Lipstick on a Pig- refreshing a 1983 GMC High Sierra

If you want to see how i did mine, find the drivabeater 2.0 thread. Its all in there somewhere....

In reply to Dusterbd13:

Thank you sir. I'll be checking that out.

Hey Guns this PU has always been OBD1 ...so for me it's pretty much plug an play on my limited ECU madness .That being said I'm wanting to see how far one can go with this platform (half arsed talking to BrianH @tbichips.com). So far I know LSA is a key part of making any quantum leaps.

Gunchsta wrote: However, do you think it's worth it to go from a carb to TBI? I'm planning on staying with a Quadrajet over a Holley to retain some fuel economy, but the TBI thing seems like a lot of additional work for very primitive fuel injection. I realize it's subjective, but is TBI better than a carb? I've never had a particularly responsive TBI setup, and I am not afraid of carburetors.

In my opinion, absolutely. TBI may be primitive, but it flat works.

Best thing I did to my 74 C10

It makes a perfect daily driver during any weather and gets good fuel economy.

Cousin_Eddie wrote:

Gunchsta wrote: However, do you think it's worth it to go from a carb to TBI? I'm planning on staying with a Quadrajet over a Holley to retain some fuel economy, but the TBI thing seems like a lot of additional work for very primitive fuel injection. I realize it's subjective, but is TBI better than a carb? I've never had a particularly responsive TBI setup, and I am not afraid of carburetors.

In my opinion, absolutely. TBI may be primitive, but it flat works. Best thing I did to my 74 C10 It makes a perfect daily driver during any weather and gets good fuel economy.

Quoted because that looks gorgeous!

I might start making some junkyard trips and acquiring some stuff. September is a busy and expensive month (re-doing the wood floors in our house and I'm in two of my friends weddings) but I might try to start grabbing odds and ends from the yard as money allows.

Does anyone have any insight into problem years/units that I should avoid? My basic intention at this point would be to try and get the cleanest looking throttle body I can find and go from there.

Gunchsta wrote:

Cousin_Eddie wrote:

Gunchsta wrote: However, do you think it's worth it to go from a carb to TBI? I'm planning on staying with a Quadrajet over a Holley to retain some fuel economy, but the TBI thing seems like a lot of additional work for very primitive fuel injection. I realize it's subjective, but is TBI better than a carb? I've never had a particularly responsive TBI setup, and I am not afraid of carburetors.

In my opinion, absolutely. TBI may be primitive, but it flat works. Best thing I did to my 74 C10 It makes a perfect daily driver during any weather and gets good fuel economy.

Quoted because that looks gorgeous! I might start making some junkyard trips and acquiring some stuff. September is a busy and expensive month (re-doing the wood floors in our house and I'm in two of my friends weddings) but I might try to start grabbing odds and ends from the yard as money allows. Does anyone have any insight into problem years/units that I should avoid? My basic intention at this point would be to try and get the cleanest looking throttle body I can find and go from there.

Hard parts are commonly 87-94 truck and full size vans. 95 was the last year of throttle body in the trucks but it was slightly different.

You want a harness out of either an 87 pickup or 87-91 Suburban (old square body style). It just drops into your square body truck and is separate from the main truck harness. Get the computer and mount bracket from behind the glovebox. Pull the ALDL and its wiring. Get the harness from the engine bay including the fuel pump relay and bracket off the firewall.

I used the entire Suburban fuel line setup and just cut it shorter.

That way I was using an OEM fuel filter.

The factory squarebody TBI trucks and Suburbans used very high quality metal fuel lines and braided hoses. I used all that too.

ECM and bracket.

This is the ECM you want. It's the most common one for basically all 87-91 TBI GM trucks. It's called the 7747 for obvious reasons.

Grab the fuel pump/ sending unit wiring harness from a TBI truck too. They are pretty much all the same. Mine came from an S10 simply because it was the easiest to access at that particular junkyard.

I also grabbed a pair of Suburban exhaust manifolds from the junkyard because the driver side manifold has the bung for the oxygen sensor to screw in to.

Miscellaneous pictures of junkyard booty.

