1975 450 SL runs too rich--need help

[JoshC450SL]

Hello all, I myself have a problem with my 1974 450SL running rich. I noticed this from the new spark plugs I changed covered in black soot.

I’ve read this entire thread and I’ve pretty much done all I can think of when approaching the problem and trying to deduct what it could be. Fuel pressure is normal at 29psi, new fuel filter, new fuel injectors with all new rubber seals all matching and all correct (part number for injectors is 0 280 150 036).

I recently took it to a ford dealership where they did a tail pipe test and the numbers read CO 11.59% and CO2 is 6.1%. I know the range is 0.5-2% range and the O2 is 1.9%. When I was there I turned the knob on the ecu completely to the left:counter clockwise and the values went up! So maybe counterclockwise depends on how you orient yourself when facing the ecu unit. Does that make sense?

Timing is set to 5* atdc like the black plaque on the radiator support frame states and the idle sets at around 700-800. I set it to around 750 or so in the middle of the range.

I’m not sure if it a vacuum leak or something. I’ve adjusted the regulating linkage to the numbers they give in 7.4-300 of tonk.ca website which has what I believe to be the entire service manual online.

So right now I’m at a loss of what it could be.

I’ve even turned the knob on the ecu under the passenger footwell completely to the left which is counterclockwise to lean out the mixture.

[subforry]

Does it start right up or take some cranking? Were all the plugs sooty?

I haven't played with the timing on mine yet. I typically time engines to the smoothest and highest RPM. Then if it pings or kicks back on a hot restart, I retard the timing. In the end the timing is way advanced compared specs. The spec timing was for fuel of the era and for emissions. A low compression engine that this can take lots of timing advance.

I have my 280SE 4.5 apart because I am making sure there are no vacuum leaks and installing new injectors. The main thing I found was the air bleed passages at the head intake ports were clogged up with carbon.

[JoshC450SL]

She starts up every time with no problem cranking. A couple of times she died right after start up. One in particular was after work one day I started the car. Backed up and then the car just died. But that was because of a low voltage battery. Battery was toast.

So what you’re saying is that my 5degrees atdc isn’t good for it? I should advance the timing to 5btdc?

[subforry]

JoshC450SL, you can give it a try and see. I am hoping to have mine running this weekend and plan to adjust the timing. I can get back with the results. I think mine is already advanced to limit of the hold down. Does it loose traction from a stop if you stomp on the gas with it in low? I know the w107 have more sophisticated rear suspension than a w108, but it should break the rear tire free.

[subforry]

I got the car assembled. Fixed any vacuum leaks, new injectors, patched/repaired the injector wiring harness, new plugs, cap, rotor.

My 4.5 has vacuum retard, which is connected to a switch on the firewall. As I understand the switch opens when the AC is on or water temp is 100c. My vac retard was directly connected to manifold vacuum at the throttle body. This is some lame stuff and completely backwards of what is needed. The timing needs to retard at low vacuum and advance at high vacuum.

I disconnected the vacuum, the engine RPM went up, as expected. The air bleed screw needed adjustment and so did the idle mixture on the EFI brain box. I didn't have my timing light, so I don't know what the timing is. I plan to readjust the hold down so I can further advance the timing. The tail pipe smell at idle is actually pretty low for a car like this.

[JoshC450SL]

My dwell angle was 26. I have adjusted it to be 32. It’s within the range of 30-34 degrees. So that’s a plus. So I then had to readjust the timing. It’s at about 7 degrees before too dead center. She runs pretty smooth.

I’ve also made sure at idle the throttle valve is closed as far as it can go without being stuck. And adjusted the gas pedal and the throttle linkage to achieve full throttle when the valve opens all the way instead of half way. I think my plugs were sooty due to incomplete combustion and incorrect combustion.

She seems to be getting better gas mileage as well. An average of 15 highway.

[subforry]

Sounds like you are getting here. 15mpg is probably pretty good. The J-Jet will usually run ok even if things are non-functioning. A few other easy things to test are the temp senders https://jetronic.org/en/d-jetronic/troubleshooting#Temperatursensoren
And the TPS calibration, see time 13:49 https://www.youtube.com/watch?v=chqXHxYFCVw

[JoshC450SL]

The temperature sensors seem to be working. I can tell a difference when I unplug the air temp sensor from the air cleaner housing. The map sensor works just fine and pulls vacuum. I’ll have to check out the throttle position switch.

I did adjust the linkage to have actual full throttle when I press the gas pedal to the floor. It wouldn’t even go half way before that. I figured that was the issue with the rich running. Not getting enough air mixture. Idle is on point as far as I can tell as well as the timing. I honestly don’t know about the timing to completely honest. I’ve gotten the initial timing down and it’s set to about 7 degrees before top dead center which is what that chart says on tonk.ca website “07.5.1 11-500/2“

Something about 7 degrees before tdc. “Installation value of ignition distributor at starting speed without vacuum”