My 95 TSi is having problems with detonation when the car is under load but while still in vacuum. For instance, off the line will be fine, shift into 2nd and it'll detonate once or twice, and then cruising up a hill in 3rd or 4th at part throttle but NOT in boost, it will detonate like crazy. As soon as I give it more throttle and it starts building boost, the detonation goes instantly away and it pulls strong.

Since it's a 1995, the crank and cam angle sensors are both behind the timing belt and non-adjustable as far as I know.

I checked the timing and it's 8*BTDC under normal operation, but drops to 1-2*BTDC (spec is 5* +- 3) when I ground the brown ecu wire. So base timing is barely in spec, retarded slightly.

Only mod is a 3" catback. Have tried brand new:
- Magnecore and Champion plug wires
- NGK and Champion stock plugs gapped to .035
- Bosch and OEM O2 sensors
- PCV valve
- Cleaned oem 450cc injectors

Plugs look (and car smells) like its running a little rich. The plug wires look like they're arcing to the cruise control cable a lot, and theres several burn holes in all 4 of the wires anytime they're near a convenient ground. No CEL's. No other issues.

Please give any suggestions you can think of, I'm pretty much out of ideas.

I'm not sure I totally understand the cables arching to other places. If you have holes in the wires then you defintiely have a problem there. No spark = no power. I don't know why you would have the holes in your wires already, but something is going wrong there, holes in the wires is the first sign the plug wires are bad.

The thing that boggles my head is that the two sets of wires I've tried were brand new! The Magnecores had holes in them within 1000 miles. I can't see any holes in the Champions yet, but the problem didn't change at all once I swapped them out.

I did notice that Plug wire #1 and #3 were the worst by far. They just happen to be the shortest and the longest cable in the bunch if that matters?



The marks line up exactly with where they sat against the cruise control throttle cable.

I know about this: http://www.magnecor.com/magnecor1/techbulletins/tech_mrbishi1.htm
But I don't think it applies since the wires were new, and never got wet.

That is weird. Flat out weird. That link you posted refers to the plugs getting wet in the spark plug holes, you are having problems at the coil pack. Never seen that before.

Good luck.

the wires are probably from moisture in the plug holes. Check for moisture in there, let it air out, and check for leaks around your valve cover gasket.

and then you can always remove the cruise control... :shrug

Magnecore wires are pieces of shit. Never buy them. Everyone I know who had them at one point in the past got rid of them in a few months. My Accel 8mm wires have been perfect for the past 3 years and 20,000 miles.

As for the detonation problem, partial throttle detonation is common. How do you know you are knocking? Are you measuring it with anything or what? How new is your knock sensor? If it is original it might be toast. Try to check that out.

Originally posted by Jeff_99gs
As for the detonation problem, partial throttle detonation is common. How do you know you are knocking? Are you measuring it with anything or what? How new is your knock sensor? If it is original it might be toast. Try to check that out.

I can actually hear the knock. It's definitely detonation, and its bad, no question about it. Sounds just like my 420a running lean under boost. It's not rod knock or lifter tick or any of that.

I am not measuring it, but its enough to pull all the timing it can because the car runs super rich once it goes into boost. I don't have a datalogger anymore, but it looks like I'm going to have to get one again.

The knock sensor is original, 100k/9 years old. I'll check/replace it.

Knock sensors get overly sensitive as/when they go out.