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1990 GMC 1500 Jimmy

Excuse me for not responding to you quicker Mr.XTC. I wasn't disregarding Mr. Zoomad's response, far from it. I'd just like to get input from as many angles/people as possible. I'm getting back into something that could wind up with more than one outcome. I'd like to have as much info as I can get, also, several times already I've had my memory jogged and made me remember stuff that I hadn't thought about in 30+ years. I never raced Chevys, I ran Mopars, but several of my buddies ran Chevys and I helped with them quite a bit.

The thing about pulling the rear end out to work on it. I'd have to study up, but I have built engines, manual 4 speed transmissions, and a couple of rear ends. I don't know if it's still done, but, I have helped set-up a ring and pinion with a brown paper bag. I remember helping to do it but don't remember how it's done. I worked at "Rhett Walker Transmission" for about 6 months in the '70's. I remember very little, especially the finer points, you know the things that you don't remember until you've already put it back together. The aw XXXX !!!! moments. I'm betting that we've all had them.

I really do appreciate everybody helping me to remember all of this stuff.

I had asked about the TBI being used on larger, higher H.P. engines. I agree with the answer about it being OK. I'm thinking about down the road, after I confirm that it's worth it to get this engine rebuilt with a RV/torque cam, possible intake, headers, etc. If I were to have to buy a new Throttle Body or get another of the same and have it rebuilt, if this one can't handle a little more motor then I'd be better off to get one that can/could with or without mods. I don't plan on racing, etc. but, if I need that little extra, I'd like to have it.

I was looking around the parts listings and saw that in 1990 that there was a 6.2 that used a mechanical fuel pump. First, a 6.2 liter is about a 372 c.i. mtr. isn't it (diesel?). Are the cams for my mtr. still being made with a fuel pump lobe just in case that there's some reason down the road to install one. They had some pretty high pressure/volume mechanicals years ago.

I'm hoping that this helps you to underststand the way that I'm thinking and convince you that I'm not quite as crazy as you think, or maybe a little crazier.

Thanks again everybody, Paul
 
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scpaul said:
Excuse me for not responding to you quicker Mr.XTC. I wasn't disregarding Mr. Zoomad's response, far from it. I'd just like to get input from as many angles/people as possible. I'm getting back into something that could wind up with more than one outcome. I'd like to have as much info as I can get, also, several times already I've had my memory jogged and made me remember stuff that I hadn't thought about in 30+ years. I never raced Chevys, I ran Mopars, but several of my buddies ran Chevys and I helped with them quite a bit.

The thing about pulling the rear end out to work on it. I'd have to study up, but I have built engines, manual 4 speed transmissions, and a couple of rear ends. I don't know if it's still done, but, I have helped set-up a ring and pinion with a brown paper bag. I remember helping to do it but don't remember how it's done. I worked at "Rhett Walker Transmission" for about 6 months in the '70's. I remember very little, especially the finer points, you know the things that you don't remember until you've already put it back together. The aw XXXX !!!! moments. I'm betting that we've all had them.

I really do appreciate everybody helping me to remember all of this stuff.

I had asked about the TBI being used on larger, higher H.P. engines. I agree with the answer about it being OK. I'm thinking about down the road, after I confirm that it's worth it to get this engine rebuilt with a RV/torque cam, possible intake, headers, etc. If I were to have to buy a new Throttle Body or get another of the same and have it rebuilt, if this one can't handle a little more motor then I'd be better off to get one that can/could with or without mods. I don't plan on racing, etc. but, if I need that little extra, I'd like to have it.

I was looking around the parts listings and saw that in 1990 that there was a 6.2 that used a mechanical fuel pump. First, a 6.2 liter is about a 372 c.i. mtr. isn't it (diesel?). Are the cams for my mtr. still being made with a fuel pump lobe just in case that there's some reason down the road to install one. They had some pretty high pressure/volume mechanicals years ago.

I'm hoping that this helps you to underststand the way that I'm thinking and convince you that I'm not quite as crazy as you think, or maybe a little crazier.

Thanks again everybody, Paul
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I don't have a huge knowledge base with GM TBI systems. I have worked on a few, but not recently enough to want to answer your question.

But as for the mechanical pump, you should be able to bolt on a standard mechanical pump from an earlier year carbureted 350. Your engine will have a blockoff plate covering the cam lobe on the bottom of the passenger side of the block, toward the front of the engine. A 6.2 diesel is 379 ci. It also uses the same cam lobe and mounting plate, so I believe the pumps can be interchanged. Rockauto specifies different part numbers, and the gasoline pump has an recirc line, where the diesel pump does not, so the pumps aren't identical.

