engine and drivetrain Adventures in 73 Tii throttle/afr tuning

[jgerock]

I believe there is a ridge on the underside of the lid of the tuna can with 2 gaps that forces you to align it correctly.  The ridge also helps keep the little gasket from slipping toward the interior of the can.

 

N

Yes- there are ridges to align the cover but you can flip it 180 degrees

[lilmo]

Yes- there are ridges to align the cover but you can flip it 180 degrees

 

Interesting.  I wonder if there are multiple versions of the lid.  Mine will only seat if oriented correctly, due to the fact that the gaps between ridges are different sizes - a long gap on the engine side, and a shorter gap on the filter side.  Learn something every day.  I'll take a look at my spare TB when I get a chance.

 

Sorry for the hijack gliding! 

[JohnS]

Made me look.  I think this is the later style throttle body.  cap only will fit one way.  Looks like the rubber cap on the bottom should be about 20mm outer diameter.  More of a grease cap than anything I think.  Use synthetic grease.

Edited July 8, 2015 by JohnS

[gliding_serpent2]

Ok, so after far too long... I finally got around to the car again after getting hung up on one of the first steps (and getting side tracked by my 1984 911 project): setting the length of the pump throttle linkage.  I was able to get my linkages adjusted such that my idle and WOT throttle positions on the pump were near perfect, with minimal play in the throttle linkages.  Turns out my rebuilder must not have followed the factory procedure, as I was only getting about 85% throttle with his original settings when the pedal was to the floor.  That or two years have slowly relaxed some of the linkages.  I ended up making the "longer horizontal linkage" that goes to the firewall about 1cm shorter than the advised 289mm in order to take the slop out of my linkages and allow approach to full throttle.  .  Overall, jamming my hands in and around the pump aside, I could do this part blindfolded now.  I think the hardest part was getting the pump throttle linkage off, and then on again.   

 

I took the car for a quick spin to heat it up for the idle and mixture adjustments, and ran into a rookie mistake... the settings by the book were to get your cold car started, but were not near ideal for a warm car.  After realizing the difference 15% more throttle makes, I limped home with my AFR running increasingly rich and I even stalled a few times if I let my RPM's drop too low.  WOT was fine however as it got me to a perfect 13:1 AFR.  Of note,the warmup regulator appeared fully extended, but as the car was on the ground, I could only guesstimate. 

 

Back in my garage, and fully warm, I began to slowly adjust both idle and the mixture screws.  I had to further tighten the idle adjustment screw to get my idle up to around 800rpm when the car was warm.  As I increased idle speed, things would lean out, so I would back off on the enrichment screw.  With some tweaking of the mixture screw I got my AFR reading around at 13:1 with minimal variability... at ~800rpm idle.

 

Where things are awry is when I use any level of throttle, I basically stall the engine by leaning it out.  Air/fuel theory tells me that the throttle butterfly is opening faster than the pump is able to keep up with fuel.  I am not sure how to adjust this without changing the throttle setting.  

 

Like the rest of the procedure,this is probably dead easy once you know the answer. Help would be appreciated.  Is it time for timing, or is it as simple as going with a richer idle to keep AFRs under throttle ideal?

 

As I await a reply I will begin to read this... http://www.bmw2002faq.com/articles.html/_/technical-articles/engine-and-drivetrain/adjusting-fuelair-ration-on-a-tii-r168

 

Looks like I need to adjust the position of the cam (fuel delivery).  I also need a helper to help with 3K rpm tuning. 

Edited August 17, 2015 by gliding_serpent

[gliding_serpent2]

A good quote from 2002Tii.org

 

"Synchronize the air/fuel proper: At full load, high speed (and even part throttle) settings are much more important than idle conditions. Yet too much time is wasted chasing a smooth idle while sacrificing full load performance.

Depending on the specific engine configuration, a CO setting of 2.5-4.5% at idle is an appropriate target but even more important is the CO reading at full load, wide open throttle. Even when the idle speed CO values are achieved, there is no assurance that the air/fuel synchronization will not go either too lean (<2.5£) or too rich (>5£) at other throttle positions."

