** SOLVED ** m42 power loss at 4300rpm

[and_e30]

I am out of ideas for this issue. Intermittently the car will have a loss of power at 4200 - 4300rpm. It happens ONLY in 2nd, 3rd and 4th gear, never in 1st. I will be accelerating no issues and once I hit that special rpm it will bog and accelerate slowly. If i let off the gas and hammer back on it will pull like normal. I just cannot narrow down this issue.

I have gone through the car quite extensively lately and here is what i replaced.

1. new fuel pump
2. new fuel filter
3. new fuel soft lines
4. fuel injector cleaner
5. cleaned idle control valve
6. cleaned mass airflow sensor
7. replaced all vacuum lines
8. checked catalytic converter, seems to be operating normal. not clogged
9. brand new coil packs
10. new spark plugs
11. new bosch 02 sensor

Please make any suggestions. This is a very annoying issue.

[Balleristic31]

Try another afm, and double check the harness going to the tps to make sure none of the wires are loose or broken at the plug.

[and_e30]

Try another afm, and double check the harness going to the tps to make sure none of the wires are loose or broken at the plug.

I actually had to replace the whole connector going to the tps. there was one wire broken off so i spliced in an entirely new connector. i triple checked the connections and it seems to be working, i also changed the tps with another one from the junk yard. problem still exists.

i used an afm cleaner on the sensor and no difference. i need to find a known working afm and swap it out to try that suggestion.

[Dj Buttchug]

plugs are new but what brand are they? also gapped properly ?

[and_e30]

Brand new Bosch part number from real oem. I didn't gap before installing. Most modern spark plugs don't need to be though. I uninstalled them twice and property torqued as well.

[jntar]

Tried a stomp test?

[and_e30]

No check engine light on. But stomp test has not worked since I've owned it :/

i checked the tps and the connector per the bentley manual and everything is in spec.


do you guys think a performance chip might mask this problem?

[jntar]

Check the cam and crank position sensors to make sure they are still in spec. Check the evap system for leaks.

Only other things I can think of. Sorry dude!

[TobyB]

Stick a meter on the afm and sweep it through it's range of motion.
If the resistance curve is not completely smooth, that can do it.

I always check fuel pressure, but that's just me.

t

[and_e30]

m42 power loss at 4300rpm

I'll check the crank sensor. Cam looked fine when I looked at it to replace the thermostat.

Could be a possible fuel pressure issue. I figured the new fuel pump would fix one of there was. Any ideas why it happens exactly at the same rpm every time? I don't know what would cause that. Maybe the ecu is so basic that at that designated rpm it just dumps more fuel into the injectors and its starved at that moment and bogs down. I'll trouble shoot this weekend and get back with updates. Thanks everyone.

[and_e30]

i checked the fuel pressure and i am about 7.5 psi low, bentley manual says it should be at 43.5 psi and i am about 36psi. When i pinch the return line the pressure goes up. I guess this indicates a bad pressure regulator.

Any other thoughts on what could cause the low pressure?

[yourmightyruler]

I had the same issue. For me, it was an overfire from cylinder #4. Cleaned the connectors to the plug, reinstalled, and it was fine.

[and_e30]

Ill try that. Thanks.

[and_e30]

I had the same issue. For me, it was an overfire from cylinder #4. Cleaned the connectors to the plug, reinstalled, and it was fine.

When i bought the car the previous owner had newish bav autosport wires on it, didn't think to look at the connections but when i did about 3 of the 4 had corrosion on them. Installed new wires, PROBLEM SOLVED.

Something so simple i over looked, must have caused a misfire at high rpm and given me that power loss. Thanks everyone for the help. Car runs like brand new now :)