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  #1  
Old 11-07-2008, 07:27 PM
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fuel pump / no hot start / w124.104 1993 300CE

Hi there I'm hoping to get some help trying to diagnose a problem I've had for some time which just got worst today...

Initially I thought I had the hot start issue. My symptoms seemed to match pretty well. Cold starts were fine. However, if I shut the car off after it was at normal temp, let it sit for a few minutes and then try to restart it, it will crank and crank but will not fire.

So after reading up on the hot start issue a few months back I gathered that a way to get around the issue is to apply some gas if the engine is cranking but not firing. So with this in mind I made sure to try if it ever happened. Well a few weeks went by and nothing happened. After a few weeks it finally happened and I had a chance to try the workaround by pressing down on the gas... but no luck! The engine would just continue to turn and start. I let it sit for a few more minutes, and tried again and boom, it starts. THe start was rough at first but quickly settled into a normal idle. I didn't think much of it at the time and to be honest, it is pretty tough to recreate the issue with any consistency.

A few weeks went by since, and today was the worst. I was downtown picking up my gf from work. So I am on the side of the road and shut my engine off while I waited. It must have been around 7 mins or so, she gets in, I try to start the car and it just starts cranking but doesn't fire. I'm thinking no big deal, its happened before, just wait a minute and try again. It seemed to work in the past. Not so this time. I tried to start the engine 2 more times (over a span of 10 minutes) but no luck. I figured I'd better understand what's going on before I drain my battery trying to start the car. Note that during my attempts, I tried both pressing the gas and not pressing the gas. I also let it turn for a max of 5 seconds at any one attempt.

I step outside and it's pretty noisy downtown, but one of the sounds I think was missing was the sound of the fuel pump. I swear I used to hear it go on when the key was turned to position 2. Can anyone verify if this is supposed to be the case? I'm talking about the one I can normally hear at the back right. In any case, the fuel pump definitely doesn't turn on, and I later verified this in my driveway (when I finally got home).

So at this point I'm out of ideas. I checked the fuse panel but doesn't seem to be any fuses blown and none that seem to be related to the fuel pump. I don't know how to check codes. In any case, after about another 10 mins of tinkering I figure let's give it another shot. Turn the key, starter starts turning and boom! Engine comes alive! WTF?? Again, it started a bit rough but settled into a normal idle within seconds.

So now I'm driving home and decide to get gas, and also wanted to see if I could recreate the situation. I go to a gas station near my house, just in case. Also, I should mention something else strange, at first I was a bit low on fuel (just below the 1/4 mark, but no warning light yet). After I got it started the fuel needle was at the empty mark (didn't rise at all, and still no warning light). After I filled up and turned the key to position 2 the fuel gauge seemed to work normally again.

So after filling up and trying to start the car, exact same problem. This time, I tried starting it a couple times with no luck. Waiting 10 mins or so, tried again. Car did fire once but died immediately. Waited 5 more mins, tried again and it starts.

Here's some other notes / questions...

- wiring harness was replaced just under 2 years ago by MB
- am I supposed to hear the fuel pump in the rear right when the key is in position 2?
- when the engine did start and was running, I could hear the fuel pump in the rear right
- 170,000mi, full MB service history with previous 1 owner
- post that seems closest to my issue but no resolution / update: http://www.peachparts.com/shopforum/showthread.php?t=206180&highlight=fuel+pump+w124

What's going on???

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  #2  
Old 11-07-2008, 07:31 PM
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and if the suggestion is to replace the fuel filter, any instructions to do that would help! do I need to get the car up on jacks?
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  #3  
Old 11-07-2008, 09:00 PM
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Next time the problem occurs , tap the OVP relay.

I would also pull the relay and see the part# on the side . If it is the original #, replace it regardless, as the part has been redesigned.