Every time I hit the junkyard I made sure an collected every single little nut, bolt, stud, clip, and widget that I could. Then I paid my local zonc plating shop 25 bucks to make them new again.

You'll need a gas tank, sending unit and fuel pump for an 87 truck. The difference is obviously, in tank pump and 87 is the only year for the baffled EFI tank. I got my tank, sending unit, and fuel pump all from Rockauto. The tank was somewhere around 70 dollars.

A lot of people do TBI swaps, but I wanted mine like factory. Every single component I used can be bought as a 91 Suburban at the parts store. Every factory clip, vacuum line, brackets, etc had to be exactly right in the final install. And, since I was patient and made multiple trips to the yards I was able to find all the little widgets needed. Some cleaning and spray paint and replating the bolts made it look better than you'd expect from junkyard parts.

I honestly don't have much money tied up here, just a metric buttload of work and fussing over details. GM did it best, I just tried to restore everything to what it looked like when it rolled off the line.

All the brackets are just restored. All the hardware is original and restored. The exhaust manifolds are restored. It was just a lot of work to offset not buying nice new stuff. The wiring harness is an original Suburban that I unwrapped, cleaned with GOOP hand cleaner, and recovered with wire loom from Amazon.

Thank you for all the info- that's really helpful!

Now that everyone has seen how Cousin Eddie does it, avert your eyes because mine is NOT going to be that sanitary. Ha ha ha.

But seriously, that's beautiful and I really appreciate the info on what computer to use. I presume they are far too simple for any issues with immobilizers. Also I have an Edelbrock performer RPM intake on the shelf, any reason to shy away from that with an adapter for the TBI? Better off to grab a cast iron TBI manifold until I can afford/score an aluminum one?

All tbi manifolds are aluminium. The major reason not to use a performer intake, or bigger cam, etc is that these computers cant compensate by themselves. Not programmed to do so. So then you head down the rabbit hole of tuning an archaic computer.....

My suggestion would ve a STOCK 350tbi swapped in whole. Make it simple. Id also use the 700r4 while i was at it.

Easy button:

Buy Fitech.

By the way, I have a lot of respect for people who can do clean wiring, that is very well done. So is the rest of the install for that matter.

In reply to Dusterbd13:

Good to know on the intake, I'll plan on grabbing one of those with the throttle body when the time comes.

The stock 350 TBI is probably a more sensible plan, but I have very limited space for this kind of stuff (1 car garage in the city that the truck just fits into) so if I can improve upon what I already have without major surgery that seems good.

So going down the rabbit hole of scope creep here, say I am successful with the TBI on the 305- can the same computer run the 350 stuff? I presume I would want to go to a different throttle body for even a stock 350?

In reply to NOHOME:

Fitech is not for me. Not to say that it won't prove itself reliable in years to come, but for now I would prefer to stick with a more tried and true OE solution. Plus I like the parts store availability of the TBI stuff.

Cousin Eddie is a god among men - his builds on the 67-72 Forum kept me up at night like a naughty magazine. Please keep it coming, Eddie!

The computers are likely different enough to be noticeable. You can google "TBI Chip Burning" if you want more opportunity to mess things up.

The 350 TBI uses different, larger, injectors - but the TBI unit is the same. The 454 throttle body has 2" bores and even larger injectors, but you might have to machine the TBI intake to fit. Google "Ultimate TBI Mods" which may gain you some power.

DIYAutoTune has a good writeup on converting a '70's Nova to TBI.

I appreciate the compliment Skinny. I don't really post over there anymore. The feel of the board has changed in the last 15 years. It just doesn't suit me anymore I guess. There's too many young Facebook generation kids throwing out guesses rather than answers and wasting everyone's time and never really helping answer the questions.

Now, down to nuts and bolts. The 7747 computer is quite universal. It was in 4.3, 5.0, and 5.7 vehicles. Trucks, vans, even S10s. The PROM chip inside is different for each engine size though. Tech tip, last PROM I bought for a TBI engine, my parts buddy at the dealership ordered me a Mexican market PROM. Apparently down below the Rio Grande, emissions aren't so important and performance is the priority. Was that chip any better than a US market spec chip ? I can't honestly say, but it was the same price. I only bought it because I was in a bind. The yards are full of donors so buying new probably won't be necessary.

