Hi all. I haven't done much work on cars, but i'm trying to learn.So anyhow, the check engine light on my 99 sunfire comes on. A buddy who has an OBD reader runs the codes for me, and i'm getting codes on both O2 sensors.. sounds like an easy enough fix, so I figure I'll try it.I got the pre-cat sensor swapped out easily enough (the one on the manifold) but I'm having a lot of trouble getting the post-cat sensor off. I don't have a hydraulic jack or jack stands, and even with a ton of WD-40 I can't get it to budge.Any ideas? I may be able to borrow ramps from a friend - would raising one side of the car on ramps be worthwhile? Alternately, I have a buddy who has a jack and stands, but it might be a couple weeks before we can get together and I'd like to get it done before then if at all possible...
Can't really offer much advice on how to get the sensor off, but I will comment that O2 sesnor codes are quite often a symptom of a different problem altogether. Especially when both sensors turn up a code.I would suggest a more thorough diagnosis before throwing parts at your problem. I understand aftermarket o2 sensors can seem relatively cheep...I know of many in the sub $20 range. This may "fix" your problem for a while, but only until the condition that caused the sensors to fail (or more likely read outside the parameters of the ECM) is corrected.Some more common sources of O2 sensor problems are: Bad MAF, air/vacuum leak, faulty injector(s), manifold leak, oil/contamination in the wiring harnes that provides reference air to the o2 sensor, and finally, 1 faulty o2 sensor can often cause the other to provide bad input to the ECM triggering a fault on the sensor that is functioning properly.
So anyhow, the check engine light on my 99 sunfire comes on. A buddy who has an OBD reader runs the codes for me, and i'm getting codes on both O2 sensors.. sounds like an easy enough fix, so I figure I'll try it.I agree with ToddTruby. The likelihood that your problem is your O2 sensors is very small. O2Ss degrade gracefully, and for both O2Ss to degrade simultaneously would be extraordinary.Depending on the sophistication of the code reader you're using, you might be able to look at the voltage from the O2Ss. You could also put a voltmeter on each of the two O2Ss, but be careful - exhaust gases are well over 1,000 F, and the plumbing gets VERY hot.You should see that once the engine is at its normal operating temperature (it's operating in closed loop), the pre-cat O2S ranges between 250 mV and 750 mV with a frequency somewhere between 10 Hz and 30 Hz, and the post-cat O2S holds more or less steady around 500 mV. The service manual for your car will give you the specifications.The service manual for your car, it will have a diagnostic chart that will help you to diagnose and fix the problem. You might be able to borrow a copy from your library or you can buy a copy from your dealer (about $100). Don't waste your time with Chilton's for a problem like this. You need something more along the line of Motor or your dealer's manual. For your Pontiac Sunfire, you can surf to (for a fee):http://www.gmtechinfo.com/Your problem is either too much air or not enough fuel is getting into the system and upsetting the O2Ss. A gas analyzer could tell you a lot. A careful inspection of the exhaust plumbing could be revealing. A careful inspection of the vacuum plumbing might be a good use of your time (but I wouldn't bet my money there).I'd check for pressure and volume of fuel at the fuel rail to rule out a fuel problem. Is your car hard to start when the engine is cold, but then it starts fine when the engine is warm? You could tap your fuel pump relay to look at the fuel pump motor and compare it to specs.I don't buy the story that you have a bad MAF. If the MAF were bad, it would throw a code, and if it didn't throw a code, then the Long Term Fuel Trim and Short Term Fuel Trim would be out of whack - maybe they wouldn't throw a code, but they'd be out of whack.Fuel injectors are not good projects for newbies. To diagnose them, you need equipment that you probably don't have lying around the house, injectors are too easy to break, and they're usually hard to get to.If you're determined to get that post-cat O2S out, apply penetrating oil, and let it soak. WD40 is the high school solution. Your local auto parts store can tell you about the college solution - I like PB Blaster. If that O2S is stubborn, then you'll have to heat the "bolt hole" without heating the O2S. A hair dryer might work, but a heat gun would work better.David JacobsTMFDj
Although I agree with both excellent replies, and I agree that there is probably a bigger problem at play here - it is worth noting it is a seven year old car, but to have both O2 sensors go at the same time, pretty unusual.
