I'm getting knock/detonation when I step on the gas. I still have plenty of power and I've checked all the plug wires and replaced them. It's hitting on all 8. I used to have a little knock but not until high rpms, now it's almost anytime the tps % is higher than 70-80. It can't be the tune because it was running too good without knock a couple weeks ago. Plus I backed down on the timing and it's still knocking. It's also surging at an idle more than it used to, and only in Drive or Reverse. P/N is good. This might not be related.

I checked the fuel filter, it's clean. I don't have a fuel pressure guage to fit the fitting. I guess that's my next step, but it rides beautiful at cruising speeds or all the way up to 60-70% throttle. I'm thinking it's a lean condition or ???not sure what else since the spark is good and every other data log field looks good.

What happens when FPR starts going bad? Any other ideas. IAC maybe? I would really appreciate it.

 

Pull the vac line and plug it on the manifold and see if you still have problems but you really need to put a gage on it.

 

^ X2. Put a MECHANICAL fuel pressure gauge on it while running and see what you get. 43.5 psi at warm idle is stock IIRC.

 

How do you know you are getting knock, via scanning software? If you are, I would try and figure out if the knock is false or real first.

 

Fuel pressure is about 35-36 running, a little more before starting. But never up over 40. How are you supposed to know if it's false or not? Sometimes I get no knock and sometimes I get up to 10 but the longer you hold it WOT the lower the knock gets. I'm using datamaster. And I was barely getting any knock 2 weeks ago when I loaded my first tune from Solomon.

What next?

 

Run 100 octane fuel. If the knock goes away more than likely it's real. If it stays, it's false.

 

Fuel pressure is actually about 41 before starting and once I unplug the FPR vacuum from the manifold pressure goes up to about 43, but during idle it's about 35. Is all that normal or too low?

I don't have access to 100 octane at the moment, but I'll be sure to try that soon.

 

What happens if it's false knock? How would you go about resolving that issue?

 

Your fuel pressure is within GM spec. No worries there.

 

The knock sensor circuit can be desensitized and/or programmed out of the PCM.

 

Check the TPS voltage. It should be between .65/.67... It's worth a try.

 

Actually, acceptable closed voltage range is between .2v and .9v.

 

I adjusted the throttle screw to close the blades and my tps voltage is .55 closed, which is normal. It was .61 before I closed the blades. I don't think thats an issue. I'm really starting to lean towards the false knock because I've checked almost everything else that it could be. If it's not too much spark advance and it's not a lean condition, then how could it be picking up detonation?

This is how it started: I was getting a misfire and the car was running like **** and of course knocking when under a load. BLM on right side went way up. It was a plug wire, so I swapped it out. I actually swapped out all of them on the right side. BLM came back down and motor was strong and back to normal, except I still can't get this knock to go away at high throttle.

I sent Solomon an email with a datalog, so I'm hoping he will have suggestions, but I'm still open to any other thoughts.

On a brighter note: my wheels and tires came in today. OEWheels C5 DD 18x10.5 with BFG KDW 295/35/18. A huge upgrade from my 225/60/16s. I'm lovin them, but would enjoy it much better if I could get this solved.

 

I read somewhere once before that the knock sensor being to tight could give you false knock as well. Have you messed with it? I have a 93 but, isn't there a knock module located in the pcm people change out with a LT4 knock module to make it less sensitive? Like RamAir said has it been desensitized through PCM programming? I'm sure Soloman knows about that but, it's worth a shot. Also, see if can check the fuel pressure under WOT, it may be falling off. Another thing, if my car is low on gas it runs lean.

 

Check the torque on the knock sensor. SpeedDensity is right, if the knock sensor is torqued too tightly, it can read false knock.
The LT4 module can be good for you if you have headers or valvetrain mods.

 

Just another update to one of my older threads. I don't like leaving the threads unresolved, especially since I've spent hours searching through threads with similar problems, but never finding the resolution to the problems.

I replaced the opti because it failed. I replaced the FPR, and fuel pressure is more consistent. I installed an LT4 knock sensor. Waiting on a new fuel pump, 255 Walbro.

The opti seemed to help or reduce the knock at least, but it's still there. The LT4 knock module didn't seem to change anything. It seems just as sensative as before.

I haven't tried high octane fuel yet, so I guess that's my next step but I honestly don't know where I would get any. I'll ask around. I run 93 octane and have been since I've had the car.

I need to also try adjusting the knock sensor and back it out 1/4 or 1/2 turn if it's too tight.

The thing that bothers me about this is that it all started when my plug wire(s) was misfiring, because the A/C pulley carved into the wire. Being my only vehicle, I drove it to work 2 or 3 days with the misfire, and after replacing the wires, the knock never went away. Could I have damaged something else by driving with a misfire?

One more thing that seems odd: if I'm cruising at 45mph in 4th gear and stomp the gas, I get knock as it's in transition to downshift, then when it drops gears, the knock seems to be less. If I drop it down in 2nd gear manually at 35-45mph, then stomp on the gas, barely any knock, sometimes none. Does this mean anything to anyone?

 

Are you saying you're getting less knock at a higher RPM?
It could actually be engine knock.....from bad parts...
If your knocking isn't getting any better after going to the LT4 knock module and you're still throwing codes, it may be a good idea to pull your valve covers and check your valvetrain.