No buzz from Frequency valve

[David T]

This is a great help, thanks. I’m going to get a replacement ECU and cross my fingers that that’s the issue.

Am I right in thinking that without the FV I would be running rich? I have a ‘separate’ but likely linked issue that my exhaust headers are getting too hot which I am thinking is unspent fuel igniting in the headers.

Actually the ECU is one of the least likely causes so don't just get one hoping it will fix the problem. Without the FV buzzing the mixture is lean but someone may have adjusted the mixture screw to try to compensate for that. The reason I said to replace the O2 sensor is, typically when the FV isn't working, the O2 sensor is bad because it got contaminated from the overly rich exhaust so it is just "Good Practice" to replace it once you get the FV going and the mixture set.

[DMC-81]

While you are troubleshooting the absence of buzzing on the frequency valve (and I agree with checking electrical connections first), it's a good time to ensure that the little screen in the top of the FV is clean.

I had buzzing but it was faint. I took off the fitting and after cleaning the screen, the buzzing was louder and the car ran better:





Also, Dave Mckeen offers a solid state Lambda relay (not sure if he still stocks it) that is a nice upgrade if you have to replace that relay.

[JKDelorean]

Thanks for the help and replies on this. I have replaced the Lambda relay, FV fitting and the ECU and now have a vey loud buzzing FV - very happy to have solved that conundrum!

I must still be very lean after all of that - I still have glowing exhaust manifolds after running for 5 mins or so. Onto the next problem!

[David T]

Thanks for the help and replies on this. I have replaced the Lambda relay, FV fitting and the ECU and now have a vey loud buzzing FV - very happy to have solved that conundrum!

I must still be very lean after all of that - I still have glowing exhaust manifolds after running for 5 mins or so. Onto the next problem!

Too rich. The excess fuel is burning in the exhaust manifold.

[Ron]

+1

...or restricted flow, retarded ignition timing...

[powerline84]

A rare problem...but I just rebuilt a car that was doing that with correct mixture. It was a clogged cat . A red hot exhaust like that will kill an oxygen sensor as well.

[David T]

A rare problem...but I just rebuilt a car that was doing that with correct mixture. It was a clogged cat . A red hot exhaust like that will kill an oxygen sensor as well.

On a car with a glowing exhaust AND a plugged cat the car will have no power. That happens after driving the car with a rich mixture for a while. Often because the plunger in the mixture unit got stuck. The other way I saw that happen is when you replace the mixture unit and the adjustment is off, it doesn't take much, it is a VERY sensitive adjustment. Yes, the O2 sensor should be replaced too.

[JKDelorean]

Thanks again,

I have the 02 sensor disconnected at the moment but will be mindful when I reconnect it. It is new though so would hope its not knackered from being driven 5 miles and being started probably 10 times in my garage.

No cat in place - I have the UK free flow exhaust. I take the point that the mixture is probably off and will certainly need adjusting for the new exhaust once everything is back together.

I think I've narrowed down my issue to the injectors which aren't spraying properly and certainly not misting/atomising like they should. Looked at using the 'jam jar' test. New ones now on order to see if that solves or helps.

I plan to fit the new injectors, 'crack' them to get roughly the right point on the mixture unit, check the spray pattern is good and then refit. I can then hopefully use my dwell meter to dial in the mixture once I'm sure my exhaust aren't exhibiting the same problem.

Slowly but surely I hope I'm getting there!

[David T]

Thanks again,

I have the 02 sensor disconnected at the moment but will be mindful when I reconnect it. It is new though so would hope its not knackered from being driven 5 miles and being started probably 10 times in my garage.

No cat in place - I have the UK free flow exhaust. I take the point that the mixture is probably off and will certainly need adjusting for the new exhaust once everything is back together.

I think I've narrowed down my issue to the injectors which aren't spraying properly and certainly not misting/atomising like they should. Looked at using the 'jam jar' test. New ones now on order to see if that solves or helps.

I plan to fit the new injectors, 'crack' them to get roughly the right point on the mixture unit, check the spray pattern is good and then refit. I can then hopefully use my dwell meter to dial in the mixture once I'm sure my exhaust aren't exhibiting the same problem.

Slowly but surely I hope I'm getting there!

Don't throw the old ones away, they can probably be cleaned. Make sure the plunger in the mixture unit is not stuck.

[iflights]

I plan to fit the new injectors, 'crack' them to get roughly the right point on the mixture unit, check the spray pattern is good and then refit. I can then hopefully use my dwell meter to dial in the mixture once I'm sure my exhaust aren't exhibiting the same problem.

What does Crack them mean?