450 SE running on 4 cylinders - PeachParts Mercedes-Benz Forum

Toy94 · #1 08-22-2006, 09:10 AM

Hi, I'm trying to help a friend of mine get a 450 SE running a little better. I pulled all the injectors at the same time because it is missing really bad and it has new plugs wires, cap and rotor. Only 4 were spraying when I cranked it over. The only ones pulsing were the outer 4 corners of the engine. I believe it would be cylinders 1, 4, 5, and 8. I read a few posts that said the fuel injection control unit could be the issue, but I wanted to check and see if there is anything else I can look at before I try and find one. Is this a common problem for these cars?
Thanks,
Ben

david s poole · #2 08-22-2006, 10:48 AM

what year is the car and is it 'd' jetronic or 'k' david poole

Tomguy · #3 08-22-2006, 01:04 PM

Your trigger points are fouled.

These are located in the bottom of the distributor and have a plug - you need to remove the distributor to remove the points. You can search "450 trigger points" or "4.5 trigger points" if you want more information, but basically, clean them if oily with a cloth, then clean the point contacts with a NONABRASIVE material such as a business card or stiff piece of paper.

Toy94 · #4 08-22-2006, 04:49 PM

Sorry about not giving the year. It's a 74 and I will have to ask him what the vin and engine numbers are. I'll check the points in the distributor. Thanks for the input.

Tomguy · #5 08-22-2006, 09:00 PM

Since the cylinders you mentioned are controlled by two sets of points (1 and 5 together, 4 and 8 together), and assuming that you watched the injectors pulled from the engine (which you can't really check on the later ones) I assumed your engine was a D-Jet EFI engine, and you need to check those trigger points - I can almost guarantee that the problem lies either with those points or the plug for them.

Toy94 · #6 08-23-2006, 09:03 AM

I will hopefully get a chance to pull the distributor this weekend and clean the trigger points up. He has been driving it this way for almost 2 months now! 0-60 is literally a couple minutes but it's his only transportation. Thanks for the help.

Tomguy · #7 08-23-2006, 10:06 AM

Maybe because I have done it so many times before, but the trigger point cleaning takes me no more than 30 minutes including engine retiming, and if I were missing two (nevermind four!) cylinders, I would not hesitate to PULL OVER, yank it out and clean them!

PILOT MAN · #8 08-23-2006, 10:41 AM

I agree with Tom, i have several times over the last 15 years pulled over to the side of the road and cleaned the trigger pionts on my 1975 350se w116, wich has the same setup as you have.

i have marked the dizzy and engine, so i can yank the dizzy on the side of the road, clean the trigger pionts and put the dizzy back with the timing being very close to correct.

GaryF · #9 08-23-2006, 11:11 AM

Did mine last weekend. Not sure if this is common but my 4 points were enclosed in small clear plastic boxes which were easily removed for the top two but I couldnt see how to remove them from the bottom pair without de-soldering the connector and disassembling the unit. I chickened out and cut small slots in the plastic so I could swipe a business card through the points.
Since these boxes are not air-tight they would not prevent the vapours contaminating the points anyway. It may be have been a Euro only mod that Merc. tried ?

Toy94 · #10 09-18-2006, 12:37 PM

So I have the car running on all 8 cylinders now, but it is running too rich, especially when idling. I have black smoke at idle and when I rev it up. I tried adjusting the air bleed on the front of the engine, but it still runs rich. Is there a procedure to adjust the idle setting? Is there a way to get a fuel pressure guage on this car so I can check the regulator pressure? Why are there two regulators by the way?

GaryF · #11 09-18-2006, 02:20 PM

The air bleed on the front of the engine is to set the idle speed, there is an adjuster on the engine management electronics to set the mixture at idle. This is a box located in the footwell. Its on the passenger side of my RHD car not sure which side it is on for LHD.
There are plenty of posts about its adjustment if you do a search.
The cold start injector located near the air bleed screw could also be leaking or permanently powered, try disconnecting the electrical plug to this first and see if it helps when the engine is warmed up.

Tomguy · #12 09-18-2006, 03:06 PM

Since your trigger points were fouled I'm willing to bet you have several leaking vac lines (especially the MAP sensor and the locking system) which WILL cause your engine to run too rich. Fix the vac leaks before touching the mixture!

GaryF · #13 09-19-2006, 03:24 AM

Quote:

Originally Posted by Toy94

So I have the car running on all 8 cylinders now, but it is running too rich, especially when idling. I have black smoke at idle and when I rev it up. I tried adjusting the air bleed on the front of the engine, but it still runs rich. Is there a procedure to adjust the idle setting? Is there a way to get a fuel pressure guage on this car so I can check the regulator pressure? Why are there two regulators by the way?

Was it the trigger points ? You havnt ended up with 4 injectors permanently on ?

Toy94 · #14 09-19-2006, 11:03 AM

It was the trigger points causing the misfiring. Now I just need to get it tuned right so my friend can pass emissions. Right now there would be no chance. I'll check all the vacuum lines for cracks. Thanks for the help.