Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

[mark1905]

97 3.0LX

So, I noticed on the first day out of the season that the motor seems a little more valve tappy sounding than normal. Loud. Still same power, no issues there. Ran fine except for the noise. Got her back home, and swapped the plugs. All of them look fine, except for #2 which looked like this..

I know the Iphone pic isn't the best, but the ground strap was melted into a little ball, and the electrode was melted down INTO the center ceramic. I've never in my life seen a plug look like this.

In the 3 years I've had her, I've changed plugs every summer and never had an issue like this. What gives?

After changing plugs, motor sounds pretty much fine except for a little louder tick than normal here and there. I'll no more once I get her under load. Doing a compression check next week.

In the meantime, what causes just one cylinder to pre-detonate like that on a sustained basis but not the others?

 

[Bondo]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Ayuh,... Probably from a Lean condition,...

Which cylinder,..??
What'd the other 3 look like,..??

 

[mark1905]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

It was cyl #2, and the others looked perfect! Light tan color all of them. No glazing..

 

[Don S]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Put in some real AC or NGK spark plugs, not those Champions, then set the timing (PER THE BOOK) not by how you think it should be done. You have a Delco EST distributor and it needs to be put into base timing mode to set the timing. Then make sure the advance timing is working properly.

 

[John_S]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Vacuum leak at the intake gasket?

 

[mark1905]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Will check timing tomorrow and report back. I'm without the manual until I get home, but does it list procedure to check advance timing? I know the base is in there..

Also, it's my understanding that the air/fuel mix can't be changed except at idle. Am I wrong?

..and yes, NGKs went in for sure. Thanks for the help everyone!

 

[zbnutcase]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

I'm with Don, Champion plugs aren't good for much other than slingshot ammo....'nutcase

 

[Don S]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Go up to the adults only sticky, there is a link to the manuals there where you can download them. You need #13

 

[mark1905]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Thanks yeah I have the manuals on the home computer, but I'm away and logging into the forum through my phone so I can't reference until tomorrow..

EDIT: just realized I can read .PDFs on the phone.. checked the process and understand completely. I'll report back tomorrow with findings.

 

[pine island fred]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Might want to consider that the intake manifold gasket is leaking at that port. FRED

 

[pine island fred]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Just noticed JOHN S already suggested that.

 

[mark1905]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

What would be the best way to check for intake gasket leaks?

 

[Bondo]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

What would be the best way to check for intake gasket leaks?

Ayuh,... Spray the area with carb cleaner or other volatile compound...
The motor will rev up if it's leaking vacuum...

 

[mark1905]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Got it..

 

[mark1905]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Just got in from checking timing.. some things:

First of all, my timing tab has been painted over by PO it looks like. The service manual shows a tab with 5 prongs on it.. mine has 6. How would I read this? Assume the bottom point starts at -8deg and work my way up? I hate/don't assume things..

So, at first glance when going through the service manual and noting plug wire locations on the distributor, I notice that they have the #1 wire being on the pole that is closest to the motor in the front. My cap is turned so that the #2 is there, and the #1 is pretty much on the outside/front pole.

I know it's hard to tell engine orientation at first in this pic. "UP" is forward. Note that the plug wire in the upper right of the cap in this pic is the #1 cyl.

I connected timing light with the jumper wire across the two white wires, and timing was reading at barely touching the top of the tab.. What? I pull the wire off, and the mark doesn't move.. still barely reading at the top of the tab. I cleaned off the bullet plugs with contact cleaner, made sure I had a good connection and all, and still.. the timing mark wouldn't move.

What's wrong here?

 

[Don S]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

You talk about the white jumper wire, but never mention the shift interrupt switch wireing, did you bypass it properly?

 

[mark1905]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

You talk about the white jumper wire, but never mention the shift interrupt switch wiring, did you bypass it properly?

First.. thanks for the timing tab clarification.

Second.. when I went to bypass the shift interrupt as per the manual, I'm assuming they mean up at the actual switch, right? Coming into the switch is a purple wire, going out of it is a white/blue wire. If I disconnect the switch and plug the purple wire into the white/blue wire, the engine dies.

How do you properly bypass the switch, and why does this affect the timing reading?

 

[Don S]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

How do you properly bypass the switch, and why does this affect the timing reading?

That is how you put power to the distriburor module to put it in base timing mode.
Just do as the instructions say and it will work like it's supposed to.

PS: Please resize your pictures to a max of 640W.

 

[mark1905]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

That is how you put power to the distriburor module to put it in base timing mode.
Just do as the instructions say and it will work like it's supposed to.

PS: Please resize your pictures to a max of 640W.

The manual says and I quote:

"3. Bypass the shift interrupt switch by disconnecting
wires at shift interrupt switch. Temporarily join the
engine harness wires together."

That's what I did, and the engine died because of it. No diagrams included as you know. The only two wires that go to the shift interrupt module are a purple wire and a white/blue wire that comes out of the distributor plug.

 

[Bondo]

Re: Causes of sustained pre-det in one cylinder only.. (check out this plug pic)

Bypass the shift interrupt switch by disconnecting
wires at shift interrupt switch.

Ayuh,... Disconnecting those wires is Not the same as joining 'em together...