What would you be doing with a mechanical fuel pump?
 
scpaul said:
I looked at that, thinking that I'd copy it. There are 76 codes on that sticker. I quickly changed my mind about that.

There's a engine/transmission rebuilding business not too far from here that has a very good reputation and has been in business for many years. They build engines from showroom stock to local racetrack and give guarantees if the build is reasonable. They will build my engine to a low end torque mtr. and put the cam of my choice (within reason) for $895 to $1000 and do the heads including springs and 3 angle valve job and smoothing the runners for $3-400.

That being said, I know that I'd really need headers ASAP. How far will the original throttle body injection go? I'm guessing that the actual injectors in a throttle body can be changed. Isn't this the same basic throttle body as they put on the big blocks?

Being retired, this will take a while. I hope gas doesn't go back up in the mean time.

Again, thanks everybody for any advice. I'm probably going to ask some stupid things since engines had points the last time that I played with them. It's been so many years since I really messed with a vehicle other than tune-ups and oil changes.

Is there a way to post a pic from a fairly new flip phone. If so, please use the K.I.S.S method to explain it to me.

Paul
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I read an article in Hot Rod magazine recently about truck "Vortex" heads. They have extremely shrouded valves with restricted ports, plus small valves. The picture in the article showed how bad they are.
I have a '90 Blazer much like yours, with those type of heads. Be sure and check with your machine shop......
 
Well, I said that I was thinking about some things. I'd bet that some of my old friends still have things laying around like Holley 780 Duel feeds, maybe an 850, Spread Bore or Thermo-Quad an I'm almost positive that I know where an Edelbrock Torquer intake is located. I wonder how it would work with a TBI set up, has anyone tried something like that, old high performance intake, new fuel system? I know that we ran more fuel pressure on our serious street cars than 7 psi. Now I'm not saying that any of this is going to happen even if it would still work. I just like to have some other ideas and know that if I need it, that the cam does still have the pump lobe. If it would work, it would be alot cheaper and easier to put a mechanical pump on than a pump in the tank. I don't know much about getting horsepower out of a TBI, but I can tune and tweek alot of the old carborators. There was a sound that a Holley or any of the other Spread Bore style carburators made when you opened the back barrels if it was tuned right. I doubt seriously if a carb would work as well as TBI because they are more sensitive to acceleration and angle affects float level, etc.

I'm rambling and it's causing me to think and remember alot of little things that are all ancient history.

Can you use one of these TBI's and change the injector rate, the injector itself, increase fuel pressure or a combination of them for an engine that's a little more than stock? Are the 1990 350 (not vortex) heads or are there a half a dozen different heads that they used. We had heads with a point, double humps, and other markings that I can't remember now. Do the newer heads have descent size valves and valve train hardware? There's just so many things that have probably changed and if I'm not told I won't have any way to know.

Y'all tell me things that are different, tricks that work, just about anything that a newbie wouldn't know.

Thanks, Paul
 
Queasy, mine isn't a Vortec. The 91's were Vortec if I'm not mistaken. Did the Vortec use TBI or was it tuned port injection, an injector for each cylinder?
 
scpaul said:
Queasy, mine isn't a Vortec. The 91's were Vortec if I'm not mistaken. Did the Vortec use TBI or was it tuned port injection, an injector for each cylinder?
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I have TBI and the two middle intake manifold bolts are vertical to the block rather than perpendicular to the head as the remaining bolts.....so they are the non-performance truck Vortec style....
This truck is a one owner, original paint with 42k miles. Previous owner is 80 years old, retired manager at the Chevy dealer he ordered it from. They are the original heads.
 
scpaul said:
Can you use one of these TBI's and change the injector rate, the injector itself, increase fuel pressure or a combination of them for an engine that's a little more than stock?
Click to expand...

Yes. It may have a different sound to it, but you have at least as many tweaks that you can put on a TBI rig compared to a Holley. Lots of folks here have done interesting things with TBI, TPI, or later MPFI systems.

You can tweak the software tune (changing the injector timing and duration), change the injector or fuel pressure (both of which change the amount of fuel delivered), or some combination. The only limit here is how much you want to play with things. If you want to tune and tune and retune it to your perfection, there are a number of aftermarket controllers that are easy to program. Changing the tune on the stock system involves burning new parameters onto a physical chip and replacing that chip each time you want to change it. Not ideal if you're going to change it more than a few times. But if you're just wanting extra fuel, oversized injectors or raised fuel pressure can be used. Some folks use adjustable pressure regulators to dial in the parameters they're looking for.

