[kg4miq]

Dennis,
This is an easy swap for you. There are two different 1BBL intake manifold plenums, however. One has an electric EGR (CAL emissions??) and the other is vacuum-operated (FED emissions). You want the vacuum-operated one, as it's a larger diameter throttle body. The only thing I had to do was drill and tap the inlet tube fitting for the EGR transducer (I chose to keep the EGR circuit intact). Just be sure not to drill TOO deep: if you do, the tube will remain loose, once the fitting is screwed into the upper plenum. A bottom tap helps thread this all the way down and get enough thread purchase to prevent the fitting from stripping. The lower plenum stays on the engine - no need to remove it. Might be a good opportunity to replace or clean the fuel injectors, as they're easy to get to, once the upper plenum and throttle body are removed.

One other thing I had to do was bend the lower throttle body bracket for the throttle cable to attach to it. I used the bracket from the original 2BBL throttle body and bent it to shape in a vise. Had to do a little bit of grinding to trim the edges and make it fit the two lower holes for the new throttle body. Once the bracket is shaped like you need it, the throttle cable should line up fairly well. I don't recall having to swap throttle cables.

No need to swap ECM or anything, as the computer has enough programming ability to compensate for the increased airflow. I did swap the intake piping and air filter housing, also, which required a little bit of work to get the plastic intake pipe to line up well. I remember rotating the plastic portion a bit, in order to make the air hoses line up enough to connect to the thermal valve on the thermostat housing and the oil vent pipe on the back of the valve cover. IIRC, I had to rotate the plastic intake pipe so the piece of tubing going to the valve cover ended up pointing up toward the hood of the truck.

Fox's comment above about the fuel rail may be a factor, if you've only got one style of fuel rail, as they are machined slightly differently and fit to the intake manifold a bit different, but this is only if you choose to use different injectors. I don't recall swapping the fuel rail.

Once it was done, Jerry saw it at a Trooper get-together down in Greenville and said it was one of the nicest running four-cylinder Troopers he'd seen. I didn't have a Jerry cam at the time, but that would've also helped. I think the '93-97 cams are close enough to Jerry's grind to make for a really peppy engine, though. If you've got the later cam, you'll be fine.

I don't currently own the vehicle, but I can still get pictures of the swap, if you'd like. Might take a bit for me to coordinate, but I don't foresee a problem.

/tim

 

[kg4miq]

Yes, Ed, that would be the way to go, except the fuel injectors for the '94+ are different than the earlier ones. The resistance is higher on the later ones (Jerry can give specific numbers), and the ones on the CAL emissions version (electric EGR) are even more different (similar to the Impulse injectors).

While it's not that difficult to rewire for the newer injectors, the ECM may have to be swapped for that, in order to match the impedance correctly.

EDIT: Dennis, I noticed you asked about advantages and disadvantages...
The 1BBL has 14% more airflow through it than the 2BBL version, per Jerry. It's also easier to adjust the idle set screw, since it's right on top. ECM easily compensates for the higher airflow without changing injectors.

The only disadvantage I can think of is the hassle of swapping it, and being careful not to drill the EGR transducer port too deeply (ask me how I know).

HTH,
/tim

 

[kg4miq]

Tim, looks like the injectors are physically different, too, and would not interchange. So that kinda messes things up!

Are the intake ports of the newer head different than the older?

...

Ed,
That is correct, the injectors are different and the ports they mount into on the intake manifold are a different size than the older 2BBL intake. Not sure if the newer injectors have a higher flow rate, but I know they have three ports in the nozzle with a definitive spray pattern, and no exposed pintle, like the older injectors have. They are not interchangeable, but the upper plenum is easily swappable, so the benefit of higher air flow can be realized using the 1BBL throttle body, but retaining the older lower plenum. It's a great combination, with relatively little effort. I'll try to get some pics up comparing the two in good lighting.

On a related note, there are two distinct versions of the 1BBL throttle body, with the smaller one being the CAL version with electric EGR, which is why I advised against it. The camshaft, however, from that version is the improved, later design, and provides a bit of extra torque, so it can be easily swapped into the earlier engines with no trouble.

