Help Troubleshooting a noise on acceleration (1 Viewer)

[Irish Reiver]

A few weeks ago I pulled the dizzy and changed out the broken plastic circle that was masquerading as an O-ring. While I was in there I decided to tweak the ignition with a few degrees of advance. I run ethenol free jucie at 89 octane so I set it to roughly 7° and was happy with my work.

Next day on the freeway I heard what sounded like a high pitched, high frequency chirping noise - like crickets on speed. It didn't strike me as pinging (I remember that as more of a clatter) but since all my troubleshooting starts with the question " what did you just mess with" I decided that this was indeed pinging. The next day I hooked up the strobe light and dialled it back to around 5°. There was a good improvement but still there. Decided to go back to stock and set it back to 3°.
I still have some pinging under acceleration. It never did this before I messed with the dizzy.

Question - is this pinging or am I barking up the wrong tree.
Also, is there something I could have disturbed removing the dizzy that would give the symptoms.

Lastly, wouldn't my knock sensor catch any pinging and retard the engine - is my knock sensor not working.

Any help appreciated.

 

[blkprj80]

Could it be "exhaust whistle"?
Can't see how timing would affect that though.

 

[Irish Reiver]

Definitely coming from the front of the truck. Could be exhaust leak but I would expect a ticking rather than chirping.

 

[ppc]

Did you place a jumper in the diagnostic port to set the ECM into base/service mode, verify that was successful by observing a constant flashing of the CEL before setting the timing?

 

[Irish Reiver]

Did you place a jumper in the diagnostic port to set the ECM into base/service mode, verify that was successful by observing a constant flashing of the CEL before setting the timing?

Sure did. And I checked it before I even removed the dizzy just to make sure my timing light was still working. It was bang on 3° before and it's bang on 3° now only now it has a sound track.

 

[ppc]

I guess the next thing to try is resetting the ECM by pulling the EFI fuse or disconnecting the battery.

 

[retrofive]

These things accelerate? Who knew.

 

[Irish Reiver]

I guess the next thing to try is resetting the ECM by pulling the EFI fuse or disconnecting the battery.

That's worth a try. Today I filled it with 91 octane and I can still hear the chirping. Is the chirping actually pinging or something else?

Tomorrow I will reset the ECU and see what happens.

 

[ppc]

Going back to read your first post again the description being a high pitch, high frequency may not be pre-ignition. I would describe pre-ignition more as a rattle. To answer your original question, a working knock sensor should cause the ECM to back off timing but I don't think it would be able to reduce any lower than was set as base timing. That is why I wanted you to confirm the diagnostic mode with the jumper.