how do i read a dwell meter for lambda AF mix

[Baby]

I thought the A/F setting affected the mix through the entire range and the idle mix screw affected only idle, but I'm probably mistaken.

I think you hit on it in terms of the base condition, based on my experience leaning out the mix with little effect on the dwell reading. I took my pressures the other day but have yet to compare them to the chart in Bentley. I'll do that later tonight and will report back.

Thanks again!

[Baby]

Fuel Pressures


This is for a 83 SC. All appear to be within acceptable range according to Bentley.



WUR (23.4 degrees C): 9.8 ohm cold


The following measurements taken at

System Pressure (21 degrees C): 4.9 bar (Bentley:

Cold Control Pressure (21 degrees C) : 2.0 bar
Warm Control Pressure 21 degrees C): 3.6 bar (time elapsed = 1:30)

Residual Pressure (22 degrees C):

05 minutes: 2.2 bar
15 minutes: 1.7 bar
30 minutes: 1.6 bar
60 minutes: 1.5 bar

[tirwin]

Originally Posted by Baby

Fuel Pressures


This is for a 83 SC. All appear to be within acceptable range according to Bentley.



WUR (23.4 degrees C): 9.8 ohm cold


The following measurements taken at

System Pressure (21 degrees C): 4.9 bar (Bentley:

Cold Control Pressure (21 degrees C) : 2.0 bar
Warm Control Pressure 21 degrees C): 3.6 bar (time elapsed = 1:30)

Residual Pressure (22 degrees C):

05 minutes: 2.2 bar
15 minutes: 1.7 bar
30 minutes: 1.6 bar
60 minutes: 1.5 bar

Hmmm... your cold control pressure is higher than I expected. Still, at 21C you should be around 1.4-1.5 bar so that looks high. I think that "ideal" CCP varies slightly from the book values depending on the average temps in your area are. Mine was almost nonexistent, which made it run very rich. I sent mine up to Tony and he adjusted it to 1 bar, which is below the spec in the Bentley but it seems to like that value much better.

Your WUR resistance is low at 9.8 Ohms -- it should be more in the high 20's (26-28 if I remember correctly). The time it takes for you to go from cold to warm looks too fast. It could be because the WUR resistance is so low.

WCP and residual look fine.

I would be great if Tony chimed in on these numbers.

[tirwin]

By the way... I'm diggin' your blog!

[Baby]

Thanks, Tim. I thought the cold control pressure was at the low end of the range for that temp (21-26 or something, but I'll check the book again.)

I wonder if that low resistance reading can be attributed to the crappy multimeter I used. I have another, and I'll check in the morning when the WUR is cold again.

I'm going to have to do some reading, but I'm curious about how a high pressure is remedied e.g., adjustment to wur, adjustment to fuel distributor...

Yeah, where's Tony? Where's Bob?


BTW, Thanks for the nod to the blog!

[Baby]

Hypothetical that may help me understand the way this works: if the mix is rich, when 3/4 throttle is applied does the lambda system compensate by bleeding off fuel pressure? If so, could it create a flat spot at a given rpm?

[tirwin]

The ECU ignores the input from the Lambda system above 35% throttle.

[tirwin]

Thanks, Tim. I thought the cold control pressure was at the low end of the range for that temp (21-26 or something, but I'll check the book again.)



I wonder if that low resistance reading can be attributed to the crappy multimeter I used. I have another, and I'll check in the morning when the WUR is cold again.



I'm going to have to do some reading, but I'm curious about how a high pressure is remedied e.g., adjustment to wur, adjustment to fuel distributor...



Yeah, where's Tony? Where's Bob?





BTW, Thanks for the nod to the blog!

A 9.x reading is pretty common.

The way the control pressure is remedied is to adjust the pin. There is a tech article -- I think it was in an issue of Upfixin der Porsche -- that covers a mod to make the WUR adjustable. I'd have to look it up to confirm which way is which. I think knocking the pin down increases CCP and knocking it up decreases it.

Only Tony knows what it will take to fix the resistance problem.

[Ronnie's.930]

Another thing you could do with the WUR is to send it to Brian B./RarlyL8 Motorsports, and have it made fully adjustable. I know that Brian Leask is not doing WUR mods anymore, but I believe that Brian B. is still handling them.

[RDM]

Originally Posted by Baby

Hypothetical that may help me understand the way this works: if the mix is rich, when 3/4 throttle is applied does the lambda system compensate by bleeding off fuel pressure? If so, could it create a flat spot at a given rpm?

After the shout-out, I had to read the blog too. Kept me up late, reading from beginning to end. Excellent work (both the blog and the car!), I really enjoyed it. Thanks for putting it up.

To lean the mixture, fuel pressure would have to increase. Remember, low pressure at startup for a rich mixture.

[Bob Kontak]

Originally Posted by Baby

Yeah, where's Tony? Where's Bob?