Unfortunately, even the 1BBL throttle bodies mount differently to the upper plenum, so they are not interchangeable, either. I have had both versions here at one time or another, and mistakenly purchased an engine with the electric EGR and smaller throttle body early on, so it's been sitting on a shelf taking up room for quite some time now. I get the feeling it seems to be GM's misguided attempt at redesigning the four-cylinder intake to use their parts (MAP, rather than MAF, for instance) and really didn't improve on the overall design whatsoever, as compared to the true Isuzu-developed 1BBL intake, which utilized the simple vacuum EGR and no GM parts, and backwards-compatible lower plenum which uses the smaller injector ports.

The CAL version really is a separate entity, as far as the intake is concerned, and doesn't provide much for modification purposes, unless someone knows of a vacuum-operated EGR which will fit the electric EGR port, in which case, this intake might actually become usable after all. The rest of the engine, however, is very much worth having, since it has smaller combustion chambers and pistons to match, and improved camshaft.

... That would lead me to believe you could bolt the later upper intake and the earlier lower intake to the '94 head and use in in an early 2.6.

That's exactly what I did with the one I modified. Newer upper plenum, older lower plenum, older throttle cable bracket shaped to fit, EGR port tapped and threaded on the upper plenum, and 1BBL throttle body with intake piping and MAF.

HTH,
/tim

 

[kg4miq]

Found a picture of the smaller 1BBL throttle body and upper plenum with electric EGR. This is NOT the one you want, but it did trigger a memory of possibly having to splice in a connector for the throttle position sensor to match the older circuit, since I think the TPS connector is the small, round, three-wire version shown in the photo. The throttle body in the photo has an electric idle air control (IAC) mounted on it as well, which makes this version unusable for the conversion.

 

[kg4miq]

HERE is the correct plenum and throttle body for this conversion, and no, I didn't have to splice the newer style throttle position sensor into the circuit. It would have been a different design - rather than a simple three-position switch type, the one in the previous photo is a typical GM-style, variable resistor TPS.

This one is the older style Isuzu three-position switch TPS (idle, off-idle, WOT).

 

[kg4miq]

DING, DING, DING! Winna', winna', chicken dinna'! Found a great write-up with pictures on here.

2BBL to 1BBL conversion (plus turbo)

Later down in the write-up, he gives a closer picture of the EGR transducer piping drilled and tapped, but it appears to me to be too deep, which prevents the pipe from locking into position as the nut around it is tightened down. I wouldn't drill it quite so deep, Dennis.

I'd love to do something like this, but with twin Webers. I know there was something similar years ago for the Chevy Luv, as my friend had one, but I haven't seen one since.

 

[kg4miq]

NOTE: This info is only if you're swapping the single barrel throttle body onto an engine with an automatic transmission.

Did this swap on another Trooper recently and wanted to update with automatic transmission information. Unless you have the newer, 1BBL throttle body with an automatic transmission already, if you do this swap, you'll need to modify the old 2BBL throttle position sensor to fit the new throttle body, and you'll have to set the transmission shift firmness cable at a fixed position, because the newer style throttle cable bracket doesn't have a provision for the auto shift firmness cable to mount.

Modifying the original 2BBL throttle cable bracket to fit the 1BBL housing allows for the transmission shift cable AND the correct throttle cable length, but that's not what I did in this case.

I had to fabricate a bracket to extend the throttle cable stop for the valve cover mount, so the original throttle cable would work properly. I've got pics of the modification to the throttle position sensor, but still need to take pics of the throttle cable stop bracket.

For the throttle position sensor, the mounting flange on the original TPS will need to be drilled to attach to the newer throttle body, since the spacing for the mounting screws are closer together, and the auto trans requires the TPS with the extra circuit.

Once this is done, you're going to need to set the TPS in the correct position. This information can be found elsewhere on this site. This is a very good mod for the 4ZE1, and provides a definite power bump. I also eliminated the EGR circuit on this engine, while I was at it.

 

[kg4miq]

Jerry, if you've got the header (or know where I can get one), I've got the truck and engine, and single barrel throttle body intake.

BTW, do you know if the later style injectors are usable with the earlier ECM by eliminating the inline resistor? Don't the later injectors have a higher impedance value? Guess I could just measure the ones I have here and rewire them to batch fire. Do they flow as much? The nozzle is quite a bit different, so I was wondering if they are more efficient or have better performance?

I'm thinking of building a 2.6L with your cam, later head with small chambers, single barrel throttle body, and headers and install it in a pickup. Would be nice if I could locate a 4WD pickup with the 4ZE1 in it already, but I've got all the wiring harness stuff here, if not. With the exception of the header, that's what I'm currently running in my daily driver, and having a lot of fun with it.

/tim