1990 300CE extremely hard start

[steve fraser]

I recently purchased a 1990 300CE (3.0L 24V engine) that starts extremely hard; cold or hot. Once running it seems to idle smoothly at about 800 rpms and has a minor drop in idle when it's put in gear.

Once the vehicle is shut off or on cold starts it needs to be cranked alot to get it to start. Once it catches it sputters until it comes up to idle and then it smooths out. I've checked obvious loose wiring connections and hoses but have found nothing. I've seen alot of postings for similar problems but none exactly like this. Any help would be greatly appreciated.

[16VAlex]

Did you smell gas once it starts?? if it is then your car is flooded. But if you don't smell any gas then try to replace spark plugs and cable and the regular tune up parts.

Alex

[stevebfl]

EHA current while cranking?

[rvenerac]

have the same engine and problem before. mb tech adjust the air/fuel mixture located between fuel distrbutor and airflow plate
using a hex wrench (or just remove the air cleaner cover and adjust the a/f mixture through the hole at the center) clockwise to richen the fuel

[Gilly]

Check the fuse in the OVP first!
I'd also ask when the last maintenance was done-spark plugs especially, but also air filter and fuel filter.


Gilly

[steve fraser]

After checking other areas I removed the OVP relay. Fuse was OK but decided to have a look see inside. Had to cut the can off but found some crappy looking solder joints. The date code on the relay was late '89 so i've order another. After touching up the solder joints (none looked like they would have caused an open circuit) I replaced the relay and the car started right up. It even seems to have rediscovered it's "cold start" high idle mode. I've also ordered all of the normal tune up stuff to give it a good maintenance update. I'll reply back after the new OVP comes in to confirm the fix.

Thanks for the replies. The website is excellent and extremely helpful!

[Gilly]

Steve
Recommending the stock Bosch F8DC4 (formerly F9DCO) plugs, nothing fancy, just the stock plugs are best.

Gilly

[steve fraser]

Gilly. I had already purchased Bosch Platinum 4 plugs and installed. Long story short.... These things are crap! Per recommendation installed a set of stock, copper electrode Bosch plugs and this WAY helped.

Next up was a learning experience. The 1990 300CE DOES have an idle adjustment through the center of the air cleaner. After trying to tweak this as I have read and getting nowhere I decided (somewhat cautiously) to disassemble this thingie because it didn't seem to be doing anything. After looking at the guts of this thing I realized the only task this performed was to act as a hex wrench extension (and seal the tube with the little o-ring) and nothing else. After realizing you have to push this thing down to engage the screw and then turn to adjust life is good! I think I have it close. The idle surges a bit but overall the starting / idle is much better.

After reading other owners troubleshooting methodologies and costs i'm extremely grateful for this website. I only hope someone else can learn from this note.

In summary, replaced OVP, plugs and adjusted idle. That's it and it seems to be at 90% Life is good. Now if I only wasn't stuck with that damn "start in 2nd gear" transmission.:p

[stevebfl]

The adjustment you talk of is not an idle adjustment. It IS a mixture adjustment and absolutely should not be done to taste. It is a precise adjustment that requires one form of reading or another. it can be adjusted by watching the EHA current or the integrater duty cycle on the diagnostic connector.

If you can feel a difference after making such an adjustment you have done it wrong.

[Gilly]

Steve
The recommended plugs are best only because they are non-resistor plugs. The resistors are in those big metal plug wire ends, about 1000 ohms of resistance, depending on model. If you start combining the resistor wire ends with resistor plugs, it's bad news. Usually these special plugs (platinum and split-fire, things of that nature) are actually resistor type plugs, meant to fit too many applications. A manufacturer like Bosch you would think would either make non-resistor plugs for applications requiring it, like MB's, or simply not have these vehicles listed in the application charts. But they're in business to make money, and they DID sell you a set of lugs, didn't they? Actually TWO sets, sounds like a win-win situation (for THEM anyways ).

On what you call the idle adjustment, you're way off base here.
That sets the mixture, not the idle. You really shouldn't be messing with that adjustment without monitoring the Lambda ratio (On-Off ratio) It's a critical adjustment. Yes, the part you mention is called the adjustment tower. If you need to adjust the mixture, you drill out the tamper-proof screws on the base and replace the adjustment tower with a new one. The new one comes with the new steel ball. You set the adjustment for mixture (which may very occasionally need to be done if certain work is performed on the engine or to adjust for engine wear), then the steel ball is hammered into the hole to prevent tampering. When you push down and engage the screw and turn, you are adjusting the top throttle plate, which is connected to the air flow sensor. Having this adjusted wrong can really mess things up later in the engine's life. I'd urge you to get it properly adjusted.
The idle speed itself is not adjustable, it's controlled by the idle control system, which is electronic. If the idle speed is incorrect, the idle control valve may be bad, or there is a problem with voltage supply (ie overvoltage protection relay), or possibly a vacuum leak "after" the control valve.

Gilly

PS I see Steve B has already commented on Steve F's previous post. I was addressing this to Steve Fraser.

[steve fraser]

Thanks for the input. I would consider myself an average mechanic. Should I try to make this adjustment myself or take it to the dealer. Will a simple DMM work for measuring the EHA current? (What does EHA standfor and where is it?)

Thanks again for the input.....

[brewtoo]

ElectroHydraulic Actuator. It's on the side of the fuel distributor under the air filter.

Do a search and you will find a ton of helpful info.