M50 E30 3500 RPM bogging

[MaxBell]

Hey dudes;

I'm just finishing up my M50 E30 and I took it for a drive and this was the issue:

1. Feels sluggish. The M20 seems like it was more powerful.

2. Rough idle. The RPMs will randomly dip a little when I'm at a stop light and the car will shudder slightly. It's annoying.

3. (The main problem) The car loses power over 3500 rpm or at WOT. I thought it might be a coil or spark plug, so I replaced all the plugs with new and the coils with used but working ones.

The resistance on all the coils is 1.4 ohms.

That smoothed the idle slightly, but the problems still exist. What else should I check?

Is it particularly important where the ground straps for the coils are? I have one at cyl #1, #2 and #6.

[325issguy]

Grounds should be on 1 and 6. Sounds like it could be a vanos or timing problem.

[MaxBell]

When you say timing, you mean the cams are off?

Is there a test of this? Should I just open the valve cover and look? What is the proper timing procedure.

[MaxBell]

Ok so I've been doing a LOT of Google searching and I've manage to track down a few other possibilities:

1. CPS sensor

2. MAF sensor - I unplugged it and the car still did this weird issue.

[MaxBell]

Ok I took the MAF off and cleaned it with sensor cleaner. I then reset the DME by removing it for 15 minutes.

The issue seems to be greatly improved. The car can hold a steady idle now and is much more powerful.

[M-technik-3]

Check for vacuum leaks as well. If the the vanos or cams or head has not been apart I would not worry about timing.

[e30rapidic]

is it a VANOS engine?

[MaxBell]

Yes, it's an M50TUB25. So Single VANOS. :)

Check for vacuum leaks as well. If the the vanos or cams or head has not been apart I would not worry about timing.

Yes, as I mentioned earlier the engine was apart for the build.

However, the cams were put to TDC, the crank/pistons were at TDC as well. Then I put the chains on the same as they had been zip tied to when they were removed.

I doubt the timing has changed. And even so, that would make a more consistent problem, not something that shows up every 20 minutes.

As for the vacuum leaks, that I will definitely check out.
Does anyone have a list/diagram of all the M50 vacuum lines?

[M-technik-3]

Sorry read what you posted and did not see any mention of what had been apart. You must have edited that portion.

You had no cracked boots of vacuum lines?

[MaxBell]

Sorry read what you posted and did not see any mention of what had been apart. You must have edited that portion.

You had no cracked boots of vacuum lines?

Nope, nothing. I've solved the first problem it seems tho.

The MAF was excessively dirty, so I cleaned it and the car is running much smoother. However, it still lacks power, which is a constantly repeatable problem. That makes me think the timing is off.

[e30rapidic]

how confident are you in the cam/VANOS timing? Sounds like its either a VSS signal or the intake sprocket was not advanced as a far as it should have been when putting the VANOS back together.

[M-technik-3]

Is your vanos working properly? Tested the solenoid?

[mattrabbit]

Is your check engine light on? My car is sluggish above 3k when my check engine light is on for bad o2 sensor.

[MaxBell]

This engine was rebuilt before it was put in the car. I just reset the timing as per the Bentley manual.

I'm starting to suspect a bad ground. The temp gauge goes wild when this problem occurs and those gauges are sensitive to that kinda shit.

HOWEVER: I have a new greater problem. I went to start the car today. I turned the key, it started for a half second and then I let off on the key. A crack/pop was heard and now the motor will barely run. It stalls after a could seconds of chugging.

[jrdeamicis]

Your timing was off and a backfire blew out the main vac line or popped your intake tube.