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89 300E intermittent starting problem...HELP!

4K views 16 replies 6 participants last post by  crorrer 
#1 ·
My 89 300E has recently developed a starting problem that I'm trying to figure out. The car runs beautifully and, 99.9% of the time, starts exactly as it should on the first crank but I've had four or five instances now where the car just won't start...once for about five days.

When this happens, the starter turns strongly but no amount of cranking will get the car to fire. The failure to start doesn't seem related to engine temperature, as it has occurred with the engine both warm and cold.

The most difficult thing has been getting the car to repeat the problem. Today it happened again (from a cold start) and I was able to verify that the car does have a good strong spark. Shortly thereafter it promptly started again before I could begin looking into the fuel delivery system! Ay yi yi.

Any ideas on where to start looking to diagnose this behavior? All help is greatly appreciated...I miss driving this old girl.

Thanks,

Chris Rorrer

89 300E
86 300E
 
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#3 ·
Thanks for the reply...I'll look into the relay.

A couple of other vital stats that I found while looking through this year's maintenance receipts from the dealer. Apparently there are two things fuel delivery related that the dealer recommended doing that I haven't done yet.

The first is that they recommended replacing the secondary fuel pump. Red flag! Could this be the culprit? I tend to think of fuel pumps dying completely when it's their time rather than misbehaving intermittently, but I don't know...what do you guys think? I'm thinking I'll replace this just as a matter of course.

The other problem that the dealer diagnosed is with the fuel distributor, or more accurately the mixture adjustment on the airflow sensor assembly. Apparently the adjuster has become buggered up and can no longer be adjusted. The dealer's answer was to replace the entire fuel distributor/airflow sensor assembly at somewhere in the neighborhood of $2k. Could this be related to the starting problem possibly? I've been reluctant to have this done since the car has been running so darned well (smooth as silk, really) but maybe it's time to bite the bullet.

Again, any insight is greatly appreciated!

Best,

Chris
 
#4 ·
Here are a few cheap things that I'd try:
1. Replace your fuel filter (if you haven't done so within the last 6 months).
2. Replace your fuel accumulator. This has been known to cause issues. It's responsible for building up pressure I think before fuel gets delivered to your cylinders. I think the part's around $90. I've read many posts where the accumulator had resolved this issue.
3. Check the top of your relay for your fuel pump. I think there's a fuse there on the top of it. Make sure it's not partially blown or something so that you've got an intermittent electrical connection causing this.
4. Could your fuel tank have a bunch of crud in it? I would think that would make your car not run right all the time so that's probably not it.
5. Hey, at $3 a gallon, sounds like your car's trying to go easy on its gas consumption for you! Remember, Mercedes Benz vehicles were engineered to have a minimal impact on your financial well-being!
 
#5 ·
Thanks for the suggestions, wvcox.

I'm replacing the secondary fuel pump per the dealer's diagnosis, so I'm going to go ahead and replace the fuel filter and check valve as a matter of course (both of these were done by the dealer about a year ago, but I may as well go ahead and do them while I'm down there.)

I've taken a look at the fuel pump relay and all looks well there. Mine doesn't have a fuse, though.

I hadn't considered replacing the fuel accumulator, but what the heck. I can't see where it has ever been done by the dealer, and while I'm throwing money at the old girl I might as well throw a little more. Looks like it'll only cost about $75 bucks...mere chump change in the realm of mercedes. ;-)

Thanks again,

Chris Rorrer
 
#6 ·
I agree w/ flyboyike I would check the fuel pump relay first,you said you checked but did you take the case off ? if your electrically savy-open the relay and look at the circuit board on the back side usually one of the solder joints has a ring around it(cracking)making a interm. contact problem can be re-soldered. I would also rec. try listening to the fuel pump when the vehicle will not start-you should here a slight buzzing at the least. The relay with the fuse on the top is the overvoltage protection relay this is the second thing I would check it has the same issues as the fuel pump relay- it is a alum. case next to the battery.
hope this helps.
Sam
 
#7 ·
Sam-

Thanks for the advice. I didn't actually take the fuel pump relay case apart, but I switched out a working relay from my other 300E and the problem persists. The relay from the "problem car" worked fine in the other car, too, so I can pretty much rule out the fuel pump relay.

I checked the fuse on the OVP relay. It looked fine, but I replaced it just for kicks. Car still doesn't start. I'll switch these relays like I did the fuel pump relay and see if anything happens. Hadn't thought of this one.

Initially I was having problems diagnosing the condition simply because it was so darned intermittent, but now the car pretty much seems down for the count. Over the past two days, it has not started at all. Which at this point is actually OK with me...as long as it stays dead, I think I can make progress in figuring out what's going on.

I'll give the fuel pumps a listen, too.

Thanks again to all for the advice...I'll report back as I learn more.

Best,

Chris Rorrer
 
#8 ·
Here's an update to my intermittent starting problem if anyone's interested...

Since this is still an intermittent problem (started up again last night, but no go today) I've been trying to pay particular attention to anything that's different when she won't start.

It appears that I can now predict whether the car will or will not start with the ignition key in the "on" position (ie the fatherst position to the right before starting.) What I've noticed is that when I turn the switch on, I'll normally hear a sort of hiss accompanied by a buzz that lasts for a few seconds coming from the area of the fuel pumps. Sounds maybe like a buildup of pressure??

When I hear this noise, the car starts up...if I don't, she won't.

New fuel pumps, accumulator, filter, and check valve are on order...I'll report back as soon as I install them this week.

Thanks again to all for the help-


Chris Rorrer
 
#10 ·
Chris,

I have the same problem with my 93 300E, at first it was intermittent, then 2 weeks ago it refused to start for about a week, after doing some research I replace the Fuel Pump relay, then it starts OK for couples day, now it is back to intermittent. I'm thinking of the Overload relay next. Pls post what you found.

Thanks
 
#12 ·
Hey. I've got a 1988 300se with exactly the same problem (intermittent starting... now it's dead). I checked the current to the fuel pump (it's near the gas tank... I think the gas filter is located just above the pump) and got nothing. No juice at all. The pump had been buzzing (or making a "swirling" noise) and turning on when I switched on the ignition but then just stopped and so did the car. I think it may be the fuel pump relay (located on the fire wall under the hood near the battery on my model). I'll let you know how I make out sometime 2morrow. Does anyone know if this my model has more than one fuel pump? Or, for that matter, a fuel pump cut-off switch? Or where either would be located? Thanks.
 
#17 ·
Just checking back in to report that the problem appears to be fixed. It turned out to be an intermittently failing secondary fuel pump that was the root of all of my problems.

Since I was under the car already and had to drop the whole fuel pump/filter/accumulator assembly I went ahead and renewed everything and kept the accumulator and one good fuel pump as spares.

Thanks to all for the help.

-Chris Rorrer
 
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