Fuel Pressure Regulator Fritzled?

[TheWolfman]

I am now embarking on my first foray into investigating the fuel system on my BAUR, something which I've not really dipped my toes in too heavily before. All started well when I ordered a cheap Fuel Pressure Meter on Amazon and all the valve attachments either leaked or broke instantaneously, I clearly forgot my mantra of 'buy cheap, buy twice' when I made that decision!After getting some PTFE tape and making all the fittings air-tight I could actually get around to taking a fuel pressure reading without fuel dripping everywhere, so that was good.

So at my fuel rail I'm getting a pressure reading of 2 Bar at the Injector rail input.According to the spec I should be looking at a Fuel System Pressure of 2.5-3.0 Bars and a Fuel System Hold Pressure of 2.1 Bars.

I'm a bit confused as to which of these values I need to be in the range of...if it's 'Fuel System Pressure' then I'm 0.5-1 Bar too low in pressure, whereas if it's 'Fuel System Hold Pressure' then I'm almost bang on:

So I then looked into whether my Fuel Pressure regulator was kaput.I removed the Vacuum line from the regulator and watched the Fuel Pressure rise by 1/2 Bar and the drop again when the vacuum line was replaced.This would indicate to me that the diaphragm was good and the regulator was working correctly.

Removing vacuum line from FPR - 0.5 Bar Pressure Increase:



Reading the Bentley manual however it states that if you clamp the fuel return line coming from the Fuel Pressure Regulator and the pressure reading rises then the regulator is knackered.In the following videos you can see this happening with both vacuum attached and not:

Clamping fuel return line with Vacuum line attached:



Clamping fuel return line without Vacuum line attached:



So according to the Bentley this is a faulty Fuel Pressure regulator and needs to be replaced.Is this because when the diaphragm is closed (maximum vacuum) the clamping of the line should have no effect and thus the diaphragm must not be closing fully or is maybe leaking?

Anyone seeking some info on this subject could do worse than watch this video, slightly odd dude but well presented information:

Fuel Pressure Regulator Diagnosis


On a side note, for some reason I'd never noticed until today that the Fuel Flap has a little bracket on it to hold the Fuel Cap.... That's neat!

[Brianmoooore]

The fuel pressure stated on the outside of its casing is the pressure that should exist between the the inside of the inlet manifold and the fuel in the fuel rail. You are measuring the pressure between the outside air and the fuel in the fuel rail.
There is a considerable vacuum inside the inlet manifold under the conditions that you are taking your measurements (idle or no engine load), so the reading on the gauge will be lower by that amount.
Pulling off the reference vacuum line makes the FPR reference to the outside air, so then the gauge should read what's written on the FPR.
When you clamp the fuel return line with the fuel pump running, the reading on the gauge will rise to the maximum that the fuel pump can produce. This reading is nothing to do with the FPR.

[TheWolfman]

Good explanation there Brian.This would explain why the pressure also rises to 2.5 Bar as that is what the FPR should be rated at.

I understand your explanation of why clamping the fuel return would increase the pressure, but wouldn't this just be the same as The Diaphragm on the FPR being shut?

What I guess I'm asking are two main things really:

A)What is the correct fuel pressure I should be achieving as Im not sure whether I need 2.1 Bar Fuel System Hold Pressure or 2.5-3 Bar Fuel System Pressure,I don't really know what the differences between these two are.[/color]

B) Is the Bentley manual correct and the FPR needs replacing?

[Brianmoooore]

The bit of text highlighted in blue says "IF the system pressure is too low........". Yours isn't, so this paragraph doesn't apply.
The pressure should definitely go through the roof is the hose is clamped at A, and the engine should run extremely rich.
The most important fuel system pressure tests are what happens after the engine is switched off. This may be what they refer to as system hold pressure.

[TheWolfman]

Well I'm not sure if my pressure is low or not, if the fuel pressure is meant to be 2.5-3 Bar as stated in Fuel System Pressure (relative to intake manifold pressure) then I am down by 0.5-1 Bar.

The pressure stays at 2 Bar when the engine is switched off...so holds pressure.I think you're right with this then,that must be what it's referring to with 'Fuel System Holding Pressure', 2 Bar would be the correct pressure, but then also insinuates that it should be 2.5 to 3 when turned on, in which case mine is low.

So in your opinion you don't think the FPR's a gonna?

