?

No, where are those located? Can you reply with a photo?

I've attached a photo of the wide needle swing I'm getting on the dwell meter. Any ideas as to how I might remedy this?


https://youtu.be/v_fyilPK32Ahttps://youtu.be/v_fyilPK32A

[mark w]

No, where are those located? Can you reply with a photo?

I've attached a photo of the wide needle swing I'm getting on the dwell meter. Any ideas as to how I might remedy this?


https://youtu.be/v_fyilPK32Ahttps://youtu.be/v_fyilPK32A


is the car fully warmed up in this video?

[David T]

Things that can affect the dwell;
Idle speed
Vacuum leaks
Contaminated O2 sensor
Worn ignition system
Dirty, leaky, bad pattern fuel injectors

[Jonty]

I’m picking the injectors are dirty. Unless all spray an equal volume and spray pattern the ECU will chase it’s tail all over the place.