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    Fuel pump diagnosis and full test routine.

    Hello All! Its been years since I've been here but now I have some information to share, and need some advice too.

    I had what can be described as a surging idle. Sometimes car is fine, but with increasing regularity until it occurred on every journey and then immediately after turning on. At speed there was no noticeable problem. The when idling, the revs would drop till the tacho hits zero, then rev to correct itself causing a surge in power. If in gear this forces the car to lurch which is embarrassing.

    LHM came on onece or twice. Sometimes started in low power assuming 6 cylinders. Sometimes the red check engine light came on.

    I took the car to a garage on dec 12th, and got it back two weeks ago no better, with a bill for 1x new MAF and 3 hours labour. Joke. This is the test procedures I have taken.

    1/ Pull individual fuel pumps fuses
    RESULT: pulling the fuse for pump 1 makes no difference, pulling pump 2 fuse stops the car within 3 seconds (on the next idle sag before the high rev)

    Because the garages misinformation (telling me DK motors are at fault) I went through the following

    2/ Rebuilt and cleaned DK motors. No change. Open and close cleanly.
    3/ Swapped Coils over. No change.
    4/ Swapped MAFS over. No change.
    5/ Garage had seen the CPS sensors were sending a signal, though one went off - presumed it was the aftermarket chips, removed these and then the CPS were both reporting RPM.
    6/ Spraying easystart to check for vacum leaks
    7/ New fuel filters
    8/ Battery check - they are fine I get about 50 starts from a charge without running (during my testing).

    Car is in good condition with having the folling parts replaced under my tenure
    Rotors & Caps
    Sparkplugs & complete spark lead set inc sensors
    Intake manifold gaskets
    Was chipped, but now BMW standard chips back in
    Fuel lines
    Injectors professionally cleaned and flow matched
    Vacum return hoses + valve (crank ventilation?) Other vac lines to DK motors as well
    Banjo bolts
    Lambda / O2 Sensors

    Ok at this point I'm fairly sure its not the sparking or the fuel flow lines. Something to do with the fuel pumps because it runs fine with one fuse out - when put back and pulling the other one it dies straight away. Runs fine at speed.

    Assuming no CPS problems, I cracked on - this is the procedure to test your fuel pump system

    1/ Check fuses 23/24 - Replace - try shorting with copper cable in case
    2/ Relay checks (blue in EML box) - tested resistances and heard the clicking. Swap over & see if problem swaps sides (mine did not). Run on approx 1.5V in closing the 12v power to pump.
    3/ Short relay 30&83 sections (see diagram on side of relay) this provides power to the pumps for sure. Listen individually. Note that one relay also activates the DME cooling fan (scared me).
    4/ Check that you get 12v at the fuses from the relays.
    (NOTE: Relays only active when running or cranking, sometimes for 1 second on making position 2, but not always)
    5/ Remove rear right hand (UK driver side) seat and access plate. Remove and re-insert round 3 pin cable. As you look at it top pin ground (grounded by DME) Left hand pin pump1, right hand pump2.
    6/ Check continuity from fuses and relays to these pins.
    7/ Put small wire into each pin of the connector and re-attach. Tricky. Use these to check you are getting 12v as expected from the front (in case a wire from front to back is bad).
    8/ I have checked resistances across these pins. Ground to either pin is ~1.5 +/-0.5 Ohms, pump1 to pump2 is (suprisingly) about 1 Ohm.

    At this point I still had no joy. Everything is as expected. Continue!

    9/ Remove pumps
    10/ Check the bolts to the pumps
    11/ Jury rig fuel pump to a 12v battery. Beware sparks + Fuel!
    12/ Compare pump operations - few seconds so they dont burn out. Beware about 200ml of fuel will eject!

    At this point I find an anomoly - Both pumps gush from the top mounted ejection port, at visually the same rate. Pressure unk at this point. However! Pump 1 (the one that was detected bad by pulling the fuses) also leaks fuel at the top of the pump, near the electrical contacts. Seems to be coming from the white bearing at the centre of the pump.

    I'm assuming this is the problem, but before I order the £400 assy (both pumps, housing and level meter) from bmw (they only have the full thing) - I'd like to ask if anyone has experience of this kind of fault with a pump.

    If no one knows I will swap the pumps over, re-install the pumps and then see if the fuse that upon movnig causes the car to die swaps as well. For my own refernce its currently fuse 24 that I remove to cause this death.

    Best regards to all. I'll try to add a picture of the top of the pump in a moment.

    Nathan

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    Re: Fuel pump diagnosis and full test routine.

    Picture of the fuel pump. Pump one is at the back, two in foreground.

    Red circle shows the area petrol is leaking (squirting) from on pump1. Pump 2 does not do this.





