Spark Knock

Status
Not open for further replies.
Joined
Sep 6, 2019
Messages
5
Location
Pennsylvania
I have a 2.7 liter 4 banger with TBI injection.

This summer I've been having a problem with Spark knock that I haven't had previously.

Details:

I've pulled the spark plugs and found 1 plug which looks pretty obvious like it has seen some detonation, while the other 3 plugs look fine.
I changed all 4 plugs and went to plugs cooler on the heat range, but it did not help.

I've checked the cranking compression. 2 cylinders at 170 (1 of which was the cylinder with the bad plug), the other 2 are at 150 and 160.

I've tried 93 Octane gas from two different stations. Even added Royal Purple octane booster which should raise the Octane by 3 FULL points. But it had no effect.
I've run Berryman's cleaner thru the vacuum port. No effect
Currently running Berrymans cleaner in the gas tank. No effect yet, but tank is still pretty full.

I have a programmable ECU and I've lowered the timing about 20% in the area where I hear the knock. (Moderate to Full Throttle) at 1800 to 2300 RPM. This helped a little, but still have the problem.

I've checked the valve lash and all seem OK.

Fuel pressure is good. Wide Band O2 sensor shows correct AFR.

Other than pulling off the Cylinder Head, is there anything else I can do to get handle on this spark knock problem?
 
"Three FULL points" means it potentially raised it from 93.0 to 93.3, but not necessarily even that much. Are you sure they don't claim 30 points? Even if they do, it is worded "may" so that doesn't mean it did.

Is there a knock sensor? On my BMW if those aren't working properly then it will ping even with 93 octane gasoline.
 
Thats the 2 TRFE? Yoda?

What plugs?

Dist or COP?

Run a tighter gap with the tune, say 1MM?

Engine prefers OE nickel Nippon Denso. or IR NGK for COP




Stay away from in the bottle octane boosters.

Is this Auto or MT?

Like Chris said check intake flange and hose ports for leak causing lean condition..

Maybe you tune prom went south.


If you cant find anything, I would run some Regaine complete.

And don't run 40 grade oil.
 
Clarification on the octane booster: It is: 30 points or 3 numbers. Bottom line at 96 Octane there was no improvement. I don't normally run any sort of snake oil in a bottle, but tried this as last ditch band-aide to avoid pulling the cylinder head.

This is a Manual transmission car, with no EGR. Single Ignition coil with Distributor.

The new spark plugs are Champion Copper RC7YC. The old plugs were RC9YC5

As mentioned, AFR is normal on the wide band so I don't suspect any problems with the tune/prom.
 
Have you checked the cooling system? Went through this with my 240sx a few years back. I was used to hearing some mild knock every now and then on hot days when using 87, but then it started doing it very frequently, even on cooler days. Checked timing, EGR, plugs, ran 89 octane, then 93, still had knock that hadnt been there before. It was progressively getting worse and I couldnt figure it out. This went on for a few weeks.

Then while poking under the hood I stumbled onto it. The cheapy replacement radiator I installed a couple years earlier had corroded and many of the cooling fins between the rows were missing on the bottom third or so, and what wasnt missing was crumbling badly. Typical hit or miss aftermarket junk strikes again. The old stock fan clutch seemed a bit easy to turn as well and didnt feel like it was pulling much air. Replaced the radiator with a better unit, put in a new OEM thermostat, and replaced the fan clutch. Knock stopped immediately, even in super hot weather and sitting in rush hour traffic using 87 octane. The knock sensor must have been pulling the timing back when this was all going on because the throttle response improved significantly as well.
 
Thanks for the info Quint. When you had the cooling system problem, were you seeing normal readings on the Temp gauge or did it read high? My car has two different sensors, one which feeds the ECU and one that feeds the Temp gauge. Both are reading normal. So it seems unlikely to be cooling unless you had your problem while still getting normal readings.
 
Originally Posted by edfiero1

The new spark plugs are Champion Copper RC7YC. The old plugs were RC9YC5


A lower heat range # is actually a hotter plug, you went two ranges hotter going from a 9 to a 7.
 
I chased a similar problem on a '97 Mazda MPV 3.0 (SOHC V6). It started when the van was about eight years old with about 150K km on the clock. I tried the octane-boosting additives to no avail. Also tried cooler plugs with no improvement. My friend had the same van and had the same problem.

