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4B90 insufficient fuel pressure at engine start

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50K views 11 replies 5 participants last post by  Alan G  
#1 ·
car is a 55 plate 320cd with approx 155k/m on the clock.

Problem has been ongoing for months now, totally and utterly intermittent, noticed a few weeks ago that car would start immediately if i could hear the "hummmmmm" coming from the passenger side floor, which meant i could avoid the embarrassment of sitting and cranking the car to no avail 30 times on a morning.

past week the car was "fine" and by that i mean the pump would prime within 3/4 turns of the key and away i went.

changed the pump yesterday for a new one and the problem has somehow GOT WORSE!!!! unbelievable.

so far iv'e swapped



green relays in the glove box, both work fine regardless of which is connected

new pre supply pump and filter

camshaft sensor (was told this can cause starting issues)

im a few hundred quid out of pocket and no closer to understanding why the pre supply pump is only intermittently turning on with the key

i have access to INPA software and a few other coding tools, from there i looked at the values for the injectors and 2 of the 4 were far higher than the other 2, but all 4 were in the green.

I fail to see how this can be connected to the pump priming, am i wrong here?

im at my wits end tbqh, need the car for one more year until i qualify in my trade and then i can resign it to the scrapyard in place of a van, but until then i rely on it heavily to get me from job to job, and this intermittent issue only serves to infuriate me.

please help !:confused:confused:confused:confused
 
#3 ·
3 months on and no closer to a solution, completely and utterly at a loss.

Injectors came back as within spec but i did change the worst one out for a recon unit, all now showing as good in ISTA

new pump installed in the tank, this has changed nothing, as expected.

fuel pressure sensor on the rail changed, nothing.

past week the car has gone from bad to worse, and it was utterly shit before.

Today i checked EACH AND EVERY fuse in the glove compartment, i also changed the green relays over for good measure, i checked the 5 fuses that sit inside the DDE compartment of the engine bay and not one of them was broken/dirty etc

Using the ISTA software i CAN make the fuel pump relay click on, but that still wont give me the pre-supply pump *hmmmmmm* i need to get the car going.

Also used the ISTA software to check the status of the key, all comes back as fine and the key is communicating with the EWS module as it should.

With ignition on in position 2 i am getting between 2-4 psi of pressure on the rail (actual) but the car says (desired) is around 400, this doesn't change until the car is running where it stays between 380-420 psi until i turn off the car.

Car will drive utterly fine until i reach my destination, from there it is a complete gamble whether i will be stranded for 30 minutes trying to get it going again or it might just fire up immediately.

Today it left me sat in the supermarket car park for 25 minutes, when i got home i immediately shut it off and on again, i did this about 15 times, 10 of those times it burst into life no qualms, the other 5 it sounded like it was turning over really really fast but simply would not *catch* and start.

I am completely and utterly at my wits end with the car and would smile from ear to ear to wake up to it missing.

If anyone can give any insight into the procedure the car goes through to start the pre supply pump i would be forever grateful, i feel as if i am chasing a ghost around a dark room whilst throwing money at it yet all it does is laugh at me and call me a cu*t.

I need this car to see me through one more year of college, after that id happily turn it into a washing machine myself, but until then i would prefer to drive it.

Please help,

Matt.
 
#5 · (Edited)
Okay, So....... I have read what i believe to be every English language post on the internet regarding this issue, i would now consider myself a certified BMW technician.

The issue ALL ALONG was the fuel pump relay which sits BEHIND the glovebox.

BMW ista+ gives the location of the fuel pump relay on my vehicle as relay #1, every post i have read on the internet gives the relay as slot 1 also

Well, i have changed everything on the car, it's been in bits more times than i care to remember, so today i figured **** IT, i have absolutely nothing to lose, so using the BMW ISTA+ software to control the relay switching on and off i worked out that i have been changing the wrong fucking relay all along........

Image


my salmon relay is #3

horn is #4

FUEL PUMP #2

A/C #1

i have come back here with an update because there is nothing more annoying than a half finished thread where OP states he will be back with future updates but never posts again.

to anyone suffering this terrible vehicle affliction PLEASE ensure that you are 100% positive you are changing the correct relays......

I could have saved myself days and hours of fault finding and hundreds of pounds in costs, had i just verified first 100% what i was changing.
 

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#6 ·
Oké, szóval........ Elolvastam szerintem minden angol nyelvű bejegyzést az interneten ezzel a témával kapcsolatban, most már okleveles BMW technikusnak tartanám magam.

A probléma MINDENKÉPP az üzemanyag-szivattyú reléje volt, ami a kesztyűtartó MÖGÖTT található.

A BMW ista+ megadja az üzemanyag-szivattyú reléjének helyét a járművemben 1-es reléként, minden bejegyzés, amit az interneten olvastam, megadja a relét 1-es helyként is

Nos, mindent megváltoztattam az autón, kicsit többször történt, mint amennyire emlékszem, így ma arra jutottam, hogy **** IT, nincs vesztenivalóm, ezért a BMW ISTA+ szoftverrel szabályozom a relé kapcsolást. be- és kikapcsoláskor rájöttem, hogy mindvégig rossz kibaszott relét cseréltem......

Image


az én lazac váltóm a 3

a kĂĽrt a 4

2. ĂśZEMANYAGSZIVATTYĂš

A/C #1

Frissítéssel tértem vissza ide, mert nincs bosszantóbb egy félkész szálnál, ahol az OP kijelenti, hogy visszatér a jövőbeni frissítésekkel, de soha többé nem posztol.

Mindenkinek, aki ebben a szörnyű járműválságban szenved, KÉRJÜK, győződjön meg arról, hogy 100%-ig biztos abban, hogy a megfelelő reléket cseréli...

Napokat és órákat takaríthattam volna meg magamnak a hibakereséstől és több száz font költségtől, ha először 100%-ban ellenőriztem volna, hogy mit változtattam.
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