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Toyota Knock Sensor Misdiagnosis

We have a 1990 Toyota RV but it is on the typcial Toyota Pickup chassie. We took it in to the Toyota dealer because we had a check engine light on and we had a significant loss of power going up hills. We were told that it was a knock sensor (computer error code 52) and that it needed to be replaced. Along with that work we were informed of at least 5 other issues including an exhaust manifold leak. So we agreed to have both the knock sensor and the exhaust manifold replaced for $2,091. When we went to pickup our rig we were told that unfortnuately the replacement of the knock sensor did not resolve the problem but in fact it was a wrist pin issue and we would now need to replace the engine. They said they could only hear the wrist pin once the exhuast manifold was replaced when they put the engine back together.

We have been told by other mechanics that they should have been able to hear the wrist pin or at least test to make sure that the knock sensor was indeed the problem. They have offered us $1000 labor refund good toward the installation of a rebuilt engine which will not cost us an additional $5,650 with the labor refund. However if we had known that we needed a new engine we never would have had the work done in the first place as we would like to repalce the engine with a 3.4L engine as opposed to the 3.0 which of course the dealer wont do. I am not comfortable with them working on our truck any more but would like to know that answers to the following questions:

  1. Could they have tested the knock sensor or determined that it was a wrist pin issue prior to doing the work?
  2. Do you think we should be refunded? If not another mechanic told us to take them to small claims court which sounds terrible but maybe that is our only option.
  3. Would you put a 3.4L engine in this rig which will give us much better power and overcome the head gasket issues that are common with the 3.0L engine or should we stick with a 3.0L engine.

I greatly appreciate your feedback as we are basically out $2000 with nothing to show for it which is appaling since we went to a dealership of all places.

Thanks for your help!!!

I think you’re entitled to a refund of the labor for the knock sensor.
Maybe take back the sensor too.
A dealer is not the place to bring a 23+ year old vehicle.

Look for a good independent, non-chain mechanic.
There’s a button at the top of this page “mechanics files”, also try

I would get a rebuilt engine installed, the new manifold will be used as rebuilt engines (long block) don’t come with manifolds.

That wrist pin noise was probably causing the knock sensor to retard the timing. The sensor often mistakes other noises for pre-ignition which causes a similar noise.

It’s one of the problems that gets missed often.

  1. No, I don’t think so.
  2. Yes, they could.
  3. Definitely no.

While thinking about this a bit I might ask for a bit more info.

How many miles on the vehicle?

Is any noise a rhythmic ticking sound at idle or is it a bit erratic?

Did it run fine other than the uphill?

Did any engine rattling sounds increase after the engine light (assuming this does not mean a zero oil pressure lamp) illuminated?

What were the other 5 issues?

A knock sensor could be tested with an ohmmeter. Tapping on the cyinder head with a hammer while the engine is idling could reveal if the sensor circuit is good or not as the engine should stumble a bit whenever the head is tapped. (Not meaning whacked.) :slight_smile:

Due to so many unknowns it’s difficult to put a finger on this and made even more so by the fact that wrist pin problems are rare.

It’s my opinion that a thorough diagnosis and testing of the engine performance and knock sensor operation would have resulted in you being told the following:

“It appears that the knock sensor operation is at least partly the cause for the lack of power and check engine light you’re experiencing. However we also noted a broken exhaust manifold which can cause both engine noise and lack of power. We are unable to determine at this time if the cause of your trouble is limited to the exhaust manifold issue or if it also lies in the knock sensor system or perhaps even a mechanical problem inside the engine. We recommend replacing the manifold for $XXX and then continuing diagnosis if needed.”

Now in defense of the dealer working on your truck, I’ve seen this fault code many times on these engines, it was a very common failure when these were still current. It has always been a failure of the wiring harness to the sensor, not the sensor itself. However, sensor and harness were always replaced together since it’s a 4 or 5 hour job to get to them. It might not have been realistic to expect the mechanic to hear a noisy wrist pin over the sound of the leaky exhaust manifold. And the mechanic has probably fixed 99 out of the last 100 knock sensor codes with just a sensor and harness, so wasn’t looking for anything else.

