Help me figure this out - M103 - PeachParts Mercedes-Benz Forum

tbomachines · #1 03-22-2010, 11:33 PM

I just got a 1990 300E. It seems to be a bit low on power...sometimes going up hills I need to completely floor it and it won't really accelerate much. Really noticeable above 2500rpm. I'm not really sure where to start...I have a bunch of parts on order like filters, plugs/wires/cap/rotor for a tune up. It sounds like there might be an exhaust leak due to a sound (sort of a hissing) but really only hear it under load and somewhat at idle. Would all of this indicate a failing fuel pump? Air pump leak? What would the symptoms be of each? Most of my gas engine experiences were with well...not overengineered engines.

I'm still trying to get my head around all of the acronyms on this board, much more complicated than the old diesels!

Car has in between 100k and 120k I believe, odometer is slow/inaccurate.

ps2cho · #2 03-22-2010, 11:58 PM

Well start with the tune items you bought and make sure to replace all the idle air hoses. Shoot some carb cleaner around the idle control valve, injectors and listen for any vacuum leaks. Start there and if you have done the spark plugs, wires, rotor, cap and idle air hoses and the problem still persists we can go from there.

Until then it will be very difficult to get a good baseline. Just snoop around underneath to find the exhaust leak. That or pay a local guy $50 to patch wherever the hole is.

Hit Man X · #3 03-23-2010, 12:06 AM

Any excessive oil consumption currently or before? Cat assy could be plugged up nicely.

Fuel pumps become very loud when about to die.

I agree, start with the basic stuff and go from there.

400Eric · #4 03-23-2010, 12:27 AM

Are you in an area where you have to get a smog inspection when you buy a car? What were your readings? Those could shed some light on where the problem might be.

tbomachines · #5 03-23-2010, 10:34 AM

Quote:

Originally Posted by 400Eric

Are you in an area where you have to get a smog inspection when you buy a car? What were your readings? Those could shed some light on where the problem might be.

Still have the temporary tag on, need to get it tested (only had it for a few days). I wanted to make it run nice and perfect before going for the smog tests. I have to drive up to CT to have it inspected and tested so it needs to pass first time or I'm stuck....keeping my fingers crossed. My parts are coming in today, will get to it if I have time before my night class.

S-Class Guru · #6 03-23-2010, 10:52 AM

Hitman may have "hit" it; all your symptoms are consistent with a clogged cat. I had one on an old Caddy, and it did just that - ran fine at low speed and idle, but just wouldn't go under power. If the hiss is coming from the exhaust ahead of the cat, then there's another strong indicator.

DG

tbomachines · #7 03-23-2010, 01:14 PM

uh ohhhhh, that would put me pretty deep into this car in terms of money spent. Anyone have any experience using a universal cat on MBs? The one on PP is $700

I know decent high-flow ones only run 100-150 bucks. It does make sense though, I'll have to get it up on the ramps and take a look under there.

Edit: The PO did mention oil consumption as a problem with the car...I imagine the valve seals are worn, common issue. I didn't really think of the down-river effects of it though. Its beginning to add up, but I don't have the money for a $700 cat. I think I'll get a universal one and have a muffler shop weld it in.

Also side note: small victory in replacing my ignition lock cylinder, raised my spirits.

400Eric · #8 03-24-2010, 07:25 AM

Quote:

Originally Posted by S-Class Guru

Hitman may have "hit" it; all your symptoms are consistent with a clogged cat. I had one on an old Caddy, and it did just that - ran fine at low speed and idle, but just wouldn't go under power. If the hiss is coming from the exhaust ahead of the cat, then there's another strong indicator.

DG

Yes, I was thinking that too, that's one of the reasons why I wanted to know the results of the latest smog test. I didn't want to say "Cats" until we had more info cause O.P. has three of them to contend with.

And while I agree the cat(s) are the front runner on the suspects list, high oil consumption doesn't guarantee bad cats. The 89 in my sig really swigs the stuff but the cats haven't given up yet!

And no, I'm not gonna bother with the valve seals on a car that has over 232,000 miles on it and isn't worth more than a 1,000 dollars! I love Benzer 1 dearly but that just ain't gonna happen! Too much else to do!

oldsinner111 · #9 03-24-2010, 08:09 AM

I've heard of upgrading to Mustang Cats.Jegs.com

mak · #10 03-24-2010, 10:09 AM

Do not forget the fuel filter replacement if there are no replacement records
mak

tbomachines · #11 03-24-2010, 01:40 PM

Quote:

Originally Posted by 400Eric

Yes, I was thinking that too, that's one of the reasons why I wanted to know the results of the latest smog test. I didn't want to say "Cats" until we had more info cause O.P. has three of them to contend with.