Tony is on vacation. I think he is either in Aust or Hawaii.

There is a great thread on adjusting the warm pressure in the WUR. I only found about this last year. Always thought the plug adjusted both.

Let me see if I can find this and post.

I have been wrapped up in several timing belt jobs but I will see what I can find.

Doubt resistance can be fixed but I'll let Tony speak to that. S/B 25+ - at least on my 090

Here is the thread - check post #13

Help with CIS test numbers (new guy)

[Baby]

Thanks, all. I've been looking at WUR threads but had yet to run across the one Bob offered.

I should probably sit tight and wait for Tony to weigh in when he gets online again before I break out the drill. I wonder, should I test all of the components individually to see if the issue could possibly have another cause before I adjust the wur?

This newer thread looks like it may prove to be useful:

Wur Check


Dru, thanks for checking it out. Sorry to keep you up late, but happy to hear you enjoyed it.

[Baby]

Bump in case Tony is back or anyone can comment on the solution for a WUR w/low cold voltage.

Been driving the car, which starts and runs fine, though there is a smell of half-burnt fuel in the garage....

Hope everyone is digging their Fridays!

[boyt911sc]

Few days before I left for my annual 4-week vacation to Carmel-by-the-Sea, CA, I received urgent requests for WUR loaners from 2 Pelican members (from Germany and Sydney). The tests were done for both cold and warm condition. And a second set of tests have to be done to confirm the previous results. I have successfully loaned these WUR's without any return so far (knock on wood)!!!! Without doing a second (repeat) test, I felt I would be taking a big risk sending them overseas. So I informed them that I'm refunding their deposits and start another transaction when I get back home.

Both decided to wait and declined for the refund. Then my good friend Bruce from South Carolina requested another WUR-090 ASAP. It was a day before my departure that I made a decision not send out any WUR loaner unless they are calibrated/tested and passed the series of tests.

And while I'm enjoying the chilly climate of the Monterey, Nick, Baby, and Jim (all Pelican members) sent emails requesting for assistance regarding their WUR's. Wait till October arrives and you'll see more posts about cold starts. I'll be back home in 2 weeks to continue the unfinished work.

BTW, for those of you who have not been able to experience the auto week here in Monterey (Carmel & Pebble Beach), just ask someone who has been here before. I don't have the words to express this experience.

Tony

[Bob Kontak]

Originally Posted by boyt911sc

BTW, for those of you who have not been able to experience the auto week here in Monterey (Carmel & Pebble Beach), just ask someone who has been here before. I don't have the words to express this experience.

Good for you Tony.

I saw Sterling Moss drive in 1995 at the Monterey Historic Races. Mark Knophler from the music group Dire Straits had a Lotus Eleven (I think) and I was able to talk to his wrenches outside his motor home parked in the pits on Saturday.

FWIW - If you go to the Monterey Historic race location on Wednesday or Thurs you can walk around (for free) and the multi-million dollar cars are just sitting all over the place pretty much unattended. You can stare and take pics all you want.

I saw my one and only 917 up close on the Wednesday before. That is a serious car.

If you have the opportunity to visit the Blackhawk museum in Danville, CA, over the mountains east of Oakland that is a treat. However, after Pebble Beach, it won't have the same impact if you did the visit solo.

[Bob Kontak]

Originally Posted by Baby

Bump in case Tony is back or anyone can comment on the solution for a WUR w/low cold voltage.

Been driving the car, which starts and runs fine, though there is a smell of half-burnt fuel in the garage....

Test your warm control pressure after driving the car for a while. Engine heat will bend the bimetallic strip over time. Not two minutes, but after it warms up. I am not sure it will take it all the way though.

Does it stink when warm - I mean truly warm?

[lonewolf]

First ,there is nothing wrong with using your sears meter.
I have a two wire version of the same thing.
I also have an LED AF meter in my car hooked up to an aditional O2 sensor to verify what I'm seeing in the dwell meter.
I've been driving the car all summer with both hooked up.

The FV has it's limits. If the dwell is pegged at 30 or below you are too rich.Car may start and idle fine but you are too rich.
If it pegs at 70 or higher you are too lean.
In other words when setting always remember ,the higher the dwell reading the leaner the sytem is .The lower the dwell reading the richer the system is .

When cold (below45F ambiant)and on startup the dwell will read 70-80 for about 10secs(maybe a little longer in colder weather) then the temp sensor (not thermotime switch) is warmed up enough(above15c) and the reading will go to 60 for a couple secs ,then will fall to 45 steady,once O2 is warmed up enough the needle with swing . The closer you get to the perfect A/F the needle will barely move and stay close to 45.

You cannot just adjust the mixture screw. You have to remember to adjust the mixture screw and idle screw together.

The idle screw also changes the AF ratio. clockwise makes it richer and counter makes it leaner.