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    Re: Fuel pump diagnosis and full test routine.

    i bought two after market fuel pumps with 255lph fuel rate.
    they work fine... but what i had to do is upgrade the internal wiring of the fuel pump carrier. to a larger gauge wire. the fuel pumps have a larger current draw and the thin ground wire could not handle the flow and heated up quite a bit.
    each pump cost me $60,- ... it's well worth a bit of engineering

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    Re: Fuel pump diagnosis and full test routine.

    Hi

    Where did you get them from? I just had to spend UK£ 200 on a BOSCH unit

    TA

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    Re: Fuel pump diagnosis and full test routine.

    hello nathan
    the pumps i got were from TRE perfomance.

    TRE performance bmw fuel pump

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    I have ordered a new pump

    when fitted will report results

    TA

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    Re: Fuel pump diagnosis and full test routine.

    By now having replaced fuel pump your problem is solved, right? When the pump gets older, it seems to work fine, but cannot maintain consistent fuel pressure when idling especially as it warms up. The DME detects insufficient pressure = no gas, and signals to cut-off engine. The fuel pump burps back into life and the engine sometimes just catches again, but sometimes dies.

    To check if this is problem, hold accelerator at about 1,000 rpm (of course with foot on brake) and see if this surging still happens. It's the sign of non-servicable Bosch pump seals getting old

    Another indication of same problem is - perfect cold and lousy hot start after few minutes of shutdown. The fuel refluxes back out of fuel pump leaving gas bubble. You then need to crank engine for a good few seconds to get engine going again and until you load the engine by moving off, it will continue to be very cantankerous.

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    They sent me the wrong one!.

    They sent me something with a top plate etc attached. I'm going to have to return it and try elsewhere, or get on sent from America I think they have just the pumps.

    Really need to get it sorted as I've just bought at 360 and between that , 8 series and my monster truck its getting a bit ridiculous.

    Cheers for your help and encouragement

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    OK new pump in

    And no change!

    I'm going to go and check now - I think perhaps I've taken the wrong pump out so I'm going to go and check by swapping over the wiring for pump1 and pump2 and see if the error swaps sides as well (checking this by pulling fuse 23 and 24 again

    Its never an easy fix - especially when your working away from your tool box.

    Report later I guess

    N

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    Re: OK new pump in

    Gets stranger.

    If I swap the cables at the pump so that pump1's electrical feed goes to pump 2 and vice versa the fault also swaps.

    I think this means that its got to be a pump not an electrical problem

    (brain a bit addled by petrol fumes)

    I took the pumps out again and the pump that does not seem to be working is the new one! If the other (older pump) is disconnected it dies immediately. If the new one is disconnected it makes zero difference to the engine.

    This is driving me batty. Next tests are

    1/ Check basic pump operation on bench with 12v source.
    2/ Flow test - put some longer tubeing onto the pump and measure how much comes out in 10 seconds etc.
    3/ Pressure test - get a pressure test kit and check the pressure at the rails.


    ponderings
    ------------------
    I was wondering if it could be the fuel lines from the pumps to the fuel rails, or the rails, or the regulation valves being shot on one side? Doesnt the fault following the electrical swap over preclude this?

    I suppose not.

    I might see if I can run a line direct from the pumps to the fuel rails cutting out the fuel lines.

    The fuel filters have been replaced. Perhaps a pipe has bent or corroded closed?

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    Re: OK new pump in

    Ok so the new fuel pump had reverse polarity.

    Problem still not cleared.

    I think I might have two problems actually. Swapping the electrical supply for the pumps (ie cable 1 to pump2) and testing by pulling fuse 23 and 24 causes indicates that the pump is still at fault. The engine dies when 24 is pulled on a 1-1 and 2-2 connection, when the connections are crossed 1-2 and 2-1 then it dies when 23 is pulled.

    However pulling the kingpin that is accessable (left hand side of the engine as you are sitting driving) always causes the engine to die, quickly. If pump wiring is swapped over then the engine still dies when the left hand kingpin is pulled. Pullin the other one (harder to get - near the computer port plug) makes no difference ever.

    I've swapped over the coils (and I had a spare) no effect
    Swapped over the DME conections - no effect.

    There is a new maf on one bank, but this is the bank thats not running. Is it possible the new MAF is... naff? I guess I need to swap them out.

    The bank that is running poorly is not getting any where near as hot as the other bank.


    Plan of action

    1/ Get pressure test of the fuel at the rails to remove that possibility.

    2/ Swap mafs

    3/ shout at it.


    Could really use a hand. What could cause one side to hardly work. Remember its not getting as hot as the other.


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    Re: OK new pump in

    When swapping electrical feed from pump 1 to pump 2 the fault also changes.There is your 1st clue that it is something other than the pumps.As TxGr8White suggest,check related electrical componants,also check for corroded connections. Good luck

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    I doubt the fuel pumps are the cause ...

