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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / November 2005What's the sensor on the air box called?
Hi Everyone, I have a 97 Buick Riviera with GM's 3800 II 3.8 engine w/supercharger. There's a sensor mounted on the air box directly over the air filter. I am assuming it's to tell the computer what the temperature of the air is. Is this correct? Also does anyone know what this sensor would be called? I have a problem with my Riviera where if I run it, get out, let it cool to 160 degrees it wont start. It turns over but nothing catches. It happens at random times. I can reproduce it by starting my car in the cold and then immediately trying to restart it, and it doesnt work. My mechanic and I cannot figure it out. Thanks, Sam > I have a 97 Buick Riviera with GM's 3800 II 3.8 engine > w/supercharger. There's a sensor mounted on the air box directly over [quoted text clipped - 5 lines] > it by starting my car in the cold and then immediately trying to > restart it, and it doesnt work. My mechanic and I cannot figure it out. Intake Air Temperature (IAT) Sensor, doubt it has anything to do with your problem. What's it responsible for? > What's it responsible for? As per GM: "The IAT sensor signal is used to adjust spark timing according to incoming air denisty." >> What's it responsible for? > >As per GM: > >"The IAT sensor signal is used to adjust spark timing according to incoming >air denisty." But even that is a little squirrily, as air density is determined not only by temperature but also by _altitude_. So the IAT is going to give the correct signal at sea level...what happens when you drive up into the mountains? The thrust of my question revolving around the supposition that the fuel/air mix is aiming at 14.7 air to 1 part fuel. How does the engine know when it is operating in a low atmospheric pressure region vs. sea level? Lg > >"The IAT sensor signal is used to adjust spark timing according to incoming > >air denisty." [quoted text clipped - 9 lines] > How does the engine know when it is operating in a low atmospheric > pressure region vs. sea level? That's where the Manifold Air Pressure (MAP) sensor (if equipped) and the Mass Air Flow (MAF) Sensor (if equipped) come into play. Sounds like you need to sit down with a good book on modern engine management systems. It will answer all your questions. ;) Steve >> >"The IAT sensor signal is used to adjust spark timing according to >incoming [quoted text clipped - 18 lines] > >Steve I've got a MAF. But no MAP. Just an IAT and a MAF as far as I can tell. Yes, I have an interest in purchasing the CDX series on engines at their website, but with the holiday season coming, my money is going to gifts for other people instead of this much needed addition to my library. Maybe in January, if nothing else comes up. I like their DVD training materials, from the www, which I looked at the other day. Sort of doing this for my own hobby/edification. In the meantime, I am picking up tidbits from this n/g and other sources here and there. When I get the CDX series on DVD, THEN yes I can come out of the closet and start futzing around without wearing a BURKA! ;-) Lg >> What's it responsible for? > >As per GM: > >"The IAT sensor signal is used to adjust spark timing according to incoming >air denisty." But even that is a little squirrily, as air density is determined not only by temperature but also by _altitude_. So the IAT is going to give the correct signal at sea level...what happens when you drive up into the mountains? The thrust of my question revolving around the supposition that the fuel/air mix is aiming at 14.7 air to 1 part fuel. How does the engine know when it is operating in a low atmospheric pressure region vs. sea level? Lg ============================================================ I think the engine hasn't a clue about barometric pressure. I think what it does is adjust the fuel trims depending on feedback from the O2S1's on side A and side B. IOW, it increases/decreases fuel injector pulse width, taking into consideration the Hg vacuum in the intake manifold. And it may advance or retard the timing accordingly. IOW, the barometric *sensor* is the exhause from the cylinders and the O2 sensor feedback to the PCM. YES? maybe. Lg > I think the engine hasn't a clue about barometric pressure. Depends on the system. Most Chrysler, older Fords and many GM systems have a MAP sensor which takes a BARO reading when the key is first turned on, the BARO reading can and usually is updated when throttle position exceeds a pre-determined level. MAF systems without a MAP/BARO sensor do not need to know barometric pressure since the MAF sensor measures the -mass- of the incoming air, Ford systems -do- infer a BARO reading at or near WOT as a method of fine tuning the fuel delivery. The methods used are not foolproof, it -is- possible to create a driveability problem when operating a vehicle thru varying altitudes. i.e., descending from the mountains of Colorado, WOT would possibly never