Two years of intermittent hard starts, please help!

[ATB88]

81k mile car, have had it since 45k miles. For the first year it had always fired up beautifully with no hesitation or stumble. Two cranks then on, to a rock steady idle, every time.

After going in and re-timing the engine as well as doing a valve adjustment back in October, ever since getting the car back together, there has been some degree of hesitation in starting the car. Basically, it has a 60/40 chance of struggling for a second or two on start up. Sounds brutal for a second or two, but eventually does start. Sometimes it fires up perfectly first try with no hesitation. I can't seem to find a pattern in when it has trouble and when it doesn't.

Every one in a while (quite rare), the car will completely fail to start on first try (it'll just keep cranking but not catch). When that happens, if I stop for a few seconds and try again, it'll start right up on the second try.

Once the car actually starts, no issues, car runs great! At least, as well as a car with stock cams runs on a stock CSL tune. But in the 7 months between when this issue started and when I switched out the OE airbox for the CSL, the car seemed to be a perfectly running stock example other than this problem.

Here are relevant seeming parts that have been replaced in the last year/few thousand miles (all OE BMW or in a few cases OEM):

-plugs and coils (NGK OE and Eldor OEM)
-MAF (Bosch OEM) ---> recently replaced by Bosch MAP for CSL airbox conversion
-fuel pump (OE)
-fuel pressure regulator (OE)
-fuel pressure regulator vacuum line to manifold (OE)
-fuel filter (OE)
-fuel injectors and o-rings (Bosch OEM)
-fuel pump relay (OE)
-pre-cat O2 sensors (Bosch OEM)
-intake and exhaust camshaft position sensors (OE BMW and OEM VNE)
-crankshaft position sensor (OEM VNE)
-idle control valve cleaned
-most CCV related vacuum lines (OE)
-secondary air shutoff valve (replaced with new CSL with airbox conversion)
-both engine bay TPS (OE)
-Alternator (Valeo OEM)
-Starter (Valeo OEM)
-Battery

Compression and leakdown test gave fantastic results.

Any advice on what to look into here? The start of this problem coincided precisely with taking the valve cover off/back on, so I checked all of the electrical connectors involved with that job -- O2 sensors, ignition coils and that little ground wire on the exhaust side of the VC. All look good and feel properly secured. Maybe they need a closer look? Anything specific to look out for? Car passes VANOS test with flying colors, and I'm certain that the valves are in spec, as I re-adjusted while the valve cover was off for the timing job after which all of this started.

Thoughts and suggestions appreciated! Can post vids of hard starts if that would be helpful!

[Bigo1087]

Did you pull the fuel rail? Injectors would be my guess.

You could have a leaky one that doesn't hold fuel pressure when you turn off the motor, as well as the other fuel issues you mentioned

have a buddy who actually just had almost identical symptoms too who replaced his with a cleaned set,

[EzM3]

So, I'm Bigo1087's buddy. I had IDENTICAL symptoms! Started fine on a coldstart, but struggled on a warm start. It was the injectors. I thought it was the fuel pump, but after replacing injectors, it fire's up perfectly. It actually runs very smoothly now too- smoother than before. Swap those injectors out for cleaned or new ones and it will be perfect. Happy to see I can help someone else out with the same issue I had.

[ATB88]

Thanks for the response! Very interesting that you say this because:

1. 6 months before these startup issues even started, when the car was still starting perfectly, I actually pulled my injectors (60k miles) and got them cleaned in pursuit of an issue with poor fuel trims (which I've been putting off making a thread on), and put em back in. Car still started like a champ, no change in behavior. It wasn't until I did work under the valve cover 6 months after cleaning the injectors that these startup issues began, and I didn't touch the fuel rail/injectors when I did the work after which the issues started.

2. I actually put in brand new Bosch injectors two weeks ago. No improvement in start behaviour, still hard starts. For other reasons, I've actually removed and reinstalled the fuel rail and injectors 3 times in the last month, each time very carefully and cleanly, and there has been no change to my hard start behaviour. Still there.

So, I feel like I can promise you that the injectors themselves are not the issue, as the hard start problem didn't appear until months after putting in cleaned injectors, and still persists with brand new injectors that were installed this month.

However, I am open to the possibility that there's something up with the fuel rail itself. But looking at it while running, I can't see/smell any sort of leak, and visually all injectors appear to be completely properly seated, and the fuel feed line looks properly seated into the rail and has a new o-ring. I use a little bit of silicone lube on all of the injector o-rings before re-installation to make sure everything seats properly. All the clips look/feel properly seated.

Any thoughts on what to look for/test? Maybe fuel pressure in different scenarios?

[EzM3]

Hm. Based on all the work you have done, I'm inclined to say that injectors are not the issue. The only other thing we changed was the fuel filter, but that is the first thing to change when a fuel issue arises. My issue came up after I (stupidly, I know. Long story) ran the car to 5 miles till empty- I made it to the gas station, but it was empty for all intensive purposes. After that, I had my warm start issue.

