My car was on the scanner the other night and my friend said my upstream O2 sensor was slow because my AFR was going rich for awhile and then lean instead of going back and forth quickly like it should. Ive also always had this problem with my car starting when its hot. Could this be an O2 issue? I think when it starts hot the car almost self floods and goes very rich because if I push the pedal down which is clear flood and crank it fires right up.
Edited 1 time(s). Last edited Friday, May 21, 2010 12:37 PM
sounds like it. the sensor is supposed to flop several times per second. if its having slow response issues, put in a new delco sensor.
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How much be the Delco one? Korey was quoting my like $20 for an upstream one from Advance.
TheSundownFire (GME Chat) wrote:How much be the Delco one? Korey was quoting my like $20 for an upstream one from Advance.
sounds like a bosch, possibly a universal one. just go to a dealer and pick up the proper o2. think of it this way, the factory one has lasted this long, may as well replace it with proper parts.
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Well if you have a decent scanner than watch the graph of the sensor. It should jump all over the place. When they go bad they usually stop reading for several seconds. It will flatline basically on the graph. It sounds like you have a different issue if the engine is flooding. The 02 sensor stays in open loop for a few seconds (if the cars hot) after the car is started. It cant calculate AFR when cranking. Theres not enough exhaust gases to calculate from. So that wouldnt be the reason for it flooding. Maybe you have a leaky injector, it would show up on the 02 sensor data as rich or a slow wave on the graph. or you can look at the fuel trim. The threshold is + or - 10% for the fuel trim. If its running rich it will be in the - b/c its trying to subtract fuel and + to add (so subtract fuel for rich and add for lean) and it has to be less than -10 or more than +10 to be considered rich or lean, if its not than it is running normally. If you can read misfires then maybe when you first start it you can see which cyl misfires from the excess fuel. Or pull spark plugs and see which one is fouled. Then continue from there. If you get some data post it and it might help in diagnosing. Hope this helps
Lots of time a faulty ECT sensor will give a hard start when hot
If it is reading say 5volts, which is fully cold -38F, it will it more gas, as the engine needs more gas from a cold start, because it vaporizes easier in cold engine temp,than a warm engine.
If you have a decent scanner, you watch see the ECT voltage
- 2004 Cavalier - 124k, owned since new
Its just a Snap On OBDII scanner IIRC. Ill try to get it on the scanner again this week and check that stuff and report back.
Checked ETC and fuel trim on start-up. 0% fuel trim on start-up and the ETC is operating properly.
Changed the O2 and the sensor still flops slow so its not the sensor itself thats causing this. Its either really rich or really lean. We don't have exact AFRs though. It wont flop quickly. He thinks its a bad injector sticking open too long and causing a rich condition on start up and during cruising causing the ECU to lean it out.
So Im at a loss. I dont want start throwing money at it replacing injectors because frankly Im poor as hell.
Bump. I want to get this running right.
fuel trim should be 0% on start up because the oxygen sensors are in open loop. Fuel trim regulates fuel off of the oxygen sensor readings when they are in open loop. what is the fuel trim reading? try going out to the car in the morning (if you have the time lol) and pulling spark plugs and shine a light in the cyl to see which one's full of fuel... if its an injector issue. also the spark plug will be fouled and smell strongly of fuel... if its an injector lol. If that doesnt show anything than back to the drawing board lol... meaning more data lol. but most likely if its flooded in the morning its a leaky injector. or a head gasket filling the cyl with coolant... dats the only other thing ive had but the billowing white smoke and no coolant is a dead givaway lol.
Ill check out the cylinders in the morning. And it is very possible that I could have a blown head gasket since its original to the car.
How do you guys feel about the MAF sensor?
It might explain my surging problem when the cars hot too.
Question...both of my cars are pretty high mileage (130,000 and 148,000 miles) and are on their original O2 sensors. Would it be a good idea to change the upstreams as a maintenance thing or should I just wait until one actually goes out?
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@Rob You need more fuel when an engine is cold so that it will warm up quickly and run properly. It has nothing to do with the fuel atomizing more easily. Cold fuel and air produces more power (debatable) because the molecules are closer together.
@Ronin J Don't change O2 sensors until they go bad. The ECM will let you know when they are bad.
@OP When you hold down the pedal while starting this tells the ECM to hold back all fuel incase your engine is flooded.
