erikrs301
NAXJA Forum User
- Location
- Allentown, Pennsyltuckey
Is there a knock sensor on the 90XJ's 4.0l? If so, how long do they tend to last? What are some symptoms of it going or gone bad?
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Knock Sensor, 90XJ 4.0l?
- Thread starter erikrs301
- Start date
Yes, a '90 4.0 has a knock sensor. Looking up from the bottom, the knock sensor is on the driver side of the block. You'll see the wires going into it, kinda looks like an O2 sensor. As far as diagnosing a bad one, I don't know. I have the original one on my '90 with over 300k miles on it and it seems to be fine. The only time I noticed any excessive knock is coming back from Moab a couple weeks ago but I believe that was some bad gas as I haven't noticed it since filling up after. I've been getting the best gas mileage I've ever got and it's running great so I see no reason for a new one.
erikrs301
NAXJA Forum User
- Location
- Allentown, Pennsyltuckey
I'm at 259K on mine and I just started getting a slight knock on this on hill on the way to work. It's happening in 5th gear when it's under a load so I'm guessing the timing is not getting retarded correctly. I managed to track one down, dealers do not have them and only a couple parts stores can special order them. Napa was the best price at $65.
satan
NAXJA Forum User
- Location
- Lakewood, CO USA
The sensor will cause the ECU to retard timing for 10-15 second intervals if there is excessive output...
... about the easiest diagnostic is to connect an AC voltmeter on a VERY low setting to the sensor (still installed, but disconnected from the harness) -- the whap (not too hard) on the block immediately adjacent to the sensor (above the sensor seems to work best - you wanna induce a fake 'knock' into the bearing journal that's there)... You should see a tiny output from the sensor --- If you have no output - you may wanna remove the sensor and tap it directly on the head (the face of the threaded area) with the handleof a screwdriver while watching the output (use a scope if you have one, but definitely a high resistance volt meter set on AC on a milli or microvolt scale...)
Alternately, you can observe the timing of your running and warm engine (above 1200 rpm) and whap adjacent to the sensor as before and watch for the ECU to retard a few degrees
If you have access to DRBII or similar diagnostics the ECU's running value (measured at 2500 RPM) should be more than 10 "knock units" and less than 100...
... about the easiest diagnostic is to connect an AC voltmeter on a VERY low setting to the sensor (still installed, but disconnected from the harness) -- the whap (not too hard) on the block immediately adjacent to the sensor (above the sensor seems to work best - you wanna induce a fake 'knock' into the bearing journal that's there)... You should see a tiny output from the sensor --- If you have no output - you may wanna remove the sensor and tap it directly on the head (the face of the threaded area) with the handleof a screwdriver while watching the output (use a scope if you have one, but definitely a high resistance volt meter set on AC on a milli or microvolt scale...)
Alternately, you can observe the timing of your running and warm engine (above 1200 rpm) and whap adjacent to the sensor as before and watch for the ECU to retard a few degrees
If you have access to DRBII or similar diagnostics the ECU's running value (measured at 2500 RPM) should be more than 10 "knock units" and less than 100...
