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what is wrong with my car?


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I have a 2006 LGT COBB catted down pipe grimmspeed catless up pipe Cobb accessport pdx etune. I have 59k on the car I am a BMW technician and do all my own maintenance on my vehicle this is the first problem I have had with my car since I bought it new. So about a mont ago I noticed when driving at a constant speed (foot steady on pedal) the vehicle seems to buck in a very steady pattern. The easiest way to describe it is it feels like someone is tapping the brakes lightly every second Its extremely annoying. the car accelerates and performs fine just when cruising it does this. This happens at any speed any gear even when on cruise control but it is most noticeable at speeds of 50mph and lower. The only code my car has set is bank 1 o2 sensor pre cat heating circuit. Cleared that and it hasn't come back don't think that's causing issue anyway. My spark plugs were overdue so replaced them problem still there. Cleaned my MAF still there put some fuel additive cleaner in ran a few tanks still there. Im beginning to think I have an injector on its way out. Anyone that has any ideas would be greatly appreciated. My next step it to take it to the dealer as I don't have access to a scan tool to minitor all 4 injector values while the car is bucking. Thanks

 

UPDATE

I did a short data log of my car while it was bucking. Let me know what you guys think.

datalog1.csv

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Really? these turbos wear out this soon? I really take care of my car and don't beat on it. Another symptom is when still and revving engine and holding it at say 2500rpm the tach and engine surges up and down about 500rpm. I really hope its not the Turbo...I don't have any coverage I guess ill take it to the dealer if its a Turbo ill put one in. Figures the first problem I have with my car may turn out to be a fairly costly one. Thanks for the input.
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Your in Jersey, Look up AZPinstalls and have them check the car out.

Mike posts here on the forums. May be he's close to you.

 

 

Don't go to the Stealership, $$$$

 

I had my Tuner data log when I felt the surging and he tuned it out.

 

These cars have been known to have surging issues.

 

One of the first ones I test drove back in mid Jun04 was really bad. I told the sales guy he should have it checked out. He said well, it just came off the transporter, the car had like .7 miles on it. The thing was not very pleasent to drive.

I think the ECU's were reprogramed on the early ones too.

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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Ok this sounds more like it. I'm going to hook my accessport up on my way home from work about 15 miles and log it. Only problem is I don't have a windows computer to download it too...I have changed my maps to the stock Cobb maps and the surging is always there. So this is a permanent problem with the ecu?
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from what I have read it can data log, also if you dont have windows, partition your HD and dual boot your(assumed) mac. A data log would help out a lot. Also, although it may be unrelated, have you done a compression test? one less thing to worry about.
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So I hooked my accessport my car and I cannot find find the monitor section the main menu to data log.is it possible my accessport has old softwareand doesn't have data logging? I am going to install the Mac osx software later and update it to see if that feature pops up.
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Well the bucking is interesting, a vac leak *should* be obvious at idle, lumpy, irregular, and shitty. A boost leak however could be a problem, the first thing I do when I suspect a driveability issue is check all the pre/post turbo connections for tightness and that nothing popped off.... a log will show us what the deal is, and if it's tune related or mechanical.... but the o2 code makes me think we'll see something funky on the AFR if in fact it is the o2 sensor. The front o2 is a vital part of the car's driveability and general running....not so much the rear o2
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On the way home from work I did monitor live data. Air fuel ratio was normal during bucking as was boost levels. Car is in vacuum when this happens anyway. I doubt there is a boost or air leak I hit Max boost and hold it fine and all my fuel trims are normal. The o2 sensor may be an issue although the fault was for the heater circuit not the signal. The injector pulse with during the bucking goes from 3.1-2.6ms interesting. Its gotta be a sensor or maybe faulty ecu. I will get a data log uploaded as soon as I can find out how to...
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On the way home from work I did monitor live data. Air fuel ratio was normal during bucking as was boost levels. Car is in vacuum when this happens anyway. I doubt there is a boost or air leak I hit Max boost and hold it fine and all my fuel trims are normal. The o2 sensor may be an issue although the fault was for the heater circuit not the signal. The injector pulse with during the bucking goes from 3.1-2.6ms interesting. Its gotta be a sensor or maybe faulty ecu. I will get a data log uploaded as soon as I can find out how to...

 

Welp, we need to see what everything is doing at once to figure what the methodology is behind the symptoms...

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OP, have you pulled your spark plugs and checked the gap? I had this exact same issue a few months ago and my plugs had expanded to over .040 Thousandths. I replaced them and it took care of the problem. The stock NGK's come already gaped at .030 Thousandths.
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It put brand new ngks in already and it didn't fix it...

 

My bad, I just noticed that you mentioned that in your first post. I blame my reading comprehension fail on Shock Top, Belgium wheat. :)

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I'm going to second the AFR sensor suggestion. I had a similar issue and replaced my front O2...the problem is no more. Sometimes the code would clear randomly and I would still have the 'bucking' issue, so maybe clearing the code doesn't necessarily rule out the O2. Still, I'm no tech...hope you find some answers!

Updated parts list since original part-out here.

 

Original Full part-out of my LGT HERE!

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Yea the o2 sensor could be the problem just odd that it only triggered on cold starts like 2 times a month ago and hasn't returned. If I replace it you guys would recommended an OEM sensor correct?
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That seems like an intermittent sensor problem to me, and if the car is sluggish it may be that it has gone into limp mode to protect itself.

 

Just check around and make sure that you don't have anything strange going on, and that includes a squirrel nest in the airbox. Have a code reader with you and read codes as soon as you experience the strange behavior. Loose hoses or bad connectors can also be suspect.

 

And take apart and look for foreign objects in the air intake, intercooler, turbo (both intake and exhaust) and the throttle valve. The exhaust side of the turbo is especially important if you have an up-pipe cat.

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i am having a similar issue, first happened tonight on the way home....i was doing about 55 or so and went to accelerate lightly but enough where boost would be used, car started bucking pretty hard, after this i noticed that my boost will not come above wastegate again, i'm gonna see what it does tomorrow but the car was fine till this happened. no CEL, and no mods except for a removed intake silencer. i don't know what this could be. previously i had an issue with the car using wastegate boost intermittantly and then hitting max most of the time. I use premium gas, im going to try a different station next time i fill up and see if that changes anything. im not exactly sure where to look being this is my first turbo car

2006 Legacy GT 5EAT Perrin UP, SPT CAI, OBXR CBE, Catless DP, Perrin TMIC, Stage 2 AP tune

Soon after BNR 16G, Infamous Tune

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  • 2 months later...
OK so I had some time at work yesterday to finally bring my car into the shop and figure out what's going on with my car. Since I can duplicate the surging by just revving engine and holding it at any rpm I hooked my accesport up and monitored the A/F ratio. While surging ratio went as low as 11 and as high as 20! Far too big a swing. I unplugged the pre cat O2 sensor obviously engine went into fail safe and A/F ratio is set to 14.7:1 and engine is as smooth as silk. This rules out a coil or injector and means the ecu is adding and cutting fuel due to a faulty O2 sensor reading. I'm 90% sure this O2 is bad but I don't know why I'm not getting a check engine light for fuel trim limit or something. Question is do I get an OEM sensor or a Denso for cheaper? Anyone know the OEM sensor part number so I can match it the Denso part number? Thanks for everyone's input I can't wait to put this issue to rest. If this fixes the problem I might be getting a cat back exhaust. Not sure which one still researching.
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