engine and drivetrain Which Tii Throttle Body Is Early And Which Is Late?

[thehackmechanic]

Seven years ago, Bill Williams posted the attached photograph of early and late tii throttle bodies, but which is which is not identified in the photograph or the accompanying text. My car is early '72 and has the TB on the left, with the long arm contacting the half-moon cam. As you may know, I've been fighting a persistent issue on lean running at wide-open throttle. Tonight I noticed that, with the FI adjusted by-the-book -- the pump and TB pinned -- the butterfly in the TB is not open all the way. Previously I brushed this off because, in wanting it not to be so lean at WOT, I thought not having the butterfly completely open at WOT would be good, but rereading the FI section of the Macartney book and an article by Redszus on the tii register, they both say that the butterfly should ALWAYS be fully open at WOT. I've double-checked the linkage 18 ways from Sunday and don't see anything wrong.

 

Soooooo... in the attached photo, am I correct that the TB on the left is late one, the TB on the right is the early one, and my car has the wrong TB on it?

 

If this is the case, and if I swap TBs and it finally fixes this problem, you will hear my whoops and hollers clear to the Pacific.

[bent]

The left one is early, right is late.  The only functional difference is the sensitivity of the idle mixure screw. The early style mixture screw is extremely sensitive to adjusment, a 1/4 turn will make a big change.  BMW switched to the later style to allow easier and finer idle mixture adjustment.  Switching between the two TBs should make no difference otherwise.

 

Did you end up getting the injection pump recalibrated?  It didn't help?

[OriginalOwner]

  since I don't know left from right ......

 

  1/4 turn makes a noticeable change .....

 

 

Cheers,

 

Carl

Edited April 28, 2013 by OriginalOwner

[jgerock]

Based on what I have seen, the one on the left with the unusual adjustment arm is for a 74tii.

 

I have (3) throttle bodies, all look like the one on the right. 

 

The one on the right with a more simplistic CO (throttle body actuator) cam is for 72 and 73tii.

 

The Blue BMW fuel injection manual shows both on page 8 and but does not have notes indicating which one is which!

 

It only says:  "Later models had a re-designed throttle housing which made CO adjustments much less sensitive". 

Edited April 28, 2013 by jgerock

[bnam]

Rob,

Either of them should open fully to WOT though.  And if yours is not opening fully at WOT, that's not the cause of the lean condition as not fully opening should actually make it richer (less air for same amt of fuel)

 

With accelerator fully pushed open, is the pump crank at the stop screw?  If it is not, the problem is between pump and pedal.  

 

Also, I thought you had mentioned shortening one of the linkages in an earlier post.  Theoretically, that should decrease the range of motion of the throttle just a bit causing it to be just shy of WOT when the pump crank hits the stop.

 

Byas

[thehackmechanic]

<<The Blue BMW fuel injection manual shows both on page 8 and but does not have notes indicating which one is which!>>

 

Yup, so you see why I want a definitive answer from the cognoscenti. Redszus and posts here on the FAQ say that the TB is curved to the pump -- early pump needs early TB. Andrew Wilson says Vern, built March '73, has the one on the right, so he agrees with you, but you two don't agree with the previous two posters.

[thehackmechanic]

<<Either of them should open fully to WOT though.  And if yours is not opening fully at WOT, that's not the cause of the lean condition as not fully opening should actually make it richer (less air for same amt of fuel)>>

 

I completely agree, yet my issue is that, even after having the kfish pump rebuilt by Hans Utke, and replacing the fuel pump to rule out a fuel starvation issue, the car STILL runs too lean at wide-open throttle (15 on the AFM). And every post says "use the AFM to tune at WOT."

 

 

I'm clocking off the list of things it could be:

 

1) Overall mixture setting on kfish pump is off. Highly unlikely; I just had it rebuilt by Hans Utke. Note that if I put a penny-sized shim under the verboten screw (having just paid to have the pump rebuilt, I don't want to touch the screw) and test it at WOT, I get a reading of about 13 on the AFM and my seat-of-the-pants-o-meter feels that the car is making more power, but this makes it run stupid rich (9-10 on the AFM) when I'm not at WOT.

 

2) Improper air/fuel synchronization. I've moved the throttle body cam progressively further over the synchronization hole, and, like with putting a shim beneath the verboten screw, if I get it in the 13-14 range at WOT, it runs stupid rich everywhere else. I've reinstalled the brand-new linkage rods I bought from Jack Fahuna.

 

3) Vacuum leak. I've looked and am as convinced as I can be there isn't one. And why would it manifest itself ONLY AT WOT?

 

4) Fuel delivery problem. I bought and installed a new E28 fuel pump (I was thinking of prophylactically changing the original pump before the long drive to and from The Vintage anyway). I changed the fuel filter as part of this. No change.

