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1984 380SL
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I am very interested on how that oscilloscope works. Please keep us informed. I am in the process of adjusting my duty cycle now and like okyourabeast, I only have a multimeter with duty cycle.
 

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1984 380SL
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Finally Received my oscilloscope yesterday so it will be interesting to see how it looks when i hook it up.
Another thing, my 35 year old timing light isn't so bright any more and my old analogue revcounter doesn't work on any of my cars including the 380SL so i wan't to buy new ones. Any tip on a good timing light and revcounter?
I have an el cheapo one from harbor freight that works great. I just use it in a dark garage though.
 

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1984 380SL
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No no, I meant the timing light. I used my wife as the rev counter. Got it good enough to pass smog!

Your duty cycle meter will work just fine on the fuel ecu.
Reading the post, I would rather get an oscilloscope than risk cracking open the ECU and shorting something. I'm going to assume you have done this?
 

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1984 380SL
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I have an el cheapo one from harbor freight that works great. I just use it in a dark garage though.
Ok, any tip on a revcounter which is what i need the most? I found this on ebay:

Any comments?
 

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Reading the post, I would rather get an oscilloscope than risk cracking open the ECU and shorting something. I'm going to assume you have done this?
I've done it many many times without issue. I just didn't want to spend $100 but an oscilloscope is just easier to do the work with since you won't be hunched over your chair.
 

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1984 380SL
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Since you have the oscilloscope, stick the probes into the X11 diagnostic port that is in the engine bay. Pins 2 (+) and 3 (-). I think that's the correct polarity.

Open your hood and look to where the brake booster is on the driver's side (US). There will be a small black circular object. Unscrew him, stick in the probes, and you're in the money!

It's much easier to use this method than the one I have to do since I only have a duty cycle meter.
Just checked the diagnostic port to attach my oscilloscope and as you can see in the picture, port 3 where i should connect the (-) is the only port without a connector. Are you sure about port 3 or is it a difference between a US and a Swedish model?
IMG_8947[1].jpg
 

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1984 380SL
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What happened, no reply for 15 days, does anybody know?

Just checked the diagnostic port to attach my oscilloscope and as you can see in the picture, port 3 where i should connect the (-) is the only port without a connector. Are you sure about port 3 or is it a difference between a US and a Swedish model?
 

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'85 300D Turbo, '91 420SEL, '92 190E 2.6, '09 C350, '12 E63 Wagon
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Looks different. Can you get access to a wiring diagram specific for your model/car? Gonna need to do some reading on how it's wired up.

Sent from my moto g(7) power using Tapatalk
 

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1984 380SL
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Hi @ed9msi , sorry I don't know how I missed this.

First, what type of car do you have (model, year, and spec)? If it's a rest of the world r107, then unfortunately your car won't have a fuel ECU and the associate frequency valve which the duty cycle is taken from.

I'm not sure about Swedish spec vehicles, but at least on the US models that had Kjet, there was an add-on emissions control system that basically pulsed the system lean to provide better fuel economy.

Does your car have a frequency valve? It should look like this:


And it should be directly across from your diagnostic connector towards the middle of the engine bay.

If your car does not have one, then this guide will not work for you. Instead, you will have to get a tailpipe emissions sniffer to properly tune or your engine or guestimate where the 50/50 mix cycle is.

My advice, if you haven't played with this screw and don't have proof someone played with it then don't mess with it! You'll have better luck smoke testing the engine and checking fuel pressures first to make sure everything is operating correctly.
 

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1984 380SL
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Hi @ed9msi , sorry I don't know how I missed this.

First, what type of car do you have (model, year, and spec)? If it's a rest of the world r107, then unfortunately your car won't have a fuel ECU and the associate frequency valve which the duty cycle is taken from.

I'm not sure about Swedish spec vehicles, but at least on the US models that had Kjet, there was an add-on emissions control system that basically pulsed the system lean to provide better fuel economy.

Does your car have a frequency valve? It should look like this:


And it should be directly across from your diagnostic connector towards the middle of the engine bay.

