check engine light...
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check engine light...
okay so here is what i think is rather odd. i just cleaned my IAC and replaced the gaskets for it and the throttle body. took it for a test drive. acted like i was pulling a boat anchor behind me for a bit then it came right out of it and took off like a bat out of hell. truck got warmed up and after i turned around to come home the check engine light came on. im thinking okay no big deal i'll scan it when i get home. i come back into town and slow down to 30mph and with in seconds my check engine light goes off. scan it and no codes found...wtf???? its a 94 bronco 302 with E4OD. any thoughts would be great.
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
Did you perform BOTH a KOEO and KOER tests? KOEO test alone may not yield a satisfactory result on its own. The KOER yields results of the responses that the system makes to dynamic changes.
From what you described, I would venture a supposition that your IAC remained stuck open until the truck warmed up. The computer, unable to compensate for the additional air in the mix, triggered the CEL while the condition existed and when the IAC finally closed turn it off simply because the condition was no longer present. Since this is a dynamic change, unless the condition exists for the last 40 operations of the engine, the KOEO test will not return the fault code.
From what you described, I would venture a supposition that your IAC remained stuck open until the truck warmed up. The computer, unable to compensate for the additional air in the mix, triggered the CEL while the condition existed and when the IAC finally closed turn it off simply because the condition was no longer present. Since this is a dynamic change, unless the condition exists for the last 40 operations of the engine, the KOEO test will not return the fault code.
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well i tried the obd I tester and it was failing to connect, when it did connect it said no codes found. we tried engine off and engine running. i'll have to check into it more when i get back from our trip. i never realized how much carbon an egr valve will leave in an intake...man i'd love to have hot tanked the upper intake on that thing. who knows it may have taken a moment to get the iac to operate. i really really really cleaned the crap out of that thing. i had to clean the back side of the throttle plates too. tons of carbon on them. i really hope i can get this idle fixed. i dont like having to worry it might stall while in gear. were the Gt 40 intakes this prone to idle issues? or is it just the truck intakes?
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Joined: Sep 2002
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From: Gateway to the West
The truck upper intakes are so tall and have such long runners with NO way to efficiently clean them since the upper plenum is cast as a single piece. The Edelbrock Performer intake at least has an inspection plate at the top of the runners for cleaning and porting purposes.
And for your IAC issue, it could have simply been a little chunk of errant carbon that stuck in the valve. If you want to know if your efforts have truly been successful AND that the IAC is functioning properly now, warm the truck up to normal op. temp. then disconnect the IAC from the wiring harness. The engine should run briefly then sputter and die. If it does not, you have enough of a vacuum leak somewhere to allow enough air into the engine to keep it idling. If it does die, shut off the truck, reconnect the IAC, clear the fault code you triggered by disconnecting the IAC and rest assured the IAC is doing its job properly.
And for your IAC issue, it could have simply been a little chunk of errant carbon that stuck in the valve. If you want to know if your efforts have truly been successful AND that the IAC is functioning properly now, warm the truck up to normal op. temp. then disconnect the IAC from the wiring harness. The engine should run briefly then sputter and die. If it does not, you have enough of a vacuum leak somewhere to allow enough air into the engine to keep it idling. If it does die, shut off the truck, reconnect the IAC, clear the fault code you triggered by disconnecting the IAC and rest assured the IAC is doing its job properly.
Cargo Master
Joined: May 2004
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Check engine light comes on when excessive emissions is being detected. Turns off if problem corrects itself. I wouldn't get too bent out of shape about it. I'm sure there are more pressing defects in your Bronco than the CEL.
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
CEL comes on when the computer cannot control engine operational parameters or it cannot get an acceptable reading from one of the sensors. The parameters programmed into the computer determine the emissions.
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Cargo Master
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Quote, The OBD II system monitors virtually all emission control systems and components that can affect tailpipe or evaporative emissions. In most cases, malfunctions must be detected before emissions exceed 1.5 times the applicable 50K-100K mile emissions standards. If a system or component exceeds emission thresholds or fails to operate within a numufacturer's specifications, a DTC will be stored and the MIL will be illuminated within two driving cycles. Unquote.
Some think that the OBD II codes are good for troubleshooting problems that are not emissions related, like a malfunctioning distributor that needs to be replace or rebuild, I don't think that.
Some think that the OBD II codes are good for troubleshooting problems that are not emissions related, like a malfunctioning distributor that needs to be replace or rebuild, I don't think that.
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Lead Driver
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From: Gateway to the West
Correct, OBD-II did not appear in the Bronco until 1996. Prior to that Ford's EEC-IV system was the standard emissions/engine control system employed. Both systems use similar sensors. OBD-II requires more sensors due to the greater accuracy with which it controls the engine.
Both systems "monitor" a group of sensors that give the computer engine temperature, intake air temperature, oxygen levels in the exhaust, throttle position, base spark timing and a few other variables. The on-board computer then uses the control devices to regulate engine operation. Insofar as they are capable of extrapolating the level of other exhaust components by getting oxygen levels in the exhaust from the O2 sensor, the term "monitor" is a very loose description of the actual operation of the system.
Both systems "monitor" a group of sensors that give the computer engine temperature, intake air temperature, oxygen levels in the exhaust, throttle position, base spark timing and a few other variables. The on-board computer then uses the control devices to regulate engine operation. Insofar as they are capable of extrapolating the level of other exhaust components by getting oxygen levels in the exhaust from the O2 sensor, the term "monitor" is a very loose description of the actual operation of the system.
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hmmm...true i didnt think about that. perhaps my main issue is fixed from cleaning everything and new gaskets but the ecu still may have some how messed up the iac working right? stranger things have happened.