Help with lambda/freq valve test please
 

All,

I bought an analog Actron dwell meter and am trying to use it to test my O2 sensor / freq valve. When I connected it to the OXS wire and let the engine warm up, I get a 0 reading on the dwell.

I verified that the thing does work, as it can measure voltage (14v) from the fuses while car is running. I know there have been some issues with some of the Actron units. This is the unit I have: http://www.summitracing.com/parts/anm-cp7605

I couldn't find the test port, because I couldn't find a clear picture of it. I did see that there's a three-prong female port, but I think that goes to a voltage regulator my car doesn't have (mine's instead internal to alt.)

The harness for the OXS is sufficiently ragged that I could clip the test lead directly to the male end of the wire connector, while leaving the wire itself connected. I get 0 dwell and, concerningly, 0 voltage from that wire.

Below is a pic of my setup. The green test lead can be seen at the bottom of the first pic, connected to the OXS wire. What am I doing wrong, or what should I look for next?

PS - car surges rhythmically at idle between 950 and 1100-1200, which is leading me to think some kind of frequency issue.

https://www.icloud.com/sharedalbum/#A25yeZFhvcMhV;6197585D-F6A8-43A5-B63C-774BAC0A7D1A

Hi Jason, I have one of those Actron meters too. I couldn't get it to work reliably either. I remember doing some searches and many people were having the same issue. I don't think it's compatible with the electrical signals at the test port. Hopefully others will chime in on this.

My test port was hidden under the rear fuse panel and I had to fish it out. There's a rubber cap on the top. See if you can find yours there too.

My car was surging and it was air leaks and a bad O2 sensor. You might just have a fuel mixture that needs adjusting but don't play with it until you can verify that you have correct fuel pressures, no air leaks and your timing is set correctly.

The old fat man waddles in......

You two prepare to get pwned and dial in your CO pretty close with the dwell meter.:D

Jason, find this under the aluminum relay/fuse plate/unit and report back.

http://forums.pelicanparts.com/uploa...1436732347.jpg

Connect green alligator clip to the pin that is fed by the green and white wire in the test port.

Ground the Mighty Actron to the bolt as shown in pic. Pretty much any old bolt will do that goes to ground.

Use dwell and 8 cyl scale - double numbers. 0-90 is duty cycle range on 4 cyl. You want dithering around 45 after doubling numbers which is 50% duty cycle. So the Actron on 8 cyl dwell should have needle a little above 22.5 and a little below as is dithers.

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Forget dwell. Duty cycle generated by the Lambda box to control freq valve is the end product of the lambda system. It's way downstream of the O2 connector.

Voltage. Different story. You should see it.

I would get a not so fat wire. Strip it back an inch or so and squish the strands into the O2 sensor female port using the male pin coming out of the clapped out connector. A back pin.

Start car and wait a minute to warm sensor and you should get a reading on the other end of the wire of less than one volt DC when MM is taken to ground. 0.9V I believe is the max if sensor is working.

Good stuff. Will advise. I'm tingling with excitement! :D

At the test port (which I found thanks) I'm getting about 2v and dwell is reading 9.5 on the 8cyl scale - dropping to 7 as it dithers. Video forthcoming

Link to video: https://www.icloud.com/sharedalbum/#A25yeZFhvcMhV;F691E508-EB4E-419A-91F7-230E37684B91

Next test is to check voltage on connector, or, because I see dithering, does that mean I have OXS voltage?

Thanks Bob for the assist!

Thanks Bob - the reason I like this forum is because of the advice from the "old fat guys" :).

I'll definitely give that another go. I wonder if my Actron box is just a bad one.

My O2 sensor was definitely kaput though. No voltage at all.

Jason, I'm pretty sure my Actron read about the same as yours is behaving. I'll digg mine out and give it a go and see what I get.

Looking at your video it seems like air leaks to me. Check all the hoses (I had loose connections around the hoses connected to the throttle body ports), the big rubber CIS hat (mine had big holes in it). Spray some carb cleaner around the runner seals and in the injector intakes (mine are leaking). I also had a huge leak from the cork gasket on the oil lever sensor on the oil tank. It's a wonder it ran at all.

G.

