Member
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...
Member
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
Member
Originally Posted by rjjablo
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.
Member
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.
Member
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...
Member
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.
Mad Scientist
Old pumps, bad check valves. Common issue.
Rarely wise to add extra circuitry, always better to fix the root problem.
'91 Dinan 860 Stage III (new 6L engine)
'91 Dinan 850 TT stage III (brand new engine) 21st Century Tech meets 18th Century Dinan...
'91 850i 6sp (mint) (sold)
'90 Dinan 750iL TT stage III (Guido - The Beast)
'94 850 CSi The Detroit Auto Show car (restored to factory perfect) (sold)
'96 850Ci, The George Carlin car
''73 3.0 csi, '08 535i, '03 X5 4.6is
...and a few other non BMW cars
Member
for testing purposes only
Did some experimenting.
Knowing the car drives very good and fuel pressure is OK when running.
The problem only occurs after a +20 minute drive and letting it rest for 1 hour.
If you leave it 24 hours, it starts up almost immediate.
Because it is a quick job I have installed “in line check valves” just before the fuel filters.
The problem was still there, no difference at all.
Only for testing I put together following:
Extra wiring to the 2 positive and 1 ground connection to the fuel pump assembly.
- 1 switch to the negative battery connection.
- 15A fuse & 1 push button to positive battery connection for fuel pump #1
- 15A fuse & 1 push button to positive battery connection for fuel pump #2
In this way I can safely operate both fuel pumps and listen under the hood how fuel is running.
I have been driving the car like this for a week now.
Using the buttons to “prime” the fuel system, just by pushing the buttons 1 or 2 seconds before turning the ignition and start.
It has been starting perfectly every time.
I will be ordering a new fuel unit from Ed, v12 Throttle in the future.
But for now, I kind of like the idea to have full control of the fuel pumps in this way.
I will install the buttons somewhere permanently and connect the wiring to the car’s battery.
I will be looking further into the fuel return,
because I am convinced the cause of the issue is to be found in that area.
Member
At this time, probably I ‘m writing to myself, but OK.
To finalize:
I replaced the two fuel pumps with 31€/p new pumps.
(level sensor works fine, housing has no cracks, already had new strainer)
Noticed the two short rubber hose connections in the unit where loose and brittle.
(no doubt those were leaking)
Car starts and drives perfectly now.
Each time, no difference if it was standing at rest 1 hour, 1 week,…
Member
Not so much writing to yourself, but think of it as writing to the future. Undoubtedly, someone will land here from search down the road, and they will be very thankful that you brought this to conclusion! The future-us thanks you.
Member
Just FYI, the pumps you installed will draw much more current than 1 to 2 split ground pin can handle heating it up and melting plastic around it in just a few months creating a leak....
The ONLY proper pump motor replacement for this assembly is the Bosch unit 69493
Member
Hi Ed,
Thanks for pointing that out to me.
I already took peace with the fact it is inevitable one day I will have to purchase a nice new unit from a certain https://v12throttle.com/ company.
So, until that finds place, better keep the tank filled up above the units level to help cool it down.
Strange though, and I am no expert, but isn't it the positive side that heats up in a DC circuit?
Hard to imagine +30 year old pumps would draw less current against brand new ones with same specs like pressure and (I think) flow.
The units I've put are (and I admit, far too cheap) replacements for the Bosch 69493 (0580314069, correct?)
These are STARK SKFP-0160125.
https://www.stark-automotive.com/cat...260659/8055294
Don't get me wrong, if (of all specialists) you say they are wrong, you are undoubtfully 100% right.
But, until my windows problem gets fixed, I decided not to throw much more money at it.
Member
The negative pin in the 3 pin connector is the one that will get hot to the point that it will melt the plastic around it and create a leak...Hi Ed,
Thanks for pointing that out to me.
I already took peace with the fact it is inevitable one day I will have to purchase a nice new unit from a certain https://v12throttle.com/ company.
So, until that finds place, better keep the tank filled up above the units level to help cool it down.
Strange though, and I am no expert, but isn't it the positive side that heats up in a DC circuit?
Hard to imagine +30 year old pumps would draw less current against brand new ones with same specs like pressure and (I think) flow.
The units I've put are (and I admit, far too cheap) replacements for the Bosch 69493 (0580314069, correct?)
These are STARK SKFP-0160125.
https://www.stark-automotive.com/cat...260659/8055294
Don't get me wrong, if (of all specialists) you say they are wrong, you are undoubtfully 100% right.
But, until my windows problem gets fixed, I decided not to throw much more money at it.
I am not familiar with your aftermarket pumps but every single aftermarket pump like hiflow for example will cause this issue.
I have rebuilt over 200 of these units prior to starting manufacturing new ones and saw this every time I received an assembly with aftermarket pumps installed.
As soon as that pin melts through the plastic assembly can be thrown in the trash.
Member
OK, so car drives great, engines runs like a dream.
Nevertheless, melting down the electrical fitting on the pump's housing, or just having the risk to make that happen is not acceptable.
For sure it will happen on a long warm summer drive, where I will be needing fuel delivered to the engine, rather than straight to my hot exhaust.
I read this topic about single pump use.
The switches an wiring I used before to operate/activate the pumps separately are still there.
I now have connected them in the way I can turn on/off each pump separately.
(in case one of the questionable cheap pumps would decide to call it a day and stop working)
Made this little modification before the 2 filters.
All works fine.
Emotionally it feels like the power is a bit less.
But that is just in my head, knowing one pump is off all the time.
(Played a bit with turning on/off each pump at a time or running them both simultaneously, absolutely no difference in engine reaction)
One concern, check valves. Will have to see how long those can handle continuous back pressure.
So, I hope now I can drive around with a clear conscience and not melt down pump housing.
One day however I will be ordering a nice new unit from https://v12throttle.com/ .
pomp2.jpg
Member
Please do not use a single pump set up on your M70 V12!!
I do not care if you buy my pump or repair your old assembly, I would just hate to see you destroy your engine....
There are several issues with this, first the OEM spec 100LPH pump doesn't have enough flow to supply the V12 with fuel at high load RPM, this will cause a lean condition.
The M73 uses a single pump capable of 140LPH for this reason.
Second, on the M70 in the event of component failure and limp home mode the ECU shuts down the pump, and NOT the injectors! Running a joint single pump will result in cylinder washdown and engine damage.
On M73 ECU shuts down the injectors to prevent this from happening.
Member
OP you are attempting to back-door solutions to problems which have already been examined in detail and solved by experts and validated by dozens upon dozens of custodians of these rare and quicky vehicles years before your appearance on the scene. You will do well not to deviate from the established norms for the many detailed reasons Ed has already given. You will regret it otherwise!
Member
Thank You Ed.
Point well taken.
So that 's a no go.
And with the recent words of a certain Sreten: Thank you for all your support to E31 owners.
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