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Old 09-20-2008, 05:38 PM   #1
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Question Series 3 3.8L UIM

Do the Series 3 3.8L engines have the same UIM issue as the Series 2? Was it resolved in any of the latest V6 engines and is one better than the other?

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Old 09-22-2008, 10:18 AM   #2
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i'm pretty sure it was fixed...
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Old 09-23-2008, 03:13 PM   #3

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The issue was fixed. The S3 UIM is aluminum based and therefore not susceptible to the cracking or softening issues like the S2.

Let me see if I can located a write up on the procedure or some general info.

Edit: Remembered a recent informative post. Some great info.

Originally Posted by agrazela
Don't know that this is "performance", but it is a "modification" so I put it here instead of in "Mechanical"

So you want to put an L26 aluminum UIM on your L36?

(This is a work-in-progress for another member here, and here'* where it is now.)

L26 aluminum UIM (from a 2005 LaCrosse):

The runner insert, PCV valve, MAP sensor (and the gasket AFAIK) are just like on the L36 plastic UIM.

L26 LIM is identical in every way to the 99+ L36 LIM with the 5/8" diameter EGR stovepipe...

EXCEPT that the L26 EGR pipe is about 1/8" shorter than the L36:

So, to avoid the EGR stovepipe protruding into the inlet airstream, you need to either shorten your L36 stovepipe OR get an L26 stovepipe. Otherwise, the L26 UIM will bolt right up to your current LIM, using the same bolts you have now.

Now for the modifications...

EVAP hole:

Whereas the L36 has it'* EVAP solenoid routed to the TB through a vacuum line, L26 UIM has the EVAP solenoid bolted right to the UIM, with it'* opening just to the right of the TB inlet (if looking into the inlet):

That hole is just the right size to tap 1/4" NPT, then plug with a pipe plug:

Alternately, that hole could be filled with epoxy.

PCV inlet:

On the L36 (or L67) TB, the PCV air inlet is in the throat of the TB (after the MAF, so the air is pre-metered):

On the L26, the PCV air inlet is the vertical "nipple" on the top:

Which is connected by some vac line into the air intake bellows on the L26, after its' MAF setup.

There is no easy way to adapt the PCV inlet hole in the L36 or L67 TB to this L26 UIM, so we have to make our own PCV air inlet.

Drill a 3/8" hole through the side of the UIM, right about where this red circle is:

Make sure that crosses through the vertical PCV inlet "airshaft", and right into the inner "throat" of the inlet:

This hole in the inner throat is the new after-MAF PCV air inlet.

I enlarged the outer part of the hole to 7/16", tapped to 1/4" NPT, and plugged with a pipe plug:

I suppose that outer hole could be drilled/plugged for a smaller plug, or even epoxied (just don't block the inner air passages).

Then cap that nipple up top with a 3/8" vacuum cap:

That nipple could be pulled out / drilled and tapped / plugged, but the vac cap was much easier. Alternatively, I suppose that nipple could be used as a vacuum source (e.g., for the vac modulator on a 4T60E, if you are 96/97 and earlier).

This should produce a clean, fully-functioning PCV system.

Adapting a TB:

Because the L26 UIM has a round inlet, it would be best to use an L67 TB (with it'* round outlet):

Since L36 MAF tables are not the same as L67 MAF tables (even between those using the same MAF sensor), you will need a tuner (or PCM) to reprogram the MAF table for an L67 TB. Use a stock, unmodified L67 TB of known year and any competent tuner (or PCM vendor) will already know the proper MAF table to put in. Use a vendor-supplied modded TB and they should be able to provide a starter MAF table. Use a home-ported TB and you better have a tuner!

ZZP makes a machined aluminum adapter designed to adapt the L67 TB to an L26 UIM or GenV */c. Here is a used one for this project:

Four of the screws bolt the plate to the L26 (in the recessed holes), and the other three hold the TB to the plate.

The aluminum adapter is kinda pricey new ($100), and I think the ZZP phenolic TB spacer could easily be adapted to this job:

ALTHOUGH you would have to block the TB coolant ports at either the LIM or the UIM to use it:

These phenolics are usually pretty cheap used. Of course, you machine your own from aluminum if you got the tools. Heck, if your TB coolant ports and EGR are blocked off, I bet you could make an adapter out of wood!

One thing nice about the ZZP aluminum adapter is that it will block off the TB coolant ports itself. OR, if you want TB coolant flow (as the patron for this project does), you can add them:

Now the TB coolant flow ports on the L26 UIM are not in exactly the same place as on the M90 casing:

So you can't just drill straight through. But if you locate the holes right, you can drill the back (side touching the L26 UIM) 7/16" bit, 1/2" deep:

And the front (side touching the TB) 3/8" bit, same depth:

They are offset, but they do meet in the middle and the coolant passages are good.

The inlet hole on this ZZP aluminum adapter is a perfect match for the machined part of the L26 UIM inlet:

However, the machined part has a mismatch to the cast part, leaving a turbulence-causing "lip" (similar to what you see in stock M90 casings):

Easily fixed with a dremel and a small teardrop carbide burr:

You could port that out more, but the rest of the throat is pretty danged smooth already so I didn't bother.

To seal all this, all you should need is a few rings of RTV on the L26 UIM inlet:

And a stock L67 TB gasket (or better yet a reuseable one like this):


OK, that should take care of function. Now there are issues of fitment.

The inlet "snout" on the L26 UIM is longer than that on an L36...especially when you figure in the adapter plate, too:

This will modify the location of the TB, pushing it toward the driver'* side about 1" to 1.5"

The harness should have enough reach to hook up all the TB sensors no problem. But, this will very likely mess with the length of the vac lines attached to that "split fitting" on nipple on the side of the TB and that go to the EVAP solenoid (1/4" plastic line) and FPR (5/32" plastic line). The lines will probably have to be lengthened with a section of rubber vaccum fitting / hosing, replaced with some longer self-bent plastic line, or replaced with rubber vacuum hose and some sort of plastic fittings. Still deciding on the best way to rectify that. This will be pretty much universal for any L36, so whatever I come up with on the vac lines should translate for anyone.

This change in TB location could screw with other things, like:
-Throttle and cruise control cable bend radii
-Fitment / "bend radius" of the stock air intake bellows

These "other things" are not necessarily universal between different car models / "generations", so you're kind of on your own there!


As far as I can tell, the plastic runner insert in this L26 UIM is the same as in the L36; unfortunately, I do not currently have an L36 insert in hand to compare side-by-side. When it comes time to test this thing, I will make sure they get more closely compared.

Also, will an HV3 insert fit in this L26 UIM? I do not know if the inner countours of the "body" of the L26 UIM are exactly perfectly 100% identical. I think the person for whom I am making this is considering an HV3, so maybe we'll eventually find out

Also, on the off chance that the outer dimensions of this UIM "casing" are not exactly the same as an L36 UIM'*, there could be a fitment issue on the bigger, bulkier alternators of the pre-2000 H-body crowd...another thing to test-fit


It will probably be a couple weeks before this thing get installed for testing, so if anyone sees anything I've overlooked, let me know!

Last edited by BillBoost37; 09-23-2008 at 03:24 PM.
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