Predetonation Issue on teh '88

[Tiggie]

Well, another engine issue on the wagon. I'm sure you guys are thrilled to see what now.

Starting about two weeks ago, the car stopped stalling when it's cold. Previously, it would stall when cold unless you nursed the gas pedal. Now it starts right up and continues running fine. Still getting 21+ MPG.
Here's where it gets a little weird. When you first start it up, it revs (to about 1800ish) a couple times. You can hear it sucking air (stock intake still in place).

About the time it started idling nicely when cold, it started lightly predetonating cruising in OD. At first I thought I was hearing things, but it's definitely doing it. It doesn't really matter how much throttle you give it or at what speed you are going. It's just a constant light predetonation with any throttle input. It never knocks hard. And only in OD, none in first or second (not sure about third).

I thought it might be a carbon buildup issue, but I blew it out really well and no change.

Never checked the timing with a light, I set it by ear when I did the intake gaskets four months ago. Never had any predetonation problems before last week. It's been doing it about 200 miles now and I don't want to melt a piston.

Ideas? Anything's welcome. If I can find a distributor wrench around here, I'll knock the timing back some and see what happens but I don't think that's the problem.

[gadget73]

first guess would be a vacuum leak somewhere making it run lean, or the fuel mix changed to winter crap and you've got a bit too much timing. I had ping problems on my truck for years, ran a half can of seafoam through the pcv valve and it went away. hasn't ever come back either. if nothing is leaking, and the timing checks out, it cant hurt any to try it, provided you follow the directions

[Tiggie]

I think it could use some Seafoam through the intake. I'll pick up some next time I'm at the store. What's the proper way to use it on a SEFI car? Through the brake booster vacuum hose?
I forgot about that winter gas change too. I haven't located a distributor wrench on campus yet and it's not something I usually carry in my toolbox . I'll put some 93 in next time I get gas and see if it helps.

[Nathan in MI]

In a pinch, you can usually get it loose with a socket on the end of a universal joint, an extension, and a 3/8 ratchet.

[gadget73]

brake booster will work, but if you can pull the pcv valve out enough to get it, it'll also clean it. The booster has a one way valve in the connector, and it goes through the tree on the firewall, not sure how well those will react to seafoam. You could also use that line that goes to the evap purge solenoid if the pcv valve isn't accessible enough, just make sure you let it "sip" slowly so it doesn't pull too much in there.

[mrltd]

Just FYI... It's Preignition or detonation. I dunno what predetonation is....

I'd bump the timing back a bit. It's not going to do it in 1 or 2nd because of the converter not being locked up. 3rd and OD, the converter is locked and there is much more load on the motor. Setting timing by ear usually ends up being way too high. I set mine like that at the dragstrip- it was 18 or 20* BTDC.

[Tiggie]

Thanks for the FYI. Didn't know that. Preignition for future reference.

Still haven't found a distributor wrench here but luckily I do have my little socket set and a u-joint that I'll give a try.

It started really well and runs better than it used to in first and second.