Fuel pump not priming

[zidney1]

Hi All,

My 1986 325i has stopped making the priming noise before turning the ignition on. As a result, its a pain to start as takes a few starts to build up some fuel pressure.

I have changed the relay (should I try another?) but fear it could be ECU related..

Any ideas?

Thanks in advance

[e30daniel]

i seam to have this problem too. i turn the key and i cant hear any audible hum before starting.mine also takes a good few turns before it kicks into life. is this normal or am i experiencing the exact same problem as zidney here aswell.
thanks

[leeparkes]

E30's dont 'prime'

[e30daniel]

ahh ok. thanks. had me worried there lol

[Brianmoooore]

If lack of fuel rail pressure is the problem (only checking with a gauge can tell!), then either the fuel pressure regulator or the non return valve in the fuel pump is leaking. BMW do a separate non return valve that fits in the fuel line near the pump as an alternative to replacing an otherwise healthy pump.

[zidney1]

Thanks very much Brian, I'll get the pressure checked and take it from there. I'll report
back..!

[zidney1]

Hi,

The fuel pressure is ok. Which I guess makes sense as after a few cranks, enough pressure is released to start. If the car is switched off and started again its fine which backs up the pressure being ok.

I'm not sure if I'm, using the right term in 'priming' but before cranking the engine a noise would appear (I thought this was the priming phase) and after a coupel of secondsthat noise would stop I'd turn the engine and the car would start straight away.

That priming/noise phase is now not happening..?

[Brianmoooore]

The rail should be up to pressure before the engine cranks. It should maintain the pressure from the last time it ran.

[bobbin1982]

did it do it with little petrol in the tank?...
As the fuel pump is more noisy with less fuel in it
Just a thought



Andy

[zidney1]

Thanks Andy and I thought that too mate but its does it with a full tank..and even if I park it at an incline!

Brian, just to be clear if its not maintaining pressure initally but is ok after pressure is built up, the non-priming is due to the fuel pressure regulator or the non return valve in the fuel pump is leaking?

[blue30]

Mine primes, but not every time. Sometimes with the ignition you hear the pump come in for about 2 seconds and go off again. Sometimes not. I assumed it was either some kind of timer or other random voodoo that decides to either prime or not... Not a lot of help I know!

[zidney1]

Sorry to hear you've got the same issue mate but this is definately the place to find the solution/voodoo cure!

[Mikey_Boy]

A random thought here - your 'priming' noise you have heard in the past... Is it the ABS pump activating?

I checked this on my 325 - ABS makes a noise on ignition on. No fuel pump priming - gets up to 3 bar during cranking.

Just a thought to add to the thread...
Mikey_Boy

[blue30]

Mine hasn't got ABS, its definitely the fuel pump that primes. I should also mention that it starts fine even when it hasn't primed though!

If you try to take a fuel line off on the pressure side without de-pressurising the system first you'll get fuel spraying everywhere - should do anyway!

[12345kevin]

As this is an '86 car it would of had 2 pumps, the main injection pump just in front of the NS wheel behind the sill and a "lifter" pump in the tank. My '86 cab did.

[zidney1]

Hi All,

Thanks for your replies and apologies for the late update..

I fitted a new pump in the end but the problem of not starting on the button is still there. That makes it a new pump, new TDC, Blue and brown sensors checked and the ECU checked.

Any more ideas? Just a shame as now it has a new cam its a different car and sounds and drives superbly (pics and write up to follow)..just the starting issues lets it all down..

[Brianmoooore]

You need to get a fuel pressure gauge connected up and see if it maintains pressure when parked.
Would have been a lot cheaper than throwing unnecessary parts at it!

[zidney1]

Thanks Brian. The pump was on its way out as developed a very annoying humming noise. I had been putting it off for a while so thougt (hoped) it would cure both issues..annoying noise has gone but the issue at hand reamined.

will get the pressure checked again and report back.

Thanks

[Brianmoooore]

If this is a two pump set up, the usual reason for the main pump becoming noisy is failure of the in tank pump.

[zidney1]

Hi Brian,

The latest is that the presssure has been checked by the mechanic and is ok. He checked the ecu and relays too which were also fine.. any more clues?

[Brianmoooore]

If it maintains pressure while parked up, then the assumption you made in the OP is wrong, and everything since in this thread is irrelevant.
A more likely cause of poor starting is one or more injectors leaking and flooding the engine initially.
An E30 engine should start on the first firing stroke after the crank sensor has shown the ECU where TDC of #1 and #6 cylinders are.
Have the injectors ever been serviced in this car's quarter century of life?

[zidney1]

Actually yes, I had them serviced at injecter tune..

[Brianmoooore]

If the injectors are good, and the fuel pressure is up when you start cranking, it should fire up immediately! Very strange.
Has the operation of the throttle position switch been checked?

[zidney1]

I know! Its so annoying and has the mechanic baffled too - especially since he knows the car for years and recently spent hours rebuilding the head. He is as keen as me to get this last glitch sorted!

The throttle position switch hasn't been checked.. What signs should I look out for here?

[Brianmoooore]

Short circuit across two of its pins when the throttle is closed, becoming open circuit shortly after it's moved off of its stop. One of the pins and the other pin should become short circuit between half and two thirds throttle.

[zidney1]

Problem solved.

Sorry its taken so long but here is the full story...

My friend (a BMW teccie) had a leaving do where I met a few teccies and one who happened to be the worlds best BMW Master Tech (apparently BMW used to run a worldwide competitons to test them and the winner was crowned the best. This event is no longer running so by default he retains the title..pretty cool eh). Anyway he and another ex BMW Tech and now independent specialist (www.west3ltd.com) heard my issues and as they were from the 'old school' understood it straight away and informed me that BMW did a modification to solve the issue.

Its called the 'leaner mod' and bypasses a part of the ecu and attaches to the temp sensor and consists of a relay..actually I'll post some pictures up of it.

Anyway, it was a pain to get hold of as the old school mechanics and parts advisiors are few and far between but I have part numbers and instructions.

The result? My cars starting is vastly improved and is as smooth to drive as its ever been.

Thanks all for help with this..esp Brian.

[Brianmoooore]

This BMW "bodge" uses a relay to switch a resistor in parallel with the 'blue' ECU coolant temperature sensor when the starter motor is engaged, fooling the ECU into thinking the engine is partly warmed up, and so reducing the fuel injected.
I thought this mod was only used on 2.0 litre engines though, not the 2.5.

[zidney1]

Thats right, I was pretty impressed with it.

Yeah, the instructions cover the 2.5 lump with different resistors available to lessen/heighten the desired effect.

[Brianmoooore]

I use a similar "bodge" on one of my LPG powered cars to stop the petrol ECU telling the LPG ECU to inject extra gas on a cold engine. LPG powered cars don't need the engine destroying excess fuelling on a cold engine that a petrol powered car does.