[Brianmoooore]

You say your gauge reads 2.5 bar with the FPR vacuum pipe disconnected and engine running, which is spot on for a 320i.

[TheWolfman]

Yes, but pressure when it is connected though is 2 Bar.The spec says it should be 2.5 - 3 Bar.Fuel pressure should be 2.5-3 Bar when the FPR has vacuum connected and the diaphragm is open if I'm correct, or am I getting the wrong end of the stick?

If the hard-starting and still high-idle (1200 RPM) isn't to do with fuel pressure, then I guess the next port of call must be leaky or restricted injectors right?

[Brianmoooore]

If the pressure in the inlet manifold is 0.5 bar below atmospheric pressure (a reasonable figure to assume), then a fuel pressure gauge that reads 2.5 bar with the FPR vacuum pipe disconnected will read 2.0 bar when the pipe is reattached.
The FPR is referenced to the pressure in the inlet manifold because the sharp end of the fuel injectors are also exposed to this partial vacuum, and this arrangement keeps the pressure across the injectors constant, and therefore the amount of fuel injected the same for a given injector electrical pulse also constant, whatever the pressure in the manifold.
As I've said in another thread, an engine can only idle at a high speed if it can get the air to do so. The amount of fuel is irrelevant, in that it cannot increase idle speed, although, of course, it can bring it down and make it rough and varying, if the mixture ratio moves too far from ideal.
Leaky injectors is one of the things you are testing for by monitoring the fuel pressure after the engine is stopped.

[TheWolfman]

So you're saying that despite the gauge reading 2 Bar when the FPR vacuum is connected, this isn't below the 2.5-3 bar spec because of the assumed 0.5 Bar manifold pressure and that the FPR is fully functioning as intended?Aha yes of course ,if injectors were leaking then pressure would obviously drop quickly once engine is off. If it's not fuel pressure contributing to hard starting,I'm not sure what else it could be as spark is good new dizzy and rotor, plugs etc...

I'm completely at a loss now as to how any extraneous air could be entering the system,I have smoke tested it twice and the only vacuum leak was on the breather hose which was then fixed.I don't think I could have been any more rigorous with this so am confident that their are absolutely no vacuum leaks.Every other possibility I can think of is within spec, other than possible faulty AFM Air Temp Sensor.I'm starting to think that maybe because it's Automatic it just idles higher and I'll never get it below 1200......

[Brianmoooore]

The gauge reading with the reference pipe disconnected is the one that matters. The reading with is connected is more an evaluation of the condition of your engine - to an extent, the lower the reading with the pipe connected, the better the condition of your engine.
IIRC, your engine has part idle control by an 'air slide valve'. I'm aware of their existence, but have absolutely no experience of them, or ho w to set them up, other than knowing that they are not the most reliable of things.
Also, does your engine have #30 in this diagram? http://2009.bmwfans.info/parts/catalog/ ... ssembly-2/

[TheWolfman]

My 'Air Slide Valve' is working as` intended, although yes they are a somewhat 'unique' contraption! I posted a thread on here about it:

viewtopic.php?f=2&t=278104&p=2955980&hi ... e#p2955980

I guess it's good news that my engine seems to be in good condition then! So you reckon FPR is ok, and a pressure reading of 2 Bar is good, although it seems like its 1 Bar under spec?As I say though,I'm lost as to what could be responsible for the sometimes hard starting, as pressure builds the moment fuel pump is on...

I can't remember where but I did see something about E30 with automatic having a higher idle.

My engine doesn't have that part as I don't have a catalytic convertor on my motor.

[TheWolfman]

Sorry I was going a bit crosseyed then!!..yes I do have that part.It's a valve which momentarily pushes the throttle open on starting and once vacuum is achieved when the engine starts it retracts....it works as it's meant to.

[Brianmoooore]

The M10 318i had a lower idle speed specified for auto models, but Autodata only lists one for the 320i L-Jetronic, and that's 800 +/- 50 RPM, some 40 RPM higher than the Motronic version.
At 1200 RPM, I'd expect there to be quite a 'clunk' when you engage drive, since the torque converter will be transmitting drive at those revs, so that begs the question, are you sure that the idle is actually at 1200 RPM and not the tacho. telling lies? An instrument cluster with a four pot coding plug will read 1200 RPM at 800 RPM.