    Nathan,
    I've read all your posts, but there are too many variables to try to answer each question.
    Let me offer my thoughts about your problem.
    If the car runs well at speed then the fuel pumps are probably fine. A small leak inside the gas tank doesn't mean the pump is not delivering adequate fuel pressure. Poor fuel pressure would be more likely to cause a problem at higher RPMs.
    A rough idle is most likely to be caused by MAF, DK motor, or electronic engine management.
    All three of those can be swapped side to side to try to isolate the issue.
    I know you said you have tried that, but please consider doing it again, slowly and carefully observing the exhaust temps before and after the swap. It is easy to be fooled (ask me how I know this!).
    If the check engine light comes on or the problem triggers a LHM, then it should generate a fault code. It would be worth the effort to find a good code reader (or BMW dealer) to read those fault codes.

    Best wishes.

    Mark W in mid-MO
    2008 335xi coupe
    1993 850Ci 6-speed

    2 turbos ..................or 12 cylinders, no waiting!

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    Thanks guys, the next steps detailed.

    Hi There Mark I thought I'd reply here.

    I've got a BMW electrics mobile mechanic coming on monday with his test machines so we can do a joint diagnosis.

    I have been changing things one at a time to see if the trouble bank swapped with the item. Only doing one at a time, then re-testing.

    Dk motors have been cleaned and they operate like each other (if I feel their movements while someone pushes the pedal).

    MAF's I've swapped over but will do so again to check

    DME's input cables have been swapped over

    I still want to swap the fuel lines over at the back of the rails and to eliminate fuel as a problem. I've noticed that at the front the small pipe on the left hand side rail (as you stand in front of the car and look at the engine) is kinked, perhaps the fuel cant get through to cycle round? Worth a check.

    Could lambda sensors cause a whole bank to fail? Physically taking these out and swapping over is worth a go, but I'll wait till said man pops round so we can see what his machine says.

    Exhaust - mine has a cross over pipe in the middle which makes things trickier but now I know about it I'll be checking the temps at the manifolds when testing.


    (The garage that I now dont trust have some diags machines, he did mention something about a CPS not showing RPM at some point, but this was only once and he thought a glitch. Could be the problem? We'll find out on monday)


    Thanks for everyones input it helps to talk though my experiments. Working on my own with limited tools, after a days work and chasing a fault around under the influence of petrol fumes, well we've all been there but it really makes a difference to have some e-help

    Nath

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    one more thing

    I see that you have replaced the distributor caps and spark plug wires (very good idea), but your post mentions swapping the coils ...
    If the coils are old I suggest that you also just replace them. They do fail with age and can cause disasterous problems with the DME modules. I don't know that they are the cause of your problem, but it is a fairly inexpensive way to avoid even more confusion as you continue the search.
    Thanks for posting your findings here - it will probably help many other owners in the future.
    Best wishes,
    Mark W in mid-MO
    2008 335xi coupe
    1993 850Ci 6-speed

    2 turbos ..................or 12 cylinders, no waiting!

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    Agreed! I would use new coils if the original

    one's codition is really unknown - there isn't a good way to test these under load (and that is where they fail-causing the bank to shut down).

    To eliminate the DME itself, swap over the plugs in the E-box and see if the problem swaps sides swaps sides, if yes, then possible DME damage (can come from faulty coil)...

    ...and the beat goes on.

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    Re: Agreed! I would use new coils if the original

    dme swap does not change the bank

    coils I have 4 of these now error does not swap sides when swapping them - and the error is most manifest at idle

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    ++ Mobile car electrician results ++

    Well we did not find the exact problem!

    He also thinks it could be the throttle bodies, so I've grabbed a pair off ebay at £170 (good deal thank heavens). I'm going to swap those in when they arrive and see. TB can not be swapped side to side as they are handed.

    Occasionally DME for cyl 1-6 would throw a knock sensor error. Once he got something about a valve and assumed perhaps throttle body, but there is apparently no real check that the car can perform on the TBs.

    Temp was wildly out, he thought it was his machine misreporting.
    Fuel pump wiring re-checked and seems ok. FYI ground on the pumps is direct to ground and from BMW original diagram the order is relay, fuse, pump (I'd wondered about this)

    One of the DME's occasionally would not appear. The system booted him out a few times. We swapped the dme harnesses over and the situation / idle did not change.

    The idle timing angle was all over the place changing 320 - 40 - minus 47 280 etc all the time. The injector timings were also changing 1.2 to 4.5 up down. His thoughts is that this is getting feedback

    At the end he said its a weird one, offered to drive around a bit with a more advnaced computer thing and monitor the engine as its going, however I think that the problem is worst at idle. Mentioned doing the coast down reset. Will do it again once I've got the new throttle bodies in as I've already both done it and been driving around 40 miles and to my mind it should have fixed itself.

    Does anyone have knowledge of knock sensors causing a die/surge idle problem?

    How about the temp sensors, can this cause a regular almost die then surge at 2 second intervals?


    Thanks for all your help guys. This board in its entirety is easily 20x more knowledgeable than the best individual mechanic!

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    What kind of car do you have?


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    1991 850


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