 

5) Cracked exhaust manifold letting in air and making the AFM artificially read too lean. Possible, but I don't see it, I don't hear it, and why ONLY AT WOT?

 

6) Something wrong with the throttle body. When I say the butterfly isn't all the way open when the pump is pinned at P4, it's almost all the way open but not quite all the way. Dave Redszus said, and there are references here on the FAQ, that the different throttle bodies are curved to the different pumps. I realize I'm grabbing at straws here.

 

6) Timing. Newly-rebuilt dizzy by Advanced Distributors, timed by the book (2500rpm at the ball, 25btdc). I've advanced the timing slightly, no change. 

 

I'm really at something of a loss. I am considering ritual suicide using my Kugelfischer tools.

 

I will check everything for the hundredth time...

Edited April 28, 2013 by thehackmechanic

[bnam]

A couple of thoughts...

 

When you had the pump rebuilt, did you get data back that showed that the pump was (capable of) putting out enough fuel at WOT (IIRC about 0.8-0.9 lbs/min of fuel)?  

 

What about the injectors?  Can they deliver the fuel needed at WOT?  Or are they the restriction in the system?

 

BTW, the TB on right is the later one.

 

Byas

Edited April 28, 2013 by bnam

[saaron]

Rob

My '72...June '72 production. Euro (which I don't think matters in this case). E12 head.

I feel for you. I thought for sure the pump refresh would be the fix. It's going beyond crazy now.

Scott

[saaron]

Actually attaching the photo might help...

[thehackmechanic]

Byas, I sent the pump to Hans Utke. He's an old-school guy. He didn't send back a Redszus-style performance curve, just a beautiful clean rebuilt pump and a receipt, so I'm trusting that it was done correctly. I also sent him the injectors for testing (they had already been cleaned and tested by Jack Fahuna, so not surprisingly, they passed).

 

Attached is the page from the tii manual showing the two styles of throttle bodies. Note the text that says "some changes were made to the pumps between the first models in 1971 and the later years up to 1974. Do NOT interchange pumps from different model years. Be sure to check the part number for the model year you're working on. Additionally, in 1974, a vacuum limiter was added to the system for deceleration control." Then, "later models had a re-designed throttle housing, which made CO adjustments much less sensitive." This doesn't explicitly say whether or not it's okay to swap throttle bodies and pumps; I'm just going by what Redszus told me.

 

I'm realizing I've probably misinterpreted the early versus late divide. I assumed the "early" throttle bodies (whichever those are) were the ones '72 through '73 without the vacuum limiter, and the "late" ones (whichever those are) were the ones for the '74 that had the vacuum limiter. I'm now wondering if the "early" ones -- before the redesign -- were only on the early '72 tiis with the 121 head and the plastic plenums, and the "late" redesigned ones were on all tiis with the E12 head and metal plenums. That would explain why Andrew Wilson and Jim Gerock -- both with '73 cars -- say their car has the one on the right. But then Scott Aaron says his car with an E12 head has the one on the left. 

 

Interestingly, realoem lists one part number for the TB, 135412526155, as valid for the entire range 1/1970 through 10/1975, with a replacement part number 13540435746 superseding it.

 

Baffled.

[bnam]

I could imagine a scenario where the relationship between the pump position and the butterfly are slightly different between the 2 designs -- therefore the guidance in the manual to keep them paired.  But, at WOT the relationship is the same for both -- fully open throttle (since the size is the same for both, they should both let in same amount of air) and fully open pump -- so there should be no diff at WOT.

 

Since there's only 2 parts to the equation -- and you've pretty much eliminated all sources of extra air, the only thing that remains IMO is to establish that you are (or not) getting enough fuel.

 

You mention a calibration curve done by Redzus.  Is that posted somewhere?  We should be able to calculate the AFR from that curve and confirm that the Tii pump will support 12-13AFR at WOT at 5k+rpm.

 

Byas

[TobyB]

Just to rule it out completely,

have you put a fuel pressure gauge

at the inlet to the k-fish?

 

Yes, you shouldn't have a problem,

but that would completely rule it out.

 

t

[saaron]

I hesitated to even throw the pic of mine in since it is Euro...I was wondering if the Euro pumps and TBs never changed because they weren't chasing any emissions goals/regs.  Maybe disregard mine since all the other cars you're comparing to are US cars, and yours is US as well. 

 

Scott

[bnam]

This curve from Redszus shows that the later pump (v6) put out more fuel at WOT (P4) than the earlier ones (v7).  If the 2 throttle bodies flowed the same at WOT, this would be about 5% (0.6 AFR) richer for the later pump.  But, there is no scale on this curve so hard to actually calculate the fuel delivery at WOT.

 

(source: Mulcahey article from Tii Register)

Edited April 28, 2013 by bnam