 

This is my problem, great idle, but everything else is too lean.  

 

Good video of the throttle linkage setup. 

I note from this that my linkage from the gas pedal up to the lever he presses, it not oem (or maybe his is not).  Mine has a curve in it. 

Edited August 17, 2015 by gliding_serpent

[gliding_serpent2]

Thoughts would be appreceated. I am still at a bit of a loss.

[gliding_serpent2]

So I went at it in a bit more detail with my dad to help at the throttle end of things in the cockpit.  I am starting to get a handle on how things really work, and all the adjustments.  Still not an expert, but starting to color inside the lines now. 

 

So I repeated the procedure as per a combination of the 2002 restoration guide, the KF manual (good for setting up linkages for idle and full throttle), and the two page article linked prior.  If only everyone would get together and combine their knowledge, no one resource has it all. 

 

A few things of note.  My Idle would change on me after using it for a while.  Nothing big, and maybe the engine just needed to warm up, but that made me think about the distributor springs.  I would be surprised as in 2012 I had advanced distributors tune it up.  Might need a look, but that is out of my pay grade. It will be interesting to see where things are tomorrow. 

 

When I did the adjustments in the throttle "tin can" with the idle and mixture screws I set my idle to about 900rpm with an AFR on my gauge at around 11:1 to 12:1 when the car was fully warm.  With this, the car would get around 13:1 holding things at 3000rpm (no load on the engine),  4000rpm was around 13.5:1, and 5000rpm was 13:1 again both when the engine is not under load.

 

Test driving (engine under load), I no longer had the stalling issues like last night from going too lean, but the car was back to running as it did before... a bit rich on very low throttle, and then progressively leans out to up to 16:1 as you progressively put your fut down to moderate through to high throttle.  Hit full throttle and the AFR goes back to just under 13:1.  Holding 3k on the road gives and afr around 14.5:1, 4K around 15:1, and 5K maybe 14:1.  It seems when you add even a bit of throttle with my car, the AFR goes quite lean, up to 16:1, and then settles down a touch if you hold your RPM an throttle.  Full throttle always brings the AFR's to 13:1 or just under. 

 

So what is going on?  One theory is that when you press the throttle, the throttle body opens faster than the fuel pump adds extra fuel, resulting in a lean situation until the pump can catch up.  Not sure if the pump fuel enrichment screw is the solution here as it enriches things across the entire rpm range.  My linkages seem to move as one, or pretty close to it  Not sure that is the cause. 

 

Another point is that my AFR's look excellent... when the car is not under load.  Things tend to lean out by 1-2 points when the car is moving and under load.  Could this be a result of cooler, fresher air outside of my garage (my garage door was open, it is a hot night) bringing more oxygen?  I may repeat my tests tomorrow night with the car fully outside.   A ram air effect from the moving car?  Or could my AFR not be as accurate when the car is under load?  It is positioned not far beyond the merge point of the primaries.  I know a few of you have the same AEM AFR meter, (Jgrock?) so I would be interested to hear opinions on how it behaves.  Do I trust my AFR's values when the car is not under load more than the values measure when it is under load ones?  My gut would be to prioritize the values when the car is under load, and just accept the richer state of affairs when not under load.     

 

He are my #1 and #3 spark plugs.  One looks perfect, 3, maybe a touch lean.  Could be lighting differences but I think I see what I see.  If my AFR's were truly going up and down I am not sure how valuable this is. 

 

#1.  Ideal burn at WOT.  Rich idle

 

#3  A little leaner under WOT than above but not bad, rich idle. 

 

Thoughts would be appreciated. 

Edited August 18, 2015 by gliding_serpent

[cda951]

Get a proper linkage set from Jack Fahuna at Pro Bimmer and report back.

