Random Service Engine Soon light

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gmbellew

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Yes, like this or very similar. Easily comes off when you pinch it and can spin around when plugged.


Not sure about having mechanical advance in TBI, I thought that timing is managed electronically.


I believe it's correct, not touched it recently, can' feel any misfire. I checked plugs some time ago and they were all fine and even.


Just had it come back on a way back home. I mean I did not check the code, but 99% chance that it's the same one :) Looks like it must be timed well when the coolant is hot enough, otherwise it will not show.

I'll do the check once again to make sure it is properly grounded and attached, also maybe I'll try hitting engine block to provoke "fake knock" and see if it will register anything.

If it doesn't help then replacement.. Looks like the sensor is available online in Poland. But having to drain the coolant once again makes it bit annoying...

my guess is it is failing the self test. it wont self test until the engine is warm. last time i ruined a sensor, i could audibly hear the pinging when it self tested, and the engine light came on right after. when you remove or install a knock sensor, always use a vice grip or something to avoid spinning the sensor internals and killing it.
 
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mtbadbob

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Yes, like this or very similar. Easily comes off when you pinch it and can spin around when plugged.


Not sure about having mechanical advance in TBI, I thought that timing is managed electronically.


I believe it's correct, not touched it recently, can' feel any misfire. I checked plugs some time ago and they were all fine and even.


Just had it come back on a way back home. I mean I did not check the code, but 99% chance that it's the same one :) Looks like it must be timed well when the coolant is hot enough, otherwise it will not show.

I'll do the check once again to make sure it is properly grounded and attached, also maybe I'll try hitting engine block to provoke "fake knock" and see if it will register anything.

If it doesn't help then replacement.. Looks like the sensor is available online in Poland. But having to drain the coolant once again makes it bit annoying
Don't drain coolant, just swap sensor quickly. You may lose a little bit , but the hole isn't that big to lose much.
 
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squaredeal91

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What I do is loosten the sensor, then I pull radiator cap and squeeze the upper radiator hose and replace cap while still squeezing the hose. Now when I change the sensor quickly usually nothing ever comes out. It's usually a dry operation.
 

AuroraGirl

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What I do is loosten the sensor, then I pull radiator cap and squeeze the upper radiator hose and replace cap while still squeezing the hose. Now when I change the sensor quickly usually nothing ever comes out. It's usually a dry operation.
Really good idea :)
 

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Sure Taylor, if you took the pressure off first. Then warm works too.

But, don't you want to let the system come alive from cold to see if the sensor is doing anything?
 

AuroraGirl

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Sure Taylor, if you took the pressure off first. Then warm works too.

But, don't you want to let the system come alive from cold to see if the sensor is doing anything?
I was joking that I like to open the cooling system at operating temperature (imagine the burns you would probably get doing that)
 

BadBowtie

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I was going to ask what year we are dealing with. Sounds like a 1987-91 now.

I had a 1983 truck with a worn out 305cid. The CEL would come on when she ran 2 quarts (or more) low on oil. That is that 2nd oil pressure sensor, down by the oil filter.

Just more data for someone else....
 

mibars

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I was joking that I like to open the cooling system at operating temperature (imagine the burns you would probably get doing that)
Oh I thought that's the recommended method for a high pressure hot flushing the system :D

I think if I create a a bit of vacuum in the system, by simply parking it hot and pinching the expansion tank hose so it cannot such the coolant back into system then nothing would even come out through the relatively small hole when I remove it.

Are there any ill effects of driving with knock sensor CEL? Would it e.g. run with retarded spark or enrich mixture to avoid pinging?

Since this engine has the knock sensor... Does it mean that it has a tiny bit more power and efficiency when filled with higher octane gas?
 

gmbellew

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No harm in not having the knock sensor as long as the engine isn't knocking. It is there purely to protect the engine. How it works is it retards the timing when knock is detected. I think up to 8 degrees, based on knock severity. Running premium fuel won't let it advance the timing any more than the computer is tuned for. So that won't so anything for you unless you were experiencing some knock and maybe the higher octane fuel would stop it.

But it will self test almost every time you drive it and the CEL will come on when the computer doesn't get the feedback from the sensor.
 

AuroraGirl

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No harm in not having the knock sensor as long as the engine isn't knocking. It is there purely to protect the engine. How it works is it retards the timing when knock is detected. I think up to 8 degrees, based on knock severity. Running premium fuel won't let it advance the timing any more than the computer is tuned for. So that won't so anything for you unless you were experiencing some knock and maybe the higher octane fuel would stop it.

But it will self test almost every time you drive it and the CEL will come on when the computer doesn't get the feedback from the sensor.
Wont the timing not be as optimal because of the fact it doesnt see a knock signal, so it will keep the timing from changing or running as high?
 

squaredeal91

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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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