Occasional hard start - bad FPR?

[griffincox]

I have an '88 (built May, '88 ) 325is. 187k miles. Been sitting in storage for 6 months and finally got it out about a week ago. I knew it would need some fuel work as there was gas smells when I put it away.

I replaced almost all the fuel line and clamps, noticed a leaking injector and have had the injectors rebuilt by a reputable place in Denver. No more fuel leaks!

Changed the oil, new NGK plugs, new air filter, adjusted valves, etc. It runs pretty good. Some odd noises from all over (suspension, maybe some engine accessories, but otherwise runs good).

The issue: occasional hard start.

I know this has been discussed, and I have read threads, but wanted to get feedback on my situation. I will assume the pump is good, the filter is pretty new, but was not replaced, and the fuel pressure regulator I believe is original (says manufactured in W. Germany!). I want to say its the fuel pressure regulator leaking pressure off the rail causing the hard start. Seem reasonable? What other symptoms would a bad FPR cause, or what else can cause hard starting?

The old bosch plugs came out consistent across all 6 (yay!) but were a bit reddish? I can put up pics of sparks tomorrow if those would be helpful. How to tell rich vs. lean and which would a bad FPR cause?

Thanks for any help! :D

[jlevie]

The plugs will be very light color verging on white is the engine running lean and very dark to black if rich.

A loss of rail pressure while the car is parked is more likely to be a bad check valve in the pump than the FPR. It is easy enough to find out if the rail is loosing pressure by teeing a pressure gauge into the rail supply line.

[griffincox]

Thanks jlevie!

A little more info. Sat over night about 10 hours. Fired right up. Yesterday when hot, two different time sitting for 1-3 hours is when it would be hard to start. So more time didnt cause it, but maybe heat does? Ill keep updated as I learn more. Just got it running two days ago.

[jlevie]

Hard hot starts probably aren't going to be a loss of rail pressure. Intake leaks or a bad ECT sensor are more likely candidates.

[dnguyen1963]

I spent quite a bit of time chasing a hot start problem. In my case, it was the elbows going into the throttle body. The catch was that these elbows come loose then tight again when the engine generates vacuum. This problem magnifies when the car has been driven around, parked, and tried to start again. Try to wiggle these elbows in and out. If they are loose then JB weld the suckers in. If you want to find these leaks in smoke test, you need to get the engine hot then plug both the intake and exhaust before you can see smoke coming out of the loose connections.

[griffincox]

Hard hot starts probably aren't going to be a loss of rail pressure. Intake leaks or a bad ECT sensor are more likely candidates.

Good to know. I figured an intake/vac leak.

I spent quite a bit of time chasing a hot start problem. In my case, it was the elbows going into the throttle body. The catch was that these elbows come loose then tight again when the engine generates vacuum. This problem magnifies when the car has been driven around, parked, and tried to start again. Try to wiggle these elbows in and out. If they are loose then JB weld the suckers in. If you want to find these leaks in smoke test, you need to get the engine hot then plug both the intake and exhaust before you can see smoke coming out of the loose connections.

Those elbows are loose. I know that. This weekend I will JB weld them in and put on some new silicone hose to the brake booster and any other areas that need it.

Thanks!

[griffincox]

Okay. So it's gotten worse. By quite a bit. This am it took quite a few minutes to get it going. At lunch was less difficult. Had to add a bunch of throttle both times. Once running it idles pretty well for an M20 and run great under throttle.

[griffincox]

And after lunch fired right up pretty much. I am still suspicious of fuel. Either too much or too little. If the diaphragm of the FPR goes bad and leaks fuel into the vac line it would effectively flood right? And if the FPR or the valve at the pump bleed off pressure it would take the pump a while to build pressure? The pump would rebuild though within what 5-10 seconds. This is way more dramatic than that.

[griffincox]

Okay. Issue persists. Starting after sitting for a long period is very difficult. Must open throttle almost 100%. Starting after the engine has just been running is quite easy. So, too much or too little fuel is my diagnosis. Is this accurate?

I ordered a new Bosch FPR and Mahle filter. Will install next week. This weekend I will secure the elbows at the throttle body and inspect for any other potential air/vac leaks. Wouldn't a vac leak cause very poor idle? It idles and runs great once running.

I also plan to put a fuel pressure gauge on the rail. I think I will find a loss of pressure but will update. If the rail looses pressure, the options are leaking injectors, leaking FPR or leaking check valve at pump, correct? How to narrow down between those 3?

If I find pressure is normal even after extended sitting what's the next step?

[griffincox]

So. Put a pressure gauge on the line. It's a cheap harbor freight one that leaks at one of the threads so I didn't leave it on long, but at shutdown it went from 40psi to 0 instantly.

I already have a new FPR And filter on the way. I am pretty sure you are right Jlevie (as always, haha). I think at 188k I'd rather just replace the pump and be done.

To clarify there is only one pump, right? Just the main one which is BMW 16141184022?
And that part has the check valve in it?

[griffincox]

Also for future troubleshooting here is what I found:

Full tank of fuel keeps a little more pressure on the system as a whole. Helps the issue.

Cool ambient temps prevent vaporization of fuel in the rail and keeps more of it liquid. Helps the issue.

Long crank will eventually start it.

One more question... Does the pump prime when key goes to run? I didn't hear it or see a spike in pressure at key on. Normal?

[TC Baur MD]

Fuel pump is activated when the engine is cranked

[studawg]

Hey OP, did you eventually fix the problem?