Hey Guys,

This morning on my way to work rolling at about 70mph my engine stalled. No precursors or warning no rough idle no sputtering just cut out and wouldn't start. I suspect that it is either the Fuel Pump or FP Relay. I did do the coils and plugs and starter over the weekend but I ran her really hard for a couple days and she was fine. Any thoughts on how to check if the relay is bad.

Any input is welcomed,

Thanks,

Gary

 

Do you have the fuel pump relay integrated into the MAS unit like I do with the early m104? If so, I think you have to put another MAS unit in to test.

For the fuel pump, I think you have to just 12v it and let it run for a minute and see how much it flows. I'm not sure on the OEM spec, but I think its about 4 Liters per Minute (for both), or about 2 Liters per minute (each). Basically, shoot for 1 gallon of gas flowed through by both pumps in a minute, or a half gallon if you test individually.

 

I will have to check but I am pretty sure the relay is on the main computer with a small fuse on it. I will look at it. Whatever the problem, it is a complete failure. No fuel at all.

 

The same exact thing happened to me, but it was from the Ignition Control Module. Exact symptoms.

Good luck, I hope it's a simple problem as that ICU cost me 550$. Used.

 

How did you test it to know that is what it was?

 

How about voltage test the connector at the fuel pump while someone turns it over.

 

Good thought. I will try that tonight. Also I have a couple of marine 12v batteries that I can run a lead from and see if the pumps themselves are bad. Looks like that relay is only about $20.00.

 

Just put a jumper between Terminal 87 ( pin 7 ) and Terminal 30 ( pin 8 ) of the fuel pump relay.

If the pumps start then the relay contact is not pulling in

 

RB Sweet. Thanks for this I will do it tonight. This is exactly what I was looking for

 

Ok so I went home last night and was getting ready to test it when I thought oh what the heck let me try and crank it over. ANd of course she started right up. I dove it down the block and on the way back she cut out again. I cranked it for about 30 seconds and she started up again. I out the car in the driveway and let it idle for about 10 Minutes with no stalling. Does this sound more Pump or relay to you guys?

 

Doesn't sound like an ICU to me. Those just totally quit, last I knew.

MY dad's CLK had the same problem, turned out to be a fuel pump. I'm not saying that's it, but the symptoms are similar.

 

mine never cut out whle driving, but every now and then it would not crank. i would have to keep trying every few minutes until it finally started. it started happening more often, i ended up changing the fuel pump relay and the OVP too at the same time, and no issues since then. not sure which one was causing the problem, but i heard they both go bad eventually, so figured what the heck, might as well save on shipping and order both together!

 

If the pump has constant power to it, typically it will either run or not run.
Pull your relays, check the fuse(s), replace it if you have a spare,and shake the relay.
If you hear any rattle then something is not right !!!
Spray some contact cleaner ( even wipe down with alcohol )on the pins and the socket and try it again.
If the problem hasn't cleared then replace the relays !

When it cuts out is it immediate or does it feel like it's starving for fuel?
Immediate would lean toward electrical, starving may be filter or FPR.
Electrical is more common with the 124.

 

Well, finally got around to testing it out and it is the FP relay. Got one on order and should be here in the next day or so. RB you were right. Crossed 30 and 87 and she started pumping immediately. Thanks fellas

 

Congratulations!

 

And now, one happy man.

 

This is a really old thread, but for those who come across it in the future... There are several other potential electrical issues. Fuse 5, ECU, ECU Relay, CMP Sensor, CKP Sensor, OVPR, K40 or HFM Control Module if one of the older W124's, Wiring to FP Relay, Wiring to Fuel Pump From Relay, Fuel Pump, Fuel Line, Fuel Rail, Fuel Hose, Fuel Pressure Regulator, Injectors, Injector Connectors, the little pins/sockets in the Fuel Pump Relay Connector or any of the other modules, MAF/MAP depending on model, DAS for 96's... I think that's about it, but I think that you get the idea. There are a LOT of things that could be causing the problem, and they are all legitimately likely candidates. DO NOT just throw parts at a problem...particularly not one like this. This stuff can legitimately be tested with just a DMM or even just a test light for most of this stuff. A test light can be your best friend! Worst case scenario...you might also want an ammeter of some kind and maybe an inline circuit breaker for chasing shorts. The circuit breaker keeps you from having to constantly replace fuses while you're searching for the cause, and the ammeter helps you find it (hint: shorts draw lots of current). You don't need an expensive digital clamp meter either. The old analog contactless ammeters are great. The needle deflects in the direction of the short. I can tell you that one good thing to check is whether or not you're missing fuel injector pulse as well. If you are, then it's not just the FP relay. You've got a problem with the engine sensing the RPM's, and that's a CMP, CKP, ECU, etcetera type thing. Obviously...check the simple stuff first. Check Fuse 5, FP Relay Fuse, FP Relay, OVP Fuse, Press on the little schrader valve on the fuel rail to see if you've got fuel pressure, Jumper FP Relay, Test OVP Relay. If that doesn't fix it though, then you're in for a bit more of a hunt. I'd probably start checking items in that order though. After that I'd check for injector pulse. That's really your next big signal after the really easy stuff...which all of the previous qualifies. Hope that helps...

 

I am having a similar issue with my 1993 320 Coupe (pre-facelift car).

The car cranks but does not start, on turning the key the fuel pumps do not come on, there is also no spark.

So far:
Fuse 6 changed
ECU changed
Crankshaft position sensor changed
Fuel pump relay changed
OVP relay changed
Fuel pump relay bridged - fuel pump fires and pumps fuel into the fuel rail
Coils found to have +12v to LT wires with ignition on

I'm not that hot on electrics so if someone can please advise me to check something I will do it as I'm desperate to solve this issue.

Thanks in advance.

 

First did you replace each part you changed over with the RIGHT one ,, ie the same part number . because they look the same means nothing .

 

 

320 Look along the loom in the engine bay . They can short out and breake the circuit .

 

Ok thanks I will do that in the next few hours.

 

Check all earth points clean them after removal and give them a dab of grease before refitting them . But the fuses will need checking out .

 

Thanks optimusprime, I have just spent some time out there.

All fuses checked, connectors cleaned and fuses re-seated.
Many loom connectors were pulled off and cleaned-up.
Every earth point I could find was removed, cleaned and replaced.

Still the same issue though, is there a specific test I could do? I can use a multimeter.

 

PM sent.