Spark Knock ! 305 Tbi

[Bob1942]

It is not a CAMARO But I now have a rebuilt 305 TBI roller lifter engine from a 1991 Camaro in my 1988 Chevy van ...It has new Clevite OEM type .060 recess dished top pistons This engine looks identical to the original and bolted right in with the same sensors as the original in the same places . Runs great BUT I have a short duration Spark Knock when the engine is lugging a little like when you go up a slight hill and give it a little more throttle at about 40 mph it will Spark Knock for just a second ! ping ping ping ! then quit ...then the "Check Engine Light " will SOMETIMES come on ! I get a 43 trouble code (spark Knock ) ...When I use the cruise control to accelerate it does the same thing ... I have reset the timing ...several times ... If I retard the timing far enough the knock goes away BUT the engine loses a lot of power and sometimes backfires ! ... I went out and filled up with fresh regular gas at a different gas station also I installed a NEW distributor assembly new plugs ,new distributor cap and rotor ... Does the 91 Camaro TBI engine require premium gas ? What is the timing specs on the 91 Camaro engine ?
How do you time the engine when you have replaced the timing cover with a pretty new one that does not have a timing pointer on it ?
...FRUSTRATED BOB

[wrightz28]

ESC problem usually result in a problem with the knock sensor circuit, the main section of the ssytem. Usually it's the wire gets scortched on the exhaust.

[Bob1942]

Originally Posted by wrightz28

ESC problem usually result in a problem with the knock sensor circuit, the main section of the ssytem. Usually it's the wire gets scortched on the exhaust.

THANKS for the reply WrightZ28 ... The wire is ok I have already checked it and ty-wrapped it away from the manifold so that is not the problem ... I have the original knock sensor still on there so that may be the problem ...I checked the knock sensor resistance it is 3900 ohms on the nose like it says in the service manual but ? ... maybe I should just get a new one and replace it to be sure ...

Do you know if this engine might need premium gas ? or were they all set up for 87 regular ? BOB

[wrightz28]

Well if it's ohming to spec, I'd leave it for now. Octane level shouldn't matter.

So if the sensor is ok, then I'd be going after the ignition timing. without the tab, you need a good ear and vacuum gauge.

A slight remote chance of something else, an EGR problem?

[Bob1942]

Originally Posted by wrightz28

Well if it's ohming to spec, I'd leave it for now. Octane level shouldn't matter.

So if the sensor is ok, then I'd be going after the ignition timing. without the tab, you need a good ear and vacuum gauge.

A slight remote chance of something else, an EGR problem?

Well I installed this engine about 200 miles ago and it has a new EGR valve ...

Come to think of it The egr ports on the intake manifold were completely filled with carbon when I took it off the old engine I had to chip out the carbon with a screwdriver ... I don't recall that the old engine ever had this knock problem ? maybe this new one would not knock if I disconnect the EGR valve hose and plugged it to test it with the EGR disabled I will try that to see what happens . Maybe it is the EGR system the EGR Solenoid or something .

I tried resetting the timing several times no improvement there it either knocks or it is way to far retarded...

I just got a new Knock sensor I figure the old one may not send the knock signal even if it does check ok on the ohmmeter I am going to try that next ...

According to the Haynes manual the spark is retarded up to 20 degrees by the ESC module ... So I am looking at the ESC module too ...

Thanks again for the suggestions I will keep at it ...and I will let you know what I find THANKS AGAIN ! WrightZ28 ........ BOB

[Bob1942]

Originally Posted by Bob1942

Well I installed this engine about 200 miles ago and it has a new EGR valve ...

Come to think of it The egr ports on the intake manifold were completely filled with carbon when I took it off the old engine I had to chip out the carbon with a screwdriver ... I don't recall that the old engine ever had this knock problem ? maybe this new one would not knock if I disconnect the EGR valve hose and plugged it to test it with the EGR disabled I will try that to see what happens . Maybe it is the EGR system the EGR Solenoid or something .

I tried resetting the timing several times no improvement there it either knocks or it is way to far retarded...

I just got a new Knock sensor I figure the old one may not send the knock signal even if it does check ok on the ohmmeter I am going to try that next ...

According to the Haynes manual the spark is retarded up to 20 degrees by the ESC module ... So I am looking at the ESC module too ...

Thanks again for the suggestions I will keep at it ...and I will let you know what I find THANKS AGAIN ! WrightZ28 ........ BOB

I FOUND IT ! I FOUND IT ! It WAS the knock sensor it checked good but did not work as good as the new one ! I connected both of them to my old oscilloscope and found that the new one would give a nice big spike on the scope when you tapped on it with a small wrench ...I found you could connect them directly to the scope no voltage needed and they work just like a microphone rap it on the base and you get a voltage spike...I tried the old one but the spike was real small compared to the new one ...So I guess old knock sensors never die they just fade away ! Thank you ! Wright Z28 for your suggestions and advice I really appreciate it ...

About the unknown sensor I found a Chevy mechanic who identified it as the sender for my dash mounted temperature gauge !! DUH ! Happy Bob in michigan

[wrightz28]

Cool beans, it's always nice to have the right tool for the right job. How did you get your hands on a silly scope?

[Bob1942]

Originally Posted by wrightz28

Cool beans, it's always nice to have the right tool for the right job. How did you get your hands on a silly scope?

I have quite a bit of electronic equipment it is all old stuff tubes etc, ...I used to work at Heathkit in the Development lab 1980 to 1983 best place I ever worked built prototypes of new heathkits . BOB

[wrightz28]

You lucky dog