I've got a real challenge for you guys!

[ELVA164]

Alright, so I'll lead with the symptom: My car will take much longer than usual (5 seconds?) to start rarely, and will only start if I apply full throttle when this occurs. Otherwise, it starts on the normal ~6 compression strokes no problem. This has occurred since I bought the car about 4 years ago, in all weather.

Now for what I've done to the car.

New stuff:
Intake elbow
ICV (well, refurbished)
Vacuum hoses around brake booster and throttle body
Cap
Rotor
Wires
Plugs (NGK ZGR5A)
Valve cover breather hose
Valve cover gasket

Other things I've done:
Used multiple ECUs, both Motronic 1.1 (153) and 1.3 (173, 380, 527) with no changes
Performed a smoke test, fixed leaks, confirmed with a second smoke test


Other than this one thing, the car runs like a charm. Idles perfectly, revs freely, pulls well, all gauges work (correctly), and so on.

If anyone wants other info, let me know! It's such an odd issue I'm curious if it sounds familiar to anyone.

[Das Delfin]

in no particular order.. tps, fpr, cps. Check valve in fuel pump

Sometimes mine takes a while to start (only when hot) and pressing the gas helps sometimes. Other times it will start on its own after cranking for a few seconds. What I mean is if I hold the key in the start position to crank over and over it wont start, but if I hold the key for a few seconds and let go, it will start after letting go. It's reall weird. But it's not a huge problem, only happens sometimes, and I have a work around

[dude8383]

Have you had your injectors serviced? Have you done a compression test?

[ELVA164]

Forgot the injectors, they're rebuilt M50 units. I have not done a compression test. There's like a flowback valve in the fuel pump, is that what you mean?

I can hear the TPS functioning and have tried two with no changes, but I guess I can't 100% rule that out.

Would a failing FPR or CPS act up once every, say 45 starts or more but be completely fine the rest of the time? Because that's how this is.

To explain what happens a little further: Most of the time, I crank for about 6 compression strokes and the car starts right up. No issues at all. When it doesn't work, the car cranks for 4-5 seconds and will eventually start, but the time between it starting to catch and fully catch is longer. So it takes longer to start...starting, then takes longer to fully catch and idle.

Also, whenever this happens and I don't wait for the car to start, it will start up immediately if I crank the key a second time. It's never taken more than two attempts.

[dnguyen1963]

The only time this had happened to me was when the fuel pump started to go. You might tee in a fuel pressure gauge to check the pressure when cranking.

[Das Delfin]

If it always starts the second time, it sounds like a fuel pressure issue. Either FPR or the pump itself. The pump's check valve also affects fuel pressure, that's what I mean

[ELVA164]

Update!

The full throttle thing is a total load, it has no effect whatsoever. It happened to me this evening and after cranking a bit with no throttle, it slowly came to life. I adjusted my front toe a little beforehand, so maybe it's an issue with the tie rods.

[AndrewBird]

I had this problem in my E34. Tried everything and everything and finally the thing that fixed it was putting a check valve inline with the fuel feed just after the fuel pump. Haven't had a problem since.

I used this guy with two of these:

https://www.amazon.com/gp/product/B001NKS48G/ref=oh_aui_detailpage_o09_s01?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B00DE7JTVC/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

Sealed them with this stuff:

[ELVA164]

Interesting. Now Das Delphin mentioned there's a check valve integral to the pump; would your situation support the theory that it may be not working properly?

[dereliiict]

Update!

I adjusted my front toe a little beforehand, so maybe it's an issue with the tie rods.

Lololololol

[TobyB]

so maybe it's an issue with the tie rods.

Oh, most definitely... bwahahahah!

If it's not the backflow valve on the pump, (which it might be)

then it sounds like your injectors have postnasal drip. The running roughly thing
after a hard start is one of the bigger indicators- you have a fuel- soaked cylinder or 3,
and it/they are taking a while to dry out.

my thought.
t

[ELVA164]

Oh, most definitely... bwahahahah!

If it's not the backflow valve on the pump, (which it might be)

then it sounds like your injectors have postnasal drip. The running roughly thing
after a hard start is one of the bigger indicators- you have a fuel- soaked cylinder or 3,
and it/they are taking a while to dry out.

my thought.
t

Is there any way to test that valve if I were to remove the pump? I'd obviously like to avoid buying a new one until I know it's the culprit.

The car doesn't run rough at all, it just takes a second to clear its throat when this occurs. After it catches, it idles perfectly and doesn't hesitate at all.

[ThatOneEuroE30]

My m20 car has similar issue I have it down to the fuel system. I'm just replacing it all since it needs done


Sent from my iPad using Tapatalk

[Ether-D]

I like the leaky injector theory. Does it smell rich when it hard starts?

[ELVA164]

There's a bit of fuel smell, but nothing you wouldn't expect from the car cranking and not starting at first. Remember, it's behaved identically with the original injectors and the rebuilt M50 ones.