300E Engine Dragging?? - Page 2 - PeachParts Mercedes-Benz Forum

350SL4spd · #1 03-14-2011, 10:54 PM

I finally got my fuel pressure stuff together and did some testing tonight. Passed both the pressure test (5.4 bar) and the flow test (easily over a liter in 40sec). So I guess the fuel pumps are ok.

Does anyone know the testing procedures for the Fuel Distributor? Is there any way to test the injectors w/o special equiptment?

JohnM. · #2 03-14-2011, 11:36 PM

If you have fuel pressure, and you don't get fuel when cracking the lines at the FD...the FD is blocked or has failed internally I would imagine. Which means that def no fuel is getting to that injector. The FI system is completely mechanical....so it's pretty simple in operation.

350SL4spd · #3 03-15-2011, 12:07 AM

What I need to do now is crack the lines for #4 & #6 at the FD and trip the fuel pumps by bridging the Fuel Pump Relay. The last test there I did only by cranking with the key, which I learn today is very different: Cranking with the key gives me 2.5 bar of FP and running the pumps straight from the Fuel Pump Relay gives me 5.4 bar.

And of course right when I should be dealing with and/or replacing this car (my daily driver) I stumble across a mint, early 72 SL. Bugger...

350SL4spd · #4 03-16-2011, 08:24 PM

I cracked a couple of the fuel lines coming out of the FD and didn't get any fuel coming out when running the FP from the FPR. I cracked one line for a cylinder that had been running & one for a cylinder that hadn't been running, but neither had any fuel coming out.

Am I missing something?

JohnM. · #5 03-17-2011, 01:55 AM

No fuel at the lines on top with verified pressure...all points to fuel distributor I gotta think. I will be hitting up the junkyards tomorrow and can send one for cost + postage. I think they charge $38.99 + tax..

350SL4spd · #6 03-17-2011, 02:11 PM

If it's not too late, I'd take you up on that offer John.

Thanks & let me know the total.

350SL4spd · #7 03-21-2011, 08:55 AM

Well, I slapped everything back together & started it and it fired right up. She idled OK, but was breaking up a bit when rev-ed. I may just try to drive it & see how it responds. Needs an oil change & I have a new fuel filter to put in too, if I ever get the time...

Does it running a bit better now after the battery of tests I put it through suggest that it's more likely to be injectors or the fuel distributor?

350SL4spd · #8 03-26-2011, 05:35 PM

Took the car out for a couple of runs this week and it runs like crap up to about 2500rpm then it opens up and runs ok. First day I took it out I'd say it was running on 5cyl and the second I'd say 4cyl.

Grabbed a used FD on eBay, so we'll see if that does it...

350SL4spd · #9 04-28-2011, 12:59 AM

Update/New Problem:

So after some fooling around I ended up needing to get a rebuilt FD (don't ask). Phil got me a great deal and I put that in tonight & it ran really good with just a bit of a miss which I immediately tracked down to cyl #1. On top of the new FD several fuel injectors have been replaced inc #1. On inspection of #1cyl I find that the spark plug has been working (not wet, dark brown in color) but that the ceramic is cracked. I run out and get a new plug, put it in, crank the car over and... bastard won't run.

5min ago it was fine. Swapped one plug out and now it won't run. If I keep my foot @ half throttle or more it'll run, but as soon as I let off it dies immediately.

I had the exact same symptoms on an M103 a few years back that ended up being a massive vacuum leak (that time it was the big one @ the bottom of the intake manifold under the mix unit). But I can't find any leaks on this one & didn't get near any lines changing the spark plug out.

I've worked on Benz's most of my life & on this particular car for almost 7yrs. I'm no genius, but I know my way around a Mercedes engine. And I'm completely buggered right now.

Any insight, tips, ideas, offer to buy the car would be greatly appreciated.

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