After 10 mins of driving, 1999 WRX loses power and coughs black smoke

[chrislaya]

Hi guys, newbie here. I bought a 1999 WRX less than a month ago. It is stock, has no modifications and has 128,000km on the clock. Guy I bought it from said it only run 400km in the previous year and was always garaged. Test drive was OK.

First thing I've done when I got the car was to replace the oil and genuine Subaru oil filter, spark plugs and fuel pump. I only use 98 octane and mindful of warming up the engine and waiting 2-3 minutes when shutting down the engine.

After having the car for a week, I noticed that after driving it for 10-20 minutes (the issue is intermittent), when I am coming off from stop (e.g. traffic light) the car coughs black smoke and loses power and stutters. This happens especially if it is going uphill. I have to rev it really hard just to "get it over the hump" and the smoke disappears. The problem happens in the 1st and 2nd gear and disappears on the 3rd and 4th gear. Then it will happen again in the next stop/traffic light. I am also mindful of the rev and only go to 3,000-4,000.

Having said that, the car is great in the first 10-20 mins and I can feel the turbo working.

These symptoms also appears on this thread but unfortunately the OP didn't come back with his findings. http://www.igotasubaru.com/showthrea...9023#post19023

My Google search for similar symptoms suggested replacing the O2 sensor, check for compression/boost leaks, excessive fuel pressure (bad fuel pressure regulator or plugged return line), leaky fuel injectors, dirty air filter or restricted air inlet, or a defective coolant sensor that prevents the engine management system from going into closed loop mode.

I am now apprehensive to drive it for long drives until this issue is solved. I am also anxious that I got a bad car and hopefully it's not expensive to fix.

Thanks in advance for your help guys!

[Zach@TTLM]

What fuel pump did you go with? Have you performed any of the compressions/leak down tests? Was there any modifications done to the car by the previous owner? This didn't happen at all during the test drive before buying it??

[chrislaya]

What fuel pump did you go with? Have you performed any of the compressions/leak down tests? Was there any modifications done to the car by the previous owner? This didn't happen at all during the test drive before buying it??

Hi Zach@TTLM, I used a Subaru fuel pump as I want to keep the car stock as much as possible. There are no modifications to the car and unfortunately I didn't experience it during the test drive. Maybe we drove under the 10 minutes mark and there were no hills to climb.

I haven't done any tests yet as I want to get some ideas before I bring it to the mechanic/tuner. Don't want to sound too n00b and get ripped off.

The owner did say the airflow sensor and knock sensor was recently replaced. I've read that you need to reset the ECU after replacing sensors. Is this recommended? Will disconnecting the battery for a couple of hours reset the ECU? Thanks.

[Zach@TTLM]

when you changed the fuel pump did you change the prefilter with it? how did it look when you pulled it out originally... are you getting any check engine lights? I have seen these symptoms caused by various different things so trying to narrow it down as best as possible...Far as the ECU goes anytime sensors are changed it is recommended. Disconnecting it will reset it.

[chrislaya]

when you changed the fuel pump did you change the prefilter with it? how did it look when you pulled it out originally... are you getting any check engine lights? I have seen these symptoms caused by various different things so trying to narrow it down as best as possible...Far as the ECU goes anytime sensors are changed it is recommended. Disconnecting it will reset it.

My friend did the work but I don't remember seeing a pre-filter - just the fuel pump. The fuel pump replaced was silver while the genuine Subaru that we put in was black.

No, I am not getting any check engine lights. Also just want to mention that I can smell petrol very strongly. I can't remember smelling such thing on my other 01 Impreza (non-turbo). Thanks for your help again Zach@TTLM.

[Zach@TTLM]

Are you only experience the issues during pull outs and hills...you got power at other points of the drive? See there is so many issues that this could be such as boost leak, fuel issue, ecu issue, cat plugged, bad ring... with out looking at it in person I am going to suggest a couple different things to considering looking into.

I would start by checking your fuel filter...if the kid didnt see any issue with the pre-filter it should be good but the normal fuel filter should be checked. Also make sure the plugs are gapped correctly. A boost leak check as well as a compression test could also reveal what is causing this.

[chrislaya]

Are you only experience the issues during pull outs and hills...you got power at other points of the drive? See there is so many issues that this could be such as boost leak, fuel issue, ecu issue, cat plugged, bad ring... with out looking at it in person I am going to suggest a couple different things to considering looking into.

I would start by checking your fuel filter...if the kid didnt see any issue with the pre-filter it should be good but the normal fuel filter should be checked. Also make sure the plugs are gapped correctly. A boost leak check as well as a compression test could also reveal what is causing this.

It is really weird. I swear the first 10 minutes I have power and then just loses after that. It just seems the turbo stops working after the first 10 minutes.

Thanks for the list of things to check. At least I can go to the tuner with these in mind.

[Zach@TTLM]

See when you first start the car things are tighter due to being cold, but once it heats up things expand at that point it can allow loss of compression, a hose crack to open more causing a boost leak and so on. If there is anything I can do though feel free to ask. Where are you located??

[chrislaya]

See when you first start the car things are tighter due to being cold, but once it heats up things expand at that point it can allow loss of compression, a hose crack to open more causing a boost leak and so on. If there is anything I can do though feel free to ask. Where are you located??

Hi Zach, I am located in Sydney. Sounds like a boost leak if that is the case as I can't feel the turbo working after the first 10 mins. And also I checked and it was the fuel filter we replaced NOT the fuel pump.

[chrislaya]

Hi Zach, I am located in Sydney. Sounds like a boost leak if that is the case as I can't feel the turbo working after the first 10 mins. And also I checked and it was the fuel filter we replaced NOT the fuel pump.

My mechanic replaced the air flow meter and seems to got rid of the problem!