erratic fuel gauge.. help

[calyon]

hi bros, am having some problem with the accuracy of my fuel gauge lately. at each start-up, the gauge will indicates a full tank (even after hundreds of km since last re-fuel). and bit by bit, it will decrease accordingly after some mileage but not in the right proportion (as it used to be a month ago). in brief, the gauge gives a false representation on the remaining fuel in the tank.anyone experince this before? can it be easily solved? or do i need to just tap some corners of the car..haha?? thanks in advance

 

[chairoger]

Get ready to replace your fuel pump(s).

 

[taabster]

Why ah Chairoger? Care to explain ah? Not because of the fuel level sender unit?

 

[calyon]

ya chairoger.. how would the pump plays a part in this r? thanks. my initial telecon feedback from workshop is that it may be sensor problem at the fuel tank

 

[jarance]

There are 2 fuel sender located under the passenger seat. On the driver side, the fuel sender have a fuel pump integrated with it whereas the left side do no have the fuel pump. Based on my observation, the fuel sender with the fuel pump have tendency to be faulty. This is due to the additional weight of the pump. When you go over a bump, the rubber absorber will absorb the shock but overtime, the absorber cannot absorb the shock and will go jerks down more than the cable slack. this will cause the cable to snap or most probably have a bad contact. That is why chaoroger say the pump unit need to be replaced coz you cannot buy the unit seperately. However, I have repaired the sender unit by resolder new cable with extra slack. To verify whether it is your sender unit that is the problem, remove the car seat and check for the connectors. One side should have 2 connectors and the other side should have one connector. the one with the additional connector is the one with the fuel pump. compare the colour of the connectors. The fuel pump connector is different from the fuel pump unit.

disconnected the connectors of the same colour and measure the resistance of each of the fuel sender. The reisistance should be around 10 to 150 ohms depending on the amount of fuel in the tank. if the value are out of the spec, open it to check further.

 

[tank34]

Hey Jarance,

am having the identical problem to Calyon, just developed it in fact over the last 2 days. Your solution is worth a try but is it applicable to the E46? It sounds more like an E36 solution, not sure whether the E46 fuel pump is located in the same area.

Also, any chance of us meeting up to get some hardcore DIY tips on how to get this done?

 

[calyon]

thanks jarance, really appreciate your detail advice. would take note on that.

talking bout it, i did have a few bumps at the undercarriage due to some super road bum and drove over some pool of water (not real flood but probably 3-4 inches deep). would that be a possibility too?

 

[jarance]

Hey Jarance,

am having the identical problem to Calyon, just developed it in fact over the last 2 days. Your solution is worth a try but is it applicable to the E46? It sounds more like an E36 solution, not sure whether the E46 fuel pump is located in the same area.

Also, any chance of us meeting up to get some hardcore DIY tips on how to get this done?

According to BMW ETK, it look similar to the e36 fuel tank.

refer to below to see the e46 fuel tank.

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Detail of the fuel sender.

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yes the procedure is for e36. I have repaired a couple of e36 with the same problem. Look at the picture for e46, I think the procedure is basically the same.

Sorry cannot meetup as I am in JB at the moment.

 

[jarance]

thanks jarance, really appreciate your detail advice. would take note on that.

talking bout it, i did have a few bumps at the undercarriage due to some super road bum and drove over some pool of water (not real flood but probably 3-4 inches deep). would that be a possibility too?

Going over a super bump is the main cause of the fuel sender having erractic reding due to the wire being jerk until it about to break.

Going over water will sometime caused your engine to stall due to water ingress to some of the connectors. Usually the car can be restart after half hour when the water dry up.

 

[tank34]

Calyon,

went to M-Speed to get it sorted yesterday. Changed the fuel pump AND the floater as described in Jarance's post. Initially, I suggested just doing an experiment and suggested to Kenny (of M-Speed) to change the floater. He advised against it saying that it "may" cause a short circuit and it could potentially crash the ECU. total costs of replacing pump and float MYR870. Gauges are now reading fine.

Ken.

 

[jarance]

Calyon,

went to M-Speed to get it sorted yesterday. Changed the fuel pump AND the floater as described in Jarance's post. Initially, I suggested just doing an experiment and suggested to Kenny (of M-Speed) to change the floater. He advised against it saying that it "may" cause a short circuit and it could potentially crash the ECU. total costs of replacing pump and float MYR870. Gauges are now reading fine.

