SEOJustin

I have obviously read all of the hundreds of thousands of posts on Knock Retard in our cars ( I have a 94 Z28 A4 ) and I have finally started to notice that I have a problem with it now as well. I'm not sure if the car had this problem when I first got it because the scanmaster wasn't powered up. I do know on my first logs I didn't see as much Knock; but after I did an oil change to synthetic royal purple 5w-30 I seem to notice more?

The main thing I want to ask about is why it would come and go, my car will have NO KR one day and the next I could show KR under any type of load.

Also, today I was passing someone driving slow on the way to work, and it was probably a 75% throttle pull to pass them; Anyway during & after this pull I noticed my KR shooting up on the scanmaster. I parked the car and worked for 8 hours, left work and I had atleast 0.1 degree KR everytime i touched the gas.... WTF!? Anyone have any ideas and what are the best places to start hunting for false knock? I have not heard ANY audible knocking atleast not over my exhaust.

*Edit - All timing tables are stock, as well as everything else other then the fan time and TCC/Shift Times.

Fatdog2

Is your car stock? Without a signature,I have no idea what you are talking about.How many miles on the car?Maybe you need a tune up.Maybe I need another beer.Sorry for the rant,it's late now.

Injuneer

At the time the KR showed up on the ScanMaster, did you check to see if there was a code for the knock sensor (DTC 43)?

Do you have any signs of oil building up in the PCV vent line, from the passenger side of the throttle body to the passenger valve cover? Oil in the intake charge can cause detonation. What viscosity oil were you running before the change to synthetic Royal Purple? How many miles on the engine?

You mention a loud exhaust - what are the details? Exhaust problems can cause false knock.

What grade fuel are you running? And what is the elevation where you live (affects octane requirement)? Did you possibly fill the tank just before you noticed the KR increasing on the ScanMaster? How much KR did you get during the 75% throttle acceleration?

Does the engine have full roller rockers? If so, do you have an LT4 knock module?

SEOJustin

94 z28 a4 with moroso CAI gmmg cat back exhaust 3200 stall stage 2 shift kit with a tune done by myself (only fan temps, shift points and Tcc so far) always run premium fuel

Car has 87k miles were lots of highway miles I bought it from the original owner a month ago. The car had plugs replaced about 7k miles ago and trans work only about 10k miles ago. It runs pretty good but I will check those things you mentioned with the oil.

The oil before was a cheap conventional 5w-30 and I only had about 20-30 psi of oil pressure while driving before the oil change; now I have 60psi+ at cruising speeds and 30-40 at idle.

I noticed from 5-10 degrees at 75% and only .1 or .2 at cruise

I am gonna try to zero out egr tables tonight to see if I can help with the KR on cruise speeds.

Injuneer

EGR helps reduce knock.

SEOJustin

Don't plan on turning EGR off, just eliminating the extra spark advance it adds. Figured if my EGR was acting up it would help; but it didn't really.

On my way home tonight I had no knock retard for the first 10 minutes of the drive, I passed someone and made a WOT pull to 75ish. During the pull I noticed the scanmaster flash atleast 5 degrees retard, although I couldn't watch it continuously as I was moving pretty quickly. After this pull, I was getting small amounts of KR for the remainder of my ride home.. Cruising speeds (55-60) about 1600RPM I was seeing anywhere from .1-.6 and taking off sometimes up to 1.5 degrees.

I am pretty confused as to why I would get MORE knock at random points.. I know the car was taken care of, but I may have to do some tune-up stuff soon like changing plugs and wires again, maybe the optispark (refuse to replace just cap +button on this car) and gonna try to do the fuel filter this weekend.

I also noticed that sometimes my cars voltage will drop down to like 12.6 will a poorly charging alternator cause knock? I know the injector pulse is based on voltage but I am unsure if it will affect fueling in this way.

In your opinion is this true knock, or false? I have got no codes for the knock sensor; but previous owner said he did get the two opti codes once a long while ago but once cleared they never come back.

Fatdog2

My manual says to use 10w-30.hope this helps.My02.I ran straight 30w in my bird years ago,but had leaks in the front crank area.

Injuneer

Actually, your manual (1993 Z28 manual, page 228) says "5W-30 preferred".

SEOJustin

Well, the car always had 5w-30 ran in it, so I figured I would stick with it. I wonder if the optispark is casuing these issues or if my problem is somewhere internal. I hope it's just a fueling issue or something like that; maybe I will have to reduce my timing a bit and see if that fixes it, or if it's coming from something else.

Injuneer

I doubt it's related to the oil. And there is no significant difference between the viscosity of 5W-30 and 10W-30, once the engine is warmed up, where both are "30". The "5W" or "10W" only applies to cold starts.

Do you have data scan/logging capability? Might be time for a data log, allowing us to look at multiple parameters simultaneously, looking for relationships, cause/effect, etc.

If you lack data logging capability, go to the "Computer Diagnostics....." forum, and look for the "sticky" for the free download of Scan9495. Works great.

With it being a low mile car, is it possible the previous owner babied it, and it has some carbon buildup, increasing the compression ratio?

SEOJustin

He definitely babied it and barely drove it. I have logs I recorded onw to work yesterday.. will upload tonight

GaryDoug

Can you hear the ping when accelerating? There might be other reasons for the sensor to indicate a knock, like bad motor mounts, rough roads, etc. My mounts went bad at 90k (LS1)

Fatdog2

Right again Injuneer as always.I have the original book that came with the car.Looked at it and it as what you said.I'm in California(you know,the place where we have no water and have to drink beer).Anyway I 'm running 10-30 for now because we have higher temps.

SEOJustin

I did find some oil in my PCV hose from the left side valve cover to the intake, where can I find a separator to keep the oil out but still draw harmful gasses from the crankcase?

I hear no pinging from inside the car when driving, but I can't really hear anything over the exhaust. If I get right up on the motor I hear no major knocks just what seems to me as normal valvetrain noise.... I did hear a rattle in the right rear side of my car, and noticed that the bar for rear suspension that is mounted in a diagonal type angle seems to be bent and the exhaust runs over top of it... Not sure what you call that bar as I haven't had a chance to look twice at it but doesn't seem like it should be bent like it is.

Injuneer

It's not likely you will ever hear detonation (knock). The PCM can pull up to 15* and the knock sensor picks up the knock before you can hear it. It you hear it, you have a severe problem.

Some people use a small inline filter made by Deutsch. It's a 90* configuration, so it fits. But the best thing to do is check the PCV valve to make sure it's still working. You also need to make sure the small metal baffle in the valve cover is still blocking direct flow into the plastic elbow. Without the baffle, oil droplets will get entrained in the flow. Also consider the possibility that there may be excessive blowby on the piston rings. Clean air is supposed to flow from the port on the throttle body to the valve cover, where vacuum from the PCV valve pulls the air through the crankcase and lifter valley to remove harmful vapor. If the PCV valve can't handle the blowby, pressure builds in the crankcase and the vapor blows out of the valve cover, reversing flow in the line to the throttle body.

A problem with the rear suspension isn't likely to cause false knock. The bar you describe - assuming its the one bolted to the chassis on the driver side, and bolted to the big arm on the passenger side of the chassis that supports the panhard rod - is simply a brace, and is bent downward on the passenger side to clear the exhaust. If you mean the panhard rod itself is bent - connects from a bracket on the driver side of the rear axle to the big arm on the chassis - then you have a problem, but its a misalignment side-to-side of the rear of the chassis.