Fuel Pressure problems?

[richy187]

My M20B25 has developed a strange problem, when I move to overtake, or try and rev past about 4-5k RPM I just lose all power and the engine makes a rumbly noise.

Its intermittent, but because I only do short runs so not sure if it clears when its warmed up properly. I but will be going for a good run tomorrow to see if that helps.

I have changed the Injectors for freshly restored standard ones, and replaced the very tired looking vacuum hose on the FPR with a brand new genuine one from BMW. I checked the resistance across the pins on the blue temp sensor this morning and cold it was exactly 4kOhms.

It seems fine throughout the rest of the rev range which leads me to suspect its a fuel pressure problem.

The only other weird thing is the state of the connector on the injector nearest the bulkhead, it has some brown gunk on it:



All the other injectors look fine.

anyone know What else could be wrong?

[mrLEE30]

remove the rear seat base, then open the small oval cover behind your driver seat, under here you will see the fuel pump, try driving around with this open and listen for a very loud buzzing noise (they do buzz a little but if it sounds like a hornets nest then this could be on its way out)

[mrLEE30]

How can you tell that from nz Will?

[richy187]

I can hear what sounds like a hissing noise from outside the car, would that be the fuel pump on its way out? I will check this tomorrow thanks

Just been for a long drive in it, and it doesn't seem as bad when its fully warmed up, revved fine all the way in 2nd, and less of a cutout more of a stutter in 3rd

[mrLEE30]

A fuel pump on it's last legs normally buzzes , and they also tend to get worse as they get warm. If it's only a hiss then as will suggests check the fuel filter and also the fuel presure regulator, but the latter can only be replaced unless you have a fuel pressure gauge. Does the car idle ok? When did you last change plugs, filter etc?

[richy187]

I did a complete service around 5000 miles ago including coolant all filters spark plugs etc. I still haven't pulled the plugs out to see if its lean/rich I will try & do that today.

Its my daily again now, and I only do 3 miles in it each way to work & back, I went out for a good hour in it last night and gave it some stick once it warmed up properly which I haven't done since September last year, and the hissing seemed worse than normal.

I am thinking its the fuel pump now, it seems to make sense as everthing else has been changed fairly recently. I don't have a fuel pressure guage everything on this engine is standard, I will do the test with the back seat out today, to try and confirm/eliminate the pump, if thats OK i might be able to borrow an FPR off a facelift M20B25 engine to save me from buying one if thats ok, will this fit/work on my pre-facelift engine?

[mrLEE30]

My pump packed in few months back and the noise was quite loud with seat off, the noise was also not a constant noise, it grew louder then quiet, but when first started it was fine. Try to borrow a pump too, 5 min job to change.

[richy187]

Just took seat out & cover off went for a drive, and although it was making a noise it wasn't loud at all. My mate round the corner has a spare engine, I doubt he has a spare pump as well, but I will ask.

Still struggling more when cold, it won't rev through it, but when warmed up a bit it stutters, but will still rev up more.

Its pishing down here now so I won't be pulling the spark plugs out until next weekend, and I'll see about getting my mates FPR off him then too.

I was planning on doing an oil change soon, so I will probably change air + fuel filters again while I am at it to see if that helps.

Thanks for your help

[mrLEE30]

Then look to fuel pressure regulator and check the distributor for cracks in the housing or rotor, or pitting of the contacts. Failing this then you need a fuel presssure gauge To check running presssure 3.2bar and check for the pressure drop over time. Not sure what spec is on this. Last resort is compression check.

[richy187]

From chatting to another friend who used to have a pre-facelift 325 I have found out I have 2 fuel pumps, one in the tank, and one just in front of the N/S rear wheel. I think it could be the external one that is beginning to fail and causing my problem.

could that be causing the hissing noise I can hear outside the car after a long run? Its definitely louder on the passenger side of the car.

[Brianmoooore]

With the two pump system, the external pump becomes noisy when the pump in the tank fails.

[richy187]

AAaaaaaaaaargh! I kind of already knew that I suppose, so now I have a dilemma...

Which fuel pump do I change?!?!?!

[Brianmoooore]

Take a wire off of the external pump, link together 30 and 87 on the fuel pump relay, and see if the in tank pump runs.

[richy187]

I'm not going to be able to look at this until the weekend now, will the engine still get enough fuel to run if the in-tank pump fails completely?

Where is the fuel pump relay?

Sorry, I'm a total electrophobe

[Brianmoooore]

The engine will run with the in tank pump failed.
Fuel pump relay is a four pin one (usually orange) under a lift off cover beside the air filter.

[Jim320i]

My chromie had exactly the same issue... The external pump is very loud and still is, but I never got round to sorting it and now its off the road and on my list of jobs to do. But when i first got here, on the drive home she kept loosing power then kicking back in when ever I tried to put my foot down a little. With a little help from Capri_rob, Brianmooore and a few other zoners, they advised changing the fuel filter and it sorted the problem out of the revs dropping off.

So just need to try what brian has advised above on mine too which I may do tomorrow.

[Kedge]

Jim, guess what i noticed kicking around in my garage earlier!?!?
Will keep it aside for you if your intank pump has actually failed.

[Brianmoooore]

Both pumps can be replaced by a later single in tank high pressure pump, plus a bit of minor plumbing and wiring.

[richy187]

The engine will run with the in tank pump failed.
Fuel pump relay is a four pin one (usually orange) under a lift off cover beside the air filter.

Thanks Brian, you're a legend,

I will test as soon as I get a chance (but probably won't be until the weekend

[PeterGreen]

I didn't realise they had two pumps; I thought that was a diesel thing. My '86 V8 also had a very loud external pump with intermitted problems (normally when warm) involving loss of power, as if not running on all 8 cylinders when under load, however an external Bosch pump with boot mounted fuel tank has sorted it.

[Brianmoooore]

Just to complicate things, some pre facelift stuff, with external pumps, apparently didn't have a low pressure pump in the tank. The way to check is to look under the access cap under the rear seat and see how many electrical connections there are. If it has a pump there will be a two pin plug to that, as well as the three pin one to the level sender.

[richy187]

I had the cover off at the weekend, but can't recall how many wires there were, i might be able to check at lunchtime tomorrow though.

Thanks all

[richy187]

I didn't realise they had two pumps; I thought that was a diesel thing. My '86 V8 also had a very loud external pump with intermitted problems (normally when warm) involving loss of power, as if not running on all 8 cylinders when under load, however an external Bosch pump with boot mounted fuel tank has sorted it.

Only just noticed your post Greeny, Thanks for the input but not sure a fuel cell is the way to go for me ££££££££££

And its a road car!!!

[richy187]

Right, it looks like I only have an external pump...



There is only one electrical connector going in to the petrol tank, and this is the fuel level sender correct?

[richy187]

Fuel filter not blocked?

Changed the fuel filter based on this advice on Saturday and problem is now resolved.

Many Thanks!!! Its great to have the old girl running right again