Mercedes-Benz Forum banner

1 - 16 of 16 Posts

·
Registered
'82 500 SEL (Euro)
Joined
·
105 Posts
Discussion Starter #1
Hi All,
I'm a newbie here, live downunder & have an '82 H.K. 500 SEL with 62k miles. The beast died the other day & the problem was no power to the fuel pump so I replaced f/p module but still no power to the fuel pump I then jumped the pins & bingo the pump was buzzing & the car started so I replaced the module again but no luck,... after a 3rd module still no power to the f/p. My question is what else does the module send/recieve signals to? or is their something else I/m overlooking?
All other electricals check-out OK.
Many Thanks in advance
 

·
Registered
Depends on the day!
Joined
·
13,337 Posts
Might be your EZL unit...

Jonathan
 

·
Registered
380sel 1983
Joined
·
31 Posts
When you write f/p relay do you mean the tachometric relay? (see attached pic)If so had the same problem. The relays have a tendancy to stick internally. I found the very scientific method of giving them a sound couple of thumps on the side of the fuse box and the replacing it worked a treat. Had no problems since. Tarquin
 

Attachments

·
Registered
Depends on the day!
Joined
·
13,337 Posts
Well, I'd try the tapping the relay bit, but if it's new it shouldn't be acting up on you like that... Who makes your replacement relay?


Jonathan
 

·
Registered
1985 500SEL
Joined
·
835 Posts
Robo:

I had similar problems..
i would first check for Feul with jumpering the relay, which u did...
so the fuel pump is ok

then I would check for spark...
pull a wire and put a used spark plug and hold it with isulated pliers and try to crank

if u don;t see spark then it could be the coil or the ignition control module

I replaced both in mine and it started right up

Good luck
 

·
Registered
'82 500 SEL (Euro)
Joined
·
105 Posts
Discussion Starter #8
Many thanks to all that have posted a reply.
The fuel pump relay is the one in the picture & all three on them have been rebuilt ( I have opened them & checked the contacts & relays ) So far I have replaced:
fuel pump relay/module 3 times
ignition control unit
coil
dizzy cap & rotor
voltage regulator
I am getting heaps of spark, however when I pump fuel into the engine (via jumping) & then reinstall the f/p module the car starts but only for a moment & then dies.
Could it be the ignition switch or some sensor designed to kill the motor after an accident ( no accident happened but just an idea)
any thoughts would be greatly appreciated
Robbo
 

·
Registered
Gertrûd - 1988 300SE
Joined
·
194 Posts
here's a possiblity, the fuel pump itself could be bad, not holding enough pressure. The fuel distributors require about 80lbs of pressure to crack open, and while the pump may be running, it could only be doing a constant 40lbs or so. This happened in my car, and I would turn the key on and off several times, letting the pump run for a bit, turning it off, repeating, etc...this would build up enough pressure for the fuel distributor to crack open and let the car start, and then moments later it would die. After this happened, it actually burned a few trace lines on the fuel pump relay (the pump was starting to short internally), so I had to replace both the pump AND the relay. Try swapping the pump with a known good one, see what happens then.
 

·
Registered
'82 500 SEL (Euro)
Joined
·
105 Posts
Discussion Starter #10
Thanks for your reply Andrew6981.... however when I jump er between hot power & fuel pump (pins 30 & 87 ) she arcs up & runs no problems, leading me to the idea of engine shutdown after an accident problem.
By the way the word "bastard" is an Aussie slang term of endearment, our Prime Minister (your President) uses the word/phrase often. My apoligies if I offended anyone.
Robbo
 

·
Premium Member
SLK55 (2006) C36 (1995)
Joined
·
3,288 Posts
sorry to threadjack, but i notice the relay says 5950 on it. Is that where the RPM cutoff is? Is that what AMG changed? Are higher rev limits available? (not looking for much, but another 500 rpm would be nice!)
 

·
Registered
Depends on the day!
Joined
·
13,337 Posts
I have never heard or seen anything of that nature.. WHen my car was smacked it still runs and starts.. As have other 560's that have been Really hammered. If, when you jumper those two pins, your car runs I can't imagine how it's not the relay. Maybe you are having an internal short in teh pump and it can not pull enough juice through the relay, but car through straight jumper? I'm really not sure...
Are you sure you're getting the correct one? There is more then one part # if I remember correctly..

Jonathan
 

·
Moderator
1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
Joined
·
5,177 Posts
Hi Robbo55,

I've been pondering this situation via the posts & the MB CDs.

Your idea: "Could it be the ignition switch or some sensor designed to kill the motor after an accident ( no accident happened but just an idea)" got me thinking.

In the mid '70s I worked as a line technician in a Volvo dealership. In '74 Volvo went to the CIS injection without a control unit. One of the features on the fuel distributor was a safety switch that would sense the air sensor plate position and open circuit power to the fuel pump relay if for any reason the engine stopped running (accident for example). For us to test the fuel pump, fuel pressure test, injectors... etc. - we first had to unplug this item.

On the 2nd CD > Function Diagram CIS-E Injection System > component B2 is labeled Air flow sensor position indicator. Also on the 2nd CD there is a pretty good picture of it (with wires attached) on the 073-220.pdf: Renewing air flow sensor. See pic below.

I have been looking for some time now and can find NO reference to either its function or setting. Yet.....

It is logical that there would be some way the fuel pump would shut off in an accident - even if the ignition was switched on.

MBL
 

Attachments

·
Registered
'82 500 SEL (Euro)
Joined
·
105 Posts
Discussion Starter #14
G'day All,
Many thanks to all who have spent time posting replys & especially to MBL87560sec for the trouble he went to with the wiring diagram - I am blown away with the generosity shown, I hope I have the opportunity to do the same for somebody else.
Now that I have a diagram to follow I shall get down & get dirty & report back with the findings.
Robbo
 

·
Moderator
1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
Joined
·
5,177 Posts
Hi Robbo,

So, how dirty did you get? More importantly, how's the car?

MBL
 

·
Registered
1980 LWB 280GE
Joined
·
3,504 Posts
Safety switch

On my M110 engine that switch is called the "baffle plate safety switch" and the wiring diagram shows it on the ground side of the fuel pump relay primary winding. Here's where it gets strange.

Just like you said, when I want to check injector function, I UNPLUG the wire to that switch. And when I do that, the fuel pump runs all the time that the key is on. I know this is how it works 'cause I've done it many times. But according to the wiring diagram, if I unplug that switch, I can't see how the fuel pump relay gets it's ground, so I've always been a little mystified by exactly how the thing works.

But for this case, anyway, I'd try un-plugging the baffle plate safety switch and see if the fuel pump starts running as soon as you turn on the key. If it does, I'm not sure how good of news that is. I only hope that the safety switch on your car is replaceable as an independent item. On my car it isn't.

You could also do a little more fiddling at the fuel pump relay socket. Rather than just jumpering it, use a probe in the back side of the socket to first see if there's power to the + side of the coil (pin 86) If there is no power to that pin, try putting 12V there and if the pump runs then the problem is in the SUPPLY to the relay. If on the other hand, jumpering pin 85 to ground lets the pump run, then the problem is in the grounding circuit of the relay primary (where the baffle plate safety switch appears to be).

Good luck!!

-Dave G.
 
1 - 16 of 16 Posts
Top