vahagn

Greetings to all,

I have got 1990 W124, 2.6l. When I push the accelerator and engine gets over 6000 RPM it loses the power. It looks like some thing switches the ignition off. When I release the pedal of the accelerator, the engine continuing to run.
Why do you thing it is like that?
Thanks,

bicylindrico

Because it's supposed to be. It keeps people like yourself from destroying the engine by over-revving. It is your fuel pump cut-off built into your fuel pump relay. Allow the transmission to shift before this happens.

vahagn

I was going to make a correction. Actually it does that by 4200 RPM. Recently I have placed second fuel pump. My car used to run with one fuel pump (a big one). And it often used to slow down and even stop when I wanted to harshly accelerate it like there is no gas. After restarting it was running as usual. I checked with MB and they told me that this car should be equipped with two small fuel pumps. So I added second pump- a small one, hoping that this will solve the problem. Now I am experiencing above mentioned problem.
Thanks for your input.

bicylindrico

If it always cuts off at 4200 RPM everytime, I would suspect something is stepping in and limiting the RPM's. If it were a component that was failing or unable to keep up, like a weak fuel pump, I would think the cut-off point would be more random and softer. I know different engine size relays would work in each other. The problem was the limiter would step in at the wrong time because the relay was reading a different RPM than the engine was truly turning. I would think a 4 cyl. relay would cause this symptom on a 6 cyl. car.

Look at your relay and confirm it has "6 zyl" or something like that. I can't remember the correct stamping. It will also have the RPM limit marked as well.

I hope this didn't sound too confusing. It's the first place I would start. Good luck.

shdoug

A long shot, but I wonder if something activates the second pump at 4200 RPM and it can't handle the current draw of the big and small pumps running together so it cuts power to both. Unplug the connector to the small pump and see what happens.

bicylindrico

They both run continuously.

vahagn

OK. I will start with checking the relay. Can you tell me where to look for it?

vahagn

Please help to locate the above mentioned relay

bicylindrico

Check behind the battery. Again, there should be engine cylinder size and RPM cut-out marked on the relay.

vanwiek

I don't know if this is true for the m103 but the m104 in '93-'95 will cut out at 4200 rpm if the gear selector is in park or neutral. Does anyone know if the m103 also does this? If it does you may have a bad neutral safety switch.

gutmann

Cutting off at around 4000rpm in neutual (N) only occurs in M104.942 (2.8) and M104.992 (3.2) with HFM. The mechanical CIS-E equipped M103 and M104.980 (3.0) doesn't have this feature.

Sorry I've no solution to the problem with the 2.6.

jgajito

???... don't you think that's a little odd?

I've seen 2 pumps on a W124 260E, one in the tank and another insdie the left front fender well... where/how did you add another pump?

I'm curious to know, how did you just decide to add another fuel pump?

vanwiek

Why is that odd? My '94 E320 also has two fuel pumps.

jgajito

^^^^^ Read the higlighted quotes in BOLD...

He said it had one and so he installed a second one...

vanwiek

Ok, yeah that is a bit odd.

jgajito

Vahagn,

You never responded, how and where did you install the second(third) fuel pump on the car? Before the TBI, in the trunk, and maybe you're talking about a regulator?

I'm lost with this situation about your fuel pump.