Fuel pressure drop

[HenryM3]

Finally got my arse in gear today to try and find out why I have hard starting on warm engine. Got a fuel pressure gauge and connected in the boot on pump outlets. Switch on pump and get solid 5 bar. Switch off and it drops quickly to around 3bar and after an hour it’s 0 bar. Activate pump again and clamp feed line. Same results. Repeat and clamp return line. Same results. So concluded that injector/s leaking. Removed fuel rail and run pump, same results and the injectors aren’t leaking. WTF.
Clamped the return line just after the FPR and switched on fuel pump, holy shit 7 bar. Switched of pump and released the pressure. This time switched on pump got 5 bar switched off pump and clamped at FPR. It’s been 2 hours now and pressure has only dropped to 4.6 bar. My conclusion at the moment is that clamping return line at the pump end just allows the return line to fill up and allows the pressure to leave the rail. So the fault is with the FPR.
I’ll see what it like in the morning. I’m hoping for at least 3.5 bar left after an overnight sit. As I’m in no hurry I’ll probably buy the "o"rings and see if that fixes it and if not get a FPR.

[MrBenn2]

Interesting follow up to what we chatted about the other day concerning the FPR, so the 5 bar pump managed much more than that?

[HenryM3]

Yes, my understanding of it now is that the pump is capable of way over 5 bar and it’s the pressure regulator that maintains the fuel rail pressure at 5 bar so there’s always a fair bit passing through it and returning to the tank. Mine did actually hit 7 bar. So obviously the 3.5 bar pump is capable of pumping in excess of 5 bar. Just having to work at the top end of its ability.
After 4 hours last night it was at 4.2 bar and this morning it was 3 bar. So ordered the 2 "o" rings to see if that sorts it, if not I’ll get a regulator. At BMW they’re £147 but the same Prieberg elsewhere is £47. The bloody "o" rings are £11 must be made of some special material sent back from Mars.

[DanThe]

If its not starting due to fuel then i would expect to see air at the injectors when you are trying to start, or no pressure rather than just low pressure
When you turn the ignition on does the pump prime for 2 or 3 seconds? It should do and you can check this with your test setup to see how quickly pressure is built

[HenryM3]

Thanks for that, if the car has sat for around 6 hours or more then as soon as you put the ignition on (not start) the pump will prime for 2/3 seconds and you will have a full 5 bar and instant start. The problem is there seems to be an area around the 20 minute siting that when you put the ignition on the pump doesn’t prime until you try to start. Then there is a 3/5 second delay/turning over before the car starts, alternatively you can flick the starter and try again and get instant start. Now on the grand scale of things this is a minor irritant. But people on here will appreciate how annoying something like this is. It is my hope that the "o" rings or ultimately a FPR will fix this. As DanThe man suggests I’m leaving the gauge connected to check that pressure holds for more than 20 minutes. I do have EWS and initial thought this was the problem but it doesn’t show any diagnostics codes.

[HenryM3]

Just done the "o" rings, sod all different. Next step is send for a FPR. Out of interest what would be the normal pressure drop on a 3.5 bar pump after switching off.

[HenryM3]

What are peoples thought on Meat & Doria parts. Everywhere is out of stock of Prieberg.

[DanThe]

I would be trying to get the priming function to work rather than trying to hold the pressure in the system.

At the 20 minute problem area if you turn the ignition off/on again will it then prime?
Also do you have the EWS chip fitted to the E30 key? Ive had several setups where the chip is taped to the antennae ring shoved up under the dash that have done some strange things, its always best to have it so the chip is taken away from the antennae and then brought back as it would when in the key

[HenryM3]

I have the 2 ignition barrels and have to insert 2 keys. It doesn’t matter whether the car sits for the 20mins with the keys fitted or I come back to the car and insert the keys the pump doesn’t prime. I have read that the pump is supposed to prime as key is turned to start but that theory sort of goes to a bucket of shit if it primes after 6 hours sitting.. I doubt there is a timer in the ECU which resets after about 6 hours. Although that theory would work if the system held pressure for that time.

[DanThe]

You should be able to turn the ignition on and off as many times as you like and the pump prime each time you get to the ignition on position

[HenryM3]

I thought that, but it doesn’t happen. First cold start primes 100% of the time. Bearing in mind that after 30 minutes there is 0 pressure so therefore should prime but it doesn’t. Any suggestions gladly accepted. I haven’t done any electrical checking. Don’t know where to start really.

[DanThe]

You mentioned that you switched the pump, does that mean you have to manually turn the pump on every time you start? If so how is it wired?

