Jerking on low rpm when pressing acc pedal (WRX 2004)
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Jerking on low rpm when pressing acc pedal (WRX 2004)
I have problem with my 2004 WRX: during a drive, while rpms are below 3000, when I press acceleration pedal, the engine starts jerking like crazy. The car is totally stock, apart from PPP (only ecu and y-pipe) and GoFastBits regulaed recirc valve.
Everyone told me, it's for sure something with ignition (the typical symptom of misfire), probably the spark plugs. So one of the first things after buying the car was changing spark plugs (to original iridium ngk, but one degree colder) - no effect at all.
Then someone told me to check if the gap is 0.7mm, so I have them checked and gap set to 0.65-0.7mm - no effect at all.
If sparks are ok, it must be coilpacks, they said. So my mechanic swapped a whole set of coilpacks to another set from properly working scooby - no effect at all.
After that, someone suggested checking the head valves clerances (but I have checked service history of a car and previous owner has done that one year before).
Apart from that I also did:
- changed PCV valve;
- added missing gasket under recirculation valve;
- do a leak test on idle with autostart spray - no leaks found;
There are no fault codes in ECU, no check engine. The car passed emission test with no problem.
Last time, I noticed some situations, in which problem does not occur, which might be crucial in finding a solution:
- when I press the pedal fully and very fast (what in my opinion eliminates ignition as source of the problem);
- when the engine is cold, during a warm up .
So from my understanding, the engine runs well in open loop (when cold, when pressing pedal to the metal, and when pressing gas pedal above 3-3,5 krpms) and jerks when pressing acc pedal in a closed loop.
Firts thing I thinked of was MAF, I watched this video:
and I thought: it must be it! I am probably missing the first spike on maf reading and this is exactly when the jerking comes on. Unfortunately, after cleaning MAF with carb cleaner and a soft brush, there is literally no effect.
Please give me some advice, what should I investigate next. Can MAF be faulty despite cleaning? How can I check if it is OK?
After reading the forums, other suspected sensors are: first lambda and Coolant Temperature Sensor. How can I check if they are faulty?
Everyone told me, it's for sure something with ignition (the typical symptom of misfire), probably the spark plugs. So one of the first things after buying the car was changing spark plugs (to original iridium ngk, but one degree colder) - no effect at all.
Then someone told me to check if the gap is 0.7mm, so I have them checked and gap set to 0.65-0.7mm - no effect at all.
If sparks are ok, it must be coilpacks, they said. So my mechanic swapped a whole set of coilpacks to another set from properly working scooby - no effect at all.
After that, someone suggested checking the head valves clerances (but I have checked service history of a car and previous owner has done that one year before).
Apart from that I also did:
- changed PCV valve;
- added missing gasket under recirculation valve;
- do a leak test on idle with autostart spray - no leaks found;
There are no fault codes in ECU, no check engine. The car passed emission test with no problem.
Last time, I noticed some situations, in which problem does not occur, which might be crucial in finding a solution:
- when I press the pedal fully and very fast (what in my opinion eliminates ignition as source of the problem);
- when the engine is cold, during a warm up .
So from my understanding, the engine runs well in open loop (when cold, when pressing pedal to the metal, and when pressing gas pedal above 3-3,5 krpms) and jerks when pressing acc pedal in a closed loop.
Firts thing I thinked of was MAF, I watched this video:
Please give me some advice, what should I investigate next. Can MAF be faulty despite cleaning? How can I check if it is OK?
After reading the forums, other suspected sensors are: first lambda and Coolant Temperature Sensor. How can I check if they are faulty?
Last edited by uxon; 07 November 2017 at 01:51 PM.
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Thanks for a reply. As I mentioned, I have checked the ECU for fault codes and there are none. I do have laptop with romraider.
I do not have stock DV, the GFB BOV was there, when I bought the car.
I do not have stock DV, the GFB BOV was there, when I bought the car.
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#10
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How much petrol is in it? Are you hard cornering and accelerating when it happens?
If yes to the above then it's fuel surge, the petrol sloshes around in the tank and the pick up sock can lose contact with the fuel causing very harsh stumbling until the fuel pump gets pressure again.
I can get it in my car with even half a tank.
If yes to the above then it's fuel surge, the petrol sloshes around in the tank and the pick up sock can lose contact with the fuel causing very harsh stumbling until the fuel pump gets pressure again.
I can get it in my car with even half a tank.
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About plugs: I am not sure, because it has been done by a shop. I asked them and they told me that spark plugs looked quite OK.
How much petrol is in it? Are you hard cornering and accelerating when it happens?
If yes to the above then it's fuel surge, the petrol sloshes around in the tank and the pick up sock can lose contact with the fuel causing very harsh stumbling until the fuel pump gets pressure again.
I can get it in my car with even half a tank.
If yes to the above then it's fuel surge, the petrol sloshes around in the tank and the pick up sock can lose contact with the fuel causing very harsh stumbling until the fuel pump gets pressure again.
I can get it in my car with even half a tank.
It is happening during normal cruising. If I am cruising with one speed everything is ok. But when I want to accelerate a little (lane change, etc.) the engine jerks 2 or 3 times before it starts accelerating.
Last edited by uxon; 09 November 2017 at 09:39 AM.
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Datalog - is there a param called that?
LTV - you mean learning view tables?
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Cleaning the MAF doesn't always work, been there done that swap out the MAF with a known good one then go from there.
