280SE 4.5 vacuum advance - PeachParts Mercedes-Benz Forum

Scotto52 · #1 06-16-2020, 06:05 AM

So I’m getting a bad hesitation after driving for about 5 minutes. This is the first time I’ve ever driven this car. I’m going to check my fuel pressure and such. But I’m wondering if my vacuum advance is working correctly. Please correct me if I’m wrong, but from what I’ve read online, I should have no vacuum at the distributor at idle. But with increased RPM’s is should have some vacuum. Also, the little vacuum switch thingy that switches the distributor from advance/retard just opens and closes the vacuum line. I’m assuming this would just be 12V on/off. So I guess my question are..
-when should I have vacuum at the distributor?
-when is the output sent to that vacuum switch thingy?
-what is the vacuum thingy correct name?
-is the vacuum thingy available?

I should probably also state, I just prior to this checked to make sure the chains weren’t stretched, adjusted the valves, adjust the points and replace the cap. The plugs I ordered didn’t fit with the wires, so I’m still using the ones that came with the car. Money and time is tight tight now. But eventually install a new rotor, wires and plugs. And probably get rid of the points and some time.

I might be jumping the gun posting this before I finish my proper tune up. But knowledge is power. Thanks in advance.

Tomguy · #2 06-16-2020, 06:26 PM

Note that this is a vacuum retard - not advance. Vac is there at idle. If you turn on the AC for example, it switches the solenoid and there no longer is vac, and your idle increases as timing advances.

Define your hesitation - going along and it just starts to chug? Low power? Flooring it doesn't go anywhere? Or it seems like it won't go, and then it does actually go?

If it's the first group I'd suspect fuel supply. If it's the second one, where it hesitates and then takes off, I'd suspect the throttle position switch.

Scotto52 · #3 06-16-2020, 10:31 PM

So it hesitates as soon as you try to give it gas and that’s it, it won’t go. I had this happen one time when moving it out of the garage.
So here’s where I’m at tonight. I don’t have any vacuum at idle to the distributor. The diaphragm will hold vacuum. And I have 16 Hg off the mainifold at idle. So I’ll have to check on that. That should be simple enough. I’m just reading this after I was in my garage.
And the million dollar question today... Can you use an oil pressure gauge be used to read fuel pressure? Some of my old mechanic friends said yes, some said no. Same with Google. So I tried it. I ran a T after the fuel line and before fuel rail and it’s components. I was only getting about 13 psi. So I changed the fuel filter and it was filthy. Like hit chocolate running out the one side. (I not sure if I can post a video, I’ll try). This car had been sitting awhile and had bad gas. I had drained most of the fuel out of the tank a few months ago.
So this weekend I’m going to take my fuel gauge set up and put it right after the fuel pump. If it reads about 13psi, my set up doesn’t work correctly. Or a weak fuel pump. If I get 30+psi, I probably have a clogged or rusted fuel line. Also, I have wires ordered. So I can put new plugs and wires in to finish the tune up.
That’s interesting about vacuum at idle to the distributor. That helps me out a lot. Thank you very much. I have another manual coming in the mail at some point next week.

Scotto52 · #4 06-16-2020, 10:36 PM

The fuel filter was pretty rusty

https://youtu.be/dJKqeQEmpWg

R72benz · #5 06-16-2020, 11:18 PM

If your fuel filter was that dirty, did you check the tank screen? It is in the bottom center of the tank. Tank must be empty to remove it, but many have found it completely clogged.
Ron F

Scotto52 · #6 06-17-2020, 06:06 AM

I just learned of this filter. The tank is completely full now. I’ll have to figure something out. More so along the line of how to properly dispose of all the old fuel.

Tomguy · #7 06-17-2020, 07:06 PM

Holy crap. Yeah, I agree, your tank should be drained, and then check the strainer - get a mirror into the tank while you can and see if the inside is bad as well.

berfinroy · #8 06-22-2020, 03:12 PM

Quote:

Originally Posted by Scotto52

More so along the line of how to properly dispose of all the old fuel.

