drtidmore

new engine random knock....thoughts?

13 posts in this topic

Today, on my way home from our daughters, at trip of about 20 miles, with the temps outside at 87 degrees, the engine died while at highway speeds.  I was able to pull off and got it to restart but it died again a short distance from home.  Fortunately I was able to pull into a shopping center parking lot.  Now in a safe location, I pulled my fuel pressure gauge out of the trunk and found NO pressure on the rail along with NO voltage at the green test connector on initial ignition on.  A quick swap of the relays on the firewall and the fuel pressure popped right up to 40PSI on initial ignition on, so the problem was a failed fuel pump relay but since the engine died while at highway speeds, that also tells me that the oil sender backup must be defective as well, so a new oil sender will be here tomorrow.  

 

But to back up a bit, when it first died and before I got to running sufficient to attempt the rest of the drive on the service roads, it idled like crap and backfire a few times, died a few more times before smoothing out more of less as long as I did not attempt too much throttle.  The new relay solved the fuel starvation issue, but now I have new issue.  Right after it fires on cranking and randomly at idle, I am getting a knock. I have put a screwdriver at various point on the engine and NO knocking heard (i.e. screwdriver held against my ear).  The noise is very similar to what I heard when the harmonic balancer decided to failed.  This balancer was installed a little over 2 years ago and under 20,000 miles ago.  I was checking things under the hood while running just a few days ago and I know that the knock was not there at the time.  The engine runs fine, the exhaust is silky smooth and again, NO knock detected coming from deep in the engine.  

 

As the backfire seemed to be the catalyst for this, the timing chain comes to mind, but this sounds more external to be honest.  I would think that with the screwdriver held to the water pump I would hear something if it was timing chain related.  Has anyone heard of a HB failing due to a backfiring situation.  

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My 92 Transport with 3800 would always have some piston slap at startup but always went away when warm. Did for 130k miles & still there when gave it to my sister.

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If the HB did fail, it would explain the start-stall condition (CPS reading failure) and if the trigger rings contacted the sensor.

An easy definitive HB check is to completely remove belt, run no longer than 5 minutes. Visual inspection is easy, remove

wheel and access panel. New doesn't mean good. The fuel cutout condition could've been enough violent to shake it loose.

 

Change oil, use a chisel (not saw) to autopsy filter- rule out bearing damage.

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Removing the belt was next on my list as that is how I finally identified the previous HB failure.  On the previous failure, even after removing it, it did NOT visually show detachment between the inner and outer sections, nor was there any mechanical looseness.  As with the previous HB failure, the knocking lacks any discernible periodicity.   After I got the car home yesterday, I did notice a very small amount of wobble in the HB, so hopefully that will turn out to be the culprit.    I am due an oil change in a few miles anyway, so I will just short it a bit so as to take a look for metal shavings.  

 

Thanks for feedback. 

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Posted (edited)

And the verdict is..............the HB is failing.  With the engine cold, I started it and there was that hard clack on initial ignition but then no knocking.  I let it run a few minutes and the random knocking started up again.  Pulled the serpentine belt...quiet as a well tuned sewing machine both on initial ignition as well as running.  Replace the belt and the knocking returned.  I let it run until the engine was warmed up just for good measure and the knocking continued, getting a bit worse as the engine temp rose.  Then I pulled the belt again, and again, no knocking.  With the belt reinstalled, I closely monitored the HB as the AC compressor kicked on and off and I can see a distinct wobble in the HB pulley as the AC compressor cycles.  The HB has a lifetime warranty on it from Autozone, so at least I won't be out the cost of the HB.  

 

I will still chisel open the oil filter just for a sanity check but I am pretty confident that the HB failed as a result of the backfires.

Edited by drtidmore (see edit history)
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1 hour ago, drtidmore said:

the HB failed as a result of the backfires.

 

Yes, exactly. If you think of it's sole purpose- to cushion the shock load of normal operation, imagine the forces generated by stop/start (fuel or electrical), backfiring, or a random electrical miss.

 

While you're in there- inspect the CPS closely for damage too, any misalignment or scuff marks.

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17 hours ago, drtidmore said:

I have put a screwdriver at various point on the engine and NO knocking heard (i.e. screwdriver held against my ear).

 

Try this in the future- much safer, more effective.

 

 

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Great tip for finding a noisy bearing.  I still like the direct against the ear for listening to the block itself as that will transmit lower frequencies a bit better.  I have already ordered in a new CPS along with the HB as the CPS is a pretty cheap part, it is easy to replace and it just makes sense any time there is even a chance that there may have been contact between the interrupter rings and the CPS.  I agree that the HB, with it's rotating mass, likely was jerked around violently during the backfires, this was just the first time I have ever encounter such actually damaging a HB.  I was greatly relieved when the engine was its usual quiet self on start up and when running once I removed the serpentine belt.  I pretty well had convinced myself that the symptoms really pointed to the HB, but having that audible confirmation was a load off the mind.   

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This is what I use and it works pretty well. I didn't have any luck finding a plastic jug that would fit on the end of it..

 

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I have a good harmonic balancer from my 88 Reatta.  I will sell it for $35 shipped to the continental US.

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Thanks for the offer, but the failing HB on my Reatta was new only slightly over 2 years ago and AutoZone provides a lifetime warranty on it, the replacement will be free.  I have already verified this at the Autozone where it was purchased.  

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Is it just from reading on here, or do Reatta HB's have a higher failure rate than other makes? Seems to be a high percentage.

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I think it's an illusion- because of the age of these cars- (and the owners) that there are certain parts that are OEM or close to it- and are bound to give up in large number spurts.

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