If your car does not have one, then this guide will not work for you. Instead, you will have to get a tailpipe emissions sniffer to properly tune or your engine or guestimate where the 50/50 mix cycle is.

My advice, if you haven't played with this screw and don't have proof someone played with it then don't mess with it! You'll have better luck smoke testing the engine and checking fuel pressures first to make sure everything is operating correctly.
My car is a 380SL from 1984 and it is refered to as "S" (Swedish) in the manual that i've seen on this forum. I've already found out that the AAV is the manual one (not electric) as in the US for the year 1984 which can be seen on the left side of the first picture. I can't find anything that looks like the frequency valve so I'm adding 3 pics from different angles in case i've missed it.

I haven't touched the screw for the mix and i doubt that anybody has since i bought it when it was only 1 year old. However on the last state inspection it passed nicely but they mentioned that it might be running to rich since there's a lot of gasoline smell from the exhaust when the car is running. They only measure the CO2 on these old cars in Sweden but i asked him to check the lambda which was around 1,37. This car runs on 95 (Europe) octane and it doesn't have a cat.compared to the German spec which runs on 98.

What values should i have on the tailpipe sniffer to achieve 50/50 mix cycle?

IMG_8977.JPG

IMG_8976.JPG


IMG_8974.JPG
 

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1984 380SL
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Hi @ed9msi,

You don't have the frequency valve. You have simple kjet! Your first picture revealed it. He would normally be living right in the middle of that picture with a cable coming out of it.

Don't bother with the tailpipe sniffer. What you should do instead is smoke the intake system and check your fuel pressure. If you see any leaks during the smoke test, replace them. If the fuel test is out of whack, start with the system pressure regulator and look at the warm up regulator next.

Give your vehicle's age, your WUR might be bad but only testing can confirm that. The good news is, your metering screw still has the protective cap on it. A virgin car indeed!

Does your tail pipe smell rich to you?
 

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1984 380SL
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Hi @ed9msi,

You don't have the frequency valve. You have simple kjet! Your first picture revealed it. He would normally be living right in the middle of that picture with a cable coming out of it.

Don't bother with the tailpipe sniffer. What you should do instead is smoke the intake system and check your fuel pressure. If you see any leaks during the smoke test, replace them. If the fuel test is out of whack, start with the system pressure regulator and look at the warm up regulator next.

Give your vehicle's age, your WUR might be bad but only testing can confirm that. The good news is, your metering screw still has the protective cap on it. A virgin car indeed!

Does your tail pipe smell rich to you?
Thanks okyourabeast!

How do i know that the fuel test is out of whack, what pressure should i have and where is a good place to measure it?

Where do i find the pressure regulator, warm up regulator and how do i test if it's ok or not?
 

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1984 380SL
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I would check the FSM I posted for you. It will outline the fuel pressure testing steps and pressure criteria.

You can get a fuel pressure test kit at harbor freight for cheap. Get the master one. Remove the Schrader valves on the fittings you use as they screw with pressure readings.

The warm up regulator is towards the front left of the engine it has a 12volr connector going into the top with two Hardline fittings.

Here's a thread on the topic. https://www.benzworld.org/threads/first-time-attempt-to-check-cis-pressures.1511113

Good luck!
 

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1984 380SL
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I would check the FSM I posted for you. It will outline the fuel pressure testing steps and pressure criteria.

You can get a fuel pressure test kit at harbor freight for cheap. Get the master one. Remove the Schrader valves on the fittings you use as they screw with pressure readings.

The warm up regulator is towards the front left of the engine it has a 12volr connector going into the top with two Hardline fittings.

Here's a thread on the topic. https://www.benzworld.org/threads/first-time-attempt-to-check-cis-pressures.1511113

Good luck!
Just checked my account but can't find anything. What does FSM mean that you posted for me?

Seems Harbor Freight don't ship overseas, I'm in Sweden, any other tip on a fuel pressure test kit that's good?
 
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