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SoCalE60

Strange RPM surge

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The engine has this strange RPM surge while slowing down and stopping.

 

Has anybody seen anything like this?

 


things that are newly refreshed on the car:

 

- MAF sensor

- Air filter

- Vanos solenoids

- vacuum pump


 

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23 hours ago, SoCalE60 said:

The engine has this strange RPM surge while slowing down and stopping.

 

Has anybody seen anything like this?

 


things that are newly refreshed on the car:

 

- MAF sensor

- Air filter

- Vanos solenoids

- vacuum pump


 

Need to scan for fault codes first.

Can be anything. Need to do proper diagnostic first. It is possible that fuel mix is lean due to air leak somewhere.

 

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On 9/7/2021 at 9:26 PM, Yuri84 said:

Need to scan for fault codes first.

Can be anything. Need to do proper diagnostic first. It is possible that fuel mix is lean due to air leak somewhere.

 

Thank you for taking the time to respond. The only codes I have anywhere on the car or for the rear wheel TPMS which need to be replaced.

 

I have noticed that with the air conditioning turned on, the mpg meter stays at the lowest mpg for a long time after I go into neutral and step on the brakes. I’m wondering if perhaps it is a vacuum problem? I am going to build a smoke tester and check for a vacuum leaks this weekend.

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I'm afraid I don't know anything other than the M57 in these cars so please take this all with a pinch of salt.....but I know that the M57 has a painful airbox cover that is almost impossible to install correctly without causing unmetered (i.e. after the MAF) air ingress. Plus plenty of opportunities for air/vacuum leaks. Your 550 is going to have less of an opportunity for that as it's doesn't have a turbo attached. Outside of that...idle control valve, MAF sensor, intake manfold gaskets.....

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On 9/9/2021 at 2:08 PM, Ollie Campbell said:

I'm afraid I don't know anything other than the M57 in these cars so please take this all with a pinch of salt.....but I know that the M57 has a painful airbox cover that is almost impossible to install correctly without causing unmetered (i.e. after the MAF) air ingress. Plus plenty of opportunities for air/vacuum leaks. Your 550 is going to have less of an opportunity for that as it's doesn't have a turbo attached. Outside of that...idle control valve, MAF sensor, intake manfold gaskets.....


I made a mineral oil smoke cannon and pressurized the intake manifold with lots of smoke. The only place the smoke came out was the PCCV valve. I used a flashlight to check around and behind the engine and there were no leaks. I did find an intake leak which I fixed and now the car drives a bit more spirited than it did before.

 

next up, I am going to check out the brake booster by the dashboard and see if that is giving me a problem.

 

Smoke rig: https://youtube.com/shorts/GhobR-razHs

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On 9/12/2021 at 10:29 PM, SoCalE60 said:


I made a mineral oil smoke cannon and pressurized the intake manifold with lots of smoke. The only place the smoke came out was the PCCV valve. I used a flashlight to check around and behind the engine and there were no leaks. I did find an intake leak which I fixed and now the car drives a bit more spirited than it did before.

 

next up, I am going to check out the brake booster by the dashboard and see if that is giving me a problem.

 

Smoke rig: https://youtube.com/shorts/GhobR-razHs

That smoke rig is awesome. I need to know how you did it. 

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41 minutes ago, iReaper1157 said:

That smoke rig is awesome. I need to know how you did it. 

+1

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1 hour ago, GoNz0 said:

+1

Thank you very much for checking out my video! The total cost came in at just about $35USD.

 

I used ABS plastic toilet flange blanking plate, a plumbing cleanout port with a screw on cap, resistance wire wrapped around a fiberglass tiki wick, some hose barbs, brass screws and nuts for the wiring, vinyl tubing, mineral oil, and silicone to seal the holes. I measured out about two ohms worth of resistance wire to wrap around the wicking and used old battery terminal clips from a trickle charger. For the threads on the cleanout cap, I applied vacuum grease then followed that up with Teflon tape to prevent smoke leaks. For assembling the ABS, l used black ABS cement.

 

https://youtube.com/shorts/ghRrmUtAZeE

 

I saw the video that this guy made for YouTube and got pretty excited at the idea of having a good quality smoke machine for an inexpensive Amount of equipment. I used an air compressor with about 3-5 psi of air through one hose to push the smoke out of the other into my engine. For even more low tech components, I was able to utilize neoprene gloves, scissors, and duct tape to cover up gaping intake holes on the engine as well as feed the tubing through a cut in one of the glove’s fingers. seriously… It is super low tech but I was able to troubleshoot like a champ.

 

 

The possibilities of troubleshooting system problems just got way better than not having a smoke machine. It feels very empowering to have something so uncomplicated but yet so useful at my disposal.

 

Just this evening, I picked up some hosing lengths. I sealed off one end of each hose with silicone. Tomorrow morning I will use each of them, one at a time, to isolate the two vacuum hoses off of the pump on the N62B48 engine to see if either of those lead to a vacuum leak.

Edited by SoCalE60
Grammatical errors, Minor details

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Well, I went into a brake shop today and talked to the technician there. He told me he had the same problem with his three series from the same year and it turned out that it was a fuel pump problem. He said he even changed out all the same parts only to find out it had been the fuel pump all along. I am not really a load the parts cannon and fire kind of person, most of the things I have replaced recently have needed it. But the fuel pump and filter?

 

Curiouser and curiouser. this is quite the rabbit hole I have fallen down.

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OK, so I’ve binned my old fuel pump and filter/sending unit and installed new Bosch components. Acceleration is nice and smooth and the engine feels lively.

 

That weird little surge still happens though when I come to a stop and the car is in neutral. Still chasing it down!

D56C959F-65BA-4C34-9C2A-FCE2243E128B.jpeg

5B653520-EBFF-46FF-8CD5-0A1288179552.jpeg

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**** SOLVED ****

 

The vacuum and pressure tester I ordered showed up last night. I went out and tested my vacuum lines and sure enough the one going from the vacuum pump to the brake booster did not hold pressure. With the help of a paint brush, liquid soap, and some water, I was able to pinpoint the leaks with the pressure tester. The nasty bits were removed/replaced and the line held pressure as well as vacuum.

 

my car runs like a champ and I can hardly wait for a weekend of spirited driving in the mountains.

 

 

C70CF7F1-9BE0-4D0E-AFBB-FDD667B9330F.jpeg

Edited by SoCalE60
Fixed minor details

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