That said, like the skin man said, the throttle body is the same for 305 and 350 spec engines. The difference is the injectors. They are color coded. Right where the wiring plugs onto the injectors, there are colored markers around the electrical pins. I know 350 injectors are orange. The other colors should just be a Google search away.

Like previously said, all TBI intakes are aluminum.

You can indeed machine the two bore holes larger and bolt on a 454 throttle body. I actually have one in my shop but decided not to. No disrespect intended to the TBI chips guy, but he has spent decades attempting to hot rod TBI engines and the level of success is modest overall. When you add a 454 TBI unit to a smaller engine, the injectors being larger, the ECM drives the pulse width down to attempt to get the A/F ratio right and you really don't wind up gaining very much in the end.

Anyone who has ever driven an 87-95 GM truck knows that these engines feel plenty peppy and will roast the tires if desired, but, honestly, they are just good reliable engines that get pretty decent economy. GM designed them for low end torque, smooth idle, low emissions, and good economy. If you can accept them for what they are intended to be, you'll be tickled every time you drive it. If you want much beyond stock performance, I feel you'll never be happy.

I've gotten old enough that a nice running stock 350 pickup pleases me. My 74 is getting 18 miles per gallon with 3.08 gears and no overdrive. That's good enough for this old bastard.

TBIchips.com is an excellent source for possible upgrades.

In reply to Cousin_Eddie:

Well said.

At this point I'm trying to pinpoint exactly what I want out of this truck in the foreseeable future. I like the TBI idea just for simplicity, but I recognize that it's a performance dead end.

I'm at that lovely point in life where my ideas outweigh my funds, so I can sit and talk all day about any number of things I'd like to try, but in the end I'm stuck with where I'm at for now. Not to say that is a bad thing necessarily, just the reality. I'm also young enough to not exactly be satisfied leaving things be, but I'm old enough that I am much better able to accept things for what they are. The 305 will produce about as much tire smoke as I want if I desire, and is pretty satisfactory in every way.

Being satisfied has never been a strong suit for me.

Gunchsta wrote: Being satisfied has never been a strong suit for me.

It gets easier the older you get.

In reply to Cousin_Eddie:

It has actually, which I'm grateful for. This has been a different year with my wedding and being in my friends weddings. I have far less surplus money which naturally makes me want to spend more.

Always seems to me like the less funds I have available, the more I want to spend. Once I have some car cash built up I'm usually less anxious to spend it.

Well in the spirit of working with what I already have in my possession, I rebuilt the carburetor last night using a previously purchased rebuild kit. It had a couple doggy spots in the throttle and was very dirty, but otherwise functioned quite well. My basic intent was to clean up, scrub down, and re-gasket the thing leaving it in mostly known good operating condition.

I was also sitting around later thinking how to a lot of the 'old school' guys fuel injection is witchcraft, and to the younger crowd that knows efi well, carburetors are also witchcraft. I don't know the coding on why fuel injection works and what the ECU is telling each injector, but carbs are a whole different level of freaky. All sorts of mechanical passages for air and metering rods for fuel and weird levers and pumps to make everything work. For as antiquated as they are they're really quite sophisticated in their own right, this Rochester Quadrajet being no exception.

Yes, I'm claiming that this dirty lump of cast aluminum is sophisticated.

And now for some reason I've lost my post preview so we might be going at this blind. Not sure what's up with that.

Anyhow- take off some torx screws (like a dozen) and the top of the carb comes off.

Being careful not to damage these little tentacles I set the top aside.

I flipped the carb over and removed a few more torx bits and the base plate came apart.

Naturally I also had to knock a pin out of the accelerator pump, remove some choke pull offs, and do some more general disassembly to get to this point, but everything came apart fairly readily. Here's the accelerator pump and you can make out the little roll pin that gets punched out.

Then with all the small bits out of the carb I cleaned all three main components and set them on the tailgate. The truck doubles as a workbench. Truck practicality knows no bounds!!

Here's my baking pan full of teeny carb bits I didn't want to lose.