Thank-you for your responses. As a follow-up to the questions asked by OK4450 here is some more information on the rig:

  1. 65K
  2. not sure we cant hear it- a skilled mechanic said it was very faint
  3. Yes the rig runs great other than uphill but is getting even lower fuel mileage
  4. No change in engine noise, it remains inaudible either before or after the check engine light came on
  5. The other items were: sparks plug wires, distributor, crank shaft seal is leaking, since they were in there they might as well do water pump and timing chain since it is so old

Also, in response to pleasedogevan2, can you let us know why we should not consider the 3.4L engine swap?

Again thanks for any thoughts and advice with what to do next.

Have you researched putting the 3.4L motor in your RV? Will the transmission and rear end handle the additional power? Is this a simple “bolt up” switch or is there any “custom” fitting needed to make mate the motor to the transmission? If you swap in a 3.4 you may have to change all the engine control modules too. Sometimes this can mean some changes in wiring. Are the benefits so significant to make it worth the effort?

Yes we have researched it and you are exactly right, it would require replacing the transmission as well however others have found that there is significantly difference in power and improved fuel economy which would be great with our RV.

Before wading into engine rebuilds or replacements you might consider getting another opinion or two.
With the hood up, engine warmed up and idling, you might listen to that noise very carefully.
If it comes across a very rhythmic tick, tick, tick then maybe it’s not a wrist pin at all. It could be nothing more serious than loose valve lash on one or more lifters.

Lash should be inspected and adjusted as necessary every 30k miles at most but is seldom done.

As to a swap to the 3.4 I can’t answer that question specifically. In the old days of carburetion and so on most things could be easily worked around. With fuel injection and electronics involved it becomes more of a challenge.

Anyhoo, just throwing the valve lash thing out there because in all seriousness a Toyota engine with only 65k miles on it should not have a wrist pin problem and with any maintenance at all should not need a timing chain either.

Engine swaps are also computer swaps and wiring swaps. There are usually problems that most people don’t want to play around with. Then, if you damage the wires during removal and installation it is even more fun to work with. Fuel line routing, fiter size and emissios stuff. I wouldn’t try it. Other people do, but where are they when you need advice?

So after knock sensor replacement and manifold repair there is still a check engine light, fault code 52, and low power on acceleration? If that is the case, then like @ok4450 suggested perhaps a second opinion to the cause of the “knock” is in order. I have experienced Toyotas with valve noise loud enough to cause knock sensor codes. Unfortunately, I believe a noisy valve is not easily corrected on your engine, as it involves removing rockers and replacing shims.

It sounds like the other items were routine maintenance. Your engine has a timing belt, not a chain, which if still original was about 10 years overdue for replacement.

The 3.4 conversion is well worthwhile as far as power and reliability if the cost to you is bearable.

Thank-you for giving us a glimmer of hope that we may not need to replace our engine OK4450 and ASEMASTER. We will look for another opinion as it seems like everything runs perfectly until we try to head uphill. Bugger to hear that the valve may not be easy to fix but at least it will be good to know if that is indeed the problem as opposed to the wrist pin. Have a great weekend and thanks again!

Definitely get the valve lash checked.

If that’s not the problem here’s a work-around strategy:

Detach the knock sensor from the engine and tie it off to the side, keeping it electrically connected.
On the next drive listen for spark knock “pinging”, especially going up hill.
Take care because the computer will no longer retard timing to stop pinging, which can be harmful if continuous.
If there’s pinging switch to 89 octane fuel.

The valve lash adjustment if needed is not as difficult as you may think. Lash adjustments are a normal part of maintenance.

Shim and bucket type adjusters are more difficult to do as compared to the screw and locknut type but it’s nothing to fret over.
Once adjusted properly, the shim and bucket type adjusters tend to maintain their setting better than the screw/locknut variety.