Hey everyone, have a problem that's just getting worse, have done what searching I could and haven't found anything concrete (but I might have an idea).

Every cold start (starts fine once warmed up), it tries to die (think it actually has once or twice). The initial start is fine, then it chugs and sputters, the ECU tries to adapt, sometimes it will recover fine, sometimes I have to give it gas (which sometimes works, not always). It'll do this about three times before it smooths out. This started last year, and has been getting progressively worse.

The only cel codes I've had recently were for the cam sensor, replaced it, code came back, read that it could also indicate a failing crank sensor, replaced that as well, no change.

I have quite a few mods and a tune by Adrian, the tune hasn't changed the startup behavior in any way, which leads me to think it could be something mechanical, or a sensor that's not throwing any errors.

So, my first rough guess is the throttle body, maybe injectors? Seems to only happen when it's in the cold start loop. Runs great once it gets through the rough start. I also think my header flex pipe has a leak in it, wondering if the escaping exhaust could throw off O2 sensor number 1 and therefore my startup air/fuel mixture?

Hoping the hive mind here might help to shed some light or point me in the right direction.

Any help appreciated, thank you in advance!

 

Start with the basics: Fuel pressure check, compression check, etc. I would also check the wiring between the crank/cam sensors and the ECU
I doubt it's related to the exhaust leak or O2 sensors. The ECU ignores the O2 sensors during the first few seconds after start-up because they don't give an accurate signal until they've warmed up (that's why they have builtin heaters, btw)

 

Would check battery voltage before cold start, should always be 12.6V minimum. If it's low can still crank but play hell with the electronics for a bit. Also, not sure the mods and tune combination, but are plugs OEM or have you gone to colder ones per the whole package? Any codes being thrown?

 

Have you tried running a can or two of injector cleaner through your gas tank? If you have varnish buildup in your injectors they would not be flowing to capacity. Your flex pipe leak is also a likely culprit since your AFR would be affected.

 

My thought was also/possibly clogged injector screens and or spark plugs. How does #2 look on the coil pack?
Fuel pump issue perhaps (? - I have no experience). When was the last time you serviced/replaced your fuel filter?

*I preformed a fuel injector refresh (new screens and O-rings) on my set of Seimens Deka 380's with a kit from injectorguy.com.
I was surprised to find that 2wo of the screens had collected a little bit of crud. I imagine if I had I not done the refresh it may have resulted in performance or starting issues.

I'm no expert.
Just a thought.

 

The behavior suggests a fuel problem. Monitoring fuel pressure before engine start and continuing through the rough running then after the engine settles down would be enlightening. 'course, this requires some tooling and knowing how to do this. Fuel pressure monitoring is risky if there's any spillage of fuel (gasoline).

But the cam sensor error requires some consideration. First is the error a sensor error or does the error indicate a cam timing error? If the latter then that calls into question the variable valve timing hardware is not working right. If this is the case cold starts can be a problem if the cam timing is not correct.

 

Hey, didn't receive email notifications for your reply comments for some reason, I'll look through them today and respond later. Thank you in advance!

 

@SuprCoop wondering if you've resolved the issue? I have something similar happening and have replaced a few things. its not critical at this point but would like to get ahead of it. thanks -m.

 

I do think my battery is on the way out, slow cranking when cold, etc. Just haven't had the money for a battery, thinking that's going to be one of the things I replace. Plugs are one step colder, have been running this setup for a couple years, no issues before now, all plugs look good. No codes other than the cam sensor, and I replaced it and the crank sensor. No change.

I don't have the equipment to do a fuel pressure check, can probably see if any friends have a compression test kit, but not sure if they will. All the wiring that I can see looks fine, and this has been getting progressively worse since last year, so I'm less suspect of the wiring. And thank you for the note on the 02 sensors.

Ran a bottle through last year when it first started, no change, might try it again as I do a lot of short around town trips. Someone above mentioned that the system ignores the 02 sensors on cold start until they're heated up, so while I need to fix the flex pipe, not sure that's the cause.

Coil pack is screamin' demon, so shouldn't have to worry about the pack. Spark plugs look good, normal. As far as I know the pump is fine, just replaced the filter, no change either way. This only happens on cold start, every start after that is fine until the next cold start. Curious about the injectors though, I replaced all the o-rings last year when I did a bunch of other work, but I'm sure they could benefit from a good servicing.

I'd definitely need to have a shop do that, I don't have the equipment (wonder if I can rent that in town...". If I recall (should have screenshot the errors), it was a p0340 or p0341. Replaced the cam sensor, error came back, read online and confirmed with a friend/MINI mechanic that the code can sometimes also indicate an issue with the crank sensor, so replaced that. Didn't change the behavior, and the code(s) have not returned (though, they only popped up once every couple of weeks, no discernable pattern, though it *could* have happened after more spirited driving. And I believe the hardware adjusts based on the sensors, so I've been waiting to see if the code(s) returns to tell if it's possibly more than a sensor issue.

I have not, work has been busy and I haven't had time to really dig into it as it's my daily driver. Luckily I have a second car, but waiting to really dig into it until I can hopefully pinpoint more exactly what to check. Don't really want the car just sitting taken apart, but if that's what I need to do, then so be it I guess.

 

Just a little update, I ordered a new battery for the car, should be here sometime this week and we'll see what happens after that.

Edit: replaced the battery, had no effect on the cold start issue. I was really hoping this would be something simple, but I'm just not sure what to check next.
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Figured I would add my own findings here in the hope that it helps someone. Replaced fuel filter, fuel pump, and oxygen sensors (not related to this, but were throwing a code anyway), and has not fixed. Will be replacing fuel pressure regulator and injectors when I do my supercharger service soon.

 

It's been too warm out to do any work on the car lately, unfortunately, but I'm also going to be checking the injectors/seals, intake, etc. It seems to be getting worse on my car, used to be when I started it, the sputtering would take a couple seconds. Now, with only changing crank/cam sensors, it barely even stays running after I start it. The progression of the symptom going from "not that bad" to "can't even drive the car" over a period of time tells me that something is degrading. Hoping it's something easy, just haven't had the energy/it's been too hot out and I don't have a garage.

 

You can rent/borrow a fuel pressure gauge kit from your local parts store. Also fairly inexpensive to buy at Harbor Freight, Amazon, etc. Some of our vendors carry them as well. Threads onto the Schrader valve at the end of the fuel rail, accessed by pulling the intercooler. Watch the boots as you R/R the IC; rubber tends to get dry and brittle with age, heat, oil etc. then tear or fall apart. Not a bad time to change them out "while you're in there" if they're looking questionable. Also make sure the vacuum line from the fuel pressure regulator is attached securely at the other end at the underside of the supercharger discharge / intercooler input horn. These have a tendency to come loose, creating a small vacuum leak and may contribute to this issue.

Fuel pressure should show and hold ~50psi after spooling up the pump before start up. See below from