Running poorly after starting

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Running poorly after starting

Postby dmcke5 » Mon Jan 13, 2020 8:42 am

Hi Guys, still chasing what seems like a never ending list of issues with my car.
Car is an 06 TbSti.

Main issue I'm struggling with at the moment is shortly after starting my car it appears to loose a cylinder for a while (at least that's what it sounds like) but after maybe 1 minute it sorts itself out and starts to idle smoothly again. A quick stab of the throttle usually clears the idle up too. This only happens when the car has been sitting for long enough to cool down completely. If I allow the car a few minutes to warm up before I leave it drives fine but if I leave straight after starting the car runs so poorly that it is barely able to accelerate for the first minute or so, especially if I'm gentle on the pedal. It also occasionally starts to feel like its lost a cylinder if I spend a couple of minutes cruising at a consistent speed (60km/h in 4th gear usually does it). When it does this dropping to third clears it up again and its usually fine from then on.
Whilst chasing other problems I have replaced Spark plugs, Coils, MAF and the Front 02 sensor so that should all be working properly. Have also had the injectors cleaned and tested and they are all good.
I've also cleaned out the main engine wiring connector (the large one on the passenger side with the big lever on it) and the other plug that lives under the intercooler (not sure what this one does, but mine constantly fills itself with oil. Does this happen to anyone else?). Fairly sure I don't have any vacuum leaks. I've run a fuel pressure gauge on the car and that appears to be fine. The car isn't using an unusual amount of oil, the coolant still looks nice and clean and there's no smoke from the exhaust.
Aside from this problem, the engine feels healthy and pulls well when under power and has no trouble right through the rev range when I'm giving it a bit.

I have a Vag-Com cable and Rom raider setup. I couldn't get it to talk this morning but once I work that out again I should be able to log whatever is needed.

Is there a way to tell which cylinder it is that's giving me grief? Not really keen to try and unplug coils while the engine is running for obvious reasons. I feel like its an electrical problem, but at the same time it seems to be so consistent in timing it has me wondering if its actually something else?
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Re: Running poorly after starting

Postby Stifull » Mon Jan 13, 2020 10:59 am

Are all the clips on the connections on the coil packs and injectors clipping/locking in place.. We have had issues with both and it causes intermittent missing especially when cold. zip ties or replacing the plug/clip has fixed it both times..
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Re: Running poorly after starting

Postby dmcke5 » Mon Jan 13, 2020 11:14 am

Pretty sure all the coil connectors are good, the new ones were a much tighter fit than the old ones I just replaced. Didn't think of the injector plugs though, I'll go back and inspect them and see how they look. I don't recall having any problems with them when I got the injectors tested though.
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Re: Running poorly after starting

Postby RX25SE » Tue Jan 14, 2020 6:39 am

I'm wondering if this is a head gasket issue? When the engine has been shut off after running for a while, the coolant is still under pressure and making its way into the cylinder. After running for a short time, it clears itself and returns to normal.
When you replaced the spark plugs, did the tips all look exactly the same? Coolant/water has a 'cleaning' effect when mixed with combustion so a faulty cylinder will have a 'cleaner' looking spark plug tip.

You could try shutting off the engine while is running poorly, then removing the spark plugs for a look. To isolate the offending cylinder, you could unplug each injector one at a time instead of the coils.
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Re: Running poorly after starting

Postby dmcke5 » Tue Jan 14, 2020 5:40 pm

It's not loosing any coolant though.
I did the plugs roughly 6 months ago and they looked fine. I took photos of them when they came out that I can probably dig out given enough time. I've probably only done 3-4000k's at most since replacing them.
I found a small vacuum leak last night that I have since corrected, but it's still having issues. Was so bad this afternoon that I barely made it down the street as I left work. I'm taking the spare car for the rest of the week so I can do some more serious investigating and not risk getting stuck or doing damage to the engine limping it back home. I'm going to clean the connectors for the coils and injectors tonight, and I might even trace the signals back to the ecu to see if I can find any bad contacts.

Also if anyone who is reading can tell me what my idle MAF voltage should be, that would be great. Google says 0.7-0.8v at idle but that's just in general, not specifically this car or sensor. I haven't had any luck finding a spec sheet so I only have that to go on. I have three sensors here and all of mine are sitting at more like 1.2v at idle.
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Re: Running poorly after starting

Postby norbs » Tue Jan 14, 2020 6:07 pm

Idle voltage should be around 1.26V when warm. Cold start probably a little higher. So yours seems ok to me. Is your tune stock? Mine surges a little when cold, but goes away when coolant temp above 60C. I've learnt to live with it as the car is fairly modified and couldn't be arsed tuning it out.
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Re: Running poorly after starting

Postby dmcke5 » Tue Jan 14, 2020 7:49 pm

norbs wrote:Idle voltage should be around 1.26V when warm. Cold start probably a little higher. So yours seems ok to me. Is your tune stock? Mine surges a little when cold, but goes away when coolant temp above 60C. I've learnt to live with it as the car is fairly modified and couldn't be arsed tuning it out.

