No Voltage at Frequency Valve

[Funracer]

Car would not start yesterday. Long story short no voltage to the FV connector.

With FP relay jumpered pump runs, interior lights work and 12V to the WUR connector. Nothing to FV connector.

I have replaced the Lambda ECU (I have a spare), the O2 relay and the fuel pump relay. Still no power at the FV connector. No voltage at pin #1 of the 14 pin connector next to the left rear shock mount.

I am able to start the car by richening the mixture. After running for a couple of minutes I pulled the FV connector. No change in rpm or AFR gauge. With everything plugged in the oscilloscope shows nothing either:



In retrospect this intermittent FV may have been happening for the last couple of years.
Looks like it has finally failed so maybe now I can fix it.

What next?
Thanks

[john walker's workshop]

Be sure that the ralay activates both 87 terminals instead of just one. The diagram on the side of the relay will tell you that. One powers the ecu, the other powers the fv. Some lookalike relays just power one 87 terminal.

[Funracer]

These are the three I have. The metal ones are from 1981-82. The black one was purchased from PP about 4 years ago. Labeled slightly different but to my untrained eye they look the same.

This morning I jumpered the FP relay and with key in my pocket got 12V at the O2 relay plug pin #30. So power is getting to the plug.

Per the bentley schematic ground is pin 85. If 12V coming in via pin 30 and not going out, either all 3 relays are bad or ground is bad. Does this make sense?

Back to the playground.

Thanks for your input

[Funracer]

Better pic

[proporsche]

as John said make sure you have the correct relay.I had same problem recently...the guy had some kind of aftermarket relay in there.So i went to my stash and found the original relay.The car runs like a rocket now..can wee the relay you are using?
here it is

Ivan

[proporsche]

i`m too slow;-)

[Funracer]

Originally Posted by proporsche

i`m too slow;-)

Ha I would never say that.

Interesting how they say “Made in W Germany”

[Funracer]

Tested relay pin 85 to ground checks good.

[john walker's workshop]

Do both 87s test hot when the relay is activated?

[Funracer]

Originally Posted by john walker's workshop

Do both 87s test hot when the relay is activated?

Not time to test that tonight unfortunately. In the mean time I thought this was interesting. Continuity between both 87 and 87A on the black one:


On both of the older metal ones no continuity between 87 and 87b:


I will test both 87s for 12V tomorrow with engine running.

Thanks again.

[john walker's workshop]

Test light into the end of the plug.

[spoke]

Originally Posted by Funracer

Not time to test that tonight unfortunately. In the mean time I thought this was interesting. Continuity between both 87 and 87A on the black one:


On both of the older metal ones no continuity between 87 and 87b:


I will test both 87s for 12V tomorrow with engine running.

Thanks again.

Your meter seems to be reading volts, not ohms.

[proporsche]

Originally Posted by Funracer

Ha I would never say that.

Interesting how they say “Made in W Germany”

'West Germany parts and tools were made before 1989...reunification

Ivan

[Funracer]

Originally Posted by spoke

Your meter seems to be reading volts, not ohms.

It’s an automatic meter. No settings other than on/off. When there is continuity the yellow light comes on and it beeps. It also reads voltage and indicates whether its AC or DC.

[Funracer]

Originally Posted by proporsche

'West Germany parts and tools were made before 1989...reunification

Ivan

Correct. I just think its interesting historically.

[Funracer]

Made some good progress today as follows.

Using one of the old metal relays, started the car and back pinned 30, 87 and 87b got 12V to all. Checked my FV plug and also 12V. Plugged it in and could feel buzzing.

Was not sure what happened since yesterday but everything was working including 14.7 afr as it should be with lambda ECU and FV functioning. Was going to go for a drive but rain shower came and I shut the engine off.

After rain stopped (30 minute) started the car. Went for a drive. Had not gone 100 feet and AFR went off scale lean and car ran poorly. Jumped out opened the hood no FV buzz. Back to the garage. Car still running back pinned the relay plug again and now had 12V at plug 30 and NO voltage on either 87 or 87b ??

While car was running decided to switch to the black O2 relay pictured above. As I started to wiggle the metal O2 relay out of the socket the car came alive again! Idle jumped up, AFR back to 14.7 as the lambda system started working. Checked again now both 87 and 87b have 12V.

Left the plug partially inserted and went for a drive:


Everything worked perfectly. Low speed off idle smooth as silk. Lambda system never quit.

Had to stop for the night but tomorrow I will investigate the plug itself. Maybe I can disassemble it to check for poor connections or corrosion. Will update then.

Thanks all!

[Funracer]

For anyone diving into the lambda plug and relay be aware the port #30 always shows 12V if the battery is attached. I took off the negative cable prior to taking the plug apart today.

Secondly, when using a DVM to test the plug/relay everything can be done with the FP relay jumpered and key on (not start). No need to actually start the car or run the injectors by lifting the air meter plate. I read somewhere that if the FP is running the FV should be as well.

The plug contacts come out by depressing a tiny burr on the back side with a small screwdriver. I had better luck pushing them out with a bigger screwdriver rather than pulling them out by the wires. Luckily I have a spare Lambda wire harness and was able to practice on the workbench first:


Once in the car I only removed sockets 87 and 87b as this seemed to be where my issue lies. The one with the black/white wire powers the ECU and the other one with the dual red/black supplies the FV. I was surprised to see they look shiny new. No tarnish or carbon buildup:


I took a small piece of fine sandpaper, just wide enough to slide into the plugs, folded it in half and ran it back and forth just to be sure the inside was clean too. Then needle nosed pliers to squeeze the already beautiful OE crimps even tighter and clamp down the “B” lobes a bit for tighter contact. Sprayed with DeoxIt5. When you reinsert the sockets into the white plastic housing remember to raise the small tab on the back so they lock into place.

Reconnected battery and jumpered the FP relay. With Lambda relay in place and back pinned port 30, 87 and 87b all showed 12V and I could hear the FV buzzing.

Took the car for a 20 minute drive and all was well, FV still buzzing when I got back.
Not saying its fixed yet. If I drive it for a month and still good then maybe so.

Thanks again JW and everyone for the help. I learn something from this group almost every day.

Regards

[AndrewCologne]

Don’t use the middle one:



One of the 87 terminals drives the FV and its solenoid valve – essentially a coil. If the current is suddenly disconnected, the coil will discharge and generate an inductive spike, which can reach 120 volts or more.
With the left and right types, when the relay disconnects pin 30, there is no direct connection between the pin 87 leading to the FV and the other pin 87 leading to the ECU. This means that if an inductive spike is produced by the FV, it will be absorbed by the internal zener diode of the peak-and-hold circuit rather than being sent through the other 87 terminal to pin 8 of the ECU.

I’m sure there is some protection circuitry behind pin 8, but I wouldn’t count on it – and clearly Porsche knew why they avoided using the middle relay type shown above.