Hacked wiring to coolant sensor?
See attached pictures. This sensor is under the j-boot. (Coolant temperature sensor I believe). Someone has hacked into the wiring harness and added a resistor. Resistor measures at 800 ohms. Resistance of the sensor is 1.4 k-ohms. (Cold engine). Could this be affecting my non idle issue? Wrong information to the DME? Or is this a common fix for something?
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Tom
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That's an ugly hack. It tricks the DME into thinking the engine is cold, probably in an ill-considered effort to make the mixture richer. Someone was probably trying to mask a lean condition. I'd remove it, re-wire the sensor normally, and diagnose from there. It's just masking problems and making things harder to diagnose as is... You might check your FQS too. Anyone who goes to that length to richen the fuel would also add fuel via the FQS (if they knew to do that).
I'll give the previous owner marks for a clever hack*, but fail him or her anyway for not going after the actual root cause. Mixture was lean because... ? Yeah, vacuum leak. Possible problem with the air flow meter, but way way down the probability list.
*He or she understood the control systems of the car better than most people, but still chose to shortcut proper repairs. Shame you were left with actually fixing it.
*He or she understood the control systems of the car better than most people, but still chose to shortcut proper repairs. Shame you were left with actually fixing it.
I’m just lucky I actually found it. But glad I did. The j-boot had many holes in it and I replaced that and my barn door was sticky as well. So maybe this is what lead them down this path originally.944er wrote: Sun May 10, 2026 9:30 pm I'll give the previous owner marks for a clever hack*, but fail him or her anyway for not going after the actual root cause. Mixture was lean because... ? Yeah, vacuum leak. Possible problem with the air flow meter, but way way down the probability list.
*He or she understood the control systems of the car better than most people, but still chose to shortcut proper repairs. Shame you were left with actually fixing it.
Holes in the J-boot would cause lean running.
But you'd have to be on a serious budget to prefer a resistor to a new J-boot. Maybe they didn't know where the leak was and didn't have access to a smoke machine? Were the holes in the J-boot obvious?
But you'd have to be on a serious budget to prefer a resistor to a new J-boot. Maybe they didn't know where the leak was and didn't have access to a smoke machine? Were the holes in the J-boot obvious?
In the annals of previous owners, I had one that suffered an exhaust leak and decided the answer was to weld up the flange -- nuts and all. (Content warning: E36 M3 not Porsche.)
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Wasn’t obvious unless you actually removed it. All on the lower side of it.jeyjey wrote: Mon May 11, 2026 3:43 am Holes in the J-boot would cause lean running.
But you'd have to be on a serious budget to prefer a resistor to a new J-boot. Maybe they didn't know where the leak was and didn't have access to a smoke machine? Were the holes in the J-boot obvious?
Guess that’s one way to do it. Loljeyjey wrote: Mon May 11, 2026 3:45 am In the annals of previous owners, I had one that suffered an exhaust leak and decided the answer was to weld up the flange -- nuts and all. (Content warning: E36 M3 not Porsche.)
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