I am looking for some history on the lower intake gasket and opinions on what direction I should go. Brief truck history I just picked this 2000 Jimmy 76k miles up from my father who got it a from a friend who let it sit in their driveway. It has its issues, a few of which I have posted about, but the one I am attacking now is California SMOG and the MPG.
Regarding SMOG, I am failing inspection because I cannot get the secondary air system to complete its test, and I also got a code for Idle Higher Than Normal after cleaning the MAF and TB. Chasing that down I have replaced the TPS and IAC with no luck but while I was in there I found this.

So it would seem I have a leak, and hoping that is a big reason for the MPG and codes. Anyway I have since purchased the new MPFI version spider to swap in and planned on doing that when I ran into a post about it saying there has been an update in the lower intake manifold gasket. So I picked up that metal upgraded felpro set as well. My issue, and question, is now should I really be doing the lower intake manifold gasket when I don't have any known problems with it?
It was said you should do the lower gasket when doing the spider just for the fake you are already halfway down into the motor but I am 1. pressed for time as I have 10 days left to get this to pass SMOG 2. I seem to have something else fail each time I put something new on to fix an issue so I am a bit wary of getting that deep in, and getting into more parts that could possible break and causes issues.

Follow up question; is it possible (without wasting gaskets) to remove and replace the lower intake manifold gaskets while keeping the spider and upper plenum attached i.e I replace the spider and upper gaskets now, hopefully pass smog) then get back into the lower intake gasket replacement (if I should even do it without having current issues) after I have 2 more years to worry about smog?

 

Your injector setup is different than on my 95, so I can't offer advice there, but I have done the lower intake gaskets before.

Not sure how mechanically inclined you are, but since you're already down to the lower intake and have gaskets, it's not much more to do them. The hardest part is pulling and installing the distributor. You have to line up the oil pump drive, and it's basically under the firewall.

What I did was get a length of #10 wire, and bend it so it had a ~3/4" 90° angle at each end. I then crawled up on the engine, and with my phones flashlight and camera on, I was able to see down in the dist hole to line it up, using the wire to turn the oil pump drove.

Other than that, it's only maybe a dozen bolts to pull the intake. It's advised to change the oil after, since even if you drain the coolant, some will still drop down into oil passages. (the intake carries water, so lowering the coolant level is necessary)

 

That is a tough call. Whether you do it now or later, I would recommend replacing the LIM gaskets as soon as possible as when they fail, they fail catastrophically ruining the engine. However, the parts to get out of the way to only do the fuel injection spider I think are less messy and are mostly annoying to do. This is in contrast to what needs to be replaced to get to the lower intake manifold that also requires getting large brackets and their accessories out of the way and draining the cooling system.

I have the original GM Service Manual for my 99 but I found this super handy. How To Replace Intake Manifold Gaskets On A GMC Jimmy 4.3 Liter V6 To Fix A Coolant Leak - GM Truck Engine Repairs

Look at the above link and you should be able to determine the amount of extra work it takes to also replace the LIM gaskets in addition to the the FI-spider.

Several notes with respect to replacing the LIM:

• Study carefully how to undo the bolt/nut that secures the lower end of the AC bracket to the block. I spent way too much time trying to get it undone before going back to the instructions above and figured it out.
• Mark the orientation of the rotor and take pictures before your take out the distributor. (I used a sharpie and crawled onto the top f the engine to mark the rotor position directly from above.) Do NOT rotate the crank with the distributor out. When you put it back in, it is likely the shaft for the oil pump got rotated anyway. With I think 13 teeth on the cam gear, it is likely that the the only way to get the distributor in and to engage with the oil pump shaft will be with it being off by a multiple of 360*/13* ~ 1/12 of a rotation. Don't fret. Consider how the angled teeth on the gear cause the distributor shaft to rotate as it is installed. Then with a really big flat-blade screw-driver, rotate the oil-pump shaft to where it needs to be so that when you drop in the distributor it ends up pointing in the correct direction. It might take a couple tries but if you have not rotated the crank, it will work fine. Do not force it place. When lined-up, it will go in nice and easy.This is how I got mine back in.
• Cut off the heads of some of the old bolts for the LIM (did you get new bolts and an inch-lb torque wrench?) and install them loosely to use as guide pins for reinstalling the LIM. I wish I had thought of doing this. Someone else posted this hint and I was all "D'oh!" as I I have done that on my old Mustang for which on the old Ford 289s from the 60s, some of the intake manifold bolts instead were studs which really helped with getting the intake manifold lined up.
• Use fresh, name-brand RTV for the front and rear rails of the block. There have been reports of the RTV that comes with the Fel-Pro kit being sub-par in performance.
• Ditto on replacing the oil after replacing the LIM gaskets as there will be water in the oil.
• Do your best to protect the innards of the engine from contamination from debris associated with removing the old gaskets; lots of towels to protect the lifter valley and to plug off the intake ports and water passages.

Gook Luck!

 

Why the hell didn't I think of this when I did mine? Would have made it a million times easier!

 

Howdy,
First of all, if Your idle is too high, then check for the vacuum tubes. If the car was sit somewhere for awhile, then You probably have them rotten.... Despite it sounds bad it's a good news. The vacuum tubes are easy to reach from top of the engine and they costs peanuts. Btw. bring the idle rpms value here and fuel trims.

Next, if you don't have a torque wrench that will match the torques specification, then don't touch the gaskets. Recently we had a topic here of a person who did it wrong and the coolant was leaking here and there. They are neither related to Your "SMOG 2". Replace top gaskets if You have to (yet I bet the vacuum leaks elsewhere).

 

I am not so worried about the mechanics as I have done several, albeit ford, engine assemblies. I guess I am really asking are these gasket an absolute, going to happen sometime soon failure, known 4.3l weakness/problem, that I should get out of the way for safety/reliability or with only 76k miles on the ticker should I not risks breaking something because it isn't leaking.

Also the other question about being able to leave the TB and upper plenum assembled and then remove the lower intake later without messing the new upper gaskets I would have just put on.

Regarding the intake studs, I too have a dedicated set for all my fords. They really should include these in full gasket sets for all 4 corners at least.

 

The idle code only came after cleaning the MAF and Throttle, which is why I went down the TPS and IAC path, but I plan to do the vacuum hoses anyway while bring it back to reliable road worthy. Another post I can't find again is regarding the vacuum line paths and the sizes. If someone can link me or let me know at least the vacuum ID sizes I need to buy rolls of that would also help.
I will try to pull a quick log tomorrow when I drive it and show the values here.
I definitely have all the tools needed just trying to balance by time left in troubleshooting if the spider leak isn't the only problem. I also don't want to do the change because I literally just did an oil change while tuning up.
Ideas on the cause of the secondary air pump OBDII test on these blazers?

 

Well, the task of replacing them is rather time consuming, than difficult. Just pay attention to marking the distributor position and the cleanliness in general (You don't want the debris to get into the engine). And, at the end. while setting the intake, make sure the RTV has cured a bit , but is yet "wet" in touch. And tighten with a torque wrench as specified. The RTV doesn't seal the coolant or oil galley, but just the engine body to the lower intake.

I thought Your main goal now is to pass the SMOG exam, which comes within a few days, and the things You have to solve are high rpm idle. Gaskets are nothing crucial in this aspect.

 

If You're short with time, I'd urge You to post some engineering data from OBD. A fuel trims on idle would be a good start.

 

That's where I am leaning, I will worry about the lower later and just replacing the spider injector, gaskets and vacuum lines if I can find the routing and size info.