1990 BMW E30 325i - Trouble Starting after Car

[chomowitz]

I have a 1990 BMW E30 325i. Recently I have had starting problems. It seemed to come on all at once.

The symptoms are that, after the car has sat for a while, the car turns over (battery and starter okay), but does not start. If I let it continue to turn (10 - 15 seconds), it eventually starts (but reluctantly). After it starts ... If I turn it off and retry starting immediately, it starts right away. When driving ... The engine seems to run fine (no sputtering, hesitation or lack of response). The problem is centered in that first start after sitting for a while.

I have done some reading and have tried the following ...
1) Replaced E30 Main ECU and Fuel Pump Relays
2) Installed external fuel check valve at Fuel Pump (under rear seat).
3) Replaced Distributor and Rotor
4) Inspected, cleaned and gapped spark plugs.
5) Checked and cleaned air filter

None of of these solved the problem. After I switched the relays (1. above), the problem seemed to go away, but it then returned a day or two later. I should also mention that the problem seems to be getting worse. Initially there were days when it would start right up in the morning. Now the problem seems to be there everyday and often after sitting for hours. Note that I live in a warm climate (FL), so being cold due to outside temperature is not an issue.

If someone could give me step by step troubleshooting from most likely to least likely, I would appreciate it.

Thank you in advance for your support ...

[D.Martijn]

I'm guessing it's your fuel pressure regulator (FPR).
Does is run rough the first few seconds when you are able to start it up?
I had the same symptoms on my 325iX. Pull the vacuum hose off and see it there is fuel leaking out.

[chomowitz]

Thanks for the input. I disconnected the vacuum line and there was no fuel in the line or coming out of the FPR.

[MrBurgundy]

you might have a leaky fuel injector that bleeds off the fuel pressure after it sits for a while..

after it sits for a while, pull each plug out and see if you can smell gas on any of them.

[chomowitz]

Thanks for the suggestion to pull plugs and smell for gas. I have a reduced sense of smell and there are gas smells already around the car from working on it.

Can you suggest another way to test if there is an injector problem?

[D.Martijn]

Testing the fuel pressure. See if it drops down a lot after letting the car sit for a few minutes.

[chomowitz]

I did a fuel pressure test. I installed a T on the fuel line to the injector rail.

I got the car to start and let it idle for a few minutes. While idling, the pressure read 36-37 psi. I then shut it down and monitored the pressure. Below is a table of what I found ...
Car shutdown ~37 psi
+ 27 minutes 32 psi
+ 39 minutes 28 psi
+ 44 minutes 26 psi
+ 67 minutes 20 psi
+ 93 minutes 18 psi
+105 minutes 16 psi
+133 minutes 0 psi

Another observation ... When I tried to restart, I'm pretty sure that fuel did not start to run until after letting the starter crank for 15 - 20 seconds. I measured the voltage on the pin that goes to the fuel pump and it shows 12 volts with the ignition key turned to start, but I didn't hear the fuel pump buzzing. Do I have two problems?

[D.Martijn]

The fuel pump only runs when the engine is cranking (via the crank position sensor)

[chomowitz]

I did some other reading and testing and found that what you say is correct. Fuel pump only runs when engine is cranking.

Since my last update, I disconnected the external check valve I had installed at the fuel pump. I found that it was not fully blocking fuel from running back. I decided to remove and return it to the vendor. The system is now in its original configuration which relies on the check valve in the fuel pump (I think the fuel pump check valve may be faulty). I'm not sure where to get a reliable check valve that will prevent fuel running back to the tank. The one I had in there was this one ... https://www.amazon.com/Muzzys-Non-Re.../dp/B01LY7WD50 . Any suggestions?

By the way ... I am running another fuel pressure test with the system in its original configuration (no external check valve).

[D.Martijn]

Try to read out/replace the blue temp sensor, here's a data sheet.

http://www.bosch-motorsport.com/media/catalog_resources/Temperature_Sensor_NTC_M12_Datasheet_51_en_2782569739pdf.pdf

Could be your injectors leaking also.. maybe there is some dirt/gunk on the nozzle causing it to leak? You could try using a fuel additive to clean them.

You should be able to test your injectors by isolating them from the fuel pump like so;
(It's better when you are with 2 people.)

When the assistant shuts the car off, clamp the pressure line and watch the pressure.
If it no longer continues to drop, then you likely have a faulty check valve in the fuel pump or your FPR isn't closing fully.

[digger]

Here is a simple check. After the car had sat for a while and would give problems if you crank it, try to INstead first prime the pump by jumping the relay then crank it . If that works many times without issues then it's probably your issue. Otherwise it's the injectors imo. What can happen is when the injector is hot ( gets heat soaked after sitting) and at low battery voltage ( during cranking) the coil cant respond properly to the pulse width requested by the ecu and you get inadequate fuel delivery. It seems the stock injectors are prone to this. This is exacerbated by higher fuel pressures as well. When I had the issue a new set of injectors cured my issue. I played with fpr, fuel pump, ecu, checked injectors for leaks and all that stuff. Of course I borrowed a set of injectors before Buying a set to check it out.

[chomowitz]

To test if it is the injectors leaking, I installed a fuel on/off valve between the fuel pressure gauge and the fuel rail. With the valve on, I got the car to start and let it idle to get to full pressure.

I then shut it down and quickly turned the fuel valve off so that the gauge was only monitoring pressure between it and the fuel pump.

Within 1 hour, the pressure went to 0 psi (from 36+ psi).

I repeated the test, but this time left the valve on and the pressure fell again within one hour to 0 psi. The same as when I tested with valve off.

This seems to indicate that the problem is between the pressure gauge and the fuel pump, i.e. the check valve in the fuel pump is bad.

Since I had a faulty external check valve the last time I purchased and installed one, I am hesitant to buy another (that MAY leak as well). I'm leaning toward getting a new fuel pump, as the check valve failure may mean the whole pump will fail in the future.

Comments?

[D.Martijn]

OEM BMW check valve part no 11631707770

[Mpolito3355]

To test if it is the injectors leaking, I installed a fuel on/off valve between the fuel pressure gauge and the fuel rail. With the valve on, I got the car to start and let it idle to get to full pressure.

I then shut it down and quickly turned the fuel valve off so that the gauge was only monitoring pressure between it and the fuel pump.

Within 1 hour, the pressure went to 0 psi (from 36+ psi).

I repeated the test, but this time left the valve on and the pressure fell again within one hour to 0 psi. The same as when I tested with valve off.

This seems to indicate that the problem is between the pressure gauge and the fuel pump, i.e. the check valve in the fuel pump is bad.

Since I had a faulty external check valve the last time I purchased and installed one, I am hesitant to buy another (that MAY leak as well). I'm leaning toward getting a new fuel pump, as the check valve failure may mean the whole pump will fail in the future.

Comments?

This is a great idea ....sorry no input on that except the internal but just wanted to say im going to keep this idea in the back of my head so thanks for that ^^ also any pics of your on/off valve???