M103 300E runs like crap. And I'm out of ideas! - Page 2 - PeachParts Mercedes-Benz Forum

Holmesuser01 · #16 07-10-2012, 09:56 AM

I know your fuel pump is working, but is it making pressure?

I replaced mine, and lots of little intermittent things like stumbling instantly went away.

It was a good investment to replace the OEM pump. It was only 25 years old, and submerged in some of the worst gasoline ever refined... It amazes me just how skanky modern fuel really is!

oldsinner111 · #17 07-10-2012, 10:11 AM

check if fuel pump ground is clean

tbomachines · #18 07-10-2012, 12:08 PM

I'll be attacking the iacv today, might make a video out of it for the blog (I'll make one of the symptoms and duty cycle as well). I imagine that if the fuel pumps were the issue that it would bog down in higher rpm but I could be wrong. They definitely spin up and are audibly on when you peek under the back of the car, no real deviation in noise but I can add it to the list after ruling out the coil and ignition module.

Holmesuser01 · #19 07-10-2012, 01:44 PM

Quote:

Originally Posted by tbomachines

I'll be attacking the iacv today, might make a video out of it for the blog (I'll make one of the symptoms and duty cycle as well). I imagine that if the fuel pumps were the issue that it would bog down in higher rpm but I could be wrong. They definitely spin up and are audibly on when you peek under the back of the car, no real deviation in noise but I can add it to the list after ruling out the coil and ignition module.

If it helps, I could hear the fuel pump quite easily from inside the car. I also replaced the fuel filter at the same time. It was OEM, and lasted(?) until 2008. I replaced the filter again when I got a used fuel accumulator early this year. Mine was leaking pressure down and being a ***** to start. Cured.

tbomachines · #20 07-10-2012, 04:54 PM

Well I MAY have found the smoking gun! I just took off the IACV and cleaned it out (also made sure it was functioning fine by supplying a 12v charge. Flipped open and closed like it should. When I put it back on, I noticed the rubber tube was a tiny bit cracked on the bottom. My stethoscope also picked up a distinct sucking sound...I was able to flex the IACV up and down slightly (we're talking maybe 1mm)and it would vary the air sound yet would clearly and repeatedly give me my symptoms. Flex down (sealing it) and it would run fine), flex up and it would give me the stalling when I revved the throttle a bit. I'm happy I finally found SOMETHING that could be leading to this issue. But, FWIW when I had the camera running today it didn't reproduce the issue at cold start, go figure. I wouldn't be surprised if very slight variations in temperature would cause that little hose to expand and contract enough to do that.

lorainfurniture · #21 07-10-2012, 05:50 PM

Amazon.com: Red Line 60103 SI-1 Fuel System Cleaner - 15 oz.: Automotive

TRY IT. My car has made a full recovery as result of this stuff. I still get a *slight* hesitation when I gas it, but otherwise is runnig well.

Those idle air hoses do help, make shure you buy genuine mercedes ones. The aftermarket ones are garbage, and wont fit.

duxthe1 · #22 07-10-2012, 09:15 PM

An easy test to find a marginal coil is to spray it with a little water, preferrably a spray bottle. If a coil is arcing out, moisture will exacerbate the problem significantly.

Adler · #23 07-10-2012, 11:12 PM

Thanks for this tip on checking out a marginal coil .
Missing could another aspect of a marginal coil .
Ad

Quote:

Originally Posted by duxthe1

An easy test to find a marginal coil is to spray it with a little water, preferrably a spray bottle. If a coil is arcing out, moisture will exacerbate the problem significantly.

tbomachines · #24 07-11-2012, 08:34 PM

Put 2 hose clamps on the end of the rubber hose that connects to the IACV. I'll eventually replace the hose itself but it looks like it goes down behind the fuel distributor which is not particularly encouraging me to do the job. I took the car for a long ride this evening and it ran perfectly which OTOH IS encouraging.

d.delano · #25 07-11-2012, 10:36 PM

The idle air hoses are critical. You must take the fuel injector lines and cold start injector off and perhaps the fuel distributor as well, I don't remember. There is one that goes down to the boot under the mass air meter and one that goes to the cylinder head. One trick to get the squeeze clamp under control while you are sliding the hose onto the cylinder head nipple is to ziptie the clamp open then cut it once you have pushed the hose home. You might as well replace the boot under the air mass meter while you are doing this. All these molded rubber bits are going to need to be renewed, and they all should be bought from the dealer, NO EXCEPTIONS or you will be sorry I assure you.