But you're getting further and further from stock dependability the further you go down this rabbit trail.
 
I know, but, I don't plan on going too far. I'm going to keep everything so it's just a matter of putting the oem stuff back on. If I leave it alone other than a cam, headers, intake and put larger injectors in the TBI. Then do a little tuning. I figure that I could pick up 20 -25% over stock depending how far I go with the cam. It will dictate just how far I can go with the other stuff. I haven't had an engine with a little beat in many years.

Y'all keep helping me think and remember, Thanks, Paul
 
Ok, TBI systems can support some modifications. They did use them on the 454's too so larger versions are out there. You can use any conventional small block cams if you want. Keep in mind to get the most of the cam, intake and exhaust modifications the tune on the ecm should be adjusted. You'll have to find a tuner locally or deal with some over the internet.

Retrograding the engine back to a carb is possible, but a step backwards in driveability in my opinion.

The idea would be get it running and see where the issues develop.

TBI heads are not the same as vortec heads by the way. TBI heads are not as desired due to the issues noted. Vortec heads on the other hand are wildly recognized as the best stock small block head gm put into regular production. They use the port design of the LT1 Corvette gen II engine but with conventional cooling as opposed to the vettes reverse flow system. When put up against an unmodified bowtie performance head the vortec out flows it. There is more potential in the bowties, but to bolt on a stock head they make solid improvements over older heads. Keep this in mind the vortec head has a different intake bolt orientation and number of bolts used so a stock TBI intake won't bolt up to it. Gm does make a TBI vortec intake but it is pricy.
 
Good Morn'in everyone, Thanks for the education and helping me remember.

ZooMad, you said that they had been put on 454's and made reference to "larger ones are out there". Do you mean that there are some physically larger, larger venturi's (barrels?) or just larger injectors? I was right about Vortec starting in '91 wasn't I? I remember opening the hood and there was something saying VORTEC and mine didn't have it, whatever it was. When I was rambling about the old hotrod stuff that I can probably still get, I wasn't thinking about the little things that get changed that keep some things from being interchanged. Can the old style (70's - 80's) stuff like intakes be used on the non-Vortec engines? How would I be able to tell anything about the heads that I have. They had shapes in the castings of the heads, how can you tell now short of checking casting numbers and for that matter while I'm at it, how about the block that is supposed to be a 4 bolt block by the old standards? If I understand: the Vortec heads are real good, but, won't go on mine or is it they will if I change the intake too? The TBI Vortec that you said was pricey, what was it put on? You are right, the idea was just to get it running. I'm probably just playing mental ping-pong, but if I wind up having to ask or talk with people that are up to date on something as basic as which heads, intake, block, etc. are compatible. There's no need to be any more ignorant than I really need to be. To upgrade the program on mine which is a OBT-1, (right?) I physically have to change chips. Where is the board with that chip located? The Vortec heads are based on the LT-! Gen II heads, were those the ones that came with the Tuned Port Injection (8 injectors) like the IROC Camaro's?

I got the pressure washer out yesterday and got it running so maybe I'll try to get someone to put some pics on line.

I'm sure that there will be more later, Thanks, Paul
 
scpaul said:
Good Morn'in everyone, Thanks for the education and helping me remember.

ZooMad, you said that they had been put on 454's and made reference to "larger ones are out there". Do you mean that there are some physically larger, larger venturi's (barrels?) or just larger injectors? I was right about Vortec starting in '91 wasn't I? I remember opening the hood and there was something saying VORTEC and mine didn't have it, whatever it was. When I was rambling about the old hotrod stuff that I can probably still get, I wasn't thinking about the little things that get changed that keep some things from being interchanged. Can the old style (70's - 80's) stuff like intakes be used on the non-Vortec engines? How would I be able to tell anything about the heads that I have. They had shapes in the castings of the heads, how can you tell now short of checking casting numbers and for that matter while I'm at it, how about the block that is supposed to be a 4 bolt block by the old standards? If I understand: the Vortec heads are real good, but, won't go on mine or is it they will if I change the intake too? The TBI Vortec that you said was pricey, what was it put on? You are right, the idea was just to get it running. I'm probably just playing mental ping-pong, but if I wind up having to ask or talk with people that are up to date on something as basic as which heads, intake, block, etc. are compatible. There's no need to be any more ignorant than I really need to be. To upgrade the program on mine which is a OBT-1, (right?) I physically have to change chips. Where is the board with that chip located? The Vortec heads are based on the LT-! Gen II heads, were those the ones that came with the Tuned Port Injection (8 injectors) like the IROC Camaro's?

