Fuel pump pulsating at idle

[BRABUS124]

Is this normal that this relay is pulsating at idle?
Just replaced fuel filter and resently it started pulsating so laud inside the cabin it's very noticeable. But that we're before the filter change

400E US spec car 1992

 

[Jim Rosenthal]

Based on my recent experience with my 500E, it appears that the LH module in your car, which regulates the fuel injection including the fuel pump, may be failing. It's probably less likely that the relay is defective, although they are not expensive to replace. But even when we could get my car running, the fuel pump was cycling very rapidly on and off. Replacing the LH module cured the entire problem.

There is a thread in the trouble shooting section which discusses my car and the problems we had with it. Lots of very useful information. Including a list of LH modules you can substitute to see if they cure the problem. I'm assuming that the 400E is similar to the 500E in this respect.

 

[BRABUS124]

This is not really a failing thing. This clicking is very clock work timed. So I'm guessing it's some kind of fault or safe mode. It follows the frekvens of the engine sonetines faster some times slower but very intensional kind of way see video. Ok it's only 6 sec and this forum is telling me it's to big. Waw are we in 90s

 

[gerryvz]

Jim is correct. You have a bad fuel injection computer that is causing the relay to click. It's very very well documented on this forum and is a now common failure.

 

[gsxr]

Yep, what Jim and Gerry said. The LH module controls the fuel pump relay. When the relay clicks consistently (clock work timed), the LH module has failed capacitors. You need to repair the LH module with new capacitors (search the forum for details), or replace it.

 

[Jim Rosenthal]

Here's the thing- we replaced the fuel pumps, the fuel pressure regulator, and the fuel filter (total about $300) before replacing the LH module. Okay, all of those replaced components were old, but really what I should have done was to replace the LH module (see the thread for a list of PNs that will work) and see if that cured the problem. OK, all that stuff was old, but I could have saved $300 bucks. I'd do the module first, before anything else.

 

[gerryvz]

If you type it into the search box, it will immediately return a few threads that are directly relevant, as shown.

If you do a full search, it will return pages of results here on the forum.

 

[BRABUS124]

Yep, what Jim and Gerry said. The LH module controls the fuel pump relay. When the relay clicks consistently (clock work timed), the LH module has failed capacitors. You need to repair the LH module with new capacitors (search the forum for details), or replace it.

Cool. Thanx to your all. I'm a educated electronic engineer and I do those kind of repairs all the time throttle bodies cruse civteol amplifiers ECU so that's an easy job fir me. I'll post pictures

 

[BRABUS124]

Sadly the seach function isn't really that good. I got no result searching for eksactly this.

If you type it into the search box, it will immediately return a few threads that are directly relevant, as shown.

If you do a full search, it will return pages of results here on the forum.

View attachment 183954

 

[gerryvz]

Sadly the seach function isn't really that good. I got no result searching for eksactly this.

Well, you are certainly welcome not to visit here and use the forum, then.

The primary search function on this forum uses Elasticsearch, which is one of the most powerful and scalable search engines in existence.

Use the search box at the UPPER RIGHT of the screen, NOT the "quick search" box at the left side. If you would have paid closer attention to my screen capture image above (where the screen name, PM indicator, etc. are), you would have seen that it was taken from the RIGHT SIDE of the screen.

Pay closer attention, my friend.

Happy searching.

 

[gerryvz]

Sadly the seach function isn't really that good. I got no result searching for eksactly this.

I guess I should teach you....

Here is the site's primary search function -- the magnifying glass at the upper right of the screen:



Here is what you get, when you begin to type characters into the search box:


The more characters you type, the more it refines the search, IN REAL TIME.


Of course, you can always click on the "Advanced Search..." button, for a full search result....



And from this specific search, there are a total of SIX PAGES OF SEARCH RESULTS. Here is almost the first page of them....



So, please investigate this site's capabilities, before you go popping off about how bad it is.

 

[BRABUS124]

Well, you are certainly welcome not to visit here and use the forum, then.

The primary search function on this forum uses Elasticsearch, which is one of the most powerful and scalable search engines in existence.

Use the search box at the UPPER RIGHT of the screen, NOT the "quick search" box at the left side. If you would have paid closer attention to my screen capture image above (where the screen name, PM indicator, etc. are), you would have seen that it was taken from the RIGHT SIDE of the screen.

Pay closer attention, my friend.

Happy searching.

I'm sorry I'm so new to this forum and all is not given logic for me. If you don't want to fill up your time with answering a noobie, fell free not to do so my friend
Happy readings.

 

[BRABUS124]

I guess I should teach you....