I wonder if the pump picked up any crap that was at the bottom of the tank and filled the fuel filter. They are so inexpensive that I think you should throw one in just to see if you haven't already.

As far as testing the injectors go, I am pretty sure you can hook up a fuel pressure gauge to the rail. Run the car, turn it off, and see if you hold pressure- it should. I think the injectors solved my issue because I'm certain I had a sticky injector.

I had a pretty scary experience which prompted me to get the injectors and fuel filter changed- when I was just cruising at 40 with some friends, my CEL came on and I had a terrible misfire- only when I hit the gas in gear (!!!). If I threw it in neutral, it revved fine (manual car). When I was coasting in neutral to see if it would go away, the car died- engine cut. I pulled over and it wouldn't restart, just crank. I let it sit for a minute and finally got it to run- with tons of smoke and unburnt fuel dumping out of the exhaust. I got the injectors changed immediately following.

You may not have this happen, but that seemed like an injector issue to me (leaky). I'd say
1. Change the fuel filter for sure
2. Pressure test the rail and see if you have any pressure loss after running.

Let me know what happens.

[ATB88]

Hm. Based on all the work you have done, I'm inclined to say that injectors are not the issue. The only other thing we changed was the fuel filter, but that is the first thing to change when a fuel issue arises. My issue came up after I (stupidly, I know. Long story) ran the car to 5 miles till empty- I made it to the gas station, but it was empty for all intensive purposes. After that, I had my warm start issue.

I wonder if the pump picked up any crap that was at the bottom of the tank and filled the fuel filter. They are so inexpensive that I think you should throw one in just to see if you haven't already.

As far as testing the injectors go, I am pretty sure you can hook up a fuel pressure gauge to the rail. Run the car, turn it off, and see if you hold pressure- it should. I think the injectors solved my issue because I'm certain I had a sticky injector.

I had a pretty scary experience which prompted me to get the injectors and fuel filter changed- when I was just cruising at 40 with some friends, my CEL came on and I had a terrible misfire- only when I hit the gas in gear (!!!). If I threw it in neutral, it revved fine (manual car). When I was coasting in neutral to see if it would go away, the car died- engine cut. I pulled over and it wouldn't restart, just crank. I let it sit for a minute and finally got it to run- with tons of smoke and unburnt fuel dumping out of the exhaust. I got the injectors changed immediately following.

You may not have this happen, but that seemed like an injector issue to me (leaky). I'd say
1. Change the fuel filter for sure
2. Pressure test the rail and see if you have any pressure loss after running.

Let me know what happens.

Yeah, all good thoughts, but filter's also 5k miles fresh (as is fuel pressure regulator). Our fuel rail actually doesn't have a test valve on it like the M54. Annoyingly, on our cars, the fuel pressure testing port is on the fuel pressure regulator housing, which is under the car at the fuel filter. Unfortunately I can't get under the car for the next few weeks, but plan to when I can and will update on results if this issue isn't solved otherwise.

Not ruling out fueling entirely, but, how about non-fuel-system related possibilities? Again, the start of this issue coincided exactly with getting under the valve cover for re-timing and valve adj -- nothing in the fuel system was touched. Could absolutely be a coincidence, but, anyone have ideas on what to check based on that?

[ATB88]

Bump bcs this makes me sad :[

[Dash1]

You can pop your valve cover and see if the timing is off. Worn spark plugs, coils. Could be a dying fuel pump, could be a lot of things really.

You could run a VANOS test if you have inpa or ista +

[ATB88]

You can pop your valve cover and see if the timing is off. Worn spark plugs, coils. Could be a dying fuel pump, could be a lot of things really.

You could run a VANOS test if you have inpa or ista +

Yes it could be a lot of things, but I've ruled most things out already: Engine is freshly re-timed with good VANOS adaptations, passes VANOS test no problem in DIS, plugs, coils and fuel pump are all new and OE :[ I'm hoping to learn about the things it could be that I haven't ruled out yet, as I've run out of ideas.

[Dash1]

[TropicalM3]

Disconnect the MAF and see? Maybe it is dying.

[ATB88]

Hm. Based on all the work you have done, I'm inclined to say that injectors are not the issue. The only other thing we changed was the fuel filter, but that is the first thing to change when a fuel issue arises. My issue came up after I (stupidly, I know. Long story) ran the car to 5 miles till empty- I made it to the gas station, but it was empty for all intensive purposes. After that, I had my warm start issue.

I wonder if the pump picked up any crap that was at the bottom of the tank and filled the fuel filter. They are so inexpensive that I think you should throw one in just to see if you haven't already.

As far as testing the injectors go, I am pretty sure you can hook up a fuel pressure gauge to the rail. Run the car, turn it off, and see if you hold pressure- it should. I think the injectors solved my issue because I'm certain I had a sticky injector.