be used so the BARO doesn't get updated, the engine will run leaner as the altitude decreases and usually doesn't correct itself unless a fuel or rest stop is taken where the engine is switched off and restarted. > I think what it does is adjust the fuel trims depending on feedback > from the O2S1's on side A and side B. Problem with that is at one extreme or the other, the fuel trims would be maxed out setting a trouble code. > IOW, it increases/decreases fuel injector pulse width, taking into > consideration the Hg vacuum in the intake manifold. And it may > advance or retard the timing accordingly. But not every system -has- a method of measuring intake vacuum. The Mercury you're driving doesn't, although as mentioned above, BARO can be and is inferred via the MAF reading at WOT. > IOW, the barometric *sensor* is the exhause from the cylinders and the > O2 sensor feedback to the PCM. > > YES? No. > maybe. Nope. >> I think the engine hasn't a clue about barometric pressure. > [quoted text clipped - 40 lines] > >Nope. So to continue this thought before I go out to Larry's Backyard Car Barn and proceed with surgery on my only vehicle ( my wife doesn't know any better so she lets me get away with this nonsense! )... I am driving say my Sable ( taurus ) into the Appalachian mountains. I did this actually with a Buick. Pinging was enormous. You almost couldn't hear anything but engine pinging because of octane deficit and pre-detonation! My taurus ( I mean Sable ) is getting less wind as air thins out. MAF senses this, leans mixture. Injector pulse width increases. I get to the top of the mountain ( I call it a mountain...you can see 5 States from Lookout Mountain! and then I start the descent. MAF senses increasing density of air, and enriches mixture to match increased O2 while at the same time shortening pulse width of fuel injectors. Is this close? Is it in the ballpark? Or is this a YER OUT! when I have to drop the bat and return to the dugout with my head looking at my feet? So it is all up to the MAF and IAT in my engine, being a Fix Or Repair Daily. Yes? maybe. Now I go and put in a NEW battery and believe the CCA is enough to do the job, because this week, Saturday to be precise, I put in 5W-20 SYNTHETIC. That means easier starts, less trouble with cold weather starts, and less friction. Going to 4 months or 7,500 miles, whichever comes first. Lg > So to continue this thought before I go out to Larry's Backyard Car > Barn and proceed with surgery on my only vehicle ( my wife doesn't [quoted text clipped - 4 lines] > couldn't hear anything but engine pinging because of octane deficit > and pre-detonation! Octane requirements go down as altitude increases... > My taurus ( I mean Sable ) is getting less wind as air thins out. MAF > senses this, leans mixture. Injector pulse width increases. Decreases. To lean the mixture, injector pulse would need to be decreased. But, as we go up in altitude, the injector pulse decreasing would still maintain stoichiometric, so the term "lean" is a bit of a misnomer. > I get to > the top of the mountain ( I call it a mountain...you can see 5 States > from Lookout Mountain! and then I start the descent. MAF senses > increasing density of air, and enriches mixture to match increased O2 > while at the same time shortening pulse width of fuel injectors. ^^^^^^^ Lengthening. > Is this close? Is it in the ballpark? Or is this a YER OUT! when I > have to drop the bat and return to the dugout with my head looking at > my feet? Other than having the pulse widths flip-flopped, you're understanding it. > So it is all up to the MAF and IAT in my engine, being a Fix Or Repair > Daily. That and an RPM signal. > Yes? > [quoted text clipped - 5 lines] > starts, and less friction. Going to 4 months or 7,500 miles, > whichever comes first. Weren't you supposed to be using 5W20 anyway? >> So to continue this thought before I go out to Larry's Backyard Car >> Barn and proceed with surgery on my only vehicle ( my wife doesn't [quoted text clipped - 46 lines] > >Weren't you supposed to be using 5W20 anyway? I do. Valvoline 5W-20. But I want to keep engine wear down and make cold starts easier on my vehicle. It can go to -20F on the thermo here, it has in the past, with windchill into -80F. Then, synthetic will be lubricating while regular dino will still be hard as a rock at the bottom of the oil sump ;-\ I am going to have fun with electricity now. You are always the best instructor. You should do it for a living. I save your posts to my newsreader because they make an interesting and informative notebook. Thanks again for you excellent instructions. I think you are the best. Lg > >Weren't you supposed to be using 5W20 anyway? > [quoted text clipped - 3 lines] > will be lubricating while regular dino will still be hard as a rock at > the bottom of the oil sump ;-\ You're forgetting, I live 90 miles north of you, 2 miles off the big pond. > I am going to have fun with electricity now. You are always the best > instructor. You should do it for a living. I save your posts