These #s are in the archieves Search " OVP "
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  #4  
Old 11-07-2008, 09:58 PM
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I will check if I have the OVP with 1 or 2 fuses but what would tapping it do? Do you think there is a loose connection? How exactly does it come out? I found this pic. It looks like there would be 2 screws holding it in?

http://catalog.worldpac.com/mercedesshop/sophio/image.jsp?title=Overload%20Relay&url=http%3A//img.eautopartscatalog.com/live/P205618126KAE.JPG
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  #5  
Old 11-07-2008, 10:04 PM
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Aechieves ... OVP
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  #6  
Old 11-07-2008, 11:02 PM
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so OVP controls fuel computer / idle control valve. does this explain why i'm not hearing the fuel pump when i put the ignition to position 2? i can swear it used to do that.

what is it that goes wrong with the ovp?
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  #7  
Old 11-08-2008, 05:01 PM
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Arthur - thanks for the tip, here's what I did so far (and I did read up on this forum about the OVP, its purpose in life, etc)...

1) I checked the fuse. There is a single 15A fuse and the fuse looks fine (metal inside still intact, plastic is nice and clear).
2) I'm not quite sure if I have the new one or not. It looks like I'd have to remove a bit of plastics to get at the 2 screws that hold it in. However, I did take a couple of pics of it.

- From the side it looks exactly like the attached picture (OVP1.jpg) which another member posted. And that OVP has the old part number "540 52 45". Attached are a couple of pics of mine (MY_OVP01.jpg).
- My OVP also looks like it has space for 2 fuses but one is actually a fake spot or something... what's up with that?

- I didn't have the problem again today. Not sure why you asked me to tap the OVP but I did anyway (I guess you're thinking there's a possible bad electrical connection)?

- If I did want to remove the OVP do I have to remove additional plastics other than the battery cover?

Thanks!!!
Attached Thumbnails
fuel pump / no hot start / w124.104 1993 300CE-ovp1.jpg   fuel pump / no hot start / w124.104 1993 300CE-my_ovp01.jpg  
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  #8  
Old 11-08-2008, 06:22 PM
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2 cents of course

I had a similar problem with my 1988 300 ce, If the car got to warm or it was hot out, I'd have to let it sit and it would start up fine. After much reading I found out if I unplugged the ovp and the fpr (& plugged them back in) behind the battery the car would fire right up without having to wait the 10 to 20 min for cool down. Then on a fluke I replaced the fuel pump relay first and of course that fixed the problem. All I can say is unplug the two of them next time the car won't start. If it starts back up you have narrowed it down to these 2 relays. Good luck
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  #9  
Old 11-08-2008, 06:26 PM
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<< Not sure why you asked me to tap the OVP but I did anyway >>

Same reason you tap any relay suspect of having a poor conection at the contactor set.

You have the old troublesome relay if it is that #, so it has to be changed regardless.
The FP relay is to the left, but b/c your car is full electronic HFM/SFI, the pump will not run w/bad OVP..which is why that is first suspect.
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  #10  
Old 11-08-2008, 06:30 PM
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Thanks again Arthur.

I think I just figured out the noises I was used to hearing. I read on this forum the w124 has 2 fuel pumps. One in the back right, and one under the hood somewhere.

Today I listened carefully and found the following:

- stick the key in the ignition, and turn to position 2
- you will hear the fuel pump in the back turn on for 1 - 2 seconds
- you will hear (what I believe) is a smaller (quieter) fuel pump in the engine bay and this one stays on consistently.

Correct?

Anyway, not sure if this had anything to do with my issue but I will replace the OVP first.
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  #11  
Old 11-08-2008, 06:32 PM
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>


NO


The pumps are back to back and mounted together.
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  #12  
Old 11-08-2008, 06:37 PM
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you can test the ovp, I can send you a document that explains how if you want. No use buying another one if its not bad. Send me an email if you want the document
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  #13  
Old 11-08-2008, 06:45 PM
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Quote:
Originally Posted by Arthur Dalton View Post
>


NO


The pumps are back to back and mounted together.
What is it then that I am hearing under the hood when the ignition is in position 2? It is a steady fairly high-pitched sound. Coming from somewhere near the plastic portion of the headers (red area in picture).
Attached Thumbnails
fuel pump / no hot start / w124.104 1993 300CE-dsc_0411.jpg  

Last edited by optimizer; 11-08-2008 at 06:55 PM.
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  #14  
Old 11-08-2008, 06:50 PM
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Possible EA actuator motor.....
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  #15  
Old 11-08-2008, 07:25 PM
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What does that do out of curiosity? Doesn't sound related to my problem but still want to know. Search didn't turn up much for "EA actuator motor"... don't know what EA stands for.

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