Ken.

woh.. you have been taken for a ride. I have never heard of the fuel sender causing a short that might crash the ECU. Please remember the fuel sender is sending a resistance of 10 to 180 ohms to the ecu to interperate the fuel level. 10 ohms is almost shorting the ECU.

BTW, did you take back the faulty part? It can be used as spare later for the fuel pump.

 

[tank34]

$@%^$&, aiyah Jarance, why did u have to be in JB yesterday.

Anyways, (Ah-Meng) at M-Speed has an impeccable track record and I got along fine with him.

I did suggest just changing the float but he was adamant I change the pair. Also, my experience with Ah-Meng is that he will usually lay out the risk and leaves the final decision to you.

But..... if you had given me this advice earlier on. I would have just change the float to see what happens. it's also tough luck that the other floater was attached to the pump.

Well, peace of mind for now.... I've got a list of things to maintain next, control arms, pads+discs and expansion tank. will be spreading that out over the year.

 

[jarance]

$@%^$&, aiyah Jarance, why did u have to be in JB yesterday.

Anyways, (Ah-Meng) at M-Speed has an impeccable track record and I got along fine with him.

I did suggest just changing the float but he was adamant I change the pair. Also, my experience with Ah-Meng is that he will usually lay out the risk and leaves the final decision to you.

But..... if you had given me this advice earlier on. I would have just change the float to see what happens. it's also tough luck that the other floater was attached to the pump.

Well, peace of mind for now.... I've got a list of things to maintain next, control arms, pads+discs and expansion tank. will be spreading that out over the year.

Sorry, changing the float would not solve the problem. It is the cable from the resistance PCB (printed circuit board) to the connectors that is the problem. Anyway, you should keep the old part for spare. they come in handy when your fuel pump failed...

 

[calyon]

ok, must thank u both for the clues. at least now i know the basic to the problem source. will send it to my usual srv master to repair it man.. (gauge still showing funny reading levels now, so have to rely on mileage driven in the meantime)

as for m-speed, no doubt about its proven skills n experience. just that at times, a lil bit pushy on things.. he's a good guy though

thanks again guys!

 

[blackrobe]

Yup, Jarance did mine more than a year back...Good job too and took a shorter time then I expected. Unfortunately, its a recurring problem... design defect?

 

[chairoger]

Just be thankful even if you change all the related components to rectify the problem, it is not that expensive.

 

[jarance]

Yup, Jarance did mine more than a year back...Good job too and took a shorter time then I expected. Unfortunately, its a recurring problem... design defect?

Could be the other fuel sender. BTW, you did remember that when I have open up your fuel sender, the rubber absorber was broken. it was not replace. maybe that could be the case of the recurring problem..

It happen to me once before but the problem did not occurred again after the cables was replaced. but then again my rubber absorber was not broken.

 

[flash]

Too bad jarance is not around in KL area anymore... . If not can get him to look at my fuel sender too. The needle goes the full sweep but it goes down pretty fast. When the needle points at close to empty and I refill, I can only put in 60 litres of petrol max. I can actually still drive for another 100km at least even if the needle pointed to empty. Ok, mine is an E34, so the fuel tank should be able to hold 80 litres. Guess the impedance of the wire has gone screwy.

 

[LCP]

Just changed my left hand side fuel gauge sender unit today... noticed that with the brand new unit, at full tank (to the brim!), my fuel gauge will only show a bit below 60 litres, around 57-58 litres.... Stable though. No such problem on my old unit (the one with leaking plastic cover) where it will show 62 litres (max capacity for E36 tank).

Any idea how does the fuel gauge on the dashboard compute the fuel level between the two fuel tanks? Technical explanation is okay.

 

[calyon]

took out both the left n right fuel sender for inspection. apparently all the wires, rubber, soldering, microchips, etc still in good condition. so they did some renewing process n stimulation (to make sure the senders' arm movement level translate to gauge measurement proportionately). pack everything back n so far so good.

damages foc, but the process of seeing the stripping process to get to the fuel sender is priceless (sakit hati la..haha). plus on a high these days while driving coz fuel overspill still giving bad odour in the cabin.

ohh plus i think some idiot opportunistic part supplier is taking advantage of the current massive demand of fuel sender (coincidence??). apparently the inventories finished for a few suppliers so the remaining one is holding on theirs like auction basis (highest bidder gets the part).