I had a pretty scary experience which prompted me to get the injectors and fuel filter changed- when I was just cruising at 40 with some friends, my CEL came on and I had a terrible misfire- only when I hit the gas in gear (!!!). If I threw it in neutral, it revved fine (manual car). When I was coasting in neutral to see if it would go away, the car died- engine cut. I pulled over and it wouldn't restart, just crank. I let it sit for a minute and finally got it to run- with tons of smoke and unburnt fuel dumping out of the exhaust. I got the injectors changed immediately following.

You may not have this happen, but that seemed like an injector issue to me (leaky). I'd say
1. Change the fuel filter for sure
2. Pressure test the rail and see if you have any pressure loss after running.

Let me know what happens.

Finally got a chance to get under the car and look at fuel pressure. Replaced fuel filter and pressure regulator again for kicks (free, thanks FCP). Took pressure readings at the pressure regulator both with and without the manifold vacuum line attached. Pressure seemed to behave perfectly as expected -- 5 bar (without vac line) while running, holds at between 4-4.5 bar after turning the engine off. Behavior when turning the ignition on (but not the engine) is that the pump primes and the pressure shoots up to 5 bar, and then drops to about 4.5 bar and holds, and then when you crank/turn on the engine it goes up to 5.

Took videos showing behavior of fuel pressure on start up in both scenarios (with and without vacuum line attached to pressure regulator), and in both videos I was able to catch some hard starts.

In the instances where it hard starts, there doesn't seem to be anything out of the ordinary going on with the fuel pressure (in the cases where the regulator was disconnected from the intake, keeps an perfect 5 bar throughout the stumbling start).

With the line between regulator and intake disconnected: https://youtu.be/wwTBwz5oHU4 (hard start at 1:30)

with the line connected: https://youtu.be/ZRlEFfOa_r4 (first couple starts are hard)

These hard starts aren't as bad as some, sometimes it's stumbling a lot harder. But hopefully these give an idea.

Pressure appears to be to spec and isn't misbehaving during the hard starts, yes? Am I missing anything?

Disconnect the MAF and see? Maybe it is dying.

Did not help :[ MAF is also only a few months old.

To give you guys a better picture of what could be going on, here's a list of possibly related parts that have been changed out at least once in the last year and are basically new, all OE parts:

-plugs and coils (NGK OE and Eldor OEM)
-MAF (Bosch OEM)
-fuel pump (OE)
-fuel pressure regulator (OE)
-fuel pressure regulator vacuum line to manifold (OE)
-fuel filter (OE)
-fuel injectors and o-rings (Bosch OEM)
-pre-cat O2 sensors (Bosch OEM)
-intake and exhaust camshaft position sensors (OE BMW and OEM VNE)
-crankshaft position sensor (OEM VNE)
-idle control valve cleaned
-most CCV related vacuum lines (OE)
-both engine bay TPS (OE)

At this point it doesn't look fuel related, but if something in the vids looks off to you then interested to hear about it. If it's not fuel, then I feel like it has to be electrical or something? Some sort of loose ground somewhere? Bad connection on the starter (though I looked at that last night and everything there looked fine)? Alternator? Some gremlin in the wiring harness?

Would be grateful for any ideas on what to try next, this is really driving me nuts!

[ATB88]

Saturday bump! Anyone have any suggestions for what else to look at? The car sounds brutal when it hard starts (it's often worse than in the videos), and this is absolutely eating at me. Feeling desperate here, willing to try anything.

The starter itself is original (Valeo unit). Based on how things sound in the hardstarts in the videos could it be the starter itself? Not sure how a failing starter behaves/sounds. It sounds like it's cranking just fine during the hardstarts, just isn't catching..

Or how about the engine ground strap from the block to the chassis? Where even is it on this car?? Tips on how to test these would be appreciated :]

Would also consider recommendations for someone to take it to in LA who is talented with diagnostics.

Thanks in advance!!

[heinzboehmer]

Saturday bump! Anyone have any suggestions for what else to look at? The car sounds brutal when it hard starts, and this is absolutely eating at me. Feeling desperate here, willing to try anything.

The starter itself is original. Based on how things sound in the hardstarts in the videos could it be the starter itself? Not sure how a failing starter behaves/sounds. It sounds like it's cranking just fine during the hardstarts, just isn't catching..

Or how about the engine ground strap from the block to the chassis? Where even is it on this car?? Tips on how to test these would be appreciated :]

Based on the videos your starter sounds fine. When my starter went, it would simply not work sometimes. I would turn the key and nothing would happen.

[ATB88]

Based on the videos your starter sounds fine. When my starter went, it would simply not work sometimes. I would turn the key and nothing would happen.

Cool, thank you for the sanity check. That's what I figured, but, also what do I know ¯\_(ツ)_/¯ Definitely want to avoid replacing that unless I have strong probable cause, getting to those starter bolts is a bitch on jackstands.