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Spark Knock #5206315 09/06/19 12:42 PM
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edfiero1 Offline OP
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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?

Re: Spark Knock [Re: edfiero1] #5206322 09/06/19 12:57 PM
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kschachn Online Content
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"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.


1994 BMW 530i, 251K
1996 Honda Accord, 280K
1999 Toyota Sienna, 430K
2000 Toyota ECHO, 284K
Re: Spark Knock [Re: edfiero1] #5206329 09/06/19 01:04 PM
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Vacuum leak.


02 Wrangler Napa high milage 10w40
87 F250 Valvoline 15w40
07 fjcruiser Car lube plus 10w30
Z400 castrol T 10w40
Can am Maveric edge 5w40
57 case tractor Chevron sae30
Re: Spark Knock [Re: edfiero1] #5206476 09/06/19 04:24 PM
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ARCOgraphite Offline
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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.


2019 VW Jetta S 6MT OCI#2 7378mi-MOTUL Specific VW508.00+VW Service Filter; '17 Subaru Crosstrek CVT OC#8 60864mi-Subaru Idemitsu 0W20 + SOA Filter
Re: Spark Knock [Re: edfiero1] #5208247 09/09/19 06:13 AM
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edfiero1 Offline OP
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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.

Re: Spark Knock [Re: edfiero1] #5208956 09/10/19 05:14 AM
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quint Offline
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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.

Re: Spark Knock [Re: edfiero1] #5208964 09/10/19 05:33 AM
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edfiero1 Offline OP
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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.

Re: Spark Knock [Re: edfiero1] #5209417 09/10/19 03:49 PM
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cjolson140 Offline
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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.

Re: Spark Knock [Re: edfiero1] #5209452 09/10/19 04:33 PM
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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!

Re: Spark Knock [Re: edfiero1] #5209687 09/10/19 09:27 PM
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wheelman1991 Offline
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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 by wheelman1991; 09/10/19 09:31 PM.

1991 Volvo 240 DL, Canadian spec car imported into the States. $400 Barn find.
Re: Spark Knock [Re: edfiero1] #5209694 09/10/19 09:46 PM
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clinebarger Offline
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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.....


2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
2010 Toyota Corolla 2ZR-FE/U341E
2000 Toyota Avalon 1MZ-FE/A541E
Re: Spark Knock [Re: wheelman1991] #5209821 09/11/19 05:39 AM
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edfiero1 Offline OP
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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

Re: Spark Knock [Re: cjolson140] #5209825 09/11/19 05:44 AM
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edfiero1 Offline OP
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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.

Re: Spark Knock [Re: edfiero1] #5210973 09/12/19 12:23 PM
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cjolson140 Offline
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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.

Re: Spark Knock [Re: edfiero1] #5211404 09/13/19 05:05 AM
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quint Offline
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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).

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