bloated feeling

[Durinck]

E31 850 1990 automatic
84.000km ( 52200 miles)

With this issue I am not (yet) at the end of things to inspect, however I was wondering maybe an expert would recognize the cause of the problem...
All help or suggestions are welcome, off course.

- Car has been standing +24H, takes a bit too long of a crank to start, but acceptable.
- Car has just been started, turned off after a minute, immediate restart, starts perfectly.
- Car has just been started, turned off after a minute, leave it for 1 or 2 hours, starts perfectly.
- Engine runs perfectly while driving short or long drives, after turned off and immediate restart, engine starts up perfectly.
- Engine runs perfectly while driving short or long drives, after turned off and leave it for 1.5-2 hours, restart takes far too long of a crank.

In this case the engine is really searching for petrol.
The moment it pulls through I hear a burbling sound in the petrol tank. (back seats are out)
Once it pulls through, it even struggles for a short time to run perfectly.

The time it takes for the engine to come back up in this case is longer than the time it takes to start when all petrol was drained from the fuel system.
The return line (fuel rail exit) is free. If I blow air in it, I hear burbles from the gas tank.
Until pressure is too high in gas tank. So pressure cannot escape from gas tank.
(car is off, batteries disconnected)

I open the fuel cap, all pressure releases from gas tank.
I noticed before there is a rather high pressure build up in the gas tank.

Tested by leaving the gas cap off, took a drive, let the car rest for 2 hours, tried to restart it.
Unfortunately with the same problem of the engine struggling to start.
So back pressure form gas tank might not be the cause here.

Fuel pump works like it should (no fuel return when not operating)
Fuel filters are newly installed
Rubber fuel lines are newly installed
I cleaned and tested all 12 (original injectors) + put new o rings on them.
Fuel pressure regulators are newly installed
I have no fuel leaks.

Fuel tank ventilation and charcoal canister not done yet.
(With the fuel cap off, this should not make a difference for the fuel line?)

I was of the idea the pressure build in the gas tank creates a too big of a back pressure to the fuel return.
Also, for some reason blowing air into the fuel return lines, maybe due to faulty parts further up the fuel system.
If this was the case, I should not experience the issue with the fuel cap off?
I have bought a fuel pressure gauche to see what is going on but did not yet use it.
When the system is empty the engine start is long but better then in the case where it has trouble starting up as described above...

[rjjablo]

I would measure fuel pressure while running

Then I would shut the car off and see if it maintains fuel pressure

Could be a split in a hose in the fuel pump

Could also be a crack in the fuel pump housing

[Durinck]

I would measure fuel pressure while running

Then I would shut the car off and see if it maintains fuel pressure

Could be a split in a hose in the fuel pump

Could also be a crack in the fuel pump housing

Yes, you are correct.
This is the reason why I got the pressure gauche.
To rule out parts of the fuel line.
I will measure between just before entering fuel rail and fuel pump.

However, a faulty fuel pump or cracked fuel pump body does not explain why I am having this issue.
The fuel system is self bleeding, so any air that would get into the fuel line due to faulty fuel pump would only cause a bad (longer cranking before) start up.
As explained, even with drained fuel system, such start is less "worring" then what I experience after a drive and having the car parked for 1.5 hours.

A total cold start 24 hours after a last drive, also not such bad start.

[dragon850]

I would say fuel pressure problem, put a gauge behind the engine fuel rails, in line.
It should read 3 bar when running. But very important after shut off it still should read 3 bar and not drop for at least 30 min.

[Durinck]

Hi Ed!
Yes, these are the kind of tests I will be doing asap.
As the car will only briefly switch on the pumps when ignition is on, I was thinking about putting a secondary power supply.
Parallel connection with a switch and a fuse to the wires that go to the pump.
In this way I can make the pumps work without having the engine on.
Or I can bridge the fuel pump relay?

Is this safe to do?
Not so much for the pumps.
But it will be difficult to explain to my wife why the house burned down...

[dragon850]

Hi Ed!
Yes, these are the kind of tests I will be doing asap.
As the car will only briefly switch on the pumps when ignition is on, I was thinking about putting a secondary power supply.
Parallel connection with a switch and a fuse to the wires that go to the pump.
In this way I can make the pumps work without having the engine on.
Or I can bridge the fuel pump relay?

Is this safe to do?
Not so much for the pumps.
But it will be difficult to explain to my wife why the house burned down...

Hi,
No, you will need to put the gauge inline with the fuel line at the back of the engine and measure with the engine ON.
You will need a 3 way T connector. It is safe as long as you clam everything down.

[cartoonz]

Old pumps, bad check valves. Common issue.
Rarely wise to add extra circuitry, always better to fix the root problem.