Losing Fuel Pressure after shut down.. FPR or Injectors?

[TC Baur MD]

+1 for m20 ---> rebuilt M50 injectors. What a difference. Bought mine here

http://www.ebay.com/itm/BMW-E36-M3-325i-525i-323is-528E-Fuel-Injectors-M50-M52-Upgrade-for-M20-Engine-/201000247575?pt=Motors_Car_Truck_Parts_Accessories&hash=item2ecc8c6117&vxp=mtr#ht_2336wt_921

[Nutzy]

I have no check valve, pressure in the rail is like zero pretty much straight away. The motor starts instantly, even after a month of no use.

Good to see you found the culprit.

[digger]

i had a similar issue the engine would crank for a while on a hot start (ie when upto temp turn it off and try start again 5-10 min later crank, crank, crank....)

i had fuel pressure decaying to zero after considerable time 30min or so.

i checked ECU, FPR, pump and not until i replaced the injectors (borrowed a set for testing) and problem solved

during trouble shooting i sent the "faulty" ones to be cleaned and check and no problem were found.

the newer injectors that solved the start issue still behaved the same in that pressure decayed even though they weren't leaking.

not sure it matters about pressure falling since the pump is primed for a second or so when you put ignition on (IIRC)

there was something about the old injectors that didnt like a hot start but never found out what actually was going on just that newer injectors did the trick.

[Quinthirty]

I actually experienced this drop in fuel pressure resulting to hard starts. I noticed that the line connected to the FPR needed some tightening. No more hard starts.

[studawg]

Good thread, thanks for posting the results, I think I may have an injector issue....

[Alex Mc]

After 3 days of driving I am an say that the starting/loss of fuel pressure issue was definitely a leaky injector. Engine runs great now.

[Alex Mc]

I just finished replacing the blue stock injectors with green M50 injectors. I also swapped in an ECT sensor despite it testing out previously.

Of note, I also swapped the stock eprom for my hot chip..

Anyway, car cranked perfectly and has run fine for 20 miles. Hot start tests out great with a short crank time. Let's hope she's fixed!

[Madhatter]

If you ever suspected the injectors, just check your oil. You'll smell of fuel and the level will usually rise as the fuel contaminates the oil.

Mine used to go up about a litre of oil every couple of months before I swapped out for a new set of injectors.

[jeffnhiscars]

Also try clamping the return line while running & ck pressure, fuel pump (pumps?) may be weak. Pressure should jump up over 60 or so.

In case someone decides to try this it strikes me as HIGHLY dangerous and likely to cause something to blow with potentially disastrous results. We are looking at full pump pressure (not the lower FPR pressure) on a running engine.

[Earendil]

New VDO fuel pump, new Interstate battery, new Bosch fuel filter and new rubber fuel lines. The problem has not gone away.

Key clue: Engine starts perfectly when cold, long start when warm

I'm going to run a FP gauge under the wiper for a few days starting this weekend.

Any additional thoughts out there? Thanks.

Coolant Temp Sensor. Based on what you've replaced so far, and the difference in cold vs hot starts, that'd be my guess. The suckers are cheap too, so unless you know the age of the one that's in there, why not?

[Alex Mc]

New VDO fuel pump, new Interstate battery, new Bosch fuel filter and new rubber fuel lines. The problem has not gone away.

Key clue: Engine starts perfectly when cold, long start when warm

I'm going to run a FP gauge under the wiper for a few days starting this weekend.

Any additional thoughts out there? Thanks.

[Alex Mc]

I realized that if I just let the car crank long enough it will start everytime, which has me totally convinced that the fuel pump is simply on its last legs.

I ordered a new (VDO) fuel pump from Pelican Parts today, along with a new fuel filter.

[Alex Mc]

You can insert a check valve, but go back and read what I said about a good pump...

Jim, I did see that but was also not sure of the fuel filter's condition. Also, a check valve would confirm where I'm losing fuel pressure.

I'll put the new filter in and see what difference that makes in terms of cranking effort, and procede with a new pump if nothing changes...

[oldmann]

This is the #16 149 068 988 for a retrofit part, It goes inline at the fuel pump outlet. Looks like a piece of fuel line, with 2 clamps.

This was originally a fix for the E34, BMW dealer part, ask to have them ck availability of this part, most counter guys don't know what it is. I've never seen this part except at the dealer, less than $20.

[jlevie]

I haven't replaced the fuel filter but have one on order.

The car is a '91 318is so I've only got the one pump in the tank.

Do I have to replace the pump in order to replace the check valve? Could you not install that valve downstream of the pump (assuming the pump is in good shape)?

You can insert a check valve, but go back and read what I said about a good pump...