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Old 08-22-2016, 02:16 PM   #1
TonyatLexington
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Default 02 LW300 3.0L V6 P0050, P0343 starts only WOT, very rough & barely running

Need help badly!! -shadetree mechanic with some tools and limited knowledge of new cars. Our family Saturn SW died returning from church yesterday requiring a tow home. Lost power and lit up the dash and coasted to a stop. Codes I have are P0050 Ho2s Heater Cntrl Circuit Bank 2 Sensor 1- not sure which one this is- (I have located three)- 1st at front on exhaust manifold, next just before CAT and 3rd just after CAT. A mechanic aquaintance told me once that if it says "Heater" then o2 sensor is bad. Will replace this one if I caould tell which one it is. Car would not restart (sounded very rough but like it almost wanted to start)- opened the throttle and it reluctantly started, then idled extremely badly. It had a tune up less than a year ago with new timing belt, plugs, and wires. They did not do the serpentine so I put that on Saturday myself with no problems. It drove to church smoothly then died out after five miles back. I took it all apart and examined it- serpentine and timing belts on and in good condition. Checked codes again just now and P0343 camshaft pos sensor A came up. I hate to just replace parts and I also have little to no money. I understand crankshaft sensor could also cause these symptoms. I have an electronic voltmeter, 12v light tester, but would need tutorial on the setting to use and procedure for testing position sensors. It had 40 psi fuel pressure at rail. Wondering if it might also be the Catalytic converter itself. I only thought to try it WOT when someone on the forum said that in this no start condition the Cam sensor not sending signal would only send spark to one cylinder and sure enough it did start, but barely runs. Also, I read something about the coolant temp sensor going bad on these and creating a poor condition? No code found except those two. This is our daily driver and has been a great car since we got it at 35K- it now has 115K. It has been smoking at start and occassionally while driving despite using it very regularly, it always did after sitting a bit, but has been getting a bit worse. Eats coolant a bit, but probably a small leak I have not been able to see. Any help would be greatly appreciated to see of we can revive our wonderful wagon!

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Old 08-22-2016, 03:05 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: 02 LW300 3.0L V6 P0050, P0343 starts only WOT, very rough & barely running

A search thru these forums will tell you which O2 sensors are front or back. And you have four; a V6 with two cylinder banks will have two sensors on each cylinder bank, a precat and post cat sensor. Our V6 has three catcons; a precat for each cylinder bank and a main one after the two precats. Ignore error codes for now until the engine can start and run. A faulty cam sensor or O2 heater doesn't interfere with engine starting. With possible false error codes, suspecting a partially blocked catalytic converter may take some patience and experimenting.

To determine whether or not one or several catcons are blocking exhaust flow and causing some of all these error codes requires removing the exhaust manifold O2 sensors (precat) on each manifold, creating (soup can?) diverters so exhaust heat won't burn nearby items as exhaust flows out these alternate pathways, and driving around the block. While loud, either the engine will startup and run better or not. Members have found their precats blocked with this method or from a good muffler shop capable of diagnosing blocked exhaust systems. When removing O2 sensors, it's recommended to warm the engine a little too preheat the exhaust manifold. Antiseize is used to prevent sensors from seizing but some effort is needed to loosen them after many engine heat cycles. New Bosch sensors have antiseize compound.

Presuming a new air filter is used, was the mass air flow (MAF) sensor cleaned and intake tubing clamps secured to ensure air flows only thru the maf sensor? A leak or damaged air intake tube between maf sensor and throttle body may cause a lean condition if the maf sensor doesn't detect 100% air flow thru it.

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Old 08-22-2016, 04:08 PM   #3
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Default Re: 02 LW300 3.0L V6 P0050, P0343 starts only WOT, very rough & barely running

That gives me a great place to try to start. Thanks! I will do as suggested and remove the pre cat o2 sensors to see if it is a clogged cat (furball?). I did notice when I went back in to make sure it was not something I did during the serpentine change that I had not tightened down the hose clamp on the throttle body. It fit on pretty snuggly anyway, so I don't expect it would have been that, but don't know.. No change after tightening clamp down. I did inspect the Mass Airflow and it looked clean. I shook a little debris off the airfilter and put it back, deciding it didn't looktoo dirty. I will spray the MAS but don't think that will be the solution. That catylitic thing looks real hard to get out and I wouldn't have thought it would've been so close to the manifold-- was hoping it was under with the rest of the exhaust for relatively easy access. Most of the bolts under there are extremely rusty. Guess I'll get to use my grinder- if it goes that way. Any other tips?

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Old 08-22-2016, 04:34 PM   #4
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2003 L-Series 3.0L Sedan
Default Re: 02 LW300 3.0L V6 P0050, P0343 starts only WOT, very rough & barely running

Start reading L300 forums to have an idea of what's already known and solutions. One member here with an L200(?) may be the first here to have a damaged catcon after 60k miles. Not his or the previous owner's fault. The previous owner may have driven too many short trips without allowing the engine to warm up completely, usually 10-15 miles, accelerating catcon blockage. I've replaced both precat O2 sensors from faulty heaters around 75k(?) miles? The second failed a year after the first one did. I replaced a worn flex coupling earlier this year by cutting off the original and clamping in a replacement. When I didn't have room to fit in the replacement, I had to remove the front down pipe - using pb blaster and an electric impact tool to loosen nuts. Once loosened, the nuts came off clean with only surface corrosion. My guess is either stainless studs and nuts are used or plated studs and corrosion resistant nuts. The exhaust system piping is a low grade stainless with surface corrosion. After many years of NYC salting, the flex pipe and muffler are the only parts replaced (@92k miles). I was amazed how well the exhaust system held up .

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Old 08-25-2016, 06:43 AM   #5
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Default Re: 02 LW300 3.0L V6 P0050, P0343 starts only WOT, very rough & barely running

Well, ok, so I removed the front o2 sensor corresponding to cylider 2 and thus my bank 2 code. It was loud but maybe the engine ran better, hard to tell, but it did run for only a few seconds, then the rpms shot up to 3k+ and I quickly shut it off. Did this twice with same result. I took off the front cat con and it had no obstruction, no rattling, blew air through it with exhaust from shop-vac= full air flow through to tailpipe. I did the same with the rest of the downstream exhaust and had full air flow the rest of the way. I did not remove the other cat con since the code was for the #2 bank and it was even harder to get to with a shield bolted around it. Not sure what to try next- the cam sensor and cranksensor add up to a bill and a half. Any ideas?

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Old 08-25-2016, 09:04 AM   #6
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2003 L-Series 3.0L Sedan
Default Re: 02 LW300 3.0L V6 P0050, P0343 starts only WOT, very rough & barely running

I don't know why the engine revved up to 3k rpm from removing one O2 sensor. Possible vacuum leak? With few vacuum lines, the only ones that comes to mind are the small blue nylon vacuum lines with rubber fittings and one larger line for the brake vacuum boost unit. The brake boost unit uses a hard nylon hose. When the O2 sensor was put back on, did you try starting again?

Drive by wire systems has the ecm (engine computer) controlling throttle. The gas pedal is longer connected to throttle. It's an electronic pedal feeding signals to the ecm. The ecm commands throttle plate movement.

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