Random Service Engine Soon light

squaredeal91 said:

I have heard this too about knock sensors on tbi not being too important. I think once i helped a friend remove knock sensor and solder in a diode or resistor to make it run good. I remember doing that but not sure what it was for exactly because we added a turbo on it.
Aside from that above, does the knock sensor also sense a ping from timing too advanced?

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I think it's only purpose is to detect knocking (even inaudible pre detonation) and retard timing accordingly. This can be from too advanced timing or from any other reason. It isn't smart enough to know anything but the signal it detects.

squaredeal91 said:

I have heard this too about knock sensors on tbi not being too important. I think once i helped a friend remove knock sensor and solder in a diode or resistor to make it run good. I remember doing that but not sure what it was for exactly because we added a turbo on it.
Aside from that above, does the knock sensor also sense a ping from timing too advanced?

Click to expand...

technically, it only is meant to sense ping when the timing is set to the factory spec and the conditions its running under encounter ping(high temp, high load for example) at that point its designed to pull timing. 8 degrees was tossed out there but im not sure to be honest. Basically, GM had a higher base timing (and maybe a more aggressive timing curve on the centrifugal advance? ( @SirRobyn0 may be of help on this explanation) and that allowed for more power. the knock sensor kept hte engine from killing itself , if that makes sense.

so if you start playing with timing, I wouldnt trust that it would keep you safe, Id just expect it to operate in its designed use properly

manual says 10-20 degrees retard. not sure where I got 8 from. sorry for the bad Intel.

Electronic Spark Control (ESC) system is designed to retard spark timing up to 10° - 20° to reduce spark knock (detonation) in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy. Varying octane levels in today’s gasoline can cause detonation in an engine. Detonation is called spark knock.

mibars said:

Okay, it's 43.
"43. Low voltage at electronic spark timing circuit"

I wonder, was it loose wire, poor connection or what? I'll monitor if this error will repeat.

For reference: Each error, including "error 12" flashes 3x, so it is 12, 12, 12, 43, 43, 43 and back to 3x 12.

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I agree with what others have said, knock sensor is the likely culprit.

squaredeal91 said:

I have heard this too about knock sensors on tbi not being too important. I think once i helped a friend remove knock sensor and solder in a diode or resistor to make it run good. I remember doing that but not sure what it was for exactly because we added a turbo on it.
Aside from that above, does the knock sensor also sense a ping from timing too advanced?

Click to expand...

I disagree with that entirely. If the knock sensor has to be disconnected for the truck to run properly something is wrong. See my response to GM below.

gmbellew said:

I think it's only purpose is to detect knocking (even inaudible pre detonation) and retard timing accordingly. This can be from too advanced timing or from any other reason. It isn't smart enough to know anything but the signal it detects.

Click to expand...

That's exactly right, and on the highway at decent RPM even with a quiet exhaust system you can get a ton of ping before you can here it in the cab, probably not enough to kill the engine on site, but enough to hurt it over time. I think folks sometimes think that well my 78' doesn't have a knock sensor. Well that 78' probably had different carb jetting (yes I realize this is TBI) a different camshaft and different spark curve in the distributor. So it's not so simple as remove the knock sensor runs better.

AuroraGirl said:

technically, it only is meant to sense ping when the timing is set to the factory spec and the conditions its running under encounter ping(high temp, high load for example) at that point its designed to pull timing. 8 degrees was tossed out there but im not sure to be honest. Basically, GM had a higher base timing (and maybe a more aggressive timing curve on the centrifugal advance? ( @SirRobyn0 may be of help on this explanation) and that allowed for more power. the knock sensor kept hte engine from killing itself , if that makes sense.

so if you start playing with timing, I wouldnt trust that it would keep you safe, Id just expect it to operate in its designed use properly

Click to expand...

System has no idea what the manually set timing base timing is and it really doesn't matter to the ESC module, but for example if the base timing is suppose to be set at 6 degrees, and the ESC system is capable of pulling 8 the it could pull it to -2. If the base timing is set to 10, then the ESC is going to spend most of it's life pulling 4 degrees and never be able to pull it down to more than 4 degrees. So doing that would handicap the system, and might allow the engine to ping under conditions the ESC should be able to handle, but yes the system will function.

Yes, timing is curved differently in the distributor.

gmbellew said:

manual says 10-20 degrees retard. not sure where I got 8 from. sorry for the bad Intel.

Electronic Spark Control (ESC) system is designed to retard spark timing up to 10° - 20° to reduce spark knock (detonation) in the engine. This allows the engine to use maximum spark advance to improve driveability and fuel economy. Varying octane levels in today’s gasoline can cause detonation in an engine. Detonation is called spark knock.

Click to expand...

You got 8 because the old standalone ESC units that were on carbureted rigs, could only pull 8 degrees, in two steps. So it had no timing pull, 4 degrees and then 8 degrees as the maximum timing pull.

Confirmed, it was a knock sensor.
Both old and new ones read 100 kOhm, but when tested with multimeter on AC volt range the old one generated just millivolts when mounted in a vice and knocking vice with a hammer, the new one spikes above 1 V in same conditions.

Old one has some damage on the hex part from the torque applied to remove it. Looks like that's sufficient to destroy it.

Location is not too fortunate as the water hits suspension parts and spills everywhere while it pours into your sleeve, plus the hole is big enough that creating bit of vacuum in the system helped nothing. At least it is not buried under intake like in newer GM engines.

Going back to the question related to high octane gas: If I understand correct this engine has a capability to benefit from higher octane gas, as it would not have to alter timing that much under high load. Am I correct?


BTW yes, it did ping under load before throwing CEL. First time I ever heard that ping pong ball in the engine bay

mibars said:

Confirmed, it was a knock sensor.
Both old and new ones read 100 kOhm, but when tested with multimeter on AC volt range the old one generated just millivolts when mounted in a vice and knocking vice with a hammer, the new one spikes above 1 V in same conditions.

Old one has some damage on the hex part from the torque applied to remove it. Looks like that's sufficient to destroy it.

Location is not too fortunate as the water hits suspension parts and spills everywhere while it pours into your sleeve, plus the hole is big enough that creating bit of vacuum in the system helped nothing. At least it is not buried under intake like in newer GM engines.

Going back to the question related to high octane gas: If I understand correct this engine has a capability to benefit from higher octane gas, as it would not have to alter timing that much under high load. Am I correct?


BTW yes, it did ping under load before throwing CEL. First time I ever heard that ping pong ball in the engine bay

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potentially. High octane gas can technically be harder to combust. However, The US and europe measure octane differently. Do you know what your Octane rating system is and what number is used for "regular" pump gas?

iirc europe uses MON to measure octane while the us uses (MON+RON)/2

Our 95 octane is about the same as US 91 octane. Since January it is almost exclusively E10, previously it was E5. We also have 98 available which Google says it's about US 93 and this fuel stayed at E5 levels of ethanol.

mibars said:

Our 95 octane is about the same as US 91 octane. Since January it is almost exclusively E10, previously it was E5. We also have 98 available which Google says it's about US 93 and this fuel stayed at E5 levels of ethanol.

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So do you use the 95 octane? if so, you are already using sufficient octane since 87 would be the factory number for your truck here in the US

Yes, I use 95 EU / 91 US octane fuel, we don't have lower octane fuel available in Poland anymore.