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Timing Confusion! Help!!!

Here is my issue. I recently bought an 88 4runner, 3.0l and had a shop replace the head gaskets. The enige was rebuilt about a year ago. The timing belt is still in great condition. I got the truck back and had a code 52 present (knock sensor) I sent the truck back to the shop and they replaced the knock sensor and the pigtail and still have the same code 52. I disconnected from the pigtail and ohmed back to the connector that plugs into the ECU, and found that the line was good.

The other issue is that I decided to check the timing. Jumpered out T1 and E (or T and E1 don't remember their lables) and hooked up my timing light. Found that the timing was running at 20 degrees BTDC. I adjusted it down to 10 but then the truck did not want to run. It lacked power. So, checked all timing items. Crankshaft pulley at zero mark, 1 pistion at upmost stroke, both cam pulley timing marks lining up with timing marks and distributor pointing at 1 spark plug. So...why is my timing not at 10 degrees or somewhat close??? This has me puzzled. I have only owned the truck for about 2 months. Can the timing being off....cause the code 52 knock sensor issue?

Shallowrunner

Reply to
shallowrunner2002
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does the distributor advance itself OK?

If not you would need a lot of initial advance to counter act it.

Mrcheerful

Reply to
mrcheerful

It sounds like the timing belt (chain?) may be a tooth off.

Lee Richardson

Reply to
Lee Richardson

When you say "ohmed out" do you mean that you checked continuity and resistance? The trouble code could be caused by an open or short in the knock sensor and related circuit. The knock sensor should be installed without any insulating tape or putty.

With the knock sensor hooked up to the wiring harness, have a helper rap on the block near the sensor while you check for spikes of voltage at the ECU connector that correspond with the raps. The ignition does not have to be on to perform this check.

The knock sensor is a piezo-electric crystal that emits a spark when knocking is detected. When the ECU detects voltage coming from the knock sensor, it retards the ignition timing.

I would make sure that the cam with the distributor is not off by one tooth. Jump terminals TE1 and E1 when checking ignition timing. Make sure you have the correct rotor.

The incorrect ignition timing could be related to the knock sensor issue but I doubt it.

Reply to
Ray O

Ray....thanks for the detailed reply. I did check continuity from the knock sensor connector back to KNK at the ECU. I do have continuity and it is not grounded. I also checked all cam timings. They are 100% correct. All marks line up perfectly on the cams, crank shaft pully and rotor .The distruibutor points to number 1 spark plug and the 1 piston is at the upmost stroke. I did short T to E1 during the ignition timing. . I am not sure what is going on. I will perform the rap the block test and post my results. Do you have any other ideas that I might try or what could be causing this issue.

Shallowrunner,

Reply to
Shallowrunner

Ray....Not really sure how to perform the rap the block test..but here is what I did. I plugged one lead end of my DVM to the KNK position on the ECU connector. I did disconnect the connector from the ECU. I then grounded my other leak end to the ground cable that was disconnected from my battery. I set my meter to AC and displayed zero millivolts. I rapped the block a few times and saw that I was detected an increase in millivolt signals. It went from zero to about 2.5 millivolts and went higher the harder I tapped. Is this telling me that the knock sensor circuit is good? If it is the case....then what is my issue? Could the valves or rocker arms be causing this fault? Would this affect my timing issue? I am totally confused.

Shallowrunner

Ray O wrote:

Reply to
Shallowrunner

I don't know if the voltage generated by the knock sensor is AC or DC, but I would imagine that it would be DC since it is essentially static electtricity. The higher voltage generated by harder tapping suggests that the knock sensor and circuit is operating normally. AFAIK, the knock sensor circuit does not measure voltage, just frequency. For example, more knocking creates more pulses, and as long as the pulses are coming, the ECU retards ignition timing until the knocking stops.

I would clear the codes by pulling the EFI fuse and see if the code returns.

You might want to try leaving the knock sensor unplugged and set the base ignition timing correctly and see if the engine runs better. Perhaps a knocking signal from the sensor is retarding the timing, which is why base timing had to be so advanced - the ECU was retarding timing so it needed to be pretty advanced so that it could retard.

While the engine is running, you might also use an engine stethoscope or a screwdriver with a long shank against the block to see if you can hear any mechanical knocking that the knock sensor might pick up.

Reply to
Ray O

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