Looking for help with 02 readings
08-04-2024, 02:01 AM
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Looking for help with 02 readings I have had this problem for far too long. Narrowed it down a bit, O2 readings are around .030 both sides at idle but climb into the .900 range with throttle. brand new denso O2 sensors and brand new spark plugs. I was unable to find any vacuum or ehaust leaks, Attached are tune and log files. Somebody please help. Is it a tune problem or is it something else? It runs awesome with the new plugs in it, but that will only last until the plugs get fouled again. This is a 383 stroker with mms heads, 237/242 cam and fast 102/102. I am running FAST 36lb injectors on pump gas.
08-04-2024, 03:38 AM
#2
You absolutely have tune problems, but you also need to sort out the throttle body problem and verify your fuel pressure. Your IAC is maxed out when the motor is cold and still open way too far when it warms up. You are not logging enough channels to be of much use for the log. At minimum you need injector pulsewidth and cylinder air added in, although there are many others that could be useful. Also, a cam with that much overlap can give false lean readings at idle, so it is even more difficult to diagnose from the limited info available.
08-04-2024, 06:18 AM
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You absolutely have tune problems, but you also need to sort out the throttle body problem and verify your fuel pressure. Your IAC is maxed out when the motor is cold and still open way too far when it warms up. You are not logging enough channels to be of much use for the log. At minimum you need injector pulsewidth and cylinder air added in, although there are many others that could be useful. Also, a cam with that much overlap can give false lean readings at idle, so it is even more difficult to diagnose from the limited info available.
08-04-2024, 02:59 PM
#5
To be more specific, that is what it should read at full operating temperature at idle with no load. This gives plenty of overhead for the IAC to open more for extra electrical load, power steering load, AC load, etc. It will, of course, be open much more when cold. Aftermarket throttle bodies sometimes can be adjusted enough with their set screw, and sometimes you have to drill a small hole for idle airflow. If adjusting with the set screw, you have to watch your throttle position sensor voltage to insure it is not too high when you are trying to idle, or the computer will always think you are holding the throttle open.
08-04-2024, 08:47 PM
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You absolutely have tune problems, but you also need to sort out the throttle body problem and verify your fuel pressure. Your IAC is maxed out when the motor is cold and still open way too far when it warms up. You are not logging enough channels to be of much use for the log. At minimum you need injector pulsewidth and cylinder air added in, although there are many others that could be useful. Also, a cam with that much overlap can give false lean readings at idle, so it is even more difficult to diagnose from the limited info available.
08-04-2024, 08:58 PM
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I have attached two more log files from today which hopefully have some more usable data. I adjusted the throttle plate today, maybe a little too far as the tps will not read 0% even after tps reset. I guess im going to have to adjust it back closed a bit and drill the plate. The IAC count did come down and after entering closed loop, the O2 sensors show better activity. The downside of this adjustment is that now when I give it throttle it will pop through the exhaust. I don't know if maybe that is a result of the computer not reading that the throttle is closed at idle. Any additionaal help with this problem would be greatly appreciated.
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08-04-2024, 10:10 PM
#8
And that would be why I suggested verifying fuel pressure. I could not be sure from your initial log, but I suspected a problem. Just to be clear, once the mechanical side of things is resolved, you will still need a full tune. I find the o2 sensor behavior suspicious, but it could just be that the fueling is really that far off.
08-04-2024, 10:15 PM
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And that would be why I suggested verifying fuel pressure. I could not be sure from your initial log, but I suspected a problem. Just to be clear, once the mechanical side of things is resolved, you will still need a full tune. I find the o2 sensor behavior suspicious, but it could just be that the fueling is really that far off.