And while I agree the cat(s) are the front runner on the suspects list, high oil consumption doesn't guarantee bad cats. The 89 in my sig really swigs the stuff but the cats haven't given up yet!

And no, I'm not gonna bother with the valve seals on a car that has over 232,000 miles on it and isn't worth more than a 1,000 dollars! I love Benzer 1 dearly but that just ain't gonna happen! Too much else to do!

Do you mean two precats (one per pipe coming off of exhaust manifold) and one main cat (after the 2:1 collector)? I've been looking at exhaust diagrams all morning. I wonder what the best way to test these would be. I could unbolt the main cat, but couldn't run it with a sidepipe dump since the O2 sensor manages the engine once it warms up.

Eventually I'd be wanting to put on a turbo with moderate boost so maybe universal cat with 3" back exhaust using universal stuff might be useful. Idk, I'd have to consider that.

tbomachines · #12 03-24-2010, 08:20 PM

update today. I put on the new distributor cap, rotor, and replaced the ignition wires. Naturally me being me, I managed to break something but luckily it was just the wire cover on top of the valve cover but still

. Anyways power seems to be a BIT better, not too much of a difference (not that I expected too much). Good thing I changed the cap/rotor though, it had quite a bit of buildup on them.

Going to do the fuel filter next, that might be the answer (I really REALLY hope) to some of my problems. I also think the trans needs to be tuned. I went looking for the bowden cable, but didn't feel like taking off the air cleaner, maybe tomorrow.
Thank you for all your inputs thus far! I'm pretty familiar with the diesels but the learning process has begun again for the gasser. Currently trying to price out turboing this bad boy, but most importantly to get it in perfect running condition before any of that.

Hit Man X · #13 03-25-2010, 01:56 AM

People tend to forget about hours on a motor too, even at 100k like you think (probably much higher, people lie when selling vehicles always). Hours will wear stuff too... pull the old plugs and take a peek for any oil build up. Cap/rotor/plugs will not last too long due to the high cruise RPM from this motor. Same goes for the fan belt/accys.

I have fairly heavy build up on my M103 on a few cyl, head R&R is planned for this summer. My oil consumption/loss is very high as my head gasket is also seeping up front. I am talking around 1 quart per 500 miles type of use.

Granted the '90+ cars received 'hardened' guides supposedly from MB, I would suspect a worn head easily. Remember also, if the car has not been driven to hot often the cat converter will not light off and can plug up too.

I would hit the main cat body with a mallet and see if you can hear any rattling... along with S-class Guru, a pal of mine had a Turbo Buick where the cat died and the vehicle would barely run past IDLE speeds. Blew out the downpipe donut gasket it was so plugged. Hacked the cat off and all was well.

So, of course do the fuel filter and see where that gets you. If not, then I would pull the cat assy and ream out the precats, they are only there for cold start emissions. You could also ream out the main cat, but the fetch decent cash for scrap so I would just cut it out and sell it.

Do not waste your time putting a turbo on this unless you convert to actual EFI and have the head redone. CIS is crap.

Car will still run without an O2.

Magnaflow/Carsound have universal high flows that are application specific to fit your ride for a good price.

400Eric · #14 03-25-2010, 04:27 AM

Sorry, site double posted. Please see below.

400Eric · #15 03-25-2010, 04:28 AM

Yes, the two pre-cats and the main cat. I don't know how strict your smog laws are but out here in Calif you can only replace your cats with stock cats or properly "certified" aftermarket cats. (Different states have different rules).

And while on that topic, here in Cali you also won't be able to pass smog unless your non-stock turbo kit has been "certified" by it's maker which of course doesn't work for us because there are no "makers" of turbo "kits" for these cars anymore. I'm gonna get around that by running my turbo car on an alternative fuel. Not trying to discourage you, just want you to be prepared for what may lie ahead.

Like you alluded to, "once it warms up", the car goes into closed loop, but before that happens, it is in open loop mode so there would be no harm in doing a full throttle power run with the cats off. If one or more of the cats are bad, your power will be back. And if I'm not mistaken, these cars are actually in an open loop mode anyway when they are under wide open throttle operation even when warm so it really shouldn't matter anyway. Still, I'm hoping somebody else here has a better test than mine for the cats. The mallet method doesn't work all the time because these things often just melt solid inside which means no rattling pieces, just a plugged cat. Go ahead and try it though, as it may catch the problem, just don't think that all is well if it doesn't rattle cause it/they may still be bad/plugged.
Regards, Eric