 

http://www.probimmer.com/Kugelfischer.php

 

Chris

[gliding_serpent2]

For sure. I was looking at his wares last night actually. Variable rates of linkage engagement and relaxation due to slop might explain why things look different with steady throttle vs progressive throttle.

Tonight i wil try to mimic more real world throttle changes when the car is stationary and see how my afr reacts in turn.

I might take this opportunity to freshen up other springs in the system, although everything does feel snappy. Any advice on other "while you are in there" parts? May give Blunt a call.

Edited August 18, 2015 by gliding_serpent

[saaron]

As I've slowly moved toward tuning my car more, I've done a few things:

 

>Bought new throttle linkage pieces, and had them measured and adjusted to the correct length, prior to installing them.  This is so I have an accurate baseline on linkage quality and length.

 

>Bought two new springs - tuna can one, and the one near the intake (might act as the throttle return spring, I don't recall exactly).

 

>I began cleaning out all the fuel screen and filters in the system.  There are several, as we all know.

 

I was doing these things first as I didn't really want to do any tuning and then find out a partially clogged filter, or worn linkage was causing the issue.  In my mind, that was just going to create re-work.  "Now I have to replace the linkage and start over".  I am trying to take variables out of the equation before really diving in.

 

Thanks for documenting what you are doing, and what you are finding.  I appreciate it.  

 

Scott

[gliding_serpent2]

Thanks scott, those two springs were on my mind. The one under the intake runners looks a bit old on my car, but seems to have life, but there is no harm in going new.

Good call on the fuel filters and such. It has been 3 years post rebuild on a low miles car that has winter storage, bound to be some buildup.

This is fun to do because it is time I take control of the health of this car... There are no local experts (one, but he is a porsche guy and very busy), so I want and should be able to do all of this.

[cda951]

For sure. I was looking at his wares last night actually. Variable rates of linkage engagement and relaxation due to slop might explain why things look different with steady throttle vs progressive throttle.

Tonight i wil try to mimic more real world throttle changes when the car is stationary and see how my afr reacts in turn.

I might take this opportunity to freshen up other springs in the system, although everything does feel snappy. Any advice on other "while you are in there" parts? May give Blunt a call.

 

There is a lot of sage advice on this forum, and once good piece of it is that the BMW factory tii tuning specs are a starting point, and you should fine-tune from there. However, one "non-negotiable" facet of tii setup is the throttle linkages.

 

You need to get rid of all linkage slop, otherwise you are chasing your tail. Move the firewall throttle lever up and down slightly and observe exactly where the slop is. The ProBimmer kit will likely take care of most of it, but sometimes the ball ends of the bellcrank/pivot pieces are loose. A quick tack weld will take care of that.

 

Once the linkage is nice and tight, then you can re-commence fine tuning.

 

By the way, your plugs look perfectly normal because your AFR is pretty close where it needs to be; the mixture is not out of range enough to make a difference in plug appearance.

 

 

Chris

Edited August 19, 2015 by cda951

[jgerry2002]

Since you have a wideband O2, you can also adjust the do not touch screw to dial in your overall mixture range.

 

Once you get the linkage figured out etc first.

 

As soon as you modify anything (in my case 2.0 to 2.2L) "everything by the factory" will run lean across the range.

 

I had the helper linkage installed by Wes Ingram when I had my pump rebuilt about 5+ years ago. It makes a huge difference. My afr is nice 13.1 under full load.

[achman]

Did you check fuel pressure at the pump yet? If you are low on pressure there, it may not make a difference what your linkage settings are. Verify 29psi at pump, it's possible it might be low an adding to the lean running problem, especially with those pistons. But I'm no Hack ...

[gliding_serpent2]

I did not check the pressure, but it was fine two years ago. I figure that when I get a chance i will replace all fuel filters, the linkages, and go from there.

My WOT and stready state rpm's at standstill (hold it at 2,3,4k) are all spot in for afr's. Need to experiment more with throttle that resembles real driving while tuning when stationary, as the afr's are leaner in real world driving...

Learning about my AEM afr sensor as much as anything.