Turning mixture screw clockwise makes it richer but also increases RPM so you turn in the idle screw to bring RPM down but in doing so you are also richening the AF which may be too much so tiny movements of each is how you do it so you are always making the adjustments at 900rpm. In other words instead of just turning the mixture screw untill you get the dwell dithering close to 45 (which you won't) ,you turn both screws untill you get there. Also ,when you are getting close the movement of the mixture and idle screw are very very small.I mean smaller than 1/32 of a turn.In fact so small you have to really get a feel for the mixture screw .Sometimes the amount of pressure needed to get it to turn makes it turn too much and you go to far.The idle screw spring can drag on the housing too making it hard to make a small turn so watch for that.You can turn the idle screw but it will turn back on you.
You are there (close to perfect)when you get to a point when you turn the mixture screw a ch clockwise to bring the dwell needle to about 42-44 dithering but the idle is 850rpm so you back out the idle screw which also leans out the A/F so needle rises to 44-46 dithering but also because you backed out the screw the idle picked up the nessesary 50 RPM to put you at 900.
Also as you do this the engine is heating up ,. if it gets over 190F that also effects the AF ratio and reading so you have to be carefull how long you spend trying to set it. If you set it with eng temps to high then when driving and when temps are normal the setting will be off.

The lifting of the sensor plate is just a rough idea of where you are and I mean rough as are some other signs like RPMS hanging up or slowly falling or falling too fast and almost stalling. These signs are telling you A/F is not right.

If you want to get really anal with the A/F like some of us with a perfectionist complex do then you need to understand exactly what is going on with the movement of both screws and how everything from those movements to ambiant temps to eng temps effect it . Getting the A/F perfect not just close makes a big difference in how the car drives and performs.
Hope that helps.

[Baby]

Enjoy your time away from the garage, Tony. Carmel and surroundings are beautiful this time of year.

Thanks, Lonewolf for the detailed info. Very helpful, and I'll heed your advice when I get around to adjusting the A/F mix.



So, with the motor having sat overnight and with the temp in the garage at 34.6 C/94 F, I hooked up the fuel pressure gauge and started the motor. Puff of blue smoke. The gauge quickly rises to between 3.4 and 3.5 bar. Idle on the rough side, no significant hunting.

10 minutes later, the gauge read the same. Idle had smoothed out a tiny bit.

I took an easy 10 minute drive around the neighborhood, gauges still connected. The needle on the temp gauge inside the car was at the first thin white mark (not the wide white mark at the bottom of the gauge). After the drive, at idle, the gauge read the same.

With just the key on, motor not running, the plug that connects to the WUR has 27 volts. The connector on the WUR shows 9 ohms. So I get full power but low resistance.

I realize I need to take apart the WUR to try to get to the bottom of the resistance issue---maybe a bad connection in there, but I'm betting that issue is independent of the richness issue.

If the warm control pressure were reading rich, I would think it might be reasonable to suppose I need to adjust the WUR until the fuel pressure is in spec, then I could try again to get a reading from the test port and set the a/f screw.

But since the warm control pressure seems ok, I'm not sure if an adjustment to the WUR, bringing it below the specified warm fuel pressure, would make it run less rich.

What do you think?

BTW, it smells bad just at startup and for a few minutes after. Once warmed up, it just smells a little rich.

[lonewolf]

My first thought is don't think there is more wrong than there actually is .
It may be as simple as your A/F is out of whack and needs adjusting and the wur and AAR are ok.
your cold/warm control pressure is right on spec. so for now leave the wur alone.

It has been 80-90F here everyday all summer.
So in the morning it's about 60-65 so just the ambient temp is warming up the WUR,AAR and temp sensor a bit so they will not be going though there full range of opening and closing time wise like they would if it is colder.


first question.
when you first start the car in the morning does it start instantly or take a couple cranks and then start.Also when it starts does it immediately idle at 1600 or what?

Second you can't have 27 volts at the connection to the wur so you have read it wrong or? should be 12V but by going by your wur test numbers it's fine and working correctly.

Hook up your dwell and tell us where it is at idle.
if using the two wire ,black to ground,red to green/white in test plug.
Once you have played with the A/F a bit you will understand how sensitive it is and how easy it is to get it out of wack .

[Baby]

Hey, Lonewolf. The deal with the dwell reading is that it hovers between 5 and 10 on the 8 cyl scale no matter what I do with the A/F screw and idle. I have leaned it out so it won't start and richened it just enough to start, and the meter reads the same. This whole thread came about because I can't get the mix to an acceptable range.

In the morning, the car fires right up the instant I turn the key, every time.

I wrote down 27 volts measured from the plug that warms the WUR. I'll check again.

I hook up the dwell meter as you describe. Reading is between 5 and 10, rich.

I get it that because its so warm, the system may not need to hit all of its check points.

I guess my question is why isn't the A/F mix affecting my dwell reading.