Preignition problems

[Executor999]

Charlie (and everyone else),
I am experiencing preignition when I accelerate between 30 and 40 mph in my G8 GT. I have the VMS tune installed using the 91 octane option because here in Oregon the highest octane gas available is 92 octane. Would you recommend octane booster when I gas up?

Thanks in advance,
Dan

[wreckwriter]

When you say preignition, are you talking about pinging/detonation? I assume so.

Obviously that's extremely dangerous to your engine so try to avoid it as much as humanly possible. Octane booster may help but its not a good long term solution. The first thing I would do is try a different brand of gas. If that doesn't help Kirk may need to adjust your tune.

[GRRRR8]

I would try a different brand like wreck said and if it doesnt stop contact Kirk. I take it this is a new issue?

[Executor999]

Well... I'm not sure if it's new... I don't recall when it started but I know I first noticed it during the summer, but wasn't sure what I was hearing. Now I'm pretty sure it's preignition. I don't recall if I heard it before I installed the tune or not. It's not all the time. More often after the car warms up. Currently I use Chevron gas.

[Executor999]

And it only occurs when I accelerate at a slow to 'normal' pace, not when I accelerate fast.

[GRRRR8]

Try 2 tanks of different gas and if that doesnt cure it contact Kirk.

[Executor999]

Will do, thanks!

[Chewy]

Chevron isn't usually bad gas so I would do like the others said and then get a hold of Kirk.

I thought the knock sensor would eliminate most of this. Perhaps it is...

[done12many2]

I had the same problem on my first tune from VMS. When we put it on the dyno, it was having to pull a condiderable bit of timing during all the pulls despite the fact that it was very rich in the area where it was pulling timing.

[-Ray-]

I'm not sure it's spark knock. I would check with a Dashhawk 1st. See how much timing is being pulled.

[Kirk@VectorMotorsports]

And it only occurs when I accelerate at a slow to 'normal' pace, not when I accelerate fast.

There should be no knock even with 87 octane fuel under low throttle with our tune. I have tested our 93 tune with 87 and under normal driving there is no knock retard. Certainly no audible knock.

Try loading the engine lightly with the brake on and see if the noise is still there.

[Steve]

Just as an FYI I've got the 93 Tune and i'm in WA where you can only get 92 as well and no issues.

[Robert@KBXPerformance]

I thought the knock sensor would eliminate most of this. Perhaps it is...


One thing to remember is that KS's are a reactive versus proactive form of spark control which means that they should only be used for a safety net but never to actually manage spark advance in an continual sense. It is always best to make sure that everything is calibrated for maximum power with whatever the mods are and the fuel being run; but without having the knock sensors actively pulling timing anywhere. There might be occasional small blips here and there but those are usually only under somewhat rare conditions.

[Executor999]

Thanks for all the info and replies. When I get back I'll have to hook up my Dashhawk and see what's going on - even though I am not adept at interpreting the data. It doesn't occur all the time but when I'm driving normally and the radio isn't on, I can here a faint rattling at times when I'm accelerating in the 30 to 40 mph range. Since it only occurs during acceleration that's why I conclude it's engine knock.

[SS Enforcer]

If it sounds like a rattle it probably is pinging and should be attended to .

There has been some problems with em here as well rattling when they shouldn't. I know logging some completely stock ones here they have also pinged so it isn't surprising.

cheers

[todds87ss]

Thanks for all the info and replies. When I get back I'll have to hook up my Dashhawk and see what's going on - even though I am not adept at interpreting the data. It doesn't occur all the time but when I'm driving normally and the radio isn't on, I can here a faint rattling at times when I'm accelerating in the 30 to 40 mph range. Since it only occurs during acceleration that's why I conclude it's engine knock.

that's odd...I now have a rattle. It is definatley a rattle, though.
To check for knock, get the tranny in manual mode, put it in 4th at 25mph or so, and slowly accelerate. That should generate the most spark knock.
Hope this helps,
Todd

[Executor999]

Hrm. I'm feeling very pessimistic about this... The first thing I'll do is get a tank of gas from Shell or 76 instead of Chevron where I usually get it. If that doesn't solve the problem, I will swap in my stock ECM unit and see if I had engine knock when I bought the car. In the worst case scenario what can be done about it?

[Robert@KBXPerformance]

Hrm. I'm feeling very pessimistic about this... The first thing I'll do is get a tank of gas from Shell or 76 instead of Chevron where I usually get it. If that doesn't solve the problem, I will swap in my stock ECM unit and see if I had engine knock when I bought the car. In the worst case scenario what can be done about it?



I really wouldn't start worrying unless it is knocking all to hell. If it does knock then take it easy on it but I wouldn't lose much sleep over it. Just try the different fuel from other stations to see what that does first. If it works then your set and it was just bad gas. Then if that doesn't work dump a few bottles of octane booster in there for temporary testing purposes to see if that assists with the knock going away or reducing. If that does have a positive affect then it is pretty much confirmed that the knock is related to timing; then just have VMS send their unit back to you and log your car while on a drive that reproduces the knock. Send that log to Vector and they can modify your tune, send it back to you and you should be good to go. I am not Vector and have personally never directly dealt with them but that is what they will likely tell you do to. If the above items such as different gas and octane booster do not assist in reducing this knock noise that you hear then it may not even be spark related noise that you are hearing. Troubleshooting is sometimes a lengthy process.

Cliffnotes: Its not the end of the world so don't worry too much about it. If it is a little overtimed for the conditions and fuel you are encountering then it can be fixed relatively easily.

[Executor999]

An update and it's all good news. First off, I have a bad memory. The gas I was using since I bought my G8 in which I experienced engine knock at between 30 and 40mph was 76 also known as Conoco Phillips (not Chevron).

Last week I filled up with Shell. The results were interesting. Initially I experienced more engine knock, between 10 and 40mph. After I got off the highway, I drove locally again and had no engine knock. This is after driving for more than a half hour to make sure the car was at normal driving temperature. I have had no more engine knock since.

I am going to fill up with Shell again and then try Chevron and monitor for engine knock. In the end, so far it just seems to be the quality of fuel.

[Cobra]

Hey Dan,

Does your Costco up there have fuel? I have been using Costco fuel (93 Octane) down here with no problems.

Some interesting reading http://www.salem-news.com/articles/january142008/ethanol_11408.php

[Executor999]

It's almost 60 degrees here in Oregon and I'm finally learning how to use the Dash Hawk to record data, so I logged data specifically for the MAF, spark retard and knock retard. Forget what I hear. There is definitely some engine knock occuring.
http://www.howervision.com/g8/g8log020302.gif
http://www.howervision.com/g8/g8log020301.gif

Anyone have any thoughts on this?

[desertg8]

I have the cortex tuner. 91 rotofab tune. I installed the kooks mids one and seven eighths and I know the cortex is over it's head. Now on full throttle it pings. Maybe it did before. But with the headers you hear it. So I tuned it back to stock. Will headers make your car run lean? I am going to go with Livernois. It is 108 outside so that does not help.