Thanks for all the responses. I definitely appreciate the feedback.It seems the consensus is that it may not be the O2S after all, but at this point I think I'm going to have to keep plugging along and get it replaced. I've been banging on the stuck one enough that if it wasn't malfunctioning, it probably is by now. also, the car is at 87,000 miles and is about 8 years old, so they're probably due for a replacement anyhow. If that doesn't clear the codes, I'll move on to some of your other suggestions (once I can figure out exactly what they mean.. heh)For what it's worth, it seems to be running more or less okay. It's been a little rougher and louder, but I figure that's probably more or less normal at this age. It seems to be smoother running after replacing the manifold sensor, but that could've just been psychosomatic I suppose. I have not noticed any difficulty in starting it, but who knows what this upcoming winter will hold.Thanks again for all the help. I'll try some other penetrating oil, and get the car jacked up to see if I can get the thing to budge.
So anyhow, the check engine light on my 99 sunfire comes on. A buddy who has an OBD reader runs the codes for me, and i'm getting codes on both O2 sensors. sounds like an easy enough fix, so I figure I'll try it.I was thinking about this post last night as I was dropping off to sleep. Yes, I know - I've got to get a life.Driveability problems are not good problems for newbies. They're fun problems to solve, but you need experience to do them well. If you don't have the experience, they can drain the enthusiasm out of you and put a bad taste for auto tech in your mouth.I would much rather see newbies start with inspecting fluids, then replacing fluids. After newbies develop proficiency there, then they could replace brake linings, and move on to replacing shock absorbers in McPherson strut assemblies (with a mentor). Replacing fuel filters (with a mentor) is a good, advanced newbie chore. Driveability would be something more experienced hobbyists would attack after they develop proficiency applying Ohm's Law, reading schematic diagrams, using Digital Multimeters and Digital Storage Oscilloscopes, and using shop manuals and other reference materials, probably with the help of a mentor.I think that it's VITAL that newbies apply safety rules.ALWAYS wear safety glasses that pass the ANSI Z78 spec. Friends will laugh at you for wearing safety glasses, but a flake of rust or a drop of fluid in your eye will ruin your day, and you'll end up visiting doctors twice a week for a month as they monitor the healing process. A few years ago, I got a grain of sand in my eye while riding my bicycle. The grain ground around my cornea for a while before it washed out. The experience was not fun, and now I wear safety glasses when I ride my bicycle.I harp on wearing gloves. Auto fluids have gotten increasingly dangerous. Often they transport stuff through the skin, and the cumulative effects of this junk can be medically significant. I wear nitrile gloves when I wrench. When newbies start wrenching, the gloves tear every few minutes, and newbies will wonder whether wearing the gloves is worth the time and expense. As newbies develop their mechanical skills and graduate to hobbyists, they'll tear their gloves less often. I wear mechanics gloves every time I'm even remotely close to a radiator (condenser or heat exchanger), and every time I'm even remotely close to anything hot. Pulling on the gloves takes a moment, and healing an abrasion or a burn takes weeks.I also harp on wearing appropriate clothes. Closed toe, leather shoes; reasonbly tightly fitting clothing; and NO JEWELRY are good starts. Shoes will protect your feet from dropped parts and spilled fluids. Appropriate clothing won't get caught in moving parts. A wedding band shorted between B+ and ground can get red hot in about 1/5 second, and other jewelry can get caught in parts or attract sparks.I think the most important safety rule is to use a mentor. Auto tech is a fun hobby, but cars and motorcycles are increasingly complicated systems of interacting systems. Too often tasks that appear easy are not, and a mentor can help you through the rough spots. I have an AAS in auto tech, and I still talk to more experienced techs when I run into problems. The service manager for the dealership that supports your car or motorcycle can refer you to a local car club, and from there you should be able to find a mentor.For reading materials, I like Motor Age:http://www.motorage.com/Motor Magazine:http://www.motor.com/For reference materials, I likeBentleyhttp://www.bentleypublishers.com/Motor Mechanical Manuals:http://www.motor.com/For electronic reference materials, I'm very fond of AllData (for a fee):http://www.alldatadiy.com/When I need schematics, I prefer Mitchell OnDemand (for a fee):http://www.ondemand5.com/By federal law, all automotive OEMs are required to make emissions and driveability information available to the public, although they are allowed to charge fees for this information. This website has a roster of these OEM websites:http://www.nastf.org/oem.htmlDavid JacobsTMFDj
Thanks again for all the help. I'll try some other penetrating oil, and get the car jacked up to see if I can get the thing to budge. Get a breaker bar on it. It will eventually break free.
