Trooper 4.3 TBI Conversion question...

[moogvo]

I am about to swap out the 2.8 TBI for one from a 4.3L as I have read on countless pages. Everywhere I call about a TBI for a 4.3L non-Vortec, I get a bunch of questions about what year... They won't go any further unless I tell them what year it is for... Are they different? If so, what year do I want a TBI from??? What vehicle???

This is a bit confusing... I am assuming that it doesn't matter, but I did want to hear from the experts first.

I am also adding in a 1" spacer under the TBI... will these mods make a real noticable difference in power?

Thanx in advance!!!!

[paulevans76]

theres a lot of people on the wire that have done this. I can't remember wht year is the best, but searching over there should yeild some positive results. i had the helix bore spacer under mine and it made a cool whistling sound and gave it a little low end.

[IsuzuCrawler]

why dont' you just swap in 3.4 cause it will bolt to your transmission, 60* GM ? there have been lots of folks on the wire to do this swap.

Good luck
Eric

[CPOM]

You need a 4.3 TB with the same amount of vaccuum ports as yours.

You need a TB with the throttle linkage on the passenger's side.

Keep in mind some gm 4.3 tbi's are mounted reversed, so one with a driver's side linkage is actually the same as yours with the passenger side linkage.

This TB is found in GM 4.3, 305, and 350 motors, NOT just in 4.3's

Donor vehicles of the 4.3 tb are blazers and astrovans. There are a ton of others, including s10's that have these tb's as well.

I am in the process of doing this swap now, and I will post a writeup on the wire when it is complete.

[CPOM]

Also: moog, get off the phone and go to a damn junkyard! There you will have the experience in how to remove the TB and intake manifold so you can practice. You can also choose which one you want based on rust, crud etc.

You have to look around to get the right one for throttle linkage and I believe he tps as well.

I think the tps can just swap over but I cut the pigtails as well just in case.

I just pulled a 4.3 tb and intake manifold from rodeo for $65. What a deal.

[moogvo]

I finally got one. It is a bit cruddy, so I imagine I will spend the bulk of today cleaning it up. I got a pretty good deal on it. $40.00. We shall see... I also got the 1" riser plate. Not the Helix tower, but we will see what happens with that as well.

[moogvo]

I finally got the conversion done. Took a 4.3 TBI from an Astro Van and mounted it on top of my 2.8. MAN! There really IS a difference straight outta the box!

Here are the problems I ran into. Maybe you can help...

1. Engine idle is WAY to high! It idles at abouot 1500 RPM on startup. After driving it idles at about 3500 RPM.

2. While driving, the check engine light comes on when decelerating. It goes back off once I am accelerating for a few seconds.

Here is what is different from the 2.8 TBI to the 4.3.:

1. The throats of the 4.3 TBI are substantially larger than the 2.8 TBI, and even larger than the holes in the Intake. I will hone those intake holes out when I have a clean weekend, and the $$ for a new intake gasket.

2. I had to swap out the TPS since the one on the 4.3 was a 90 degree vertical type. The electrical connector wouldn't reach.

3. The 4.3 TBI does not have all of the vacuum attachments the 2.8 TBI had. There is one small one missing. I suspect this is why it idles so high.

4. The 2.8 TBI was drilled and tapped for the throttle linkage bracket to bolt directly to the TBI. I had to drill and tap the new one so that plate would bolt back into the stock position.

5. The stock Isuzu accelerator cable eyelet which attaches to the TBI was too small. I had to drill it out so it would fit over the stud on the new one. Also had to drill out the spring clip that holds the cable in place.

Here are the problems I ran into by adding the 1" TBI riser plate inder the TBI:

1. Had to disconnect the fuel lines from the bracketing system to move them around enough to fit into the line position an inch higher. This was a royal pain in the ass! Those metal lines are tight, and there isn't really any room to work around them!

2. some of the sensor wires were too short when tied down into factory position. I had to untie them and move them around so they would reach.

3. The plastic pipes that go from the driver's side valve cover to the air breather will be too short. You will have to replace it. Same applies to the PCV valve line that runs from the passenger's side valve cover to the back of the TBI. These are molded plastic pipes from the factory, but I imagine you can use a good sturdy hose to make these connections.


This is definately a worthwhile project, but it is not a direct swap. While the connectors are all the same, they may point in different directions. Be prepared to take the sensors off of your old throttle body. Also, if you are not comfortable drilling holes in your new TBI unit, you will need to find someone who can do it for you, or fabricate a new throttle cable hold down bracket that bolts to something else.


As a sidenote,

Does anyone know where I can tie these vacuum lines in so they get the proper vacuum??? It is the line that comes out of the back of the TBI furthest to the passenger's side and immediately splits into 3. One goes to the air pump, one is a rubber hose type line, and the other is that really small plastic line. Do I need manifold pressure for this, or can I tie it into the PCV line?

[paulevans76]

moog

glad you got it done. i ran into some of those same problems when I did my tb spacer. for the fuel lines, I undid them from their little bracket and used zip ties elsewhere.

as for the vacuum, i can't help too much. on mine, I couldn't get it to idle right until i plugged a few, crossed a few, etc. eventually you can find a way, just takes a little creativity and

for the valve cover breather, I recommend getting one of those little air filters for it and popping it in there. i just ran mine off to the side and it would occasionally spit dollaps of murk here and there.

btw are you using the injectors from the 4.3 or the 2.8? most found the 4.3 run it rich except when used on the 3.4.

anyways good luck as always, you'll be smokin those 33's in no time

paul

[moogvo]

Yes. I am happy to have it done. I did the same thing with the fuel line bracket... What a PITA!!!

I have been screwing with the vacuum lines all night... nothing makes any diff. A friend of mine suggests the IAC motor may be stuck...

I did not use the 2.8 injectors. I might have to switch them out. They do dump quite a bit of fuel.

I would also like to bore the intake holes a bit for added flow. I am not sure I am ready to take a grinder to my intake tho...

Once I fix my speedy engine issue, (A friend of mine works in a shop and can print out the vacuum diagram) I am still missing that one vacuum nipple on the back of the TBI... Not sure how I am going to take care of that one yet.

[paulevans76]

be careful on the intake removal/installation when you do it. i fawked mine up after doing it a few times. the stud/bolt holes are VERY easy to strip out. then you got leaks and that's all she wrote. take your time putting it back on and follow the torqueing procedure, cause it ain't fun doin it twice, believe me.

and while you got the valve covers off, might as well throw on some roller-rockers, eh?

[CPOM]

http://members.shaw.ca/betterthanyou/28to43/28to43.htm

This details adding another vaccuum port on a 4.3 TBI with creative drilling.

It also says that all IAC motors are the same regardless of TB and injector size.

[moogvo]

Excellent... I am going to take off the TBI today and drill the needed vacuum port. I will let you know how it goes!

[moogvo]

Nice article... very informative.

I have pit the 2.8 TBI back on the Trooper for now. I think I am going to re-build the 4.3 TBI and put all the necessary vacuum ports on it. I still have the 1" riser plate in there, so we shall see how it goes.

I re-did all of the vacuum lines... That was a PITA! Especially the one that went to the bottom of the air pump... Took me an hour to figure out where it went!!! Then I couldn't reach it. That one was a BITCH!

Anyway, the check engine light went out so apparently it likes what I did... I did notice a lot of black soot in the tail pipe. The exhaust is all less than a week old, so I know it is from that other TBI.

Thanx for all the help on this!