Had a faulty one on a bug a few years ago, didn't show up any errors specific to the MAF sensor, just a few missfire errors now and again. The car has run error free for the last 6 years
MAF, the MISFIRES AND FART sensor
Had a faulty one on a bug a few years ago, didn't show up any errors specific to the MAF sensor, just a few missfire errors now and again. The car has run error free for the last 6 years
MAF, the MISFIRES AND FART sensor
Last edited by Steve001; 11 November 2017 at 01:46 AM.
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The other log is when temeperature is higher and car is jerking when pressing gas pedal.
Cleaning the MAF doesn't always work, been there done that swap out the MAF with a known good one then go from there.
Had a faulty one on a bug a few years ago, didn't show up any errors specific to the MAF sensor, just a few missfire errors now and again. The car has run error free for the last 6 years
MAF, the MISFIRES AND FART sensor
Had a faulty one on a bug a few years ago, didn't show up any errors specific to the MAF sensor, just a few missfire errors now and again. The car has run error free for the last 6 years
MAF, the MISFIRES AND FART sensor
Last edited by uxon; 12 November 2017 at 10:56 PM.
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OK, I have logged some data. First log (with temperature below 60 Celcius degrees) is when everything is running OK, so I press gas pedal and car accelerates normally.
The other log is when temeperature is higher and car is jerking when pressing gas pedal.
Steve001 did you have the same symptom as I do? I mean 'jerkiness' from low rpm?
The other log is when temeperature is higher and car is jerking when pressing gas pedal.
Steve001 did you have the same symptom as I do? I mean 'jerkiness' from low rpm?
I'm not saying you have the same thing, but well worth investigating IMO Do you know anyone with a bug, blob or hawkeye WRX or STi as the MAF is the same on them all, just to borrow one to see if that cures your problem. Dead easy and simple just 2 philp screws and a plug connection
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My DD software won't read your log files,I've had a look using data zap and I can't see anything strange,maybe the fuel pump duty is high 100% at light throttle but this might be normal? Can you take a screen shot of learning table views,might be some answer there?
There is a really helpful mapper @bludgod ,sometimes can be found in the engine management section,he might spot something unusual with your data.
There is a really helpful mapper @bludgod ,sometimes can be found in the engine management section,he might spot something unusual with your data.
#21
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in romraider logger - hit the "show LTV" button on the left hand side. Save as image and upload here we'll see what's up.
Also - cleaning maf sensor rarely works if its at the stage where it's causing problems just replace it.
Are you using an aftermarket air intake or a standard airbox?
Also - cleaning maf sensor rarely works if its at the stage where it's causing problems just replace it.
Are you using an aftermarket air intake or a standard airbox?
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My DD software won't read your log files,I've had a look using data zap and I can't see anything strange,maybe the fuel pump duty is high 100% at light throttle but this might be normal? Can you take a screen shot of learning table views,might be some answer there?
There is a really helpful mapper @bludgod ,sometimes can be found in the engine management section,he might spot something unusual with your data.
There is a really helpful mapper @bludgod ,sometimes can be found in the engine management section,he might spot something unusual with your data.
in romraider logger - hit the "show LTV" button on the left hand side. Save as image and upload here we'll see what's up.
Also - cleaning maf sensor rarely works if its at the stage where it's causing problems just replace it.
Are you using an aftermarket air intake or a standard airbox?
Also - cleaning maf sensor rarely works if its at the stage where it's causing problems just replace it.
Are you using an aftermarket air intake or a standard airbox?
I have OEM intake and airbox. Car has about 160k miles of mileage.
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For a standard airbox the A/F corrections look a little high but would need to see the LTV info to confirm it - if so then it's a leak or sensor fault. Leak testing with spray won't show you much unless it's really bad, you need to get it properly smoke/pressure tested to confirm.
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I attach screen from LTV. One note though, it's quite fresh, I reset ECU lastly when I cleaned MAF. I think that before reset the value in 10-50 range was smaller, about 6% (and there where maybe 3 spots on FLKC table with values about 3.
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@fawor, I assume that no symptoms during warm up and under full throttle exludes a general problem like with exhaust valves.
How does your car behave during warmup? Or if you press full gas pedal immediately? In my case under these conditions car is working with no problems.
How does your car behave during warmup? Or if you press full gas pedal immediately? In my case under these conditions car is working with no problems.
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When is cold it is jerking till 3k, looks like it is loosing preasure below, engine stops when on neutral
Warm similar but no engine stops
Cold or warm feels ok after 3k revs
Engine menagment light flashing constantly but no codes in ecu
I do not think You will get other symptoms when Your exhaust valves gave up
Warm similar but no engine stops
Cold or warm feels ok after 3k revs
Engine menagment light flashing constantly but no codes in ecu
I do not think You will get other symptoms when Your exhaust valves gave up
Last edited by fawor; 17 November 2017 at 05:06 PM.
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When is cold it is jerking till 3k, looks like it is loosing preasure below, engine stops when on neutral
Warm similar but no engine stops
Cold or warm feels ok after 3k revs
Engine menagment light flashing constantly but no codes in ecu
I do not think You will get other symptoms when Your exhaust valves gave up
Warm similar but no engine stops
Cold or warm feels ok after 3k revs
Engine menagment light flashing constantly but no codes in ecu
I do not think You will get other symptoms when Your exhaust valves gave up
Bludgod, do you know how the ecu alghoritm differs when engine is during warmup and with normal temperature? Which sensors are not being used during warmup?
Last edited by uxon; 17 November 2017 at 05:47 PM.