Here is the site's primary search function -- the magnifying glass at the upper right of the screen:
View attachment 184005


Here is what you get, when you begin to type characters into the search box:
View attachment 184006

The more characters you type, the more it refines the search, IN REAL TIME.
View attachment 184007

Of course, you can always click on the "Advanced Search..." button, for a full search result....
View attachment 184008


And from this specific search, there are a total of SIX PAGES OF SEARCH RESULTS. Here is almost the first page of them....
View attachment 184009


So, please investigate this site's capabilities, before you go popping off about how bad it is.

Thanx alot for teaching I like that post alot. Informative helpfull. You didnt had to make the first post my opinion. It useless to be writng to each other that way. So let's continue the better way. I'm looking forward to learn. I my self is a master at out own forum in Denmark having 1000 of peoples respect of all my own informative info's about the 124 so I can guarantee I have just as much to teach if not more knowledge than most people have on the 124

 

[Jim Rosenthal]

Brabus124, I suggest buying a used LH module on eBay or from a local used parts source. Look at the thread on my car under the Troubleshooting category- there is a list of suitable LH modules in there. Not all of the LH modules have the WOT hp boost, but for this purpose you don't need it. If it restores your car to normal function then you have your answer.

From what I've read, the capacitors in the original LH module go bad and cause the problems. My original module is with a fellow forum member out West who is going to swap in new capacitors and we'll see if that helps the problem. I will post something in my thread about my car under Troubleshooting.

 

[BRABUS124]

Brabus124, I suggest buying a used LH module on eBay or from a local used parts source. Look at the thread on my car under the Troubleshooting category- there is a list of suitable LH modules in there. Not all of the LH modules have the WOT hp boost, but for this purpose you don't need it. If it restores your car to normal function then you have your answer.

From what I've read, the capacitors in the original LH module go bad and cause the problems. My original module is with a fellow forum member out West who is going to swap in new capacitors and we'll see if that helps the problem. I will post something in my thread about my car under Troubleshooting.

I got them changed. I'm an eksperinced electronic engineer my self. I makes tons of those repairs

 

[dreaming.haze]

I got them changed. I'm an eksperinced electronic engineer my self. I makes tons of those repairs

Nice! Doing the same thing currently in hopes to cure my pulsating fuel pump relay. Have you tested things out yet on your end?

 

[BRABUS124]

Nice! Doing the same thing currently in hopes to cure my pulsating fuel pump relay. Have you tested things out yet on your end?

I just put the boks in the car and it works perfect. It cured the clicking relay. So I'm great full for who helped me here with this isue. I so good at the normal 124s but the V8 has a difrent system etc. So dident really know that isue but happy to see it worked to replace the old capacitors.

 

[Jim Rosenthal]

Good for you!!! And you saved all the money that I spent because I didn't do the LH module first, like I ought to have done. Idiot me.

 

[dreaming.haze]

I just put the boks in the car and it works perfect. It cured the clicking relay. So I'm great full for who helped me here with this isue. I so good at the normal 124s but the V8 has a difrent system etc. So dident really know that isue but happy to see it worked to replace the old capacitors.

Same as you, just finished off replacing the capacitors on the 5.0L LH module and it cured my clicking fuel pump issue. Now to just wait a few more months to get it back on the road this spring. Thanks @Alphasud40 for the group buy on the capacitors set, worked a treat.

 

[Alphasud40]

I just wanted to mention that all cars on this forum with the LH ECU need to have their capacitors replaced. The most recent control unit I replaced the capacitors in fortunately didn’t have any circuit board damage due to leaking capacitors. These are drying up causing the capacitance to decrease to the point where they become resistors in the circuit. 4 out of the 6 changed had zero capacitance. So I think it’s safe to say based on time they should be replaced before you experience a failure. Besides the potential for outright shorting having no capacitors in a circuit opens the possibility to microprocessor damage.
I have no experience with the comfort module but its possible capacitors are failing in those as well in addition to any electronic module in a 30+ year old car.

 

[dreaming.haze]

I just wanted to mention that all cars on this forum with the LH ECU need to have their capacitors replaced. The most recent control unit I replaced the capacitors in fortunately didn’t have any circuit board damage due to leaking capacitors. These are drying up causing the capacitance to decrease to the point where they become resistors in the circuit. 4 out of the 6 changed had zero capacitance. So I think it’s safe to say based on time they should be replaced before you experience a failure. Besides the potential for outright shorting having no capacitors in a circuit opens the possibility to microprocessor damage.
I have no experience with the comfort module but its possible capacitors are failing in those as well in addition to any electronic module in a 30+ year old car.

To this comfort module idea, looks like this guy down in Australia has a decent video on things: