Hi I have an e36 325i with the following things done to it: ACschnitzer cams, big throttle body, chip. headers & full exhaust, 4.10 diff. Say Im trying to do the speed limit of 60kmh. The car will speed up to 60 great and also gear down great but it has a problem staying at one speed. It either wants to speed up or gear down. So the car gets these hick-ups when I try to keep it at one speed. Now this is not a problem when the engine is still cold, but as soon as it worms up the problem is there. I was thinking maybe oxhygen sensor? Car needs dyno remaping? some other sensor? 4.10 diff ratio is too high?? Help.
The basic problem is that you have been p***ing about with a perfectly good car. At a guess the changes to the ESU program don't agree with the all the other mods and the mixture is too rich.
If you want a go faster BMW then get rid of the 325i and buy a 330i or a
Technically, 4:10 is too low, not too high. Higher numbers are a lower gear ratio. I can't imagine why you would put 4:10 on a car that can't fit tires that would need to be offset by gear ratios. But, to each his own.
You've replaced the cams, messed with the throttle body, changed the chip, monkeyed with the exhaust, and you are asking us what went wrong? I can't begin to guess what your trouble is.
Does the Cruise Control hold the speed properly?
Assuming you can't keep a constant speed with your foot, have you considered that you have moved the power band to a place where speed control will be very difficult? Let's say you still had the car is stock form, but was driving at 60 in 3rd gear instead of 5th. The motor would be churning out power at about 4000-ish RPM. At this speed, the throttle would be very ticklish, more gas will speed the car easily, less gas will slow it. Now, you have swapped the gears (increased engine speed much the same as using a lower selection in the transmission would do), altered the fuel delivery system so that it is more sensitive, and altered the exhaust so it can allow the engine to respond faster.
I can't see any other result than the one you got. Put the car where the engine is running along at 3000-ish RPM in 5th gear, and see if the speed is easier to maintain. In my car, that would be about 70 MPH, in your car it will be more like 55-ish. Since the power curve has been moved, the gas pedal will be far more responsive than in stock form.
Another unintended consequence of your modifications should be that the car is now slower than it was before. The engine will reach Red Line long before it gets to the top ground speed that it should be able to attain. The car is electronically capped at 130-ish MPH. As it turns out, that is also very close to the mathematical top speed of the gear ratios. When the car is running at 130, the gears dictate that the engine will be running very close to redline. Now that you have altered the gears, Red Line will arrive before
130 is reached, resulting in a slower car. The engine will have better response because the power curve is moved, but will reach it's top speed earlier in the car's progression down the highway. Your changes would be good for the track, but I'm not sure they will be what you really want for the street.
If your foot keeps speed okay, but the Cruise Control varries too much, then I'd suspect the cruise control's linkage being loose. The cruise pulls the linkage to speed up, then holds steady, except that the linkage is mal adjusted so the car slows, then speeds again, then slows, and repeats.
I would like to thank everyone for responding to my question. I have had the ecu remaped and the car is running sweet now. As for the person who wrote that I should stop messing around with the car and buy a 330i or 540i or M5, first of all I would like to say that I only like 3 series. No wonder the M5 would be faster everybody knows that!!! As for 330i and 540i whatever man...my car would blow them away. I just needed help with my car, dont tell me what I sould be driving or what I sould be doing to it. But thanks for the 2nd half of your input. No hard feelings.
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