edfiero1
07-17-2019, 09:47 PM
I have a 2.7 liter 4 banger with TBI injection.
The last few times I've driven I've encountered spark knock when in 4th gear under load. This is a new problem that I have not encountered previously.
I topped off the tank with Sunoco 93 Octane, and also dialed back the timing via EBL Flash about 10% in the RPM range where I'm hearing the knock. However neither of these things seemed to resolve the problem.
I pulled the plugs and found 3 of the 4 looked pretty normal and while one appeared to show signs of detonation.
I have a 180 degree thermostat and operating temperature is normal. There is no EGR.
Not sure if this is significant or not, but I've taken a few short drives (around 10 minutes) and don't hear the knock. It seems like it manifests only on longer drives 15 minutes or longer.
I tried to get a temp gun on all the headers. Each seemed to measure in the 500-600 degree range so I couldn't see that the cylinder with the questionable plug was any hotter or colder than the rest.
I checked my valve lash and found the INTAKE valve on that questionable cylinder to be just a little too tight. I backed it off less than a 1/4 turn and brought it back to where it should be. That didn't seem like enough to me to cause a problem.
Finally I did a cranking compression check. I had 2 cylinders measure right at 170. One was the that which had the bad plug, but the other one measuring 170 had a normal looking spark plug. The other two cylinders were 150 and 160.
I put in spark plugs that were 1 heat range cooler. That did not help the problem. Neither did the valve lash adjustment. Also, I ran a can of Berryman's cleaner thru the vacuum port for good measure, but no change. The engine only has about a 1000 miles on it. So I wouldn't expect a tremendous about of carbon build up.
Why would only 1 plug show signs of knock?? (Its TBI so there is only 1 fuel injector)
Anything else obvious I should be checking?
The last few times I've driven I've encountered spark knock when in 4th gear under load. This is a new problem that I have not encountered previously.
I topped off the tank with Sunoco 93 Octane, and also dialed back the timing via EBL Flash about 10% in the RPM range where I'm hearing the knock. However neither of these things seemed to resolve the problem.
I pulled the plugs and found 3 of the 4 looked pretty normal and while one appeared to show signs of detonation.
I have a 180 degree thermostat and operating temperature is normal. There is no EGR.
Not sure if this is significant or not, but I've taken a few short drives (around 10 minutes) and don't hear the knock. It seems like it manifests only on longer drives 15 minutes or longer.
I tried to get a temp gun on all the headers. Each seemed to measure in the 500-600 degree range so I couldn't see that the cylinder with the questionable plug was any hotter or colder than the rest.
I checked my valve lash and found the INTAKE valve on that questionable cylinder to be just a little too tight. I backed it off less than a 1/4 turn and brought it back to where it should be. That didn't seem like enough to me to cause a problem.
Finally I did a cranking compression check. I had 2 cylinders measure right at 170. One was the that which had the bad plug, but the other one measuring 170 had a normal looking spark plug. The other two cylinders were 150 and 160.
I put in spark plugs that were 1 heat range cooler. That did not help the problem. Neither did the valve lash adjustment. Also, I ran a can of Berryman's cleaner thru the vacuum port for good measure, but no change. The engine only has about a 1000 miles on it. So I wouldn't expect a tremendous about of carbon build up.
Why would only 1 plug show signs of knock?? (Its TBI so there is only 1 fuel injector)
Anything else obvious I should be checking?