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Dj, ASE Certified Technician
Category: Toyota
Satisfied Customers: 1910
Experience:  ASE Master Tech, 30+ years in automotive repair.
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4runner: We have been told that our 1993 Toyota 4Runner needs

Customer Question

We have been told that our 1993 Toyota 4Runner needs a new knock sensor, and I already know that the valve gaskets are leaking...would that cause lack of power in the engine
Submitted: 1 year ago.
Category: Toyota
Expert:  Dj replied 1 year ago.
Hello and thank you for trusting us with your question. I'm DJ.
If the knock sensor or circuit is faulty, the check engine should be on. If the light is on, the computer (ECU) goes into a default mode and retards the timing. This causes a lack of power and horrible gas mileage.
Have you got a check engine light on and did the mechanic get a code 52 when he did the testing?
Let me know and we'll figure this out.
Customer: replied 1 year ago.
We took the car to a local mechanic, and spent weeks, off and on, diagnosing things. They put in a new knock sensor, new harness to the knock sensor, new computer and tried to reset it, when they did, it ran great for about quarter of a mile and then the light would come back on and retard the timing, and it would lose power. FYI, while we had it in, they replaced the spark plug wires and the timing belt. (He also said that he got a second knock sensor and computer, in case one or the other was faulty) help?
Expert:  Dj replied 1 year ago.
Do you know what the code is that's turning on the check engine light? Is it a code 52 or something else?
Customer: replied 1 year ago.
Yes, I did confirm that it was a code 52.
Expert:  Dj replied 1 year ago.
The code 52 is by far the hardest code to clear on a Toyota.
When I replace a knock sensor, I solder all the connections. I've gotten burned on too many of these. The signal from the knock sensor is electrically very tiny. So any corrosion, weak connectors, bad ground, anything can cause the signal to fail to get to the ECU.
But first I would have the mechanic advance the timing 10 degrees, clear the code and test drive it. I've seen instances where the damper ring on the crankshaft pulley slips so when you think you are setting the timing correctly, you are actually retarding the timing. It happened on my own 1991 4Runner.
Let me know if the engine pings or if it changes the problem.
Customer: replied 1 year ago.
The mechanic said that he did this very thing!
Expert:  Dj replied 1 year ago.
Then I'm out of ideas. There's nothing left in the system. But I can explain how the system works.
The mechanic sets the base timing. The ECU assumes this is correct.
When the engine runs, the ECU advances the timing until it hears a ping from the knock sensor.
The computer retards the timing 4 degrees and expects the pinging to stop.
If the ECU doesn't see a signal when it advances the timing, it triggers a code 52.
If the ECU sees a signal even after it retards the timing, it will trigger a code 52.
It sounds like he's got the bases covered, so here's some things he may not have checked.
A loose bracket or something in the engine causing a noise that the ECU could interpret as a ping.
Low compression could cause the engine to be not able to create a ping.
But almost all the time, the problem is the wiring from the sensor to the ECU, even if the parts are new.
I'm going to opt out and put your question back into the expert pool to see if somebody else has any ideas on this.
Please don't respond to this message or it will lock up your question and delay an answer.

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