Awesome, thought that would be the case since all of the 02 sensors I have here agreed. Stock tune. This is far from a little surge, this is full on misfiring to the point where I am unable to accelerate at all. I'll pull the video out of the dash cam tonight and see if it managed to record much of the sound
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Re: Running poorly after starting

Postby RX25SE » Tue Jan 14, 2020 8:08 pm

Is it definitely a misfire on one cylinder only?
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Re: Running poorly after starting

Postby dmcke5 » Tue Jan 14, 2020 8:12 pm

Nope, not necessarily. That's just what it sounds like to me when it's idling. When I go to take off it feels like it's running out of fuel, but I've checked fuel pressure and had the injectors professionally tested and cleaned. I'm going to take all the injector and coil connectors off tonight and give them a clean and see if it improves. Failing that I'll pull the plugs out and see if anything has changed since I last replaced them.
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Re: Running poorly after starting

Postby RX25SE » Wed Jan 15, 2020 9:44 am

It might be worth eliminating a single cylinder missfire. If you plan on unplugging the injectors anyway, unplug them one by one when the engine running poorly and note changes (if any) each cylinder makes to idle quality. If one cylinder makes no change to idle, then diagnose that cylinder only such as spark plug, coil or injector; if all cylinders affect the idle then concentrate on thing that affect all cylinders such as vacuum leaks, faulty temp sensor, cam actuators and the like.

I would be diagnosing exactly what the fault is before trying to repair it.
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Re: Running poorly after starting

Postby RX25SE » Wed Jan 15, 2020 9:45 am

Im assuming there are no codes?
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Re: Running poorly after starting

Postby dmcke5 » Wed Jan 15, 2020 10:30 am

RX25SE wrote:It might be worth eliminating a single cylinder missfire. If you plan on unplugging the injectors anyway, unplug them one by one when the engine running poorly and note changes (if any) each cylinder makes to idle quality. If one cylinder makes no change to idle, then diagnose that cylinder only such as spark plug, coil or injector; if all cylinders affect the idle then concentrate on thing that affect all cylinders such as vacuum leaks, faulty temp sensor, cam actuators and the like.

I would be diagnosing exactly what the fault is before trying to repair it.


Makes total sense, and that is the approach I would be taking if I was able to go around and unplug each one in time. Unfortunately, the idle usually clears up within a minute or so of starting and obviously the plugs are quite challenging to get to on this car (especially on the coils) so covering them all within a minute of starting the car would be quite difficult. Even if the idle clears up the car still runs like crap for the first few minutes, so I could drive a few meters down the road, pop the bonnet and repeat the process multiple times to try and find whats going on that way.

Last night I did find that one of the injector plugs has a broken clip. I'm trying to organise a replacement connector today to remedy that, but for the time being I've got a zip tie on it to try and keep it in there properly. It couldn't be helping, but it didn't seem loose enough to fall out or come loose either so I'm not certain that's the cause. I also pulled the ECU out last night and found that oil had worked its way all the way down to one of the ecu plugs. I knew the main connector below the intercooler had a bit of oil in it (which I had already cleaned out thoroughly) but I had no idea it could make it that far up the wiring loom. It was pooling around the pins for the crank angle sensor so that could definitely have been contributing to the problem. I've check the sensor itself and that is not where the oil is coming from so I will have to inspect everything else that is connected to that part of the loom to work it out.
For now, the plugs all cleaned up and it felt promising on the test drive last night so I brought it to work with me again today to see how it goes after sitting in the sun all day. I'm not calling it yet though as I've been fooled before, so I'll see how it goes this afternoon....
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Re: Running poorly after starting

Postby dmcke5 » Thu Jan 16, 2020 1:55 pm

Bit of an update, still not running properly.

The problem is getting worse, barely made it home yesterday. Its now completely un-driveable until the car has warmed up, but now even when its warmed up its getting some pretty major misfiring (only ever when cruising or gently accelerating, never a problem revving out or whilst on boost). The fact its now more consistent will hopefully make it easier to track down the issue. I have now had a chance to give all the injector plugs a good wiggle while the car is running badly, with no effect. Haven't re-checked the coil connectors again yet but they were only off a week ago and they all looked good at the time.

I have noticed that the car runs quite well immediately after an ECU reset (either through Rom-Raider or a battery disconnect). Obviously its little down on power initially until the ecu starts to bring some timing back in but once that happens it starts to run poorly again. I guess that means it could have something to do with the timing advance, either that or the AFR's that its learning. I'm still pretty confident its not an AFR problem as I've pressure tested the intake, the MAF checks out okay and I've only just replaced the front 02 sensor a few months ago. I've also had a standalone 02 sensor on the car to test AFR about a month ago and it all looked good. I've also mapped both sides of intake and exhaust VVT and they all appear to be responding pretty evenly.

I think my next step is going to be checking the Cam, crank and knock sensors and trying to work out how the oil is getting into my wiring loom as that may lead me to a faulty sensor or something. Might also pull the plugs again and look for any signs of trouble. Still no check engine light.....

Any further suggestions welcome.
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Re: Running poorly after starting

Postby RX25SE » Thu Jan 16, 2020 5:40 pm

Did you end up eliminating a single cylinder missfire and check for codes?

Alternator output and battery condition may cause ecu issues.
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Re: Running poorly after starting

Postby bigBADbenny » Fri Jan 17, 2020 10:03 am

Sharpie’s UEC fuel rail & injector soak.

This is more relevant, according to the source, to pre 05 cars.
Worth a try though.

Also, can you please post a learning view, with at least 20km of driving post ecu reset? (Ecu reset not required though)

viewtopic.php?f=17&t=36178&p=446851#p446851


...
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