Hi Guys,

Here's mine all hooked up. *Seems* to be working but reading really low? Low duty cycle would indicated a rich condition? Is this a valid value I'm getting here? 6 * 2 = 12% duty cycle? Jason I think yours reads better than mine.

http://forums.pelicanparts.com/uploa...1436744412.jpg

My injector seals fail the carb cleaner test. They are quite loose on the driver side. Working up the courage to pull the injectors and replace them with new seals. I feel like the best way to do this would be to pull the whole CIS and renew on the bench. I want to fix those and do a pressure test before I start messing with the mixture.

Overall the car runs strong with good power and revs great. I just would like to tune it up to be the best it can be.

gazzerr yours is running just a bit lower than mine. Was that picture at the high point or the low point? Mine goes between 10 and 7 on the 8cyl Dwell scale.

Hey Jason, I didn't take that much notice to tell you the truth but it did dither very very slightly - I wouldn't say it was moving much at all. It is supposed to oscillate some as the OXS box responds to the O2 sensor I believe. My O2 sensor is brand new. When the worn out O2 sensor was in the meter read almost nothing. I would like to find out if the measurement on the meter now is in fact correct.

Have you seen tirwin's write up?

http://forums.pelicanparts.com/porsche-911-technical-forum/758788-cis-troubleshooting-dummies-2.html

I've got the same actron meter and it doesn't work on my 82 sc, it read way too low.

Bought an inexpensive chinese oscilloscope and it worked for me. I think good multimeters also have a frequency measurement as well, but have never tried one.

Thanks blpetry. Mine is also an 82 SC. I can't imagine we could be reading this low and still have a car that functions well. Where did you get that oscilloscope from?

Bob what model number Actron do you have?

This is the one I have.

http://www.amazon.com/gp/aw/d/B00C5TLV3O?vs=1

blpetry that oscilloscope scares me...I'm glad it works for you but I feel like I'd need a PhD to use that. My MM has a duty cycle function which I may try next.

Re the Actron: I guess we are waiting for the old fat man to come back and tell us the rest of the procedure we need to follow! :D

My needle was definitely moving along with the RPM, so I know I'm getting a reading of some kind, but like you and blpetry said, it seems to be reading far too low.

I've also ordered the repair part that the Pelican member Louie85 sells for the male side of the harness connector - mine is totally disintegrated. Not sure if that is part of my problem, but it definitely is broken so needs fixing.

Yep. You are correct, Sir.

The low numbers don't indicate the Mighty Actron is wacked out. It means the O2 sensor is picking up a way too rich mixture and is fighting as best it can to combat that.

Thing is it works a little backwards from intuitive thought. I will state this from memory but I think I remember it right.

Let's say your O2 sensor says 0.8V based on the amount of oxy in the exhaust. That means rich. That voltage goes to the box. Box says "lean it out" through a reduced duty cycle. Dwell meter drops down. The meter is not reading rich, it is telling you it is fighting against rich.

Everybody wants to hit the 3mm screw right away. However, I do not think a wee test to get a feel for how to tweak it using the dwell meter is a crime. Importantly, don't dial it in to "22.5" and walk away. Air leaks, fuel pressures, etc need to be addressed to make sure you are not simply masking another problem.

OK - You got a handle on it. 10 to 1 it's a valid number. I have seen it on mine in the way back.

It ain't the number you want. You may find as you seal off leaks the number drops more. But your head is on straight.

Thanks Bob and blpetry.

Bob thanks for confirming. I'm going to chase the vacuum leaks a little more like you said. I think the PO was definitely messing with the mixture to tune out the vacuum leaks because the shear off screw in the top of the fuel distributer has been removed.

Went out and tried my trusty actron meter again tonight. Hooked it up immediately before performing a cold start (open loop, cold engine, O2 not functioning yet) and it went to 10 degrees and pretty much stayed there like I remembered. The meter is not defective as I use it often to set the mixture on my 84 vw gti, which has an almost identical (albeit smaller) CIS system and the mixture is set exactly the same way.

If you hook the dwell meter up and it doesn't go to 22.5 degrees or higher on cold start open loop operation, it isn't reading correctly. You can also force the open loop by disconnecting the O2 sensor, but be careful with the connector in the engine compartment, they are prone to breakage.

