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1989 Mercedes-Benz 300E
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Discussion Starter #1 (Edited)
1989 300E Intermittent Stall / Test / IDEAS / HELP

Hey,

I know there is a lot on this subject but I ran some tests and was looking for some insight. The car shows no ABS lights but I'am not ruling out OVP as its original. Fuel Pumps make buzzing noises the relay is original also. The car stalls like it has a mind of it own. It will shut off usually every other day or 2. Sometimes it will do it once but the problem seems to have gotten worst. Usually does it 3 times. When it stalls depending on my speed if I'm on the highway it will show no sign of shut off and if I press the gas it will not accelerate but the Vacuum/Economy gauge will move, 4 seconds later the dash is a Christmas tree. At slower speed like 40 mph or stop lights it will just up and quit and the dash will light up like a Christmas tree. Also I'd like to add it stalls less frequently in cooler temperatures but will still do it, and it takes 2 MIN LIKE CLOCKWORK FOR RESTART. Now I did a test I removed OVP for a day or 2 and the car ran fine (no stalling) but like a dog, guzzling gas and much slower. The idle was a bit better then with OVP after it warmed up. No cpu by doing this or any other sensor, so it dosent exactly tell me its OVP. I'd like ideas as its getting to be a severe problem???
 

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Immoderately Caffeinated/ Vintage Moderator
T5
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17,022 Posts
Next time it stops check for spark. No spark I'm betting the crank sensor. I just went through exactly the same thing and the warmer the weather the longer it took to start sometimes not until the next day. New sensor fixed it.

If you have a multimeter, next time it stops and if you have ascertained it has no spark stick the meter (on OHM's) on the sensor (red on the inside, black outside) end that goes into the EZL. Should have a reading of around 800. If you get a low reading like 450 it will give you intermittent problems and if, like mine you get zero when it stops you've hit pay dirt.

If you have spark then the fuel pump relay could be the culprit. Test by pulling the relay and bridge terminals 87 and 15. The pump should run continuously.
 

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1989 Mercedes-Benz 300E
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23 Posts
Discussion Starter #4
Thanks, fuel pump relay is on to do list for today as a test. But yeah I was thinking crank positioning sensor. Problem is its been like this for awhile and will restart every time after 2 mins. Sometimes it will do it again 2 min down the street or sooner depending on how hard i hit the gas etc. But it will shut off at idle just takes longer. So I'm hoping its a fuel pump relay. I was under the impression bad crank sensors put you on the side of the road with no start ups for up to hrs or more. I never had that.
 

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1989 Mercedes-Benz 300E
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Discussion Starter #5
KEEP THEM COMMING???????? I have gotten a response from Rob at w124-zone. And he says the same try fuel pump relay first. I had that on order and it's here at my local store. I will try that and see if that fixes it and post the result. The crank position sensor makes sense but dosen't fully explain the 2 min restart usually longer, unless mine is losing ohms here and there. But I guess highway shut offs rule out OVP. OVP usually effects stalling at lower speed or slowing and shows an ABS light. Any more ideas? I'm open??
 

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Immoderately Caffeinated/ Vintage Moderator
T5
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17,022 Posts
I think you've answered your own questions.

When it stops can you hear the pumps in the 2 minute no-start window? If you can't, make up a bit of wire with connectors and do the bridge next time it stops.
 

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Immoderately Caffeinated/ Vintage Moderator
T5
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I forgot to mention the coil. What you describe can be generic type symptoms of a failing coil. My VW transporter would stop dead then start again a minute or so later - until it wouldn't start at all. Worse in the warmer weather. You can test cold and it will seem okay.

The only real coil test that I know of is to replace it.

Good luck!
 

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1989 Mercedes-Benz 300E
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Discussion Starter #8 (Edited)
ANSWER/WINNER:

This is the back of the old fuel pump relay. When I attempted to pull the old relay out the plastic cover slid of which should not happen. You can see scratches and glue from where someone opened it. And best of all a nice burn mark and some solder that definitely was not done by a machine. It has been re-soldered and since I put the new relay in it has not shut off after running it on and off, idleing it etc. It has only been a day but after this many starts it should have shut off by now lol.


Also I'd like to note that this is the original MB chip. It has a microprocessor in it since they send fuel signals to and from the ecu. The microprocessor says made in Taiwan and the plastic says made in Germany. Everything is made in fucking taiwan so for those of you who say only German parts look a little closer at them. The plastic is from germany not the chip. Doesn't matter where its from just trust the brand. A lot of parts are refurbed or defective. Still the fuel pump relays and most electronics are from taiwan. (casings, plastic, etc maybe Germany).

IN THE END JUST BUY THE NEW PART DOESN'T MATTER WHERE IT COMES FROM WHO EVER TOOK A SHOT AT SOLDERING THIS THING IT APPARENTLY DIDN'T WORK OUT. ALSO ON THE NEW PART YOU WILL HAVE 10 PINS AS OPPOSED TO THE ORIGINAL WHERE IT WAS 9 PINS. ORIGINAL OVER VOLTAGE PROTECTION RELAYS HAVE 1 FUSE AS OPPOSED TO THE NEWER ONES WITH 2 SPADED FUSES. GOOD IDEA TO GET THESE THINGS REPLACED SOONER OR LATER.

+1 FOR THE FUEL PUMP RELAY:) (I'LL REPOST IN A FEW DAYS TO CONFIRM - 264 MILE TRIP TOMM.)
 

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2008 E350 4M, 2016 Audi Allroad, 2019 Audi Q5
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I called it! ;)

Try retouching it and/or doing the oven trick before sending it to the graveyard. Those relays new are expensive!
 

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1989 Mercedes-Benz 300E
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Discussion Starter #11 (Edited)
JUST WANTED TO GIVE THIS A BUMP AND CONFIRM THAT THE FUEL PUMP RELAY WAS INDEED THE PROBLEM. OVP RELAY WENT ABOUT 2 MONTHS AFTER. FUEL PUMP RELAY AND OVP RELAY ARE A COMMON CHEAP PROBLEM ON THESE CARS. FUEL PUMP RELAY DOSENT MATTER WHERE YOU GET IT. JUST STAY AWAY FROM AUTOZONE OREILY AUTO PART DID THE TRICK FOR ABOUT 90 BUCKS AND WAS NASCAR LICENSED. OVP RELAY A WHOLE OTHER STORY MAKE SURE ITS 50 BUCKS. DONT GO CHEAP AS THE NEW ONES HAVE TWO DOUBLE SPADED FUSES AND THAT SENDS SIGNALS TO EVERY ELCTRONIC COMPUTER IN YOUR CAR. *I BOUGHT THE CHEAPER OVP RELAY AND IT DOES THE TRICK BUT HAD RPM FLUCTUATIONS EVERY NOW AND AGAIN. CAME WITH TO CRAPPY FUSES WHICH I REPLACED WITH NAME BRAND AND HAVENT HAD ANY PROBLEMS. BUT I'D RECOMMEND BITING THE BULLET ON THE OVP RELAY AND STAYING CHEAP ON THE FUEL PUMP RELAY. JUST GO TO A TRUSTWORTHY AUTOPARTS STORE.
 
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