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Old 07-27-2017, 09:56 PM   #1
Pavane
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Throttle Body Port

Once and for all I will have this vacuum line fiasco figured out. I'm about done, but this last issue has me stumped, so I'm asking the M10 gurus out there!

I have an '85 318i that's undergone every M10 issue out there. This latest issue is figuring out my ignition timing. I have the distributor back to factory specs, but I've lost a lot of power doing so. Couldn't get the car above 60 mph when I could easily go 100 before I adjusted the distributor.

I check my vacuum advance but the vacuum line was connected to the throttle body port. The Bentley manual on page 5-19 states that the vacuum line to the solenoid valve goes to the manifold, not the throttle body. Ok, no big deal I connect the hose to the nipple on the bottom of the manifold. But my fuel pressure regulator line is already there! So, I read further into the manual until I see the diagram on page 6-6 saying that the hose of the regulator is supposed to go to manifold vacuum. Hmmm, well I guess I'll have to tee both the vacuum advance and fuel pressure regulator lines together to this manifold port. Does this sound right to all of you?

Lastly, now that the vacuum hoses are reconnected, what the heck is this leftover port on the throttle body? I can only imagine that this is a ported vacuum source, which leads me to think that the vacuum line to the vacuum advance solenoid goes here ( mind you, this is where I originally found my vacuum advance line plugged into).
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Old 07-28-2017, 05:59 AM   #2
loki_
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On my m10, I have:

intake manifold vacuum port: fuel pressure regulator

left throttle body vacuum port (closer to the firewall): capped off because my IAC is deleted.

right throttle body vacuum port (farther from firewall): running to the right port the vacuum advance solenoid

bottom vacuum line on the vacuum advance solenoid: to the distributor


everything has been running normally in this configuration for about 4 years. I don't really feel like the distributor vacuum would have that great of an affect on power.

beside being down on power, does the engine otherwise run smoothly (no bucking/jerking)?
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Old 07-28-2017, 09:06 AM   #3
Pavane
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It's smooth until around 3-3.5k rpms then there's light bucking. Acceleration is now excruciatingly slow too. I'm wondering if I set my initial timing at 0 degrees instead of 10.

So, the port that I have circled is supposed to be for the vacuum advance? The left one next to it is connected to the charcoal canister and the one below it is for the the crank case vent.

Last edited by Pavane; 07-28-2017 at 09:14 AM.
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Old 07-28-2017, 09:14 AM   #4
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Does the bucking vary depending on throttle? Like, does it happen the same if you're at wide open throttle and if you're just barely pressing on the pedal?

I have that port going to the vac advance (side port). Then the bottom port on the vac advance goes to the distributor. I have my charcoal canister deleted so I just have that left port capped.
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Old 07-28-2017, 10:32 AM   #5
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It happens during acceleration to freeway speeds. Normal acceleration around town is fine but low rpms are a tad lethargic (probably M10 characteristic?)

It's an M10 so I'm not expecting much, but I know the higher rpm problem is definitely not normal.
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Old 07-28-2017, 10:46 AM   #6
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does it happen at wide open throttle too?
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Old 07-28-2017, 05:52 PM   #7
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It will do that above 3k rpm and I can barely get the engine above 5k.

This is how my vacuum solenoid is set up. #1 hose is going to the distributor and #2 is coming from the throttle body. The solenoid clicks when I remove power from it but I don't know if the internals wear out. There's 12V going to it from the vacuum advance relay when the car is on. The coolant sensor measures continuity when the engine is warm and the air temp sensor is measuring 1.04 kOhms at 90 degress F.
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Old 07-29-2017, 02:05 PM   #8
Pavane
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Talking

Ok, quick update:

So, I plugged all the vacuum lines as you suggested, loki_. Unplugged the hose going to the distributor, started the car, but it idled kind of low, so I pulled out the timing light to check and see where the timing was for the distributor. I saw the mark on the flywheel, but then I advanced the timing to see if there where any additional marks. Lo and behold, there was! This was a bigger mark, which suggests that this is the mark the engine needs for the initial timing. Tightened the dizzy and took the car for a drive.

Holy hell this car is driving 100% better. My 0-40 feels so much more enthusiastic, the engine is smooth through the rpms and I can bring the car to freeway speeds. No hiccups whatsoever.

Still need to test the idle emissions and fuel mixture, but this..... this is awesome.
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Old 09-19-2018, 04:53 PM   #9
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Hey Pavane I am running into the same issue on tracing vacuum lines. Can you confirm the ports and which lines you ran where? I have been replacing lines that were so old they broke so I have no idea what is supposed to go where.

Glad to hear the M10 is running strong, hoping to get mine there as well.
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