Engine knock in a BMW 325ci

[daveco]

Tech question-Own a '04 325ci, recently had it superchipped, dyno'd, and power has increased slightly (torque by an extra 10lb ft) One thing was mentioned to me afterwards by the operator; he said the engine was pinking a bit. I thought knocking would affect engine power? Is the chip the culprit? Any thoughts would be a help.

[b.johnson]

Yes the chip is the problem, its too lean for the fuel you are using, pinking, knocking, deting, ratteling. all the same thing, 2 options to fix it, 1. use a higher octain fuel (v-power) or 2. get it remaped for it to run on 95 octain.

[daveco]

I'm going back to the chip fitter he said he'd do a diagnostics check, he's almost certain that it's the coils and not the chip though he woulod say that. I'm guessing he'll just fob me off and say nothing is being detected. It was in a BMW garage last week and they found nothing wrong either-It's bloody annoying!

[vixpy1]

Running it on V-power should sort the problem, but might not. I'd go back to superchips and get them to make you another chip, either running less lean or with less timing. Not the first time i've heard of a superchips causeing knock to be honest

[350zwelgje]

What type of knock are you talking about? The low speed knock you can hear (the picking). High speed (= high revs) knock is very difficult, as there is too much noise around. A knock sensor is able to detect both, and chipping can cause both. If your car has a knock sensor it should provide a signal to the ECU, and probably eliminating part of the new program. Although running lean causes mainly low speed knock. Would go back as well, and try to get to the bottom of them detecting knock. If they are good, they should be able to get rid of it as well.

Rob

[AntMat]

I would have thought that the fuel demands might have been too high at certain times. This is not uncommon in competition engines and usually adjustment of the fuel pressure regulator or the fitting of a rising rate unit can help to solve the problem.

[daveco]

350zwelgje said:

What type of knock are you talking about? The low speed knock you can hear (the picking). High speed (= high revs) knock is very difficult, as there is too much noise around. A knock sensor is able to detect both, and chipping can cause both. If your car has a knock sensor it should provide a signal to the ECU, and probably eliminating part of the new program. Although running lean causes mainly low speed knock. Would go back as well, and try to get to the bottom of them detecting knock. If they are good, they should be able to get rid of it as well.

Rob

It is knocking under heavy acceleration mostly, quite hard to hear, but it is there. The engine revs at idle are not fluctuating and fuel consumption is normal. I've put an octane booster in with the fuel and there has been an improvement, knocking occurs less frequently. It's going into the BMW dealership today to check the clutch, will I tell them about the knocking? They are un-aware of it being superchipped, this wouldn't show up if they did a diagnostics check would it?

[wantmorepower]

Tesco 99 or Shell VPower (98) plus an octane booster (+2) might help. Part of most chip upgrades is the advancing of ignition timing to produce more power. This can only work successfully and safely if you are taking sufficiently high octane fuel. In effect the chip upgrade is taking away part of the safety margin engineered into your engine by the manufacturer which allows it to run on a range of fuels down to the low/mid 90s. As long as you use high 90s you should be able to exploit this safety margin for a bit more power via more advanced ignition timing.

I wonder how reliable these knock sensors are. I have almost the same car as you but mine's the 330. Even on 98/99 octane i do notice a little tiny bit of pinking under load at 1500-2000rpm (say 2nd gear uphill 15-20mph if i try to accelerate) so i have worries that the knock sensor might be faulty.