My 89 325i 117k mi runs exceptionally well, pulls to redline, starts instantly, returns ~21-25mpg with a heavy foot.
Quite rarely it will have hard starts that feel to me like inadequate fuel pressure - turn over with nothing then catch and run 100% okay. This happens infrequently enough to be a non issue. I've changed the fuel filter but not done any other testing. Battery is new and very strong. Fuel level never below half.
In the Polar Coldpocalypse (1 degree F) things got a little worse. I felt dead spots off idle then she actually died while driving. Pulled over, had a hard start per above then all good. Has been 100% since. However this inspired me to take some action. Do the later M20 cars have a test port for fuel pressure? Is the regulator a likely culprit?
I am in general all tuned up valves adjusted, relatively new plugs, cap rotor etc, intake boot replaced, no vac leaks to my knowledge, idles like glass.
I've had the exact rare hard start you're describing, with everything else in similarly good shape, and I've never figured it out. I agree it seems like random loss of fuel pressure at the rail. Admittedly, I haven't taken the time to test it mostly because I haven't wanted to, haha. My car also stalled for the first time a few days ago when it was so cold, then felt a bit rough for a second when I restarted it before smoothing out and being 100% fine again.
Very odd.
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Wow good to know I have company! Even if we're both stumped...
The other reason I suspected fuel pressure as a problem is I want to say the rare hard start coincides with when I sit down and instantly twirl the key to start without letting it build fuel pressure by leaving the key at 'run' for a sec. It also seems that trying to start immediately after the hard start leads to more hard starting and letting it sit a few seconds helps.
I don't really read a huge number of threads on FPR replacement/problems so I'm not sure if its worth throwing ~$100 at the part for its own sake but I don't love the idea of the problem stranding me.
I suppose as I write this what comes to mind is that the fuel pump is working a whole lot harder than the regulator and that might be the part to throw $160 at before the regulator...
Last edited by somecarguy; 01-26-2019 at 02:19 PM.
Interesting thread here: https://www.bimmerforums.com/forum/s...ght=hard+start
I'm going to check those vac lines now.
Do you every get a slight 'hunt' in idle? At very cold temps I do, even as I pull off and load the engine I can feel a little surging. 10 seconds under load its gone and everything is A-okay.
To test the fuel pressure on a 325i, you need a fuel pressure gauge, a Tee to fit the fuel hose, another short section of hose and 2 clamps. Remove the fuel hose near the thermostat housing that goes into the fuel rail, not at the FPR, attach the Tee to this hose, the other end of the Tee to the short hose which clamps back to the fuel rail. Then attach the gauge to the Tee. You can test fuel pump and the FPR. Proper functioning is about 43 PSI. When you close off the hose on FPR the pressure will go considerably higher. When you shut off engine, pressure should stay around 43 for approx 10 min or longer.
I had an occasional hard start when warm, longer than normal cranks, then it seems as if a couple of cylinders would fire then the rest would follow. Sometimes even after the long start, it would trigger those cylinders then not start.
When i replaced the clutch a few days ago, i replaced the O2 sensor as well since the exhaust was out and access was a lot easier.
It now cranks and fires up right away when cold or warm, however with 209,000 kms and the original O2 sensor, i was expecting smoother engine response and better fuel economy, looks like start up "fix" was due to a seriously bad O2 sensor for me.
O2 sensor is an interesting idea...
OP, the fuel pump doesn't start in these cars until you start to crank the engine.
I've found, for whatever reason, I can get the car to start during a long crank if I floor the throttle. I can't explain it, but it is repeatable.
Last edited by ELVA164; 01-31-2019 at 08:50 PM.
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Ill need to check the Bentley but on the 911 with similar Motronic the 02 sensor was not an input to the ecu until operating temp was reached. I will need to pay close attention now to whether or not I get this problem at cold starts. 02 replacement never a bad idea on an old car...
Thanks re: fuel pump.
Last edited by somecarguy; 01-27-2019 at 11:19 AM.
The vacuum line to the regulator looks sound but taut as though someone has trimmed and refit it at some point. Ill likely re do that and give it new fuel lines while im at it. Are you guys using Gates products or other for fuel lines?
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I’m looking at how the regulator works and trying to think what opening the throttle would do while cranking. I want to say i do this too. I suppose that would allow some vacuum to reach the regulator thereby helping the diaphram open thereby increasing fuel flow presuming that something is preventing the pressure of fuel as supplied by the pump to sufficiently depress the spring loaded diaphragm. Presumably because it is old and crusty or suffering from extreme temperatures
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Wait a minute I have that backwards when the diaphragm moves it would presumably allow more fuel to return to the tank? So if the spring weakens over time there would be lower fuel pressure?
I definitely In that case do not have a theory about the throttle opening
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Because the regulator is at the end of the fuel rail it would seem that it’s failure mode would come from a diaphragm sticking open or a too week spring allowing too much fuel to return to the tank and insufficient pressure at the rail.
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You have more vacuum at idle in the manifold than at drive speed, dont you? So the regulator probably getd held open for less pressure at idle and closes to allow more pressure at higher rpm
No e30s again.
As a man who detests an intermittent problem I got a new fuel pressure regulator, 8 x 13 fuel line and vacuum hose. This ought to tell me if the regulator is the source of the problem.
How difficult is it to replace the engine bay fuel lines in a 1989?
Last edited by somecarguy; 01-31-2019 at 08:08 PM.
Not at all difficul
Access the aft portions from below? Anything need to be removed?
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It's pretty straightforward, as long as the pipe end isn't corroded and the clamps are alright. I'd say get the bottom of the hoses from underneath, but they're easy to reach once you're there. Thanks for doing that research. I wonder if the TPS could be a factor? I'm fumbling in the dark when it comes to that stuff.
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Id expect some manifestation of drivability issues with a tps bug. I guess my feeling is the cold and or hot starts have more exposure to a fuel pressure issues than electric. Leaking fuel injector seals could be a place to check. Either way ill update the thread.
Thanks for advice.
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I know mine at least is not injector-related, as it happened the same way both before and after I had my M50 injectors rebuilt and I installed them (correctly, I suppose I have to say). Looking forward to updates.
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Yeah when I had the injectors from the 911 cleaned and balanced (similar mileage and year) The report came back that they were pretty much within 5% of new. I suppose renewing the O-rings is always a good thing.
This replacement was not difficult. The fuel lines were in quite bad shape the line at the rail started leaking while I was unscrewing its clamp(first pic). Both lines showed some cracking. I can’t really say if the regulator had any problems or not I suppose if doing this again you could replace the lines leave the regulator and see what results. Restarts are impeccable but then they always were pretty good. I will report back if the long cranking problem returns.
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How much did the new regulator cost you ? The new vacuum line ? And yes on an M20 the replacement is a 5 minute job. Gotta love the M20 - important things were not hidden and jammed into tight places like the M50x.
Reg was not cheap, bout a hundo. Fuel and vac lines were very affordable and left me with extra. Used oetiker clamps.
That is expensive. But you'll never have to bother about it again.
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