I got the pressure washer out yesterday and got it running so maybe I'll try to get someone to put some pics on line.

I'm sure that there will be more later, Thanks, Paul
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Your truck is equipped with OnBoard Diagnostics (OBD-1), which GM called ALDL (Assembly Line Diagnostic Link).
 
I will say that sometimes a person can start thinking about too many things , and asking so many questions , that it all gets overwhelming and confused .

Not that I haven't done it myself....
Of course I have!
And you already referenced ping pong..
 
If I remember correctly the 454's used larger injectors. Larry used the same TBI unit when he built his 454ss clone from a 4.3 truck. Just added the bigger injectors.
No, the vortec line didn't start in 91. The vortec name started on the 4.3 v6 in 93 if I remember right. It was a central port injection setup that raised hp/tq over the TBI version. To add confusion, gm sold both at the same time. In 1996 is when the v8 vortecs came out. Also central port injected, meaning the injectors were all in he center of the intake with plastic tubes leading to poppet valves at the ends. That is when the good heads came to be. Yes they came from the genII LT1 used in the 1992-96 vette and 1993-97 Camaro and firebird. The intake bolt pattern went from 12 bolts like they had from 55 to 8 bolts. The bolts also go straight down vertically rather than being perpendicular to the head.

Changing away from the obd1 computer system does not happen with a chance of the chip. The chip has the software to run your particular combination. Changing to the later obd2 system requires moving to a later style of fuel injection like the vortec or upgrading to the genIII engines otherwise known as the LS.
 
I guess that I'm trying to catch up on 25 years of auto tech. Most of these questions are for my education, the one about the TBI mods was so I'd know if that was one of my possible changes for H.P. along with a few other inexpensive changes. I did know that the injection pulse can be changed by the duration, quantity, and timing. I just can't see myself trying to change the OBD-1 to a OBD-2. That just seems like it has the potential to be an electricians nightmare. Remember that I said that I was trying to get some education, well I'm still learning bunchs. Will the Torquer intake fit the heads that are on it? Did GM still play games with the heads, cams, etc. during the time of my '90? If so, what that we have talked about, TBI included, would make a reasonable basis with some backbone. No matter what I wind up doing, I'll probably wind up with headers and an intake if possible. Does things like port matching still done and how much can I expect out of it. That used to be almost free horsepower depending on just how bad of a mismatch it is. I've never gone as far as cc'ing the chambers extreme runner work. I have matched ports, got 3 angle valve jobs and smoothing runners and plenum areas. Will the older small block intakes (early/mid 70's to around '90 or later) go on my engine without too much trouble?

Remember that I'm retired/disabled, but it just takes me longer and I still know how to get in touch with some of my old buddies other than visiting the cemetary, although quite a few are there for various stupid stunts and fate too.

I'm hoping that y'all are starting to understand what I'm up to. I have been approched about messing with Drag cars again and a few ago I was offered a seat in a turn key dirt car. I don't have the reaction times or speed to do what I/we once did, unless I'm not concerned about the other people out there.

I'm thinking about maybe bringing the rear up a couple of inchs so that it sits level. The way it is now, it looks like I've got a load of shine on and I just don't like that look. It's been mentioned that the stock 4 shock set-up it has on the front end isn't the best any more. It still has the original shocks that it came with.

Somebody figure out how I can get Pics on here/net after it gets it's first bath in 9 - 10 years. I have never been a big car washer.

Talk to me people and give me info and ideas, Thanks, Paul
 
As far as raising the rear, my '90 wasn't quite level when I put a 1 inch block, (called a zero-rate, from Offroad Design )
under the rear .
I have since put a 9.5" , 14 bolt under, which combined with the spring perches that I used, got me an additional 1" to 1.25". It is now a little too high in the rear, but I don't know if I will bring it down. It has a rake to it, but if I load much in the back, I may like it!
 
My window sticker says that it has the H.D. trailering Special Equip($407). The hitch came on it from the factory and I've been told that it's load equalizing, H.D. Front Springs ($62), Rear 2 stage multileaf springs (?). I put the 33's on it and don't have any rubbing even on the front. I had just thought about putting 2" (+/-) blocks in the rear.

How do you tell if a hitch is a load leveling type?
 
