Question: Why do you keep ignoring the obvious? Your injectors that were tested in 2007 need rebuild with new nozzles in 2021. Noise and roughness at cold start are one of 3 things:
1: Air ingress. Super common source is the fuel preheater system that I mentioned way back in this thread and you ignored. Air problems in these cars will usually work themselves out in the first 30 seconds or so of running.

2: Compression. Again, mentioned by myself and others and ignored. Compression results from 2011 are irrelevant in 2021.

3: Worn injectors. I really do not care if the car hasn't moved an inch since 2007 when they were last checked. Things change.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

He now edited the post including "Inspected and pop tested the injectors on February 25, 2021"

As I have written, my injectors were rebuild and properly balanced to 135 bar. Perhaps I need to check IP timing.
Thanks for the link

Since the OP is Canada, their "Imperial" gallon is 4.54L instead of the 3.78L of a US gallon, or roughly 1.2 US gallons.


When I had my 300SDL tuned properly, I had multiple highway trips where I did 28-30mpg in it. If converted to Imperial gallons, that would be 33-36mpg Imperial. Assuming the OP is reporting in Imperial gallons, it's a very believable figure.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

That makes sense. I average 27mpg in the US.

Considering how the OP is fixated on finding something else wrong, I'd be surprised if anything else was done to them other than looking at them and checking pop pressure. There's so much more to injectors than just what pressure they pop at. Spray pattern, chatter, internal leakdown, and external leaking are all super important parts of the puzzle that are easy to overlook.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

IP timing is easy to check on these engines. Pop the plug out of the side of the IP, spin the engine to TDC on the crank pulley and make sure the cam is lined up at 0 timing. If the cam is off more than 2-3˚ it's time for a new chain as the timing is not adjustable on the 603's. The good news is that the chains don't really wear on these engines until they get to super high mileage, my very worn out 300SDL engine was still only 1˚ stretched at mileage high enough to have worn the cylinder walls slick.

With the crank and cam at 0 timing, look in the hole on the side of the IP and check that the timing mark is centered in the hole. If it is, great. If it isn't, you can loosen the adjustment bolts on the IP and rotate it until it is.

Be aware that with freshly rebuilt injectors, or after doing delivery valve seals, it's normal for these engines to be pretty noisy. Even with worn in DV's and injectors they have a bit of a "cackle" at idle due to the vertical injection and starburst shaped combustion chamber in the piston crown. The later engines with inclined injection and the "moose horn" shaped combustion chamber are extremely quiet in comparison.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

When checking the ip timing on a 603 by looking through the hole on the side of the ip the crank is supposed to be 15 degrees after tdc and not at tdc

Correct. I forgot to skip ahead to ATDC after checking cam/crank timing. Some vehicles are 14ATDC others are 15ATDC, a sticker on the radiator support should show which is used on the vehicle in question. My '86 300SDL was 14ATDC, and the '91 350SD was 15ATDC for reference.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I will do steps 1 and 2 once I get around them, and I will post my results.
I pop tested the injectors last month, and all of them were at 1900 PSI (131 Bar). All of them had good spray patterns.

Can you suggest to me the best possible way of bypassing the pre-heater?

A few years ago, I replaced the fuel filter and fuel intake hose located at the gas tank filter that was leaking. There has not been any improvement in start-up shaking and smoking.
2 years ago, I replaced the IP delivery valve seals.

I inspected the fuel valve, and there was no evidence of a leak. It does not mean it does not leak. There is no fuel pressure on this valve. But it can always ingress air. It was a simple process to eliminate the fuel heating valve and the heater. I bypassed both of them. I started the car this morning while it sat at an overnight temperature of 35°. The Car started with hardly any shake and with minor smoke. I test drove the car and it has 20% more power. It used to have intermittent pulsation on the accelerator pedal, which I do not experience anymore. I used to notice air pressure in the gas tank on every fill-up. It used to make a whoosh sound each time I opened the gas cap. I knew there was an air ingress from somewhere. I have been chasing it for the longest.

I have been able to resolve this issue with your support.
Thanks for your help and persuasion to make this change, and finally eliminate one of the issues.

That fuel heater thermostat is a terrible design. I've never had one that didn't leak air (none ever leaked fuel), even after rebuilding with new O-rings. It is the most common source of air in the fuel system on the 60x engines. The lift pump is very aggressive and the fuel preheater system is on the suction side of the pump. The O-ring in the plastic end of the preheater thermostat does not provide good protection against air ingress on the suction pulses from the lift pump. The issue is compounded because MB chose to use fuel line smaller than Bosch recommends so the suction in the lift side of the fuel lines is much higher than it should be.

The next most common source of air ingress is the rubber fuel lines under the hood. The correct size is 7.5mm. The way the barbs are formed on the metal fuel lines at the firewall, 8mm or 5/16" hose will NOT clamp down tightly and WILL allow air ingress.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Interesting. I replaced my lines recently with IIRC 5/16 hose and engine seems louder, but it coincided in time with new injectors. Maybe they do take up air I'll need to investigate!

Stick clear tubing on the return line from the filter to the hard line on the firewall. You'll see it full of air in the morning with the 5/16" hose. Believe me, I tried 4 different brands and 3 different types of hose clamps after everyone on this forum was ADAMANT that 5/16 is fine. It simply isn't and several other people here have had the exact same experience I have. It'll work for a few days to a couple weeks, but it *WILL* leak air. Perhaps on the 61x cars it's fine, but NOT on a 60x car.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)