Years later I pulled the intake manifold to repair oil and coolant leaks, and found the PCV valve buried under a bunch of plumbing. I had never thought about it as a potential cause of pr-eignition, and had never changed it. It was plugged solid. I changed it out, and never heard any pinging again.

Worth checking!
 
I am guessing that the op's engine is the 2.5 Pontiac iron Duke. Used in fieros and 1980's gm cars and the s10. (The only 2.something liter I can think of that was tbi, with a distributor, and mated to a manual transmission. )
 
Last edited:
Are you being purposely vague? The only 2.7L I4 I can think of is a Toyota?

TBI with no EGR? That's interesting! Did you delete the EGR?
PROM is GM terminology.....
 
Originally Posted by wheelman1991
I am guessing that the op's engine is the 2.5 Pontiac iron Duke. Used in fieros and 1980's gm cars and the s10. (The only 2.something liter I can think of that was tbi, with a distributor, and mated to a manual transmission. )


The Iron Duke is the closet Production engine to what this is. It is a non-production engine, a Pontiac Super Duty (SD4). 2.7 liter. Used in the NASCAR Goodys Dash racing series. And YES!! It's in a Fiero.
smile.gif
 
Originally Posted by cjolson140
Originally Posted by edfiero1

The new spark plugs are Champion Copper RC7YC. The old plugs were RC9YC5


A lower heat range # is actually a hotter plug, you went two ranges hotter going from a 9 to a 7.


That is NOT my understanding.

https://www.briskusa.com/spark_plug_cross_reference_heat_range_chart

This chart clearly shows a lower number is a cooler plug. Cooler plug to dissipate heat more quickly.
 
Originally Posted by edfiero1
Originally Posted by cjolson140
Originally Posted by edfiero1

The new spark plugs are Champion Copper RC7YC. The old plugs were RC9YC5


A lower heat range # is actually a hotter plug, you went two ranges hotter going from a 9 to a 7.


That is NOT my understanding.

https://www.briskusa.com/spark_plug_cross_reference_heat_range_chart

This chart clearly shows a lower number is a cooler plug. Cooler plug to dissipate heat more quickly.


Hmm you're right. Seems that NGK and Denso are the opposite however, and that is what I've used in the past, hence my mistake.
 
Originally Posted by edfiero1
Thanks for the info Quint. When you had the cooling system problem, were you seeing normal readings on the Temp gauge or did it read high? My car has two different sensors, one which feeds the ECU and one that feeds the Temp gauge. Both are reading normal. So it seems unlikely to be cooling unless you had your problem while still getting normal readings.


Honestly I dont remember, the needle on this gauge barely moves anyway. Two minutes after a cold start it shoots up to just below the third line and stays there whether is -10F or 110F. This engine also has the two different temp sensors but neither has required replacement.

When all the knocking started I wasnt even looking for a cooling issue because the radiator wasnt that old, it wasnt loosing coolant, or doing anything else to indicate a typical cooling issue. I just kind of stumbled on the corrosion and crumbling radiator while checking all the other usual spark knock culprits (plugs, cleaning EGR, checking timing, etc etc).
 
Originally Posted by cjolson140
Originally Posted by edfiero1

The new spark plugs are Champion Copper RC7YC. The old plugs were RC9YC5


A lower heat range # is actually a hotter plug, you went two ranges hotter going from a 9 to a 7.


NGK is that way. Every other plug manufacturer... it's cooler.

NGK: 9 -> 1, Cooler -> Hotter

Champ/Auto/Denso: 1 -> 9, Cooler -> Hotter

Numbers are just reference.
 
Might not be ignition timing related, could be cam timing? Are you reading the plugs or do you have a knock sensor that is pulling timing? Any noise can be seen as spark knock by the knock sensor.
 
Originally Posted by kschachn
"Three FULL points" means it potentially raised it from 93.0 to 93.3, but not necessarily even that much. Are you sure they don't claim 30 points? Even if they do, it is worded "may" so that doesn't mean it did.

Is there a knock sensor? On my BMW if those aren't working properly then it will ping even with 93 octane gasoline.



It's 3 whole numbers....aka 30 points... That is what the RP octane boost states on the container.
 
Last edited:
Status
Not open for further replies.
Back
Top