At this point I had cleaned, scrubbed, picked, and was generally pretty satisfied with the condition and cleanliness of the carb, it was time to put it back together! But not before taking a couple pictures of some castings I kinda liked. I gotta say- you guys may dislike carburetors, but this thing really is kind of a work of art. The inner castings were really smooth and crisp, and there was clearly a lot of effort into making this thing work. It has the small primaries and the large secondaries so I have the performance of a 750 cfm carb, but under normal driving conditions it acts like a much smaller 2 barrel carb. This was the first Quadrajet I've been into, and compared to a Holley this is like a space shuttle. These were used on a million vehicles for a long time, and mine was one of the last. It's always interesting to me to study the 'best effort' of a particular thing. Years of GM engineering and research culminating in the particular design I rebuilt. So because I was nerding out, yeah I snapped some casting pictures.

They even put the company crest on this thing.

Made in USA.

After that assembly was just the opposite of disassembly. I'll admit I skipped some steps (float level- I never had a problem with the thing dying on hard stops or running out of fuel so I left it alone) but it all went back together fairly nicely. The accelerator pump rod was a bit of a bear to get to stay down while I weaseled the primary metering rods back into the jets through the float securing piece, but I made it happen after a couple of tries.

An odd design- the primary metering rods. Had to wiggle the gasket in and kind of through these bad boys, while making sure the rods themselves entered the jets. Tedious.

Like new!! Well... More shiny than before!! But will it function. . .

Tune in next time to find out!

Bolted back into place... It looks so much cleaner than before!

At this point I got my hose out and turned the spigot on (in case of unwanted external engine fires) and turned the key. As to be expected it cranked for a bit before the bowl filled with fuel, but once it got fuel it fired right up and sat on high idle nicely. Revved up good and sounded good. No leaks either! So I went for a test drive and looked at the pretty sky after a rainy day.

It seems to run good! I adjusted virtually nothing, just cleaned and replaced gaskets, so it should function as well as before, which it does. The accelerator pump seemed a bit shoddy before causing part throttle response to be poor. I put a new accelerator pump in and that seemed to help the part throttle response. I made a few full throttle blasts around and it seemed to work nice, but it got a little loaded up once I got off the highway last night. I adjusted the idle screw about 1/4 turn and fired it back up, seemed to clear itself up. I noticed the rubber seal that goes around the accelerator pump rod was pretty tight at first so I'm hoping that was just sticking a bit and with a few cycles it will free itself up and glide nicely.

I drove it to work today, cold start was good, choke worked as it should and came off when it should, and it didn't get loaded up when I got off the highway. I also didn't get into the secondaries at all so that's still a question mark on the functionality of my 'rebuild'. I'm satisfied though! It's cleaner, has new gaskets and rubber parts, and should be good to go (pending some fine tuning) for miles to come.

It was also fun taking the thing apart and getting even the most basic understanding of it's functionality, cleaning it up, and putting it all back together.

I love the adjustability of the Q-Jet. I made the APT accessible on mine so I can tweak the cruise mixture.

In reply to SkinnyG:

I'm still impressed that a 750 can achieve 20 mpg in a big pickup. I want to get a q-jet tuning book and learn more.

I used Cliff Ruggles' book. It's very good.

In reply to SkinnyG:

Thanks I'll try to pick one of those up in the future. Reviews online are all pretty positive.

Been driving the truck with the rebuilt carb for a couple of days now and it sure runs nice. Throttle response is way better and it actually moves part throttle. Before part throttle was really muddy so it was kind of a cruise or wide open type of feel. I do think I need to re-set the idle mixture screws as it seems a little rich at idle now. I'll get out the vacuum gauge and go to town.

Has anyone (SkinnyG) come up with an improvised tool to turn those buggers? they are like a rectangle head and the hole around them doesn't seem big enough to get any kind of a socket in. If not I can buy/borrow the proper tool no problem just curious if there's something obvious that I'm overlooking.

I bought the tool for doing those mixture screws way back, so I've never improvised anything. My '77 has old-school slotted head screws, so I keep a vanilla screwdriver in the pocket of my 70's tweed seat cover.