E36 fuel pump: diagnosis & replacement
United Bimmer Do-It-Yourself Disclaimer: The following tutorial is meant as a guide and is not guaranteed to be complete or 100% accurate. By following this DIY, you understand any work done on your car is at your own risk and we hold no responsibility if you break something. If you feel uneasy with this risk, we recommend you take your car to a professional mechanic to have the work done. Otherwise, enjoy yourself and good luck!
The fuel pump can fail either from old age, and inadequate fuel supply. Driving with less than 1/4 tank of gas can overheat the pump; the fuel actually keeps it running cool, and debris or sediment from the bottom of the tank can block the pump's filter, causing it to get overworked. If you suspect a bad pump, there are a few things to check before pulling it out.
The order of electrical flow through the fuel delivery system is fairly simple: The DME (ECU) sends a signal current to the main DME relay, which in turn feeds the signal current to the fuel pump relay.* From there, the current flows through the fuel pump fuse before heading down to the fuel pump. This whole circuit is complete and live whenever the ignition is cranking or the engine is running. To summarize:
DME--> DME relay--> Fuel pump relay--> Fuse #18--> Fuel pump.
*Technically, the (+) leg of the DME relay is already hot, and it's the (-) leg that is grounded to complete the circuits.
Testing the relays can be a painstaking process, so you'll want to leave that till later and do the easy stuff first. The most obvious is the pump fuse, which is #18 in the fusebox. If that checks out okay, then remove the back seat bottom by pulling up at the locations indicated by the arrows:
There may be other stuff you have to remove first, like the side bolsters on coupes. But in my car they're integral to the seatback, so I'm not sure about that. But once the seat bottom is off, look on the right side of the vehicle, you'll see a section of padding that is cut into a circle. Pull it up to reveal the metal cover, and remove the 4 Phillips screws to open it. Careful- there's a flimsy foam gasket underneath it. Here's what you'll see:
As you can see in the photo, mine had a ton of crud on it; the clamp on the return hose wasn't tight enough. Yours probably won't look as dirty. At this point, have someone crank the engine while you listen for the pump.** The sound is unmistakable; a medium to high pitched buzzing, and you only have to get as close as a few inches to hear it. If it's buzzing, then the fuel pump is not your problem. If there is no sound, disconnect the pump wiring harness and test the leads for current while the engine is cranking. The green/violet wire is the positive, and the remaining wire is the ground (ground wire can be either brown or brown/green). You should see +12v while the engine is cranking.** If not, then move on to testing the relays & sockets.
**Alternatively, you can make the circuit go live by removing the main DME relay and installing a fused (15A) jumper wire between sockets 30 & 87 (see below).
TESTING THE RELAYS & THEIR SOCKETS
When troubleshooting the relays & sockets, you can refer to the photo below (relays removed). I don't see how the socket and pin locations could be different, but verify your individual application anyway by matching the socket to the pin numbers on the relays. What will not change is the pin numbers and their functions; these are standard Bosch type 12v relays. Note that the DME relay has two 87's: one feeds the fuel pump relay, the other feeds the fuel injector valves. This is known as a Double Pole Single Throw (DPST) relay, as opposed to the fuel pump relay, which is a Single Pole Single Throw (SPST).
You will need a multimeter, +12v power source & ground to test each relay. Connect relay pin 85 to ground. Set your meter for a continuity test, and attach the meter probes to pins 30 & 87. When you apply +12v to pin 86, you should hear an audible "click", and the meter should indicate that 30 & 87 have been bridged (continuity confirmed). If not, then the relay is bad.
If the relays check out okay, there may be a break or short in the wires leading to the pump. Move on to the relay sockets. Test for continuity between the fuel pump relay socket 87, and the green/violet wire at the pump (remember that fuse #18 lies in between these two points). Then test for continuity between the other wire at the pump, and a ground source. If those check out, then the wiring is okay.
On both relay sockets, #30 should be reading +12v at all times. At this point, a fault at the socket or the wiring harnesses is beyond the scope of this writeup, and this is where the setup between the different model E36's will begin to vary. Furthermore, if you haven't found anything wrong by this juncture, then it's no longer a fuel delivery issue, and you should be looking elsewhere for the culprit of your problem.
REPLACING THE FUEL PUMP
If you're positive that the fuel pump has failed, then the rest is a cakewalk as long as you follow a few simple but important rules:
--Don't smoke . . . duh!
--Have your radio code handy (if applicable), then disconnect the (-) battery cable.
--No cellphones, portable lights, or anything electronic/electrical in the vicinity.
--Do not use battery or electrically operated tools- hand tools only.
--Do not perform this in a closed garage- ensure adequate ventilation.
--Remove the gas cap to relieve pressure in the tank & lines.
--Wear goggles and rubber gloves. Seriously.
--Gas tank should be no more than about 3/4 full, or it'll get really messy.
When ordering your new pump, make sure to also buy the seal ring, shown in photo below. Notice that the fuel level sender is integral to the pump assembly. You can also use the same identical procedure to replace the fuel level sender on the left side of the car. The white rectangular thing is the aforementioned filter that gets clogged up.
Begin by disconnecting the wiring harnesses, and let the car sit for about 10-15min to dissipate any possible remaining current. Then disconnect the fuel hoses. Have some paper towels handy, as some fuel will spill out. Go easy when pulling off the hoses; they may still be under some pressure- this is why you want to wear goggles. Unscrew the collar ring counter-clockwise. BMW makes a special tool for this, but it's not necessary. Use a flathead screwdriver and tap gently with a hammer to get it going, as shown in photo below. Then turn with your hand the rest of the way.
