Redtbi

I have a frustrating knocking issue that won't go away. I have a 92 gmc sierra with a 350 tbi with a small cam 256/268 (212/218 @ .050), 1 inch spacer, adjustable FPR running at 15psi. I've had an issue with knocking ever since the swap. I finally put a wideband to help aid with this(I've done many VE learns with the narrowband) and I've been doing open loop learns as well. There's been many corrections but it still knocks in open loop acceleration and when it upshifts. There's a shift kit that pretty much jolts the whole truck and so it shifts around 2500 to 1600 so the AE kicks in. I am not sure if this is false knock because of the jolts but I also think it could be AE. However it still knocks under load and randomly when accelerating. The AFR when driving around ranges from 12-15. I also have turned down the spark in those areas but it still persists. If anyone needs datalogs I will gladly provide them.

Street Lethal

iTrader: (16)

With a naturally aspirated setup, the fueling would have to be really off to be knocking the way you're describing. It's more than likely in the timing, or as you stated it could be false knock. Throw up a datalog so we can take a look...

RBob

iTrader: (1)

Which swap, cam, engine, ECM?

The hard shifting trans will cause false knock. Not much you can do about it, although there are some workarounds. Can desensitize the sensor, can make the knock retard recovery rate at that RPM faster.

RBob.

Redtbi

Here you go.

Redtbi

Cam swap, had a mail order tune on it and it did not perform well at all. Then i swapped to the EBL and it was better but it was still a definite issue. I don't think I will desensitize the sensor but I will look at increases the recovery rate. I threw a datalog in another reply in a .zip if you want to take a look.

RBob

iTrader: (1)

There is excessive AE when you are pulling out from a stop. Can see the AFR drop into the 10's. So you definitely want to reduce the volume of AE.

Can also see it when it shifts (as you mentioned), for that need to reduce MAP AE.

RBob.

Redtbi

I reduced it after I learned about the false knock when shifting. However there is still random knocking during acceleration. It is exemplified in this datalog. (it starts after 13:25 and continues throughout to the end of the log)

daferris

iTrader: (8)

Not to hijack this thread but how tight is the knock sensor supposed to be torqued into the water jacket? I also am getting knocks that seem to be random that I can't get rid of. I have the sensor at about 15 ftlbs is that too tight? can that cause the problem? It's a new standard motor parts sensor for a '88 5.7 Iroc with the stock knock filter using the P4 ecm

RBob

iTrader: (1)

Factory spec is 11 to 14 ft/lbs. I tend to stay on the lower end of that scale. I've also been known to mount the knock sensor on a metal stub to reduce it's sensitivity.

RBob.

RBob

iTrader: (1)

The knock you are getting is minor, mostly 1* of retard and a spot where it was 2* of retard. The high retard of 8* at 1200 RPM, 40 KPa is due to key-off on a running engine. That is to be ignored as it is caused by the ESC module being powered down immediately at key-off while the ECM continues to run.

At this point I wouldn't worry about it. I would reduce the AE as it is still too high.

When you get a chance check the spark plugs for signs of knock:

http://www.dynamicefi.com/SparkPlug.php

RBob.

daferris

iTrader: (8)

Thanks!!! I'll try backing it off a little.

Redtbi

I reduced the main SA table from stock about 75% and used values as little as 1* and I still get knocks. The AFR is safe also. I'm going to pull plugs tomorrow to inspect and will probably replace them. I will update after that.

RBob

iTrader: (1)

OK, be sure to use the less expensive no-frills copper core plugs. Since you reduced the SA so much and it didn't change anything, false knock. Still check the plugs when you take them out.

RBob.