misses at 5500rpm, bucks like crazy under load.

[Kershaw]

1988 325ix. 5 speed. 390k miles.

Last week it started having a hard rev limit of 5500rpm so i began to diagnose potential problem areas. the rev limit varied with no discernible pattern. Sometimes it was 2000rpm, sometimes it was 6000rpm. I do know that it will buck like crazy if you accelerate quickly in gear, no matter what was changed. it will drive smoothly as long as the acceleration is slow. It's not really drivable and it's my only car right now.

I am at a loss and thinking the next thing I fucking swap will be cars.

Things I have tried:
Fuel pressure gauge, fuel is at 3 bars.
Injector harness.
Injectors.
AFM.
TPS.
CPS.
DME.
Main relay.
Spark plugs.
Plug wires.
Cap and rotor.
the entire fucking engine harness.

So I'm fairly certain I've swapped everything electrical that makes a motor run. I don't know what else to swap except the entire motor. Or car.

Please help. I am at a loss of things to do next.

[sayed ali]

Does it cuts when you rev it on idle? Did you adjust the tps properly?

[Kershaw]

a different throttle body with a tps already on it was swapped first. then my original tps (cleaned out) was reinstalled and verified to be in the correct position with a multimeter.

[R1ckM]

Having a similar issue, i think it might be a sensor or some sort with my case though. Its 88 ix.
Try adjusting the vavles, timeing?

[Kershaw]

Yeah, I'm going to look at the valves and cam shaft today. Maybe the camshaft has some weird wear or something.

[Kershaw]

Valve train looks good. Compression 160 160 160 170 165 165. Swapped cluster and new alternator belt.

I have no clue.I'm out if things to check.

[dnguyen1963]

Vacuum leaks? When you accelerated quickly, the engine could have made some connections loose; thus vacuum leaks and bucking of the engine.

[Kershaw]

So... I replaced the cps wheel. "Vibration damper" on realoem. The toothed wheel the crank position sensor reads.

That "fixed" it. It still occasionally bogs under wot. But it drives just fine now.

I don't understand how that hunk of metal could be defective.

[dnguyen1963]

The CPS is a magnetic device. The tooth wheel is a simple mechanism of changing the magnetic field that the CPS is reading. My guess is that the CPS is going south on you. Is your wheel covered with oil? How clean is the CPS?

[Kershaw]

It's not the cps. My cps is brand new and reads 515 ohms. If you read the original post you'd see I wrote that I already replaced it.

I just don't understand how the toothed wheel being replaced could fix it. It's not like hunks of metal go bad. It was definitely an electronic issue though, holding a voltage tester on the coil line you could see the voltage drop. Definitely a timing issue.

[jeffnhiscars]

I don't see where you tried swapping coils.

[dnguyen1963]

It's not the cps. My cps is brand new and reads 515 ohms. If you read the original post you'd see I wrote that I already replaced it.

I just don't understand how the toothed wheel being replaced could fix it. It's not like hunks of metal go bad. It was definitely an electronic issue though, holding a voltage tester on the coil line you could see the voltage drop. Definitely a timing issue.

Did you get OEM CPS? The right voltage reading from a crappy CPS can still give you all kinds of problems.

[Kershaw]

The coils from two different e30s were tried. The cps is band new oem.

The car pulls smooth to redline now anyway. I'm serious when I said replacing the vibration damper fixed it.

[tinkerputzer]

The hub where it mounts to the crank and the toothed wheel are separated by rubber. It is possible for them to shift throwing off timing. It has been known to happen. gstuning on e30tech posted about it happening to a customers car awhile back.

[Kershaw]

That was my friend's best guess as to the cause. I've never heard of it happening before. Thanks for the info.