Greetings Zu folk, I visit this site daily but lack of time prevents daily posts. Being the only computer I can utilize is at work, I find time to read and athat's about it. However I value the expertise on this board very much. With that I have a few questions for some of you guys who have done this 3.4 swap. I took my troop in to a mechanic, discussed in length what it would take to do this and they have finally cleared the hump (drilling and tapping the starter holes). It's taken them quite some time, but I really understand the task at hand for someone who has never done this particular swap. 91 Trooper, 2.8 over to the 3.4. Now that they have drilled and tapped the holes, I wonder what problem they will run into next. I've read about the intake possibly needing bored out, possible different injectors and possible different computer or chip install. Is all of this necessary? They have told me that they believe all of this is not necessary, but they also told me that relocating the starter wouldn't be either. Granting them the patience and realizing they needed to learn the hard way, I left them alone to do just that. Ed Mc e-mailed me all of his info and I in turn printed most of the viable info out for them to use as well. Do you guys think now that they have relocated the starter successfully, all they have to do is reassemble, drop it in and things should be ok? I just want to avoid having to take it back in once I get rid of the loaner I've been driving since this all began. Any opinion or details is greatly appreciated. <img src="/forums/images/graemlins/cheers.gif" alt="" /> Thanks again.

JC

2.8 Intake manifold, injectors, throttle body and ECM can all be used to get the rig back on the road as quickly and easily as possible

From what I've read it is advised to step up to 4.3 injectors, since they are larger they will be better matched for the fuel requirements of the new block. Don't forget though, that injector size doesn't change how much gas is delivered since all of that is regulated by the computer. To better understand it, you want to match the range of fluid flow of your injectors to the fuel requirements of the engine.

You can opt to bore your intake manifold to 1 11/16" and use a matching throttle body from a 4.3L chevy. This will just give you better top end performance and throttle response but is not required. I made a step by step writeup you can find by searching under "4.3" and my username.


Don't change your ECM. When the power is removed from it for a while then reconnected, some of the variables specific to your engine will be re-set and this will include the slight increase in displacement.

I think the throttle body is the one to worry about next.
You can get by with the original one, but the truck will run rough.
I bought an old throttle body off of an 89 (I think) GMC jimmy with a 4.3 v6. The bolt pattern is the same if you want to bore your intake manifold to match the bigger holes in the bottom of the 4.3 TB. I didn't have that kind of time, so I took off the top half (injector assembly)of the old 2.8 TB, and bolted on the top half of the 4.3 TB.
Works pretty good. Problem is, I said I was going to bore the intake at a later date, and here I am over a year later and I haven't done it yet. Probably never will.

As Chris said, you don't have to put the larger TBI on but if you're looking for performance, I'd advise you to at least have the intake bored out to 4.3 specs. Even if you just use the 2.8 TBI, this leaves you the option of bolting on the larger TBI later.

You will need to upgrade to 4.3 injectors as stated or the rig will 'lean surge' when cold. If you use 2.8 injectors, once in Closed Loop it'll run better but will probably be down on power 'cause the 2.8 injectors can't flow enough.

You can 'cheat' and jack up the fuel pressure on the 2.8 but this requires disassembly of the top half of the injector pod, the part containing the fuel pressure regulator. Then you take a pair of pump pliers or Vise Grips to the ring at the bottom of the regulator and twist to snap the spot welds holding it in place. Then you can tighten up the pressure on the spring to increase fuel pressure and this may work well enough to where you won't need to change injectors out.

You don't need to change the ECM or anything else if you take care of the TBI issues. Make sure all the original smog equipment is functional including EGR.

Besides the starter mods, one other issue the mechanic should address is fitment of the oil filter adapter. There will probably be an interfering casting on the block that needs to be cut/ground away to allow the Isuzu adapter to fit.

They should also be aware that only 2 bolt holes per motor mount line up. This is OK, nobody's motor that I know of has fallen out yet!!!

Another detail, make sure they put in a new tranny input shaft pilot bushing (if manual trans). This bushing is Oilite-type and must not be assembled with any grease on the pilot shaft.

Also recommend you use a 3.1 clutch out of a Rodeo 4WD. Must be a 4WD/MUA5 tranny as the 2WD versions use Borg-Warner trans. Surfacing the 2.8 flywheel is mandatory if you do this, as the 3.1 clutch disc is larger diameter. It definitely has a better feel than the 2.8, as I can attest by use of a 3.1 clutch in my 'stroker' project.

Make sure they have observed that the lifters auto-rotate when the crank is turned. 3.4's are notorious for lifter/cam lobe wear and if each lifter doesn't rotate the cam/lifter are shot. Use the HT 3.4 cam if you replace, this also requires use of matching valve springs/retainers.

Anyway, I think these are the high points. If I think of anything else I'll post later.........ed

<img src="/forums/images/graemlins/lol.gif" alt="" /> Mine did this summer on Medano pass Colorado. A rarity I hope. The bolts may have come loose, then sheared off because they were loose. Then the engine's oil pan fell down onto the skidplate, breaking off the oil pressure sender squirting Mobil One on the way down. When I repaired it at CoZu the sheared off bolts were easy to turn. Again I think it is a rare thing <img src="/forums/images/graemlins/cyclops.gif" alt="" />


Edit: driver's side also

I have broken the mount bolts on the driver's side, but that was from using the Trooper as a tractor pulling a wheel-driven hay rake. I dropped the front-end into a large hole and the mount bolts were the victim.

I'm thinkin' the bolts may have been innocent!! <img src="/forums/images/graemlins/notooth.gif" alt="" />

Perhaps a dab or 2 of blue Loctite on the threads might be in order.

but that was from using the Trooper as a tractor pulling a wheel-driven hay rake

Perhaps a dab or 2 of blue Loctite on the threads might be in order.

Or...maybe not using it as a piece of farm machinery. <img src="/forums/images/graemlins/smile.gif" alt="" />

Michael
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Those are exactly the opinions and suggestions I was looking for <img src="/forums/images/graemlins/kewl.gif" alt="" />, thank you very much. Time to get on the horn with these cats. I guess I just needed to hear it again, in shorter form. I have already given them the new 2.8 clutch and the probability of attaining a 3.1 clutch now is slim to nil. Again, thank you.
<img src="/forums/images/graemlins/cheers.gif" alt="" />
JC