Power FC Knock

[Silvia_Drift]

I am having a huge bogging issue that seems to be related to engine knock according to my Power FC.

I have been driving the car aggressively for a few days now. The car was driving fine but now has started to bog violently under load.

Basically, if I give the car full throttle under 4000rpm, the engine will basically hit a brick wall at around 4700rpm (massive bog). After this the engine will pull perfectly to redline.

At the same time as the engine bogs, the cat converter light flashes (JDM car similar to CEL). I thought the cat was overheating and making the engine bog so I punched it. This didn't help. I later found out that this light indicates excessive knock.

Looking at the PFC commander, when the engine bogs, the knock readings will be excessively high around 100. I'm not sure if the bog is causing the knock sensor to read high or the other way around.

I tried pulling timing at the RPM and load that the engine bogs and knocks at but nothing happened. I also re-initialized the PFC and again no dice.

Also, the knock readings are very low once passed 4800rpm.

It is also not a fueling problem because the max injector duty that I am seeing is around 71%.

Here are the vehicle specs:

1991 Nissan Silvia
Power FC D Jetro
Nismo 555cc injectors
S14 T28 turbo
full 3 inch exhaust
FMIC

Anyone have any idea what is going on?

[jspaeth]

I am having a huge bogging issue that seems to be related to engine knock according to my Power FC.

I have been driving the car aggressively for a few days now. The car was driving fine but now has started to bog violently under load.

Basically, if I give the car full throttle under 4000rpm, the engine will basically hit a brick wall at around 4700rpm (massive bog). After this the engine will pull perfectly to redline.

At the same time as the engine bogs, the cat converter light flashes (JDM car similar to CEL). I thought the cat was overheating and making the engine bog so I punched it. This didn't help. I later found out that this light indicates excessive knock.

Looking at the PFC commander, when the engine bogs, the knock readings will be excessively high around 100. I'm not sure if the bog is causing the knock sensor to read high or the other way around.

I tried pulling timing at the RPM and load that the engine bogs and knocks at but nothing happened. I also re-initialized the PFC and again no dice.

Also, the knock readings are very low once passed 4800rpm.

It is also not a fueling problem because the max injector duty that I am seeing is around 71%.

Here are the vehicle specs:

1991 Nissan Silvia
Power FC D Jetro
Nismo 555cc injectors
S14 T28 turbo
full 3 inch exhaust
FMIC

Anyone have any idea what is going on?


Hmm that sounds weird. If you reinitialized the PFC, the tune that is in there is NOT good for 555 cc injectors.


What tune are you running, are you tuned for that turbo and those injectors?

Why did you reinitialize it then?

[Silvia_Drift]

I re-initialized so I could start from scratch and make sure it wasn't a tuning error. After I re-initialized, I reset the injector settings so that the car would run properly.

I have basically been tuning the car myself.

The AFR and timing have been set very conservatively and I'm not sure what is causing the bog and knock.

[jspaeth]

Ok as long as you reset the injectors....sounds like you know what you are doing.

that is really weird that you are getting that knock, especially if you have lowered the timing more than what's in there....

[Silvia_Drift]

Yea, I'm thinking it may be an ignition issue. I'm gonna try replacing the spark plugs and if that doesn't work, I'll try replacing the coil packs.

I am 90% sure that the engine is not knocking since the tune is so conservative and I am also running 94 octane.

[Silvia_Drift]

Well I changed the spark plugs and nothing changed.

I'm thinking its the CAS now. When the car bogs, the timing goes to zero and the injectors shut off. I'm gonna test another CAS and see if the issue persists.

[slider2828]

turn off the knock sensor... see if anything changes....

[VATOCLOWN]

i had the same issue at about 4600-4700 i would see high knock like 70-90 but just spikes turned out to be boost leak and tps setting. it didnt realy matter how much timming i pulled it would still show knock

[Silvia_Drift]

Fixed, it turned out being the CAS.

[jspaeth]

Nice, thanks for following up!

[slider2828]

That is interesting....