to my > newsreader because they make an interesting and informative notebook. I did do it for a living. Extensive travel wore me down. Airlines suck! Now that I have a few dozen (+or -) pins holding my legs together, wire across my ribcage and a few stents, I can only imagine that they'd suck even more. > Thanks again for you excellent instructions. I think you are the > best. Thanks. >> >Weren't you supposed to be using 5W20 anyway? >> [quoted text clipped - 21 lines] > >Thanks. And, may your recovery be quick and complete! Lugnut > Hi Everyone, > [quoted text clipped - 11 lines] > > Sam If this sensor has a three wire connection, then it's your Mass Airflow Sensor. It's very unlikely that your MAF could cause a no start at a given engine temperature, because it stays at underhood temp (much lower). I would think about testing the ignition control module outputs to the coilpacks to see if it is failing when the car acts up. The ICM and coils *are* affected by engine temp on your 3.8 (right on the engine). Toyota MDT in MO usshopkins@yahoo.com wrote in news:1133225476.286015.126870 @g14g2000cwa.googlegroups.com: > Hi Everyone, > [quoted text clipped - 11 lines] > > Sam Hi, Firstly the sensor on the air box is called IAT, this just changes the spark timing of the engine depending on the temperature of the intake air, thats all. Normally retards the spark in the region of -28 to 24 deg C, and advances the spark in 24 to 40 degC and again retards the spark for above 40deg C The changes in the altitude and load( throttle opening) is read by MAP sensor. At higher altitude the multiplier reduces the amount of fuel, and sea level it increases. Now coming to your problem with riviera, this kind of problem is called vapour locking. If you have started noticing it now and was not there earlier,then u first need to replace the pressure regulator in the fuel system. If the pressure regulator has worn out and the system pressure has fallen, fuel gets vaporised (phase change) inside the rail or the pipe connecting the rail. Hence the pump will not be able to develop pressure and pump the fuel. If you continue to run the vehicle further on, you will notice a steep fall in the fuel economy. If you cant find the pressure regulator, write to me again, i would be glad to tell you more. Regards Raja Bangalore The 160 nostart condition started 4 years ago. Maybe would happen 2-3 times a year. Now it happens 10-15 times a week. Recently it has started to stall at high speeds. It'll chunk a little (like a neutral drop in) then die. Does it going up a hill. One time it did it and the engine was completely silent for about 3 seconds as I coasted and then all of the sudden it restarted itself. When it does the high speed stall I have to pull over and crank and wait for about 5 minutes before it restarts. The last time I could hear certain cylinders firing, but it just wouldnt catch. Is there anyway I can test for vapor lock? I only have a window of 2 seconds to 5 minutes to do this and i'm usually in good clothes in a parking lot when it happens.... =( usshopkins@yahoo.com wrote in news:1133276399.719842.117420 @g43g2000cwa.googlegroups.com: > The 160 nostart condition started 4 years ago. Maybe would happen 2-3 > times a year. Now it happens 10-15 times a week. Recently it has [quoted text clipped - 9 lines] > seconds to 5 minutes to do this and i'm usually in good clothes in a > parking lot when it happens.... =( 160deg no start and high speed stall happens for two seperate reasons. I mean to say that 160deg no start happens for vapour lock and stalling at high speeds can be due to several reasons, Firstly if this 160 no start is happening from past four years then you should report this to manufacturer. They might have not done the vapour lock tests at all before relaesing it to market. or they might have fixed a defective pressure regulator. To do a test on vapor lock you need to choose a pretty hot day, drive till 170deg, leave it in idle for two mins, or switch off immediately and wait for a minute. Then try to start, if the engien starts then there is no vapour lock. This can be avoided to a little extent if the fuel pipes (if hanging or touching the engine) be re-routed such a way they avoid direct contact with the engine. High speed stall can happen for two reasons if you filter or the pump strainer is clogged if the cdi or coil ignition is not generating enough energy i have seen in some fuel injection bikes where the high speed stall happens even when the electrical connector to the injector might get loose due to higher vibrations. i suggest to check the filter first. Find a mechanic who has an OBD2 tester and he can determine if the sensors and good or bad. He should be able to determine your problem without all the hindsight and guessing in this thread. Or buy one yourself and learn how to use it. There are several out there that run on a laptop fairly cheap. > Hi Everyone, > [quoted text clipped - 11 lines] > > Sam It doesnt throw any codes.
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