300e/ No Start
 

I HAVE 1990 300E/2.6L WITH A NO START. CAR HAS DUAL FUEL PUMPS. :mad:

ok. what happens when you turn the key? does the starter crank the engine at all? are you getting spark and fuel?

Engine Turns Over, I Have Spark. What Is The First Check On The Fuel System?

Turn ingition to On, listen to verify fuel pumps operate behind R/R wheel; if no response, remove fuel pump relay (behind battery & cover) and bridge #7 &#8 pin receptacles with jumper, with ignition switch to ON, if you hear fuel pump runs, it may be your relay (about $130.00). Anyone with other ideas?

I have the same problem with my '92 300TE 4Matic, but don't know how to check to see if I have a spark. Could you explain how I do that? Also, is it a procedure that requires two people?

Like with Todd's car, when I turn the key to start, the engine cranks fully, but it won't catch. The oil pressure increases, but the tach doesn't move. I have tried pumping the accelerator to see if I can smell gas and I cannot. I also cannot hear anything in the viciinty of the fuel pumps - no buzzing or hissing. I checked the OVP relay and the fuses are fine and the contacts clean.

As for the fuel pump relay, what does it look like? When I checked the OVP, there were two other relays beside it, both black and about the size of a small book. One, closer to the battery, was maked "4matic", and another closer to the firewall, was unmarked but for some numbers. Was that it? Finally, can you explain to this moron what you mean when you say to just "bridge #7 & #8 pin receptacles with jumper". Thanks for letting me piggy-back on Todd's post and for your patience with these basic questions.

Fuel pump relay
 

link to pic

It's the relay that starts w/ "89". Note that this picture was taken off a 190e, but the relay location should be the same on the 300e.

I'd check the fuel pump relay 1st, then leaking or failed fuel pump.

Thanks for reply and picture! I'll look later, but the size may be different in my car, because the OVP, (which is also shown in this picture), is beside a "small book" sized, (approx. 4" L x 3.5" H x 1.5" W), plasitc box marked "4Matci" sitting upright on edge in a bracket, which I presume contains a relay or two, and appears to have a plug-in, (or fuse?) connector on top, not a square relay like in this pic. There's also another similar sized box is behind it, also with a plug-in connector, so I'll check its numbers to see if that's the fuel pump relay. Maybe mine has moved to the front of the battery since I recall there were some relays there too...

One more question about the OVP: is it possible for the OVP to have croaked, but the fuses and contacts still be good? That's what I found,(good fuses and contacts), and why I'm now following your lead to the fuel pump relay. Hopefully that's it, 'cause I really don't feel like crawiling under a dirt and salt coated car in a cold New England cement floor'd garage to learn how to change two fuel pumps and a filter as I go! Thanks again.

By contacts, I'm assuming you mean the pins that connect to the junction outlet.

The OVP failure is that the solder joints on the INSIDE of the relay eventually come loose. Some here have cracked the case open and just resoldered the loose joints. I just went ahead and replaced mine...and the fuses and contacts on my old one were fine, btw.

Yes, G-Benz, by "contacts", I meant the pins. Since you say the OVP relay can go bad even though outwardly it appears fine, I think I'll try replacing that first, especially given my experience with the MB dealer today when their service department told me that my '92 300TE 4matic was not fitted with a fuel pump relay, because that part did not show up on their computer!!

After I provided the car's VIN number, the dealer said that maybe the relay was part of another relay, such as the A/C or kick-down relay, but just not listed as such, because there was no part number for a fuel pump relay. I really don't want to have to have the car towed to them for repair now - who knows how much it will cost me to have them blunder through until they "cure" the problem. I don't suppose anyone knows the part number for the fuel pump relay for the 124? I tried to offer the part number on the photo link provided by Chamorro for the 190e, but they said that would not be correct, as it was for a differnt model and year car. Maybe so, but I thought it'd at least be worth a try . . .

Fintail and TODD
 

Looks like the 90-92, 6-cyl w124 models had the Fuel Pump and AC compressor relays combined w/ the MAS Relay, aka "Engine Management Relay".

Ask the folks @ the parts counter about the MAS, or Engine Management" Relay.

Thanks Chamorro, I'll do that first thing tomorrow and see what they say. That could be just the ticket too, since before my car refused to start, it had been stalling occassionally whenever the AC was turned on and the car was slowing down or was just starting out from a stop. It never stalled if the AC was off, so maybe that problem was an early indicator that this relay was going bad?? I'll let you know what the dealer says and what I decide to do based upon that.

Well I went to the dealer again today armed with the new information about the relays, but, not surprisingly, they said that their computer schematics did not indicate any such relays, including an "Engine Management Relay" for my model year car. They said they would need the car to do a diagnosis on it, even though they had the VIN number, to detemine what is faulty, and after spending so much time on the car, I just gave in. The car was flatbedded to the dealer via MB roadside service, but I gave them strict instructions not to do any service other than diagnosis without first calling me. Once they ID the problem, depending upon what it is, I may find it less expensive to have the car towed to my house so I can do the repair myself, rather than face the possibility of being gouged by the dealer, but then again, I may just have to bite the bullet, as it is COLD out . . . .

Final result: MB dealer says the no start was caused by a split vacuum line for the idle control valve, and the stalling with the A/C on at idle was caused by the main ground being loose. That's it. Interesting how the symptoms of one thing; bad OVP & MAS control unit/fuel pump relay, match that of another; split vacuum line. I have renewed trust in the dealer now, but I'll still continue to rely on this excellent forum for my DIY efforts. Thanks for all the suggestions.

Glad you found it. Sometimes it's the stupid simple things that bite you.