Make a note of how the pump is oriented in the tank- you'll be putting the new one on in the same way . . the harness receptacles should face towards the front of the car. Once the collar ring is removed, pull up on the whole pump housing. Easy does it- take your time so you don't make a mess of the fuel. You'll have to do some slight finagling to get the unit out, but it's not difficult at all. The seal ring should come off along with it; if not, pull it off the rim opening.
Installation is the reverse of removal. Don't forget, the seal ring goes on first before you drop the pump in. A little past hand tight on the collar ring should be sufficient- you don't want to crush and deform the seal ring. Hook up the hoses first before the harnesses, in case of any stray arcing (not likely). New pump installed:
Reconnect the (-) battery cable and start her up. Reset your clock, radio, & power windows***, and you're good to go :)
***To re-initialize your power windows, close all doors and turn ignition on. Fully open and close window, holding the button in for at least 5sec in the closed position. Repeat for other windows.
when my fuel pump went up i could hear it while i was sitting in the drivers seat. sounded like a lawn mower in the distance.
another handy tip i didnt know when mine died, sometimes you can give it a nice tap with an open end wrench or something like that, it may start pumping again. it could get you a mile down the road or so. in my case, i could have gotten it home, i was that close. . .
on my pickup truck I have been working on I also took out the fuel pump relay and cranked it, to get the fuel out of the lines, not sure if you have to do that with the e36.
Great writeup. Will try on my friends car. This will make a faster job. thanks.
nice write up, will bear it in mind for future reference.
Tested fuel pump from other source of 12v = works
Tested voltage on connector = 11v on 2 of the 4 pins, and the other 2 pins receive voltage when i try to start the car. so all 4 pins are getting voltage while cranking the car
Now, i connect fuel pump to the connector = pump don't work?
fuel doesn't pumps checked it. what could be wrong?
another tip in hand. If any of the fuel pump is damaged, the best solution would be replacement. That way, you can be sure that the fuel pump will remain functioning no matter what.
a bad fuel pump can affect when you press your gas pedal hard and your car stalling on the high way
This is a great write-up. I've been searching over the net for this kind of detailed DIY. Well. my brother is planning to replace his fuel pump with airtex over the weekend but we're quite newbies in troubleshooting the car. Lucky to found this post so we can easily replace the fuel pump on my brother's car. Thanks for sharing it. :thumbup
Well done Dudesky. Fantastic. Clear precise and easy to follow but most importantly, factually correct. I read this and double checked all the things I had checked and then went and bought the fuel pump complete(ie with the fuel gauge sender unit/float and the filter all attached) and literally threw it in in about 10 minutes from go to whoa. Can I add BMW have some funny non reusable hose clamps but you can pull the hoses off and push them back on. If you do this recheck for leaks befroe you but the cover back on and the seat down. If they are leaking I would replace the hose clamps for safety, the large hose is send and the other(thinner) is return(2 slightly different sizes. Looks like about 10mm and 8mm but you could use a screw type hose clamp, not that fool BMW thing. Thanks so much for this post
Fuel pump or filter
I've got a problem with my e36 320i 96 model, the fuel pump doesn't make any buzzing sound when i crank the car, but when i remove it and place it inside a bucket with water and connect it direct to the battery it works, it pumps water out of the exit pipe (my petrol pump got one pump, it's blue in color) which proves that it works but when inside the petrol tank it's not functioning. And when i check fuse 18 there's no power but other fuses have current. I'm confused, i changed the relays but still no luck and i changed the fuel filter about a month ago and my previous filter was stucked, could it be the same thing but why there's no current on fuse 18. If my fuel lines or pipes are stucked with dirt why the fuel pump doesn't buzz. Please help, in South africa the electric parts are not returnable or exchanged, so i don't want to guess. And Thanks for the great diy write up.
I have a 1997 840ci with a slightly different fuse / relay layout. I am trying to determine which fuse is #23 & #24 as well as the fuel pump relay since I am not getting 12V to the pump itself. I am getting 12V to the fuel sending unit so that would mean the relay is faulty since I have checked all of the blade fuses already.
Can someone tell me specifically, based on the pictures below, which relay is the fuel pump relay? Thanks in advance!
Strangely, the fuse / relay diagram on the inside cover of the box does not lend itself well to identifying which relay is which.
What started the problem was a lack of fuel delivery, naturally so I correctly figured that the fuel pump had failed...I was partially correct.
But even after installing the new OEM pump, the voltage is not reaching the pump itself so since the blade fuses are in good order, the relay is the culprit.
If you can pin point the proper relay for me, that would be a tremendous help. Thanks!!!
Dudesky, I know it's been a long time since you posted these instructions, but I have to tell you that you saved me a TON of money and a ton of TIME!!!! My fuel pump went out on me in my E36 Convertible when I was leaving town the day before Thanksgiving... 1/8 of a mile from my house. Had to push the car back in the garage and drive my truck (daily driver) out of town. During my 24 hrs out of town, I googled the symptoms of my car to help understand why the hell my car died. I found your post, and when I got home the day after Thanksgiving... I DID EVERYTHING THAT YOU INSTRUCTED AND HAD THE JOB DONE IN 1.5 HRS. And, that's including the 30 min drive time to NAPA Autoparts to buy a factory fuel pump/full assembly. My car is running like a champ again!
THANK YOU, THANK YOU, THANK YOU! This is the best post I have ever seen!
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