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Discussion Starter #1
i have a 90 rolla and it has black smoke and it takes alot of gas. i took it to a mechanic he told me that everything look good. he did all diognostics and everything looked clean. my uncle and i checked everything out and still could not figure it out. i used 2 cans of intake cleaner through the intake valves. still smokes the spark plugs i changed and they are already black the 3rd week they been there. i put a hell alot of STP fuel injection cleaners like 2 things per fillup at the gas station, then i added 1 more when my tank was half way. i was wondering if anyone had any advice or had this similiar problem. i been pulling hair out of my head to figure this one out. please help any advice is well apprieciatted.
 

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Resident asshole
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Maybe its the intake cleaner that you're putting into it. OR you're leaking oil to the cyls, check your oil levels.
 

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well first things first is that putting MORE cleaner/additives than is reccomended does nothing but harm your engine. If your spark plugs are black after 3 weeks and your exhaust is black that means that it is running rich (too much gas) mabee your air filter is plugged and it is choking itself all of the time, or you arnt getting enouch spark to ignite the gas, or you need to replace your injectors OR your computer is malfunctioning and sending too much gas to air.

Jeff
 

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Discussion Starter #4
i changed the air filters and did everything that i could think of but thanks i will look into those things that you mentioned.
 

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change the o2 sensor.... black smoke means you're not burning all of your fuel.... i'm guessing your o2 sensor is out.... when it doesn't read correctly it always reads lean, and adds extra fuel...
 

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Discussion Starter #6
toyotaspeed90 said:
change the o2 sensor.... black smoke means you're not burning all of your fuel.... i'm guessing your o2 sensor is out.... when it doesn't read correctly it always reads lean, and adds extra fuel...
that was the first thing i did that was the first thought i did that and still same problem. i thinking about checking the injectors but i wont do it by myself i get my uncle to help me since i do not totally know what i am doing. if the injectors are ok then i know it has to be the computer malfuncitoning. i checked the fuses and the compacitorsand relays. god this is soo confusing.
 

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Maybe the manifold absolute pressure sensor (MAP) is screwed up? This sensor tells the engine computer how much vacuum is in the intake manifold, which gives the computer an idea of how much fuel is needed at the injectors. If the MAP is defective, it could cause the ECM to think that the engine is getting more air than it really is, so in response the ECM ups the amount of fuel the injectors spit into the engine (causing the black smoke). Could be an intake air temp sensor (IAT), too. This tells the computer how hot or cold the air entering the engine is (cold air is more dense than hot air), which allows the ECM to adjust the fuel delivered by the injectors. If it is defective, then it could be telling the computer that the air entering the intake is cooler (and therefore denser) than it is, causing the ECM to deliver too much gas. It also might be a defective fuel-pressure regulator. EFI systems use electric fuel pumps located in the gas tank to deliver a constant high-pressure fuel flow to the injector rail. The pressure at the injectors is usually about 40 psi. To keep it from going much over (or under) 40 psi, the injector rail has a fuel pressure regulator. This regulator allows excess fuel pressure from the fuel pump to be bled off through a return line and go back to the fuel tank. If this is defective, then the injectors could be getting way too much fuel pressure, which might cause an over-rich mixture. Could also be a bad throttle postion sensor (TPS). This gizmo is on the side of the throttle body, and lets the engine computer know how much you are opening the throttle when you step on the gas pedal. If this is defective it usually causes a hesitation or stumble in addition to the black smoke, but it might be something to check. You might also consider checking your timing and your exhaust gas recirculation (EGR) system. Good luck, and let me know what you find out (cuz' I have a '90 Corolla too!:lol: ) Regards, Aaron
 

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Discussion Starter #8
how can i go about checking the map sensor. i looked at it breifly where it is at on my car and i was wondering how do you check it.
 

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i woulda thought youd get a check engine light if a sensor was bad.
obviously the mechanic missed something...
i gotta go with cobra in the idea that its in the fuel system.
this IS confusing....
 

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Discussion Starter #10
i got a map sensor off a wrecked toyota like mine off ebay i hope this works the sensor was only 8 bucks. i am waiting for it to get here i will let you know if it isi nto that then i go to the next thing down the list.
 

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If its blowing black smoke its running rich... i'd go with toyotaspeed on this one... check your 02 sensor...

*edit* sorry, didnt read far enough down.. you could also maybe be having the same problem i'm having... Just got my car back from Perth Petrol Injection.. turns out the vacum hose on the fuel pressure regulator is pulsing causing my a/f mix to run rich/lean/rich etc.. Could be that. If it is... you need to get a dampner of some sort or find a constant manifold pressure vacum and tap into that.
 

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A check engine light will often only come on if the sensor registers a value that is beyond the ECM's preprogrammed operational range for that sensor. The sensor could still be malfunctioning while staying in the range that the computer says it should be in. Does this make sense? If the proper range of a sensor is 1-10 volts, then the check engine light will often only come on if it registers 0, 11, or 12 volts. However, if the sensor is supposed to be reading 5 volts and for some reason it is instead reading 9, the check engine light will not come on even though there is a malfuction (because 9v is still in the 1-10v operating range). In short, it could be a sensor even though there is not a check engine malfunction light. This is rare, though, and other things should usually be checked first. With black smoke, the engine is either getting too much fuel OR not enough air, so check the air intake system, too. The '90-'92 Corollas also have what is called a "cold-start injector". This opens to give the engine a bit more fuel when it is cold, and is supposed to shut off when it is warmed up. If it is stuck, then it could be giving the engine a perpetually rich mixture, thus causing the black smoke from the unburned fuel. The cold-start injector is located right on the front of the intake plenum above the fuel injector rail. Just look for the fuel line that goes to it. This might be the next thing to check. Good luck!:D Regards, Aaron:D
 

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Discussion Starter #15
thank you aron it makes alot of sense my uncle and i did check the cold start injector but i doubt we knew what we was doing when we checked and that is what the mechanic said what it could be because he had a similiar prob with his toyota.
 

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I would check for a cracked exhaust manifold also; any leaks will screw up the O2 sensor readings.
Other than that, I'd try the map sensor.
And don't over use the fuel additives; they'll soften/ erode the injectors, fuel pump parts if abused.
Saw a new Lincoln run very rich after it's owner had done what you described, had to get all new injectors to run again.
Good luck
 

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I think that one of my 02 sensors if malfunctioning since my corolla gets only about 20 mpg.

I have not checked to see if there is black smoke coming out of the exhaust but I do get a strong exhaust smell.

Since i have two o2 sensors on my car, which one affects the fuel economy? the one close to the engine or the other one by the catalytic converter?

thanks!
 

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Discussion Starter #20
I no longer will have this problem since i proudly bought a 98 camry and no longer will own my corolla once i sold it but thanks to everyone for the advice
 
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