Zogy
Greenie Member
(long post sorry,, I tried to be concise)
I thought I would pass on some recent experience regarding diagnosing a rough cold start and misfire situation. I noticed that the engine was a bit rougher starting than normal (or so I thought), and started throwing a P0302 (misfire cyl #2) error code once the engine was warm. The misfire was consistently reported on Cyl #2. I switched coils, and then separately spark plugs, but the misfire continued to show up only on Cylinder #2. So I reasoned that it was likely carbon build up (spoiler alert I was wrong it was a bad injector).
So I decided to investigate the issue of carbon build up in a direct injection engine. During cold start the ECM would pull timing way back, the vacuum would take a nose dive, and the engine would run really rough; and sound like if is misfiring. This got me looking into “cold start misfire” for a DISI 2.3L Turbo motor. Well that turns out to be a VERY deep rabbit-hole; and solution seems to be all over the map (i.e. no consensus as to the cause). I did find one website that explained in detail, why carbon build-up can be an issue with direct inject engines, which is worth checking out.
(looks @ 8:00 onward, with a key point @ 9:05)
The bottom line: DISI engines will run like crap (sounds like a misfire) briefly during a cold start-up. I understand that this is by design, and is done to get the catalytic convertors to heat up more quickly, by dumping a very rich mixture into the exhaust. To check this behavior you can bypass the cold start function, by briefly holding down the accelerator during a cold start (and release it after the engine catches) and the engine should run smoother.
So I bought the walnut blasting stuff and proceeded to clean my valves. It actually went quite well; time consuming, but straightforward. I also took the opportunity to take my injectors to a local shop and have them cleaned and flow-checked. The shop reported that all of them had poor patterns prior to cleaning. And after an ultrasonic cleaning the patterns and flow all checked out. I’ll note that I labeled the injectors (with tape) when I gave them to the shop, but they returned them without the labels. I later found out that they do engrave the cylinder numbers in the plastic near the electrical connector.
After putting everything back to together (in random locations) the car ran fantastic … but then when warm the misfire again surfaced, but this time in cylinder #3. So it was pretty obvious that I still have an injector issue. The injector shop said that that is virtually unheard of after cleaning/calibration; but such crappy-luck is typical for me, when it comes to cars. So, I bit the bullet and ordered new OEM injectors …. and viola the problem was solved. My MS6 now runs like a champ!
So a few takeaways from my recent experience:
I thought I would pass on some recent experience regarding diagnosing a rough cold start and misfire situation. I noticed that the engine was a bit rougher starting than normal (or so I thought), and started throwing a P0302 (misfire cyl #2) error code once the engine was warm. The misfire was consistently reported on Cyl #2. I switched coils, and then separately spark plugs, but the misfire continued to show up only on Cylinder #2. So I reasoned that it was likely carbon build up (spoiler alert I was wrong it was a bad injector).
So I decided to investigate the issue of carbon build up in a direct injection engine. During cold start the ECM would pull timing way back, the vacuum would take a nose dive, and the engine would run really rough; and sound like if is misfiring. This got me looking into “cold start misfire” for a DISI 2.3L Turbo motor. Well that turns out to be a VERY deep rabbit-hole; and solution seems to be all over the map (i.e. no consensus as to the cause). I did find one website that explained in detail, why carbon build-up can be an issue with direct inject engines, which is worth checking out.
(looks @ 8:00 onward, with a key point @ 9:05)
The bottom line: DISI engines will run like crap (sounds like a misfire) briefly during a cold start-up. I understand that this is by design, and is done to get the catalytic convertors to heat up more quickly, by dumping a very rich mixture into the exhaust. To check this behavior you can bypass the cold start function, by briefly holding down the accelerator during a cold start (and release it after the engine catches) and the engine should run smoother.
So I bought the walnut blasting stuff and proceeded to clean my valves. It actually went quite well; time consuming, but straightforward. I also took the opportunity to take my injectors to a local shop and have them cleaned and flow-checked. The shop reported that all of them had poor patterns prior to cleaning. And after an ultrasonic cleaning the patterns and flow all checked out. I’ll note that I labeled the injectors (with tape) when I gave them to the shop, but they returned them without the labels. I later found out that they do engrave the cylinder numbers in the plastic near the electrical connector.
After putting everything back to together (in random locations) the car ran fantastic … but then when warm the misfire again surfaced, but this time in cylinder #3. So it was pretty obvious that I still have an injector issue. The injector shop said that that is virtually unheard of after cleaning/calibration; but such crappy-luck is typical for me, when it comes to cars. So, I bit the bullet and ordered new OEM injectors …. and viola the problem was solved. My MS6 now runs like a champ!
So a few takeaways from my recent experience:
- If you have a misfire on a specific cylinder: swap coils and plugs; and if the misfire doesn’t track with either of those, it’s likely a bad injector (I know that’s pretty basic, but and even after cleaning, it could still be bad, so make sure you track the cylinders where the injectors where positioned and put them in different cylinders when you install them, so you can see if they track location)
- Walnut blast your valves if you have never do it. Your engine will rev much more freely, be more powerful thru the power band, and generally run much smoother. (you can inspect them with a cheap side-facing borescope thru the sparkplug holes when the valves are open)
- DISI motors just generally run like crap (misfire-like) briefly during start-up. This is by design. But a random misfire when the engine is warm is not normal, and is a reason to investigate.