Since the exact same meter is proven to work properly on Bob's car, and the parts catalog does show that there was a change to the brain box around 81, I'm wondering if we're looking at different signals. I'd be interested to see what Bob's signal looks like on a scope.

I think a good next step for the OP would be to try the duty cycle on your multimeter and see what it tells you.

Can I hijack this this thread a little. Having similar probs and trying to get the car smogged. Is this the FV to my 81 SC?? If not, what is it?


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I'm confused, 'cause Pelican's schematic would suggest no, but Vertec and others show something similar to this.

Thanks blperty. My car was hot when I hooked mine up. I think you are right when you say the guts of the Actron have changed. I was wondering what model Bob has. I'll try again cold when I get a chance. And yes I'm paranoid about that O2 connector! Mine seems in good shape so I'm gun shy to mess with it.

Westy - I *think* that might be the cold start injector that mounts on the back of the CIS airbox. I've never removed mine so I'm not 100% sure but the electrical connector and mounting block before the actual injector there sure looks like it. I'll take a look at the PET.

Yeah here you go - cold start valve:

1982 Porsche 911 SC Targa - Fuel Injection - Page 1

That is the cold start valve. It is very close to the frequency valve location wise. The frequency valve does not spray it chokes or unchokes pressure in the "control pressure" line that changes the pressure in the lower half of the fuel distributor allowing it to piss out more or less fuel to the injectors.

CP7605 Sorry for delay.

No worries thanks!

+1. Yes, it goes to like 60 on the 4 cyl scale. Valid point.

Mine is stone cold. I will check in a few.

Thanx guys. That valve clicks just fine. Guess what apparently doesn't? Yup, FV. At $560 bucks for a FV, me thinks I'll have to find another avenue! Maybe one from from a Mercedes or BMW!!!!!

Frequency valve, working fine it is, young Skywalker.

You buy anything and the fat man cuts you. You have a signal delivery issue.

Have been nippin' at the bottle again? You are not Fecklar! Hmmm???

The plug for the FV has appropriate power. My guy says he put a stethoscope on the FV and it just weren't clickin' away. This is all to pass smog so when I sell it I can include potential CA buyers. With the coin that's gone into it, I might drive it til next spring and sell it then. Hate to pay and not play at least a little.

Hell yes, I been nippin'.

Lemmie do the setup for the plpetry thing. Cold start with Lambda - high duty cycle check.

So what you are saying is that there is voltage to the freq valve? Appropriate power is confirmed? What I don't know is what type of signal comes from the lambda box to the freq valve. There is some kind of voltage, but it cannot be a constant 12V. It has to vary given it feeds duty cycle.

FWIW - freq valve does not click, it buzzes. But if there is nuttin, there is nuttin.

I have my ego defined through a fully separate imaginary creature.

http://forums.pelicanparts.com/uploa...1436843283.jpg

I didn't write down the number, but IIRC he said a low of somewhere around 6v and a high of 11 point sompin or other. Lambda was replaced a few years back. He!!,,,almost everything has been replaced in the last few years. Makes wanna go down and work on my Camaro. THAT I understand!!! http://forums.pelicanparts.com/suppo...leys/loki5.gifhttp://forums.pelicanparts.com/suppo...leys/loki5.gif

Now ur gonna say Fecklar is imaginary. Oh sure, whatever you say boss!!!

Ok - that makes some sense. FV has to be fed with something. It's a 12V car. What else can it send? Voltage is pretty much it.

Bwa ha ha ha. Doing searches on Fecklar. Give an old man a chance.

Cripes - Why did you make me look up 73RS Z28. So beautiful. So simple. So powerful. I had a 69 Opel GT in 73.

Let's not discuss.:D

I'll try the cold start open loop on mine ASAP and report back.

Yeah I love my 911's flat six but I don't mind a good old fashioned V8 either :).

Just performed test - mind you this is on my car - not indicative of the population.

Went right to 22 on the 8 cyl scale. Was looking for more. Steady as a rock. Touched throttle linkage, I mean touched, pressure - not movement - went to 35.

I got my own issues.:)