[TheWolfman]

Yep, you're right there,there is somewhat of a 'clunk' if that's what you technically call it.Maybe a 'smooth jolt'??

Well thats interesting you say that ,because I mentioned that in another thread regarding this.I wanted to get the Revs verified as I felt like the idle 'sounded right' and had a suspicion the tach may be off a bit... where could I find the cluster coding plug? This could end up being quite the funny ending to this saga...

You're still not committing to telling me my Pressure and FPR are ok though Brian....

[Brianmoooore]

Your fuel pressure and regulator appear to be in full working order from everything you've posted on here.
Coding plug can be seen by removing the front trim panel of the instrument cluster. It's in the lower right corner, and will have a part number on it which can be used to see if it is correct for your engine.

[TheWolfman]

Nice one Brian! Like I said you are without question 'The E30 Don'!

Trim panel by the headlight switches?I'll have a peek tommorow hopefully. One thing that leads me to think this is a possibility is that the tach seems 'lively' and can hit 7k quite easily when on kickdown

[TheWolfman]

I feel like a black sheep in 'The Zone', not only is the motor a 'lowly 320' but also an AUTOMATIC!!! The Horror!

[Brianmoooore]

Th trim panel directly under the cluster, that you have to reach up behind and spin the two knurled nuts off. (Put pressure on the front of the panel. directly in front of the nuts, and they spin off easily).
You may have to undo the two screws holding the bottom of the next piece of trim to read the numbers on the plug.

[TheWolfman]

So it looks like I don't have a 'Coding Plug' Per-Sé....as it's pre 1986 my 'coding plug' looks like this :

.....I have no idea where this goes, nevermind how it actually works!

[Cloggy Saint]

No idea what that thing is but the coding plug is #11 on the diagram. NLA from the dealer but I may have one spare if you need.

[TheWolfman]

Thank's for the kind offer Cloggy Saint but my cluster doesn't actually have a slot for the coding plug, that's why it's greyed out in the OEM diagram.I think it's because they were only fitted post 1986.Like I said i've got absolutely no idea how that 'coding plug' (that's what its's called in the diagram) works....looks a bit mental!

[Cloggy Saint]

They all have a coding plug! This is the part you're looking for.

[TheWolfman]

I can verify that they definitely don't ALL have a coding plug on the front.Early Pre '86 clusters do not as you can see here:

[Cloggy Saint]

Learn something every day!

[Brianmoooore]

That black plastic thing is the coding plug on early clusters, as Wolfman says. Where it fits is fairly obvious on the back of the cluster - the slot for it is still present on later clusters.
Unfortunately, I have absolutely no experience of these early clusters as well as air slide valves. I've no idea how this version of the coding plug even works, but since it appears to be no more than a piece of plastic, I assume it works small switches of some kind on the circuit board.
The good news is that they seem to be available for not much money.

[TheWolfman]

Everydays a s school day on here Cloggy Saint!Especially when Brian's involved...

After some investigation, that 'weird bit of plastic' works by basically bridging a circle of solder points on the back of the Tach's circuit board.Which points are bridged is dependent on the 'coding plug' you have and this sets the appropriate readings on the Tach.

They do seem to be cheap, but I can't really find much information on which one is the correct one although the OEM number is definitely the right one for 320i, it seems many people sell them for 316i with that OEM number which definitely isn't the correct one.On the right path though, I'll post more concise info on this in another thread as it's a whole new topic really, and clearly one that's shrouded in a bit of mystery.I also think i'll get the Rev's verified before I think about the Coding Plug as it means taking the whole cluster out, and in my experience the less fiddling with 'em the better!

Any more ideas on the sometimes hard starting if not fuel pressure issue?

[Brianmoooore]

Pity if it turns out that the tacho. is reading right! That would have been a simple answer to the problem.
One common cause of poor starting is leaking injectors. The leaked fuel makes the mixture drawn into the engine too rich to ignite until most of it has evaporated and been expelled out of the exhaust.
Leaking injectors are checked by monitoring the fuel pressure after the engine is switched off. Have you done this, and if so, how long is presssure maintained?

[TheWolfman]

Yeah,I'm kind of hoping the tacho isn't correct to be honest...As odd as that might sound!

Leaky injectors was my only other possible cause I thought of, but yes fuel pressure seems to be held pretty sturdy after engine shut-off, if the injectors were leaking I'd expect to see a significant drop in pressure pretty quickly right?