94 4Runner 22RE sudden poor mileage Codes 52 and 25
01-15-2019, 02:38 PM
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94 4Runner 22RE sudden poor mileage Codes 52 and 25
Hi All. First, I want to say I tried searching this subject before I made a new thread. If it exists already and you can advise me on how to search better, I will remove this thread and look at what you recommend. Now the issue, per the title, this issue started about two months ago with the codes listed. I thought maybe loud valves had triggered the knock sensor, so I adjusted them and they did quiet down, but the codes soon returned. My mileage has dropped between 80-100 miles per tank. BTW, the mileage drops every winter with the onset of cold temps and recovers when it warms up again. Can't find a good thread on diagnosing that one, either. I have read that this vehicle is OBD one and so cannot be accessed for serial data. I thank you in advance for your wisdom!
01-15-2019, 03:03 PM
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You CAN read the OBD 1 serial data https://www.yotatech.com/forums/f116...reader-278801/ (hard to imagine that title could evade your search), but it's not going to help you much.
You don't understand the knock sensor; it's not an "idiot light" to tell you when the engine is knocking. Instead, the ECU constantly advances the ignition timing until it just starts to knock, then backs off. it can only know it's knocking if the knock sensor says so. If the knock sensor stops talking, the ECU throws 52 AND dramatically retards timing to save the engine. (crappy performance, bad mileage)
The sensor itself is basically bullet-proof, but the wiring is not. The ECU is trying to pick out a delicate signal in an (electrically) noisy environment, so the sensor cable is shielded. If the cable is baked or otherwise damaged (after 24 years!), the signal can't get through.
Start there; find the sensor wire, and inspect carefully. I'm not as familiar with the 22re; someone else may give clearer direction.
You don't understand the knock sensor; it's not an "idiot light" to tell you when the engine is knocking. Instead, the ECU constantly advances the ignition timing until it just starts to knock, then backs off. it can only know it's knocking if the knock sensor says so. If the knock sensor stops talking, the ECU throws 52 AND dramatically retards timing to save the engine. (crappy performance, bad mileage)
The sensor itself is basically bullet-proof, but the wiring is not. The ECU is trying to pick out a delicate signal in an (electrically) noisy environment, so the sensor cable is shielded. If the cable is baked or otherwise damaged (after 24 years!), the signal can't get through.
Start there; find the sensor wire, and inspect carefully. I'm not as familiar with the 22re; someone else may give clearer direction.
01-15-2019, 04:38 PM
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You CAN read the OBD 1 serial data https://www.yotatech.com/forums/f116...reader-278801/ (hard to imagine that title could evade your search), but it's not going to help you much.
You don't understand the knock sensor; it's not an "idiot light" to tell you when the engine is knocking. Instead, the ECU constantly advances the ignition timing until it just starts to knock, then backs off. it can only know it's knocking if the knock sensor says so. If the knock sensor stops talking, the ECU throws 52 AND dramatically retards timing to save the engine. (crappy performance, bad mileage)
The sensor itself is basically bullet-proof, but the wiring is not. The ECU is trying to pick out a delicate signal in an (electrically) noisy environment, so the sensor cable is shielded. If the cable is baked or otherwise damaged (after 24 years!), the signal can't get through.
Start there; find the sensor wire, and inspect carefully. I'm not as familiar with the 22re; someone else may give clearer direction.
You don't understand the knock sensor; it's not an "idiot light" to tell you when the engine is knocking. Instead, the ECU constantly advances the ignition timing until it just starts to knock, then backs off. it can only know it's knocking if the knock sensor says so. If the knock sensor stops talking, the ECU throws 52 AND dramatically retards timing to save the engine. (crappy performance, bad mileage)
The sensor itself is basically bullet-proof, but the wiring is not. The ECU is trying to pick out a delicate signal in an (electrically) noisy environment, so the sensor cable is shielded. If the cable is baked or otherwise damaged (after 24 years!), the signal can't get through.
Start there; find the sensor wire, and inspect carefully. I'm not as familiar with the 22re; someone else may give clearer direction.
Last edited by PA4runner; 01-15-2019 at 04:39 PM.
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