Wow, TMFDj.. thanks a ton for all the advice!What you say makes a lot of sense, and I'll certainl take it under consideration. Fluids are probably a good idea, and I may start doing that sort of stuff myself as well (at least on this car, leave the new one to the dealership for now.)As for the other suggestions of good newbie projects, I'll keep that list around. The problem is, I have a car with 'driveability' issues now, but it's not in need of brakes, shocks, struts, fuel filter, etc.. so that poses a problem in following your ideal order of things. While I'd love to be able to start off with simpler things, I'm somewhat limited by what needs fixing on a car that I've got access to.On the safety point, I couldn't agree more. I've been wearing glasses, and gloves (but only when near hot areas) and NEVER jewelry or open toed shoes. I've got a little bit of a background in woodworking, and am extremel familiar with electronics, both of which have their own safety considerations which in many cases seem to overlap with auto mechanics.Thanks again for the informative post. I'll have to look through all those links!
I was thinking about this post last night as I was dropping off to sleep.Awesome post!This should be included as part of the FAQ ------->ßillƒ
and move on to replacing shock absorbers in McPherson strut assemblies (with a mentor).Been there, done that last year for the first time and it was a blast! Saved a TON of money, by the book it is almost 8 hours labor for a Pontiac Grand Prix. We did the whole car in under three hours, OK,OK, so there were five of us and we were moving like a pit crew once we figured out the spring compressor and secured a second one to move in parallel.
Awesome post!This should be included as part of the FAQ ------->ßillƒI second Foolish gods, part of the FAQ -------------->
You should see that once the engine is at its normal operating temperature (it's operating in closed loop), the pre-cat O2S ranges between 250 mV and 750 mV with a frequency somewhere between 10 Hz and 30 Hz, and the post-cat O2S holds more or less steady around 500 mV. The service manual for your car will give you the specifications.I agree, the problem is most likely not the O2 sensors. Best to check with your voltmeter as TMFdj suggested.If that O2S is stubborn, then you'll have to heat the "bolt hole" without heating the O2S. A hair dryer might work, but a heat gun would work better. I don't see how a heat gun could ever get it hot enough, but its worth a try!What sometimes works with exhaust bolts is to heat the bolt cherry red with a gas welder, then remove it just after the color goes away. Don't ask me why it works, and i don't know if there is a way to make that trick work with an 02 sensor. If you don't mind breaking it and the pipe is strong enough (and held firmly in place), use an impact driver.If and when you put the new one on, use some antiseize compound on the threads, just in case you or someone you know ever has to take it off again!
I harp on wearing gloves. Auto fluids have gotten increasingly dangerous. Often they transport stuff through the skin, and the cumulative effects of this junk can be medically significant.I couldn't agree more. Back in the '80s we never wore gloves and i regret that to this day. The harsh solvents get absorbed into the skin and attack organs, God knows what damage that does long-term- but kidney damage, tumors, failure, skin cancer etc are noted for gasoline alone- (http://www.cenex.com/%5CLinkedContent%5CPDF%5CRF%5CMSDS%5CUNLEADED-GASOLINE-WITH-ETHANOL.pdf#search=%22benzene%20target%20organs%22.) Even used oil contains benzene and other potent carcinogens, so, hey, be careful out there!
I also have a 99 Sunfire,(130,00 miles) and once or twice a year I was getting a multiple O2 sensor failure codes, but they always checked out fine. After grousing about this to an AutoZone parts counter fella, he mentioned I should try tifghtening up my gas cap, and make certain it was sealing correctly. 100% of the time the problem has been fixed by retightening my gas cap. I replaced my gas cap in the Spring last year, and I haven't seen an error code since...$6 for the new gas cap.Now, if I could only figure out why I have to replace the water pump once a year...and always in July or August. At least it's an 'easy' fix in this car. --------------rfmjbs-who thinks she's going to preemptively replace the $30 water pump in March next year to avoid this 3 hours in the heat misery :)
Now, if I could only figure out why I have to replace the water pump once a year................................................... Pardon my for asking but,is it failing as in leaking OR is the engine just running too hot and the garage guy throws another water pump at it ? Sounds kinda strange :)Pete
Now, if I could only figure out why I have to replace the water pump once a year...and always in July or August. At least it's an 'easy' fix in this car.There's definitely something wrong there. A water pump should be a 100k mile or 5+ year part. The first thing that pops into my mind is grossly overtightening the belt that drives the water pump. That would put an excessive load on its bearing and lead to a premature failure.--Peter
Failing as in leaking.
Peter,I can imagine a few ways that 'overtightening' might have happened while my dear hubby was swearing at it last summer :) I'll mention that possibility to my DH when he gets time to fix it next week. I'll tell him to be much more careful this time. The one time the car was seriously overheating (instead of just gushing out coolant), it was a fan motor that was out... and strangely enough, I felt that was a MUCH more difficult component for me to replace even though only a handful of screws were involved. It only took 90 minutes, but I used a LOT more harsh language when I did it. The plastic housing for the fan motor was incredibly resistant to removal. Thanks!
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