Knock problem

[pwhite]

After my motor rebuild I got a knock at wot in low gear it would show 19* of knock for about 2 frames on the scan master o2s in the 820 range. then it would go away for the rest of the run. it will not knock if I gradually get on it in 3rd gear. I can run it from 55 mph all the way to 100 no knock . it will do this with 116 oct. at boost levels as low as 12 ibs. I thought it was my tranny but I recently replaced it with a th 400 and the same problem is still there. If its false I can not find it (checked all the usual things dp ,exhaust ect ect) I found a vac leak on my intake but dont think this is the problem do to the way it runs in third. Could it be an injector that leans out when a sudden hit of boost and catches up after the knock retards the timing?

Thanks for any help (sorry about the long post )

 

[MistaScott]

You need to get some scan numbers. If you were leaking vac you could have been leaning out since that allows air into the system and raises BLMs to 150. The result is detonation.

The knock could be false but at 19* I wouldn't keep my pedal into it. That's a lotta knock.

 

[77tech9]

Could you hear the knock from inside the car?
I've gotten a 9 once with a problem with fuel pump and it was VERY loud inside car.

 

[pwhite]

I can not hear the knock from inside the car it only stays for about 1 to 2 frames on the scanmaster . Has anyone ever heard of a injector causeing this problem. one not putting out fast enough when I spool it quickly . have my intake off and while my injectors are out i am going to have them checked.

I will get more scanmaster numbers when the car is back running but I think the bls were around 115 to 135 range at wot

thanks

 

[pwhite]

Finished installing my intake and took a ride . I still have the same problem as described above . no more leak on the intake. I dont hear the knock I guess it could be false.... still looking. bl on scanmaster are 105 at idle and 130 at wot. for some reason after driving for a while I could only make around 16 # of boost I started at 20 # any ideas . if I spray carb cleaner around the injectors it idles up. is this a vack leak?

thanks

 

[MistaScott]

If your blms are at 105, you are running very rich so I wouldn't suspect a vac leak.

Make sure the car is in closed loop idle, full operating temperature before looking at blms. I'd drive it around a little bit. BLMs should be jumping around at 128 plus or minus 10. 105 is the low extreme meaning the ECM is struggling to remove fueling.
What is your fuel pressure set at?

Common causes of low blms are bad MAF, bad injector, too much fp, o2 sensor, ecm.

 

[pwhite]

Thanks will check the fp last time i did it was at 44 line off . the bl numbers were taken after a 15 min drive. what do you make of the boost falling off after a bit of driving.

 

[MistaScott]

If it was consistently at 20 pounds before now I'd suspect sometihng blew off like a wastegate hose. Check all the connections/hoses between the turbo and the throttle body. Make sure you have the correct orifice in the y-fitting for the wastegate hoses. If none of that works then look at the wastegate itself.

 

[pwhite]

Found boost problem ( hose slightly off vac block )

so how do I check for the low blms . Pull injectors and have them flowed? will replace O 2 sensor soon. Could what ever is causeing my low blms be cause my knock problem.
the problem seems to get worse after the car warms up good

thanks

 

[MistaScott]

What is your MAF reading at closed loop idle? It should be 5-6 gps at idle and approach 255 at WOT. Low BLMs indicate a rich condition so it wouldn't explain knock.

Check fuel pressure too. Then go to injectors and change o2.

Check out Razor's post on BLMs in the Library section of t6p.com.

Always reset the ECM after making any changes so it can learn the new fueling.