1982---911SC Targa CIS,frequency Valve chech

[vizail]

John

I unplug the OXS relay while the engine was running and hot and nothing happened. I use a stetoscope in order to listen to the FV as sugested in the 101 911Porsche Proyect book.
Other thing is that when cold or fresh start not warm, the engine runs and hesitate and I get no response when I actuate the accelerator(It doesn't accelerate) just when it get hot enough or after a minute or two. After it gets hot is other story.


Vic

Ah..! forgot to add thsi is an 82 911SC Targa..!

[emcon5]

You don't need a stethiscope, if you put your hand on it, you should be able to feel if vibrating.

If you removed the relay and nothing happened, then the next step is to replace the relay.

Tom

[fireant911]

To add to Tom's recommendation... in replacing the Oxygen relay - please be aware that all five-pronged relays are not the same. I tried going the inexpensive route with simply an auto parts store's five-pronged relay and my car ran like crap. As my memory serves me, the actual 'real' relay had a Volkswagon and Audi symbol so you may be able to obtain one locally at those dealerships at a cheaper price than at a Porsche dealership.

[vizail]

Wath about the 1.2 to 1.5 Volts reading at the cables(plug ) that feed the Frequency valve. How mush Voltage I have to get there.
Yes I put my hand over the FV many times to see if I can feel some vibrations but no luck just the low Voltage on the terminals..!

Vic

[Thack]

If you don't have 12 volts going to the freq valve the ECU is not working right. You can test your ECU relay by unplugging it and plugging back in while your car is running. If you feel the click then it is working. If it is not working replace it since you said it was getting 12 volts. They are only $7 in the USA. It is a BOSCH part that came on many BOSCH FI systems of your vintage. I can sell you one if they are not available in PR or you can buy them from this host site.
If it is working your ECU may be bad. Mine was bad and my freq valve was not working. I bought a Volvo 240 ECU that worked as a test unit. It operated the freq valve(you can hear and feel easily) but didn't work properly with the Porsche FI system so I had to get the correct Porsche part. You can borrow it if you need it.
You can then test the ECU /freq valve operation by grounding your O2 sensor connection wire from the side of the egine bay to any ground point on the engine. Your car will run richer and it will die or rev up depending upon how rich or lean your car is running. Either way you should notice a difference.
I bought a used ECU for $30 that came from a Porsche 924 Turbo. They have the same part no. as the 911. I doubt it is cold enough in Puerto Rica to wory about your cold start valve. Go the route of the relay and ECU and let me know if you need the test ECU.

Mike

Mike

[vizail]

Mike and all you Guys

Thanks again..!
I'm finding a lot of corotion on each and every terminal and conecction on this Porsche, so I will clean an lubricate the cables ends and conectors. I will perform the sugested Tests . Since I'm getting such a low Voltage at the FV (1.2 to 1.5 V) I will clean specially this connector. One question. The Connector on Top of the Bridge and firewall distrubutes the electricity to the Fuel Injector System? Do I have to get the click from the ECU when I disconnect the OXS relay or I have to disconnect the ECU..?
Cordially
Vic

[vizail]

One more
Can I check the OXS relay alone? Is there a particilar test procedure departing from 85+ to -30. I mean the OXS relay test , not pluged.

Vic

[john walker's workshop]

relay test. with 3 jumper wires,
ground 85,
12V to 30,
then jump 12V to 86 to activate it. it should click.
the relay should then be giving 12V to 87 which goes to the computer, and 12V to 87b, which goes to the frequency valve and enrichment relay.

following this advice, you could simply give 12V to the 87 and 87b terminals (both at the same time) on the relay plug to see if the frequency valve starts to buzz. engine needs to be running when this is done or you won't notice anything.

[vizail]

Thank's JW

For the moment I check the relay for continuity and I'm geting "0" voltage between 30 and 85, I'll now make the 3 wires for the jump test. I'm begening to suspect that the ECU is not working properly.

Cordially
Vic

[john walker's workshop]

30 to 85 has no continuity until the relay is activated. never mind the continuity tester for checking the relay. use a test light.

[vizail]

John W

I performed the test with the 3 jumper wires.
To begin with I prepare 2 red wires w/alegator clips in one end and female conector in the other, and one black wire the same way.
Then I got to the battery and jump wire the 30 to the + battery terminal and -85 to ground. Then I jump wired # 86 and "click" . I disconnect 86 from the + terminal and click every time . Then I left the jump wire on 86 and check the delivery of voltage on 87 and 87b getting a 12.2 volt readings on each one of them.
The obvious conclution is that at least the OXS relay is working properlly and delivering power to the computer and the frequency valve.
I also took the time to clean lubricate each and everyone of the cables terminals . every fuse, relay, and conector in the fuse terminal as well as the engine compartment spetially the firewall connector.
Since is getting late I will run the engime tomorrow and see what happens.
I'm begining to suspect that the ECU is defective I also have to tahe the ECU out and clean and lubricate the connectors.
Is there a procedure that can verify continuity in the ECU?

