Hey there,

Been a while since I last posted. Figured I'd throw up my latest problem and see if you guys can help me out.

Run down of the car:
396 Forged/splayed/9:1 static cr
Vortech V-1 A-TRIM (i know, it's just a baby...will be T-Trim eventually)
A-trim maxed out makes 5psi
Injecting Water/Alcohol (no IC, this instead)
Running a PCMforless tune
Car is my daily driver

Here's the deal, car runs and drives great. I have a scanmaster, and at WOT there is ZERO knock. However, there is a great deal of timing being pulled during part-throttle or even at idle. The knock goes away completely as soon as you get above the 20-30% throttle threshold. BTW the "knock" is never audible, only sign of it is the scanmaster display of timing being pulled.

Does not Knock when cold; ever. Soon as its nice and warm, goes into closed loop the scanmaster will begin to show 1-9 degrees being pulled even at idle. If you flick the throttle it goes away for a second or two, comes right back. Same when driving around town at light throttle 1-8 degrees timing being pulled. Seems to be worse when it idles. It will cycle to as high as 9 degrees being pulled just sitting there. Otherwise, it normally stays around 1-4 degrees. Soon as you ease into the throttle it goes away. This engine is pretty new, I built it this summer, has approx. 5,000 miles on it. Never really noticed this low/part throttle knock issue until the weather got really cold.

Question's are: 1) Is part throttle knock this high (if real) bad or dangerous to the engine?

2)Could this be false knock? if so, why only at low-part throttle?

The car deserves to be dyno-tuned, haven't had it done yet. Poor college kid here. If this isn't a dangerous scenario, I will wait to have the car dyno-tuned.

I've had a history of my PCMforless tunes containing too much timing. I have a hunch there just might be too much timing all across the board on my tune. I'm able to compensate for it WOT with the water inj. But 9 degrees at idle? makes me question it simply being the tune.

Thanks in advance,
-Andrew

 

false knock? try some higher octane gas and see what that does. the part throttle tuning might be a tad off

 

I have the same problem. I have never seen knock on any wot run but at little or no acceleration only. I was wondering if it was false knock and may have been from the exhaust or something besides internal engine parts. I figure the timing might be affecting my performance.

 

Yeah, I was thinking about mixing some race gas in, to test the false knock theory...I may just do that.

Anyone knowledgeable in this area know if part-throttle knock is potentially damaging? This is my biggest concern.

 

Any real life detonation can be dangerous. But, that's what the knock sensor is for...to tell the PCM to pull timing if necessary. I don't think you have to worry much about any damage being done to the motor because timing IS being pulled and the fact that you don't hear the motor detonating.

What octane gas do you run in the car? Does the motor have roller rocker arms installed on it? Do you have the LT-4 knock module installed in the PCM?

 

try some higher octane or pull more timing and see if that does it. But a dyno tune will be your best bet.
Just think of what you ll spend digin into the motor if have a boo boo???
Im 23 and still in college (ya i no) and broke as a joke so i know where your coming from. But sh*t man throw it on your credit card or something, the 300-400 could save you a g or 2.

 

92 is the HIGHEST octane available in my area; it is what I run. Yes I do have GMPP 1.6 rr on the car. And I am running the stock knock module.

I am debating about purchasing some tuning software and cable as an alternative to dyno tune. Cheapest dyno tune within 120 miles of me is $475-$500. 95% of the shops I called will not touch my stock PCM. I think last time i priced out tuning software and cable it came in around $300 said and done...that sound about right?

Thanks for the help.

 

No need for a dynotune so to speak. If higher octane fuel doesnt work (which I bet it wont) I would get tunercats software and lower the timing in the cells where you are seeing knock. Example:

You may be at part throttle and seeing 30MPa @ 1500rpm (~100MPa is WOT).

You go to the 1500rpm column and find the cell that is in the 30MPa row and change the timing value in that cell. This will get rid of the knock if its real.

Jon

 

Sounds easy enough. I wanted to get into doing my own tuning eventually...might as well start now.

Thanks again.

 

LT-4 motors use a different knock module because they were equiped with roller rockers. They are "noisier" than the stamped steel rockers. This condition can cause a standard LT-1 knock module to pull timing due to the false knock created from the additional noise of the roller rockers. Why don't you first try replacing the LT-1 KM with one from an LT-4 before you start changing the PCM tune.

 

unless you are worried about performance i wouldnt worrie too much about it. there are quite a few people out there with LT1s that dont know jack about how the computer works and dont tune after headers and i know they are seeing the false knock. hell i even went about 2 months with headers and no tune and saw false knock but it didnt hurt anything.

 

For a couple reasons. A) car needs a tune regardless of this knock issue. PCMforless did a great job of getting me into the ballpark, but this tune is nowhere near optimal. B) Hmm...I was under the impression that a standard LT1 KM will work, even with RR's...I didn't have an issue with it on the previous 350ci motor.

Couple questions about the LT4 km. I was under the impression it was simply a "less-sensitive" sensor. Instead of say an entirely different sensor with a different frequency range it listened for. Is this correct? If so, I like the idea of keeping my sensitive stock piece in place; at least until I get a proper tune on the car.

 

I'm a little unclear about what you are saying here.

Performance, driveability, fuel economy etc. are all associated with one another so if the PCM is pulling almost 10 degrees of timing (for whatever reason) I myself would be concerned about it. Why should you not be worried about it. Timing has a huge impact on those things listed above. For this reason, the problem should be diagnosed. I believe that most people that post here are interested and/or worried about performance.


The installation of headers, while they do have a very positive affect on the performance of the motor, don't require the PCM to be tuned. The PCM has enough "adjustment" programmed into it to compensate for better breathing/flowing exhaust. Additionally, adding headers to the motor will not in and of itself cause the motor to see false knock and the general concensus is that a louder exhaust and/of headers will not generate "noise" in the frequency range that the knock sensor is able to "hear".

 

One of two things are happening. Either the motor is detonating and the knock sensor and module are telling the PCM to pull timing away or the motor is seeing a "false" knock and the sensor and module are telling the PCM to pull timing from the motor. In either scenario, because up to almost 10 degrees of timing is being pulled, the engine's overall performance, driveability, fuel economy etc. is suffereing. This situation is not dangerous to the life of the motor because the PCM is retarding the timing.

The question is why the timing is being retarded. My suggestion of installing the LT-4 knock module was due to the fact that the motor could be seeing a "false" knock from the use of the roller rocker arms installed on your motor. GM felt compelled enough to re-design the LT-1 knock module for the LT-4 motors for this reason. The cost is realitively cheap and that may be all that is needed to eliminate the retarding of the timing. Another suggestion is to add some higher octane "racing" fuel to the existing fuel alrady in the car and see if the knock retard is reduced or goes away. By doing this, you will be able to determine if it is a false knock or real. The fact that you are running 5 lbs. of boost and don't get any knock retard at WOT suggests it is false knock. Sorry for the lengthy/rambling post.

 

Good info!

Thanks for the help,
-Andrew