[HenryM3]

When I said I switched it on I had the relay out and a jump wire just to get it to pressure up again. I suppose I should get the multi meter out to see where the power to the pump stops after the initial start.

[MrBenn]

Been working on mine today. Tried to do a few tests for you.
Mine does not prime every time I turn the key. It will prime the first time. If I start the engine and quickly turn it off and on again it also won't prime on the next start (or not obviously for a few seconds) but it starts immediately.
If I leave it for a few (say 5) minutes it will prime again for few seconds.

[HenryM3]

That’s really brilliant of you to do that. So I must have a wiring problem, as I have it in bits atm I’ll look at the wiring after the FPR turns up from AUTODOC. I can discount the ECU as I have 2 and both act the same way.

[MrBenn]

You are very welcome. I hope it sheds some light on the matter.

I had a strange problem this morning where the ignition switch not wanting to play ball. At first nothing, then after a few tries a few lights would flicker, then a few gauges would move..... then the fuel pump fired and after many tried it finally started. Just throwing ideas out there

[HenryM3]

I’ll try and spend some time tomorrow with a multimeter to see when and where the pump gets power.

[DanThe]

When I said I switched it on I had the relay out and a jump wire just to get it to pressure up again. I suppose I should get the multi meter out to see where the power to the pump stops after the initial start.

I expect it will be at the relay, the relay has an ignition live Red/White from the main white relay, the output is Green/Purple to fuse 11, the switch is triggered by an earth signal from the ECU

[HenryM3]

On the electric side I’m confused. This first pic is the earth wire for the fuel pump relay.
If I do a continuity test from where I’ve bared the wire to the relay I get a reading of .450. If I add an earth to the relay I get continuity and the buzzer.

With the added earth the fuel pump runs every time the ignition is switched on/off. Which would probably solve the hard start problem. Won’t know for definite till I fit the new FPR when it arrives. Can anyone tell me why or is there a reason why I get a reading of .450 on the multimeter. As you can see there are two earth wires joined and I don’t know where the other one goes to or what component it earths. Would I potentially doing the other component/s harm by having a full earth to the fuel pump relay.

[MrBenn]

As my ignition was being weird yesterday, I'd be more inclined to believe Dan, who says it should prime every time. But Wait for an answer from the experts.

Mine doesn't have EWS anymore. I was wondering if you always take both keys out? And if that might be something to do with it?

[HenryM3]

Dan, I just looked at a wiring diagram and see that the earth at the relay is triggered from pin 69 on the ECU, problem is that it switches the earth on at cold start, pump primes, engine starts. If you switch off and try to start it doesn’t trigger the pump again till you start cranking. I’m reluctant to replace the ECU earth with a chassis earth as that would have the pump running permanently the ignition is on. I assume the cold start prime is linked to the coolant temperature sensor. Perhaps if the new FPR holds pressure for a while it will be enough to do the job, maybe, should do, I hope so, fingers crossed, etc etc.
Yes I do always remove both keys.

[Brianmoooore]

Dan, I just looked at a wiring diagram and see that the earth at the relay is triggered from pin 69 on the ECU, problem is that it switches the earth on at cold start, pump primes, engine starts. If you switch off and try to start it doesn’t trigger the pump again till you start cranking. I’m reluctant to replace the ECU earth with a chassis earth as that would have the pump running permanently the ignition is on. I assume the cold start prime is linked to the coolant temperature sensor. Perhaps if the new FPR holds pressure for a while it will be enough to do the job, maybe, should do, I hope so, fingers crossed, etc etc.
Yes I do always remove both keys.

Pull the plug off of the temp. sensor to check. Disconnected sensor = very cold engine, as far as the ECU is concerned.

[HenryM3]

Cheers, I’ll do that tomorrow

[HenryM3]

No joy, so it doesn’t get the info from the temperature sensor. Not doing anything else till the FPR arrives .

[HenryM3]

I haven’t given up on this as I have been back and forward to Ireland as my mum is very ill in Enniskillen hospital. Priorities an all that.

[HenryM3]

Well the FPR arrived and got fitted, Used a jump wire to prime the pump and see how the pressure held up. 100% better, holding over 3 bar for hours. So with uplifted spirit I refitted inlet manifold an all the other bits and car wouldn’t start. I had fuel, wet plugs, no spark. To cut a long story short I discounted the crank sensor because it was new 6 months ago. Big mistake, buy cheap buy twice, eventually bunged in an OEM and it started instantly. Hard hot start seems to be fixed. Maybe not as instant as when pump primes on cold but quick enough not to be annoying. It was more annoying that the crank sensor packed up while working on something completely unrelated.