I've been following your thread and was going to speak up about the idle air hoses but held off. Do NOT use aftermarket idle air hoses, you have been warned. I ordered the one that goes to the cylinder head from the AZ place, I think it was made by CRP Industries. Complete waste of time and money. Didn't even bother trying to make it fit, it was obvious by looking at it that it would not. Horrible quality crap. Had to get a dealer part which fit perfectly of course and didn't cost but maybe $10 more. For the one that goes to the air boot under the air mass meter, I bought a Meyle from I can't remember where, I think Fastlane. Again, crap. This one sealed at first, fit perhaps a little too tightly though. Car ran really well for a time. Then that hose split at both ends and the car wouldn't hold an idle. This hose failure cost me a tow to an indy, an hour's worth of his time, and a replacement part from MB at his markup, all because I wanted to be cheap with an idle air hose.

Really people aftermarket parts are utter ****e, learn from my screwup and don't waste your time.

ps2cho · #26 07-11-2012, 11:21 PM

As d.delano says, stick genuine MB on this item if nothing else.
I also got stuck with no-start condition due to a crack in the hose that I REPLACED. CRP brand. It cracked on the underside out of sight. Luckily I found it 2 days later after scratching my head. It was less than 1 year old.

Follow this as for the trick to get the one that snakes under the intake manifold:
http://w124-zone.com/articles.php?article_id=35

97 SL320 · #27 10-19-2012, 08:06 PM

Quote:

Originally Posted by tbomachines

Put 2 hose clamps on the end of the rubber hose that connects to the IACV. I'll eventually replace the hose itself but it looks like it goes down behind the fuel distributor which is not particularly encouraging me to do the job. I took the car for a long ride this evening and it ran perfectly which OTOH IS encouraging.

Was this the final fix?

I'm working on a 91 300SL M103 24 valve that has similar symptoms and am looking for engine specific information not general "how to fix the problem" information.

The car was sitting for 3 years just prior to me buying it and I drove it onto the trailer without issue. ( The car was parked due to slipping reverse. ) The motor / trans are coming out and be replaced with a M104 / 722.6 conversion so I'm not interested in spending much time / $ but I'd like it to run better so it can be sold off as mechanically the motor is great.

Most of the time it has a clockwork smooth idle then sometimes slight roughness, put it in gear and the motor is still smooth. While still in gear, feed throttle and most times the motor will shake / ping very heavily to the point that the car barely moves. Overall the condition is getting worse sometimes affecting idle.

The old fuel has been run out and about 3 gallons of fresh burned off. I've run cars with old fuel before and none were this rough or intermittent. The dist cap / insulator dish had some carbon tracking that has been cleaned, plugs were carboned up and have been cleaned. Past that I have not done much.

Any ideas? Thanks

tbomachines · #28 10-19-2012, 08:11 PM

Unfortunately there was no "final fix" on it. I took off the valve cover and re-hooked everything up. Somewhere in there, it fixed what was wrong. I have to imagine that it was some sort of vacuum leak, although even after sealing the IACV hoses it still acted up. Since removing the valve cover, it has been running fine, passed inspection and driven a few hundred miles

I'm just as baffled as everyone else. I have to imagine it was vacuum related although there were electrical connections here and there that I had to unplug and reconnect. I'd feel more comfortable if I replaced something and it started running perfectly again but eh...guess that's the way these older cars work sometimes! Makes sense since gasoline engines pull the most vacuum at idle and under load at low RPMs so if there was a leak there would be unmetered air entering and it would lean out. Duty cycle values were fine though....weird.