Cordially

Vic

[john walker's workshop]

the next thing to do is test the relay when it's attached to it's plug. see if the wires in the plug do the same thing as the jumper wires did. use a test light only, and be sure 85 gets ground. test for ground by attaching the test light clip to 12V, which makes it light when the point touches ground. (the opposite of the normal hookup). in the end, you need to get 12V to 87 and 87b. do you?

[vizail]

John W
Yes I did get 12 V to 87 and 87b

I reconnect the relay back half way in to the connector and perform some readings . My digital voltimeter is telling me that 30 is getting 12.5 Vots and distributing the same voltage to the rest of the cables 86, 87 and 87b , Of course -85 is negative (ground ). As I said before I'm beginning to suspect the ECU. By the way.., the relay is a VW.

Cordially
Vic

[vizail]

Is there some elementary ECU check procedure that I can perform with my Digital Voltage Meter. Since I don't have a Bosch KDJE-P600
Tester
Vic

[Gunter]

Vic: Yes, the relay for the ECU is VW 821 951 253. Get a spare! Some relays are used by VW and Porsche. Is your OX sensor still plugged in? That is the unit sitting on top of your CAT converter and a wire goes from it to a plug-in right under your CDI module. The OX sensor can be unplugged without any problems but the Frequency Valve has to work. Can you get a spare ECU? Get a used ECU.
I see on page 970-8 Bentley manual that there is one wire Blk/Red coming from the relay 87B going through the Frequency Valve and another Blk/Red coming out of the FV going into the OX Control Unit. It looks to me that the power for the FV comes from the relay pin 87B and the ground for the FV is controlled by the OXS Control Unit? Somebody confirm this, please. The solenoid actuation for the OXS relay is coming from the Warm Up Regulator (WUR) Red/Wht wire. Another second wire Blk/Red on terminal 87B is going to an Acceleration Enrichment Control Unit. I don't know where this AECU is located because my '80 does not have it. But, with the engine running, is there 12V on the Red/Wht wire that controlles the solenoid on the OX sensor relay? It should click when you pull the Red/Wht wire on and off.

[john walker's workshop]

pull the cover off the computer and see if there is any corrosion inside on the circuit boards. if you have a strong magnifying glass, you can check all the solder joints for cracks. the crack usually looks like a circle in the middle of the solder joint. get a magnifying glass with the smaller, more powerful mini glass built into it. works better for close-ups.
yes, the computer modulates the ground for the frequency valve. the freq valve is basically just an electric injector. it opens and vibrates when it has 12V on one side and a pulsing ground on the other. you could duplicate this to a point, at least to see if the freq valve will make any noise, by making a plug to it with 12V on one side and a ground wire hanging off the other, which could be touched to ground repetedly. you should be able to hear and feel the valve operate if it's not defective.

[vizail]

Gunter and JW
Thank's for the reply
I will perform the Inspections and the test sugested tomorow since is 8:30PM and is already very dark rigth now

I'll keep in touch.!

Vic

[vizail]

Gunter and JW . This is very funny..! the relay on my 1982-911 SC number is 171 906 381. The AECU is 911 617 131 00 and the ECU Unit is a BOSCH 0 280 800 055 I see no Intens corrosion in he Board , but I see some strage melting in a component of the ECU. I will try to post some Pix Today.
Vic

[Gunter]

171 906 381 may very well be the right relay; there are cross references for different relays. As long as you have pin 87 and 87B supplying 12V to the Frequency Valve and the ECU. Activate the relay so that there is 12V to the Blk/Red wire from pin 87B to the Frequency Valve. Do you have 12V at the Frequency Valve? Is your ECU also getting power? Do you have a electrical schematic for your car?

[vizail]

Gunter

I jumpwire the relay as sugested .
I took 2 red wires one end with female connector and the other end w/aligator clips .One black(-negative) wire riged the same way. I placed one red wire to terminal +30 and
the black wire to -85(negative) then I took the other red wire and activate the relay via +86 ,it click's real nice .Then I left the +86wire connected . I check if the relay was delivering to +87 adn +87b.I found a good delivery to 87 and 87b no problem(12V). Now I have to reconnect the relay and chek if I'm getting Voltage to the ECU Female Connector. I have the Bentley Book with the schematic diagrams. I have to see wich one is the female clip that energise the ECU from the relay. Do you know wich one is?
Cordially
Vic