Questions concerning 124 series V-8
 

1993 400E

Our '93 400E has begun having some very intermittent starting/stalling problems. A couple of weeks ago I drove home (about 10 miles) and things were running fine. Within an hour of arriving home I went out to move the car and it would turnover and catch for just a second and then die. This happened numerous times. After a couple of hours had passed I went out and it started like normal and continued run fine until about a week later when it stalled on my husband as he was going through the parking garage at work. It started right back up, though. Over the weekend, I went out to move it for a wash job (it finely quit raining). It started for a few seconds and then died...but started fine on the second try.

It had it's 60,000 service about 10 months ago which included the rotors.

I have read through a lot of the posts and need some help/clarification.

1. Does this car have a fuel pump relay? If so, where exactly would it be located on this car? I ask because the local MB shop says "no", that it is somehow built into the Mass Air Controller and yet the our service CD indicates that it does have a relay (k27). There is a relay under the back seat (passenger side) with a part # 001 542 96 19. What is this relay for?

2. My understanding is that this car does not have a OVP. And that the Base Module replaces the OVP on this model. Is this true? And does the base module seem to have the same problems as the OVP?

3. Would running diagnostics give us codes for faulty relays and modules? Independent shop says, "no".

By the way, the wiring harness was replaced just over two years ago.

Any suggestions/ideas or specific answers to my questions would be greatly appreciated. This is such a fun car to drive but don't have a lot of confidence in it these days.

Thanks-

MB FRAU

Frau

The 400E fuel pump relay is located under the passenger seat, its on the right side of the seat as I recall.

The 400E does not have an OVP relay - the function of the OVP relay is, I believe, performed by the base module. There is a fuse in the module that will blow but I don't think the idle is effected by that fuse as OVP failure is with the K-jet systems.

I would check fuel pressure and read out the codes in the ECM as a starting point. You may also want to check the caps,rotors and plug wires too. I'm not sure if relay failures will set a diagnostic code - maybe someone with the M119 codes could check.

My 400e had an intermittent rough idle/stalling problem that disappeared when I changed the infamous engine wiring harness. I was hopefull that might be your problem but I see you have already changed it.

TimFreeh-

Thanks for your input!

We have checked all the fuses on the base module and they are in good shape.

You mentioned ECM...I assume that stands for engine control module?

MB FRAU

ECM does stand for engine control module but adding a "s" makes it more appropriate.

Codes should be checked on all engine modules: LH (fuel), DI (ignition - there are two), EA/CC/ISC (electronic accelerator/cruise control/idles speed control) and the BM (base module). You might also want to check the DM (diagnostic module) although it won't show a running problem that isn't shown in one of the other modules. It can tell you which other module to check.

There will often be codes thathave no bearing so be carefull.

My intuition tells me that you should simply replace the fuel pump relay. The stalling behavior mirrors my experience just before the same relay failed in my 6-cylinder. It might test out just fine for awhile (hence the car running for awhile then stalling again) and then give up the ghost (mine failed on Halloween evening with a car full of little goblins and fairies) at an inopportune time.

Perhaps others have better ideas.

It certainly is easy to try a new fuel pump relay - it would be a good first step. It would be really nice if you could try a fuel pressure test when the car was not starting. This would verify the fuel system was delivering fuel.

I forgot that the 400E has so many systems that must be checked. Its kind of funny since all these systems are interfaced via a databus. You would think that it would be possible to access all the codes together. Maybe that is what the diagnostic module is for....I'm way over my head here.

As I recall all the codes can be read and reset using a standard impulse counter but its not quite as easy as the K-jet systems because the impulse counter has to be hooked up to a 38 pin diagnostic connector (and the pins on that connector are mighty small!!) There are very nice breakout mushroom adaptors that make access to individual pins easy but the connector is a couple hundred dollars. I don't have the diagnostic manuals for the M119 engine and a quick check of my 124 service CD rom does not seem to detail the procedure for code readout. Maybe somebody here could direct you to a source for this info.

Having trouble on exact location of relays/modules
 

Okay, I'm going to come back to the issue of the fuel pump relay location on this model ('93 400E).

The electrical troubleshooting manual (model 124 - vol 1) off of the service manual CD (page 00-B.2a - relay and control locations) references page B.2/4, figure 12, part K27, as the fuel pump relay module for model 124.034. This figure is showing the relay to be located under the backseat (passenger side) near the vacuum pumps. The relay that is currently there has a part # 001 542 96 19. I think Tim's post would concur with this.

I called Phil (fastlane/partsshop) to verify that this indeed was the correct relay. Phil said that the relay under the backseat is indeed the same relay "used" for the fuel pump relay but in this case (under the backseat) it is the aux. fan relay. He sent me a picture that shows the fuel pump relay being up in the engine compartment (in the center) near the firewall. The local MB shop also says it's in the engine compartment near the OVP (which this car doesn't have!

Help!! I want to make sure that we are looking at the correct relay! Why would the service manual give one location while the experts are telling me something different?

Thanks-
MB FRAU

I have never replaced the K27 relay before. It is only used on the 124.034 and .036 cars. Looking in the ETM I can verify the location frame B 2/4 figure 12. this is from the print version. That figure shows it under the seat.

I have replaced numerous K9 or K10 aux fan relays or their fuses; checked the circuits many times at these relays and they are in the back of the fuse box.

Do Mercedes use a transfer pump to get gas to the main pump? The 500 had some of the same problems because of a bad gas cap which was giving it vapor lock at least I think.

Frau

Your description of the relay location is correct. I'm sure it is the fuel pump relay because I have pulled it out while the car was running to de-pressurize the fuel system. The car will run for about 1 second after you pull the relay.

I would pull my backseat out and check your part number but my 400e is on loan tonight. I'll have it back tomorrow AM and will cross check the relay part number tomorrow. I'm 99% sure you have the correct relay based upon your description.

Hope that is your problem.