Assuming the gas in your Mercedes is unleaded and not THAT old (you said a matter of months, not years, get a hand or electric fuel pump and transfer it to a new car. Just be careful that the pickup fuel line isn't at the lowest point in your Mercedes tank where it might pick up some debris.
These first generation Bosch "D-Jetronic" are tricky. They will run, sort of, when one or more of the parameters are out of whack, but they will NEVER run WELL unless they are all spot on. they are:
1) Fuel pressure. You're already on to that. When the pump and filters are all clean and working right, the "Fuel Pressure Regulator" must be set to 30+/_ psi.
2) Fuel injectors. Bosch's injectors are very well designed and made. At minimum they should be professionally cleaned and matched for flow and spray pattern if not already done sometime in the last couple of decades.
3) Vacuum/fuel leaks. Lots of little hoses. Renew unless you know from inspection they hve been renewed in the last 15 years or so. INCLUDING the little short pieces that go from the fuel rails to the individual injectors. Gas leaks @ 30psi are dangerous.
4) Auxiliary Air Valve (AAV). Part of the warm up mechanism. The valve is supposed to close off supplementary air supply as the engine warms. They gat sticky with age and don't close properly, causing the idle to "hunt" in neutral. Look for a tutorial on this site for how to disassemble and renew it. Not hard, but not intuitive, either. Require so judiciously applied force.
5) Trigger points. Unique to the D-Jet system. They are located in the lower half of your distributor. Distributor removal necessary to inspect, clean and lubricate. They last a long time but maybe not 50 years! They carry very little voltage, so the actual points (4 sets) are probably OK, but the fiber blocks that ride the cams may be excessively worn if they haven't been lubricated, like, forever. The shoulder should be not much less than 1/8".
Bosch makes a repair kit, but its expensive.
These points are also subject to oil contamination rising up the no longer new distributor shaft. Other than just cleaning the trigger points for now, I suggest fitting an absorbent disc of some sort below the trigger points to block oil from getting to the trigger points. See other posts on "oily trigger points".
6)Throttle Position Sensor (TPS). On the right side of throttle body. Tells the ECU how long to open the injectors. The adjustment of this little gem is very touchy. If you don't have any symptoms of hesitation, crappy idle (assuming the other parameters have all been delt with) or a noticeable "on-off" fuel delivery sensation when you lift and apply throttle at modest speeds), leave it alone.
7) Plug wires must be sold core and plus non resistor type.
8) Compression. Valve lash. Valve guide seals (smoke on deceleration) Valve timing---this engine has a long chain that gets excessively stretched in time.
Now go have fun!

Scotto52 · #9 06-22-2020, 08:08 PM

Hey thanks a lot everyone! So here’s where my dumb ass is at...
Upon replacing the fuel filter I also took the back off the fuel pump apart and looked for tarnish, which was good. It was replaced at some point. Something I learned is the odometer isn’t working. So I had originally thought the car sat for about 15 years, because the mileage was the same. So I’m not exactly sure now. (I got it at an estate auction) As I was blowing air through the fuel lines from the engine back to the filter, I soon realized I was on the wrong line. I didn’t know the pressure line comes all the way up to the front to the fuel rail. Doh! I was tested pressure on the return line. Lesson learned. I also bypassed to the solenoid going to the distributor. So now I have vacuum at idle. I took her for a bit of a longer drive today. After about 10 minutes the hesitation comes back. So much that even at a stop sign, the slightest amount of throttle she almost stalls. So back in the garage for now. I have tomorrow off, so I might go back in and check some items. I still need to clean off the crank pulley so I can set the ignition timing and maybe check dwell. I’ve never done that, I come front the new era where all you do is plug it in and read a data list.

So the things that are rolling around in my mind.

