I have a 1991 TA with a 350 TPI. The plugs that are installed on the car are NGK UR45GP (0.060 gap) when I believe they should be NGK UR4GP (0.040 gap). All of the specs are the same between the plugs minus the preset gap from what I can see online. I pulled a plug and it's gapped at 0.050-0.055. Would this larger gap be enough to cause a spark knock?

 

By spark knock, do you mean detonation?
My 2 cents:
A gap that large is very hard on a stock ignition system.
It can cause a misfire = not firing situation.
Close those gaps down to .035-.040" or replace the plugs.

 

 

No plug gap does not affect detonation. Heat range of the plug could affect it. If the electrode gets too hot it will ignite the charge before the ignition event.

GD

 

do you have any pictures of your plugs you can post up? Might be some good plug readers here that can read what they may be telling you?

 

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near as I can tell the brownish color indicates a slightly rich mixture... which is good in the sense that lean mixtures would be more prone to detonation

maybe soemoen else with more experience in plug reading may notice something else?

 

Try backing the timing down a couple of degrees and see if the knock counts drop.

 

in a different thread on the subject he had indicated he pulled out 10-12 deg of spark and it the ECM was still pulling out up to 20 deg of spark...

 

OK. So put in a different set of spark plugs to see if the knock counts decrease. Plugs are cheap. Throw in a set of cheap AC Delco copper plugs. Only really nice thing about those platinum plugs is that they'll last longer so you don't have to change them as often. On some cars, a plug change can take a while.

I run NGK copper race plugs in my race car. I don't need some fancy high end plug to ignite the fuel but I also don't expect my plugs to last 50,000 miles either.

As for heat range. You want the coldest plug possible that won't foul up.

 

AlkyIROC....can you recommend a specific plug I should try? Given these things are a PITA replace in my driveway without a lift, I only want to do it once. I currently have NGK UR45GP gapped at 0.055 (pulled a couple of the easy to get to plugs and checked them). Given I'm trying to root cause why my knock sensor is picking up knock from something real or false (LOOOONG story), I was thinking of trying a colder plug gapped at the spec of 0.035. Maybe NGK UR5GP?

 

Not sure what plugs are recommended for those heads but typically Delco R45T is a common plug for GM. R45TS is an extended tip and may also work.

 

The plugs called out are an NGK UR4 (universal, heat range 4). You can go to like an iridium with a lower heat rating - which would be a UR55IX - iridium plugs run cooler anyway and will last 60k+

GD

 

his UR45s are already a little cooler than the UR4s.

but I guess overall I'd be shocked if his plugs are responsible for up to 20 deg of knock retard...

 

Oh they clearly aren't. Told him that already. But he has them out so eff-it. Put in some quality Iridium plugs I say. And if you drive it hard or are planning any upgrades - might as well go one step colder. Not going to hurt anything.

GD