EpiglottisDynasty
New member
- Joined
- Oct 26, 2021
- Location
- El Paso, TX, US
I picked up a 1994 940 a few months ago, and it was audibly detonating every time I got on the gas, even on 91 octane. I replaced a dead in-tank pump, all vacuum lines and the stuck pre-heat valve, cleaned the MAF, put in colder spark plugs (two heat ranges colder) and an 88 degree stat, and replaced the fuel filter. It's less severe, but it still audibly detonates, even on premium, and even well before the kickdown detent. No detonation the first couple of minutes of driving, but after getting up to temperature (middle of the gauge) it is nearly impossible to accelerate without getting some.
I've probed the MAF, knock sensor and the Lambda with a meter... voltage on the MAF at idle is right where it should be, knock sensor isn't an open circuit, lambda ticks nicely back and forth at idle... and actually swings rich when opening the throttle. I don't have a tool to pressure test the fuel line, but there is no sign of leakage at the FPR vacuum line, and removing and plugging the vacuum hose shows the expected rich condition at the lambda. Checked the timing, and it is right on, at least by the markings (checked on the t-belt gear, not the dampener.) No obvious signs of vacuum leaks, unless there is one in some unexpected place. Tried blowing smoke up a vacuum line, didn't see any coming out anywhere. If I open the throttle quickly, I'll get a couple of quick louder clacks, and then they stop, so the knock sensor must be picking up something, but some small random crackles persist after. It has a Bosch injection system.
I'm kind of at a loss here. It isn't incredibly severe, and you can't feel it, but it is audibly there, and it is definitely more noticeable than my LH2.2 240, which, I was under the impression, is more knock prone.
I've probed the MAF, knock sensor and the Lambda with a meter... voltage on the MAF at idle is right where it should be, knock sensor isn't an open circuit, lambda ticks nicely back and forth at idle... and actually swings rich when opening the throttle. I don't have a tool to pressure test the fuel line, but there is no sign of leakage at the FPR vacuum line, and removing and plugging the vacuum hose shows the expected rich condition at the lambda. Checked the timing, and it is right on, at least by the markings (checked on the t-belt gear, not the dampener.) No obvious signs of vacuum leaks, unless there is one in some unexpected place. Tried blowing smoke up a vacuum line, didn't see any coming out anywhere. If I open the throttle quickly, I'll get a couple of quick louder clacks, and then they stop, so the knock sensor must be picking up something, but some small random crackles persist after. It has a Bosch injection system.
I'm kind of at a loss here. It isn't incredibly severe, and you can't feel it, but it is audibly there, and it is definitely more noticeable than my LH2.2 240, which, I was under the impression, is more knock prone.
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