Is the fuel tank really that dirty, and after about 10 minutes the internal screen is getting too clogged? I going to keep driving her until the fuel level gets down to a reasonable level to change the screen. She’s still good to pick up take out and grab a six pack when needed. I should probably hook up my pressure gauge and monitor.

I’m also thinking about a vacuum leak after she warmed up. I’m going to spray some 2+2 around some vacuum lines, intake mainifold and such to see if the idle changes. I need to research this AAV valve a bit more.

I also found this vacuum valve, I’m thinking I could use this to replace the solenoid on the vacuum line going to the distributor. https://www.***************/pn/0015407097

I need to look into these trigger points as well. What exactly is their purpose? I’m guessing that there’s four of them, so maybe there sending to signal when to fire the injectors?

Thanks again for your time and knowledge!

Scotto52 · #10 06-22-2020, 08:11 PM

www.***************/pn/0015407097

He’s the link to that valve again

Scotto52 · #11 06-22-2020, 09:14 PM

Guess I can’t link that. It’s a “ Pierburg Vacuum Valve; 3-Way Switchover Valve with 3 Vacuum and 2 Electrical Connections”

Graham · #12 06-26-2020, 09:59 AM

Quote:

Originally Posted by berfinroy

Assuming the gas in your Mercedes is unleaded and not THAT old (you said a matter of months, not years, get a hand or electric fuel pump and transfer it to a new car. Just be careful that the pickup fuel line isn't at the lowest point in your Mercedes tank where it might pick up some debris.
These first generation Bosch "D-Jetronic" are tricky. They will run, sort of, when one or more of the parameters are out of whack, but they will NEVER run WELL unless they are all spot on. they are:
1) Fuel pressure. You're already on to that. When the pump and filters are all clean and working right, the "Fuel Pressure Regulator" must be set to 30+/_ psi.
2) Fuel injectors. Bosch's injectors are very well designed and made. At minimum they should be professionally cleaned and matched for flow and spray pattern if not already done sometime in the last couple of decades.
3) Vacuum/fuel leaks. Lots of little hoses. Renew unless you know from inspection they hve been renewed in the last 15 years or so. INCLUDING the little short pieces that go from the fuel rails to the individual injectors. Gas leaks @ 30psi are dangerous.
4) Auxiliary Air Valve (AAV). Part of the warm up mechanism. The valve is supposed to close off supplementary air supply as the engine warms. They gat sticky with age and don't close properly, causing the idle to "hunt" in neutral. Look for a tutorial on this site for how to disassemble and renew it. Not hard, but not intuitive, either. Require so judiciously applied force.
5) Trigger points. Unique to the D-Jet system. They are located in the lower half of your distributor. Distributor removal necessary to inspect, clean and lubricate. They last a long time but maybe not 50 years! They carry very little voltage, so the actual points (4 sets) are probably OK, but the fiber blocks that ride the cams may be excessively worn if they haven't been lubricated, like, forever. The shoulder should be not much less than 1/8".
Bosch makes a repair kit, but its expensive.
These points are also subject to oil contamination rising up the no longer new distributor shaft. Other than just cleaning the trigger points for now, I suggest fitting an absorbent disc of some sort below the trigger points to block oil from getting to the trigger points. See other posts on "oily trigger points".
6)Throttle Position Sensor (TPS). On the right side of throttle body. Tells the ECU how long to open the injectors. The adjustment of this little gem is very touchy. If you don't have any symptoms of hesitation, crappy idle (assuming the other parameters have all been delt with) or a noticeable "on-off" fuel delivery sensation when you lift and apply throttle at modest speeds), leave it alone.
7) Plug wires must be sold core and plus non resistor type.
8) Compression. Valve lash. Valve guide seals (smoke on deceleration) Valve timing---this engine has a long chain that gets excessively stretched in time.
Now go have fun!

Great summary. I have lived with my Djet for past 30 years. Your check list is excellent. I may post/link it over on BW where I have a 107 owner with similar problems.