I started pressure washing my '90 Jimmy today. It was coming out pretty good right up to the point where I ran out of gas for the pressure washer. I found almost no rust at all. All I found was above the drivers door in the rain gutter. A spot about the total size of my fingernail had gotten surface rust, mainly discoloration, can't feel it just see it. The fiberglass back half roof has had the sun bleach out the silver/gray on the top surface. Other than these and a few stone chips the paint is in pretty good shape.

What would be the best/easiest way to repair the paint. I think that I'm going to scuff the fiberglass and spray it with rattle cans. Unless you are at least 6'6" and try, you can't see it. It didn't appear to have had any primer on it from the factory. On TV they keep advertising sp[ray that matches the OEM colors. I don't expect to get a perfect match, but I'd like to come close. Were the fiberglass tops glossy from the factory or just satin. I think that I can tape off the whole fiberglass top, spray 2 or 3 coats, more if necessary then scuff and spray it with satin or clear. Where it is parked is between my house and the neighbors and doesn't get much wind unless there's a storm.

There's bound to be some minor rust trying to start or is started where the trim meets the paint. There's a liquid that is supposed to stop rust and chemically change rust to something else. I have used it on some other things and it seems to be working, but it hasn't been but about 6 months at the most since I used it. I was wondering if I could more or less inject it into the trim/paint joint and stop or at least slow it down until I can get it painted, probably in about 2 years, I hope. I just thought about the trim might be aluminum and I don't know if it's supposed to be used on aluminum. Does anyone know if the trim is aluminum?

I appreciate any advice, Paul
 
Just throwing a note in where Zoomad mentioned 454 TBI units. 454 TBI units are indeed bigger (bigger bores) and higher flow rate injectors....except 94 & 95 454's where they used two 305 (5.0L) injectors in the typical big block throttle body but increased the fuel pressure from 12 psi to 24 psi
 
Larry, Thanks, I figured as much, but didn't know which was right since depending on a few things and the tune, either or both could be done.

Any Idea how much cam it would take for me to use the 454 TB and probably use slightly smaller injectors or can something similar be done by reducing the fuel pressure. Is there a % of pressure at which an injector looses it's ability to properly spray/distribute the fuel?

I still remember the basics, but so many details that make so much difference have changed. Before it's over I figure that most of the little tweaks that we used years ago now can't be done or are fixed by/through the computer. I think you said that '94 and '95 TBI's used 2 305 injectors and the fuel pressure was raised from 12 to 24 psi. What did they do on the earlier models?

I realize that just about any info that I could want is available through this computer, but I am on a fairly steep learning curve with it too. I ask a question about how to do something and get the answer easy; just do this, set that to this,right click, then...... When the conversation is over all I am is confused. Just keeping and understanding the jargon is more than I can do at this point. I have gotten a LITTLE better but not a whole lot.

Thanks again, Paul
 
scpaul said:
I started pressure washing my '90 Jimmy today. It was coming out pretty good right up to the point where I ran out of gas for the pressure washer. I found almost no rust at all. All I found was above the drivers door in the rain gutter. A spot about the total size of my fingernail had gotten surface rust, mainly discoloration, can't feel it just see it. The fiberglass back half roof has had the sun bleach out the silver/gray on the top surface. Other than these and a few stone chips the paint is in pretty good shape.

What would be the best/easiest way to repair the paint. I think that I'm going to scuff the fiberglass and spray it with rattle cans. Unless you are at least 6'6" and try, you can't see it. It didn't appear to have had any primer on it from the factory. On TV they keep advertising sp[ray that matches the OEM colors. I don't expect to get a perfect match, but I'd like to come close. Were the fiberglass tops glossy from the factory or just satin. I think that I can tape off the whole fiberglass top, spray 2 or 3 coats, more if necessary then scuff and spray it with satin or clear. Where it is parked is between my house and the neighbors and doesn't get much wind unless there's a storm.

There's bound to be some minor rust trying to start or is started where the trim meets the paint. There's a liquid that is supposed to stop rust and chemically change rust to something else. I have used it on some other things and it seems to be working, but it hasn't been but about 6 months at the most since I used it. I was wondering if I could more or less inject it into the trim/paint joint and stop or at least slow it down until I can get it painted, probably in about 2 years, I hope. I just thought about the trim might be aluminum and I don't know if it's supposed to be used on aluminum. Does anyone know if the trim is aluminum?

I appreciate any advice, Paul
Click to expand...

Post pictures. The gutter trim on some trucks is an aluminum add-on (removable with screws), but on others it can be stamped into the steel roof. I have both styles between my 3 vehicles.
 
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