Adv_rider · #13 06-30-2020, 10:54 PM

Quote:

Originally Posted by berfinroy

Assuming the gas in your Mercedes is unleaded and not THAT old (you said a matter of months, not years, get a hand or electric fuel pump and transfer it to a new car. Just be careful that the pickup fuel line isn't at the lowest point in your Mercedes tank where it might pick up some debris.
These first generation Bosch "D-Jetronic" are tricky. They will run, sort of, when one or more of the parameters are out of whack, but they will NEVER run WELL unless they are all spot on. they are:
1) Fuel pressure. You're already on to that. When the pump and filters are all clean and working right, the "Fuel Pressure Regulator" must be set to 30+/_ psi.
2) Fuel injectors. Bosch's injectors are very well designed and made. At minimum they should be professionally cleaned and matched for flow and spray pattern if not already done sometime in the last couple of decades.
3) Vacuum/fuel leaks. Lots of little hoses. Renew unless you know from inspection they hve been renewed in the last 15 years or so. INCLUDING the little short pieces that go from the fuel rails to the individual injectors. Gas leaks @ 30psi are dangerous.
4) Auxiliary Air Valve (AAV). Part of the warm up mechanism. The valve is supposed to close off supplementary air supply as the engine warms. They gat sticky with age and don't close properly, causing the idle to "hunt" in neutral. Look for a tutorial on this site for how to disassemble and renew it. Not hard, but not intuitive, either. Require so judiciously applied force.
5) Trigger points. Unique to the D-Jet system. They are located in the lower half of your distributor. Distributor removal necessary to inspect, clean and lubricate. They last a long time but maybe not 50 years! They carry very little voltage, so the actual points (4 sets) are probably OK, but the fiber blocks that ride the cams may be excessively worn if they haven't been lubricated, like, forever. The shoulder should be not much less than 1/8".
Bosch makes a repair kit, but its expensive.
These points are also subject to oil contamination rising up the no longer new distributor shaft. Other than just cleaning the trigger points for now, I suggest fitting an absorbent disc of some sort below the trigger points to block oil from getting to the trigger points. See other posts on "oily trigger points".
6)Throttle Position Sensor (TPS). On the right side of throttle body. Tells the ECU how long to open the injectors. The adjustment of this little gem is very touchy. If you don't have any symptoms of hesitation, crappy idle (assuming the other parameters have all been delt with) or a noticeable "on-off" fuel delivery sensation when you lift and apply throttle at modest speeds), leave it alone.
7) Plug wires must be sold core and plus non resistor type.
8) Compression. Valve lash. Valve guide seals (smoke on deceleration) Valve timing---this engine has a long chain that gets excessively stretched in time.
Now go have fun!

Thank youy for that.
Ive been living with some on/off surge while coasting around 30-50 km/hr

Tomguy · #14 07-01-2020, 12:23 PM

Is your foot off the throttle when coasting at those speeds? DJet has a fuel cutoff that you may be hitting when off the gas.
How high does your car idle?

Graham · #15 07-01-2020, 12:36 PM

Quote:

Originally Posted by Tomguy

Is your foot off the throttle when coasting at those speeds? DJet has a fuel cutoff that you may be hitting when off the gas.
How high does your car idle?

The fuel cut off only actuates when foot is 100% off pedal if throttle position switch is properly adjusted. The engine does not surge when that happens. It just picks up again when rpms drop to about 800-900.

On my SL, I have an AFR gauge on dash. You can see the AFR go from say 14 to 18 when you take foot off pedal. Then you see it recover back to 14 if you just touch the pedal. No surging. 18 indicates fuel has been cut off.
I was out in the car today and noticed it still working as it should!

Adv_rider likely has a different problem. It could be the throttle position switch (TPS). There is a write up on BW 107 in stickies on how to dismantle and check the TPS. Maybe a link here somewhere too under my name.