GM SCPI - Why?

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paulo57509

paulo57509

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I've been driving my Dad's 2003 GMC Safari every so often just to keep the fluids, etc. flowing and I was wondering why GM would design a crazy FI system like Central Point Injection (other than they're GM)
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At least the version in my Dad's van is sequential. Don't get me wrong, I've always been a GM fan. I just haven't been able to find any real kind of articles explaining the good/bad about this system. The few article I have come across are mostly negative.
 
My first instinct is to respond "why not?"

I'm guessing this was an interim step by GM to allow them to remove carbs and buy some time while redesigning engines to take sequential systems.

My '89 S-15 Jimmy had it and I never had a problem.
 
Originally Posted By: opus1
My first instinct is to respond "why not?"

I'm guessing this was an interim step by GM to allow them to remove carbs and buy some time while redesigning engines to take sequential systems.

My '89 S-15 Jimmy had it and I never had a problem.


I highly doubt that, as they had sequential fuel injection on other engines before this setup even came about..........

perplexes the H out of me that they made this setup, I have only heard bad about them. Also the intakes are prone to leaking and are a serious job to do compared to removing an intake off a LSx or such.....
 
Why the GM side terminal batteries that are prone to be stripped (over-torque) or come loose (under-torque)? You mean you really can't repackage the space under to hood for the extra 1 inch of headroom? Using a common size battery will ensure the customer to be able to get fresh, readily available replacements down the road, but nooo, I guess they need to be different for the sake of being different...
 
The 4.3 is old school and they don't want to throw any technology at it unless they have to for emissions. Lucky (?) for us it runs clean enough without fancy shmancy stuff.
 
Originally Posted By: Jonny Z
Why the GM side terminal batteries that are prone to be stripped (over-torque) or come loose (under-torque)? You mean you really can't repackage the space under to hood for the extra 1 inch of headroom? Using a common size battery will ensure the customer to be able to get fresh, readily available replacements down the road, but nooo, I guess they need to be different for the sake of being different...

54.gif
Not hard to find a battery at all.
 
Originally Posted By: ls1mike
Originally Posted By: Jonny Z
Why the GM side terminal batteries that are prone to be stripped (over-torque) or come loose (under-torque)? You mean you really can't repackage the space under to hood for the extra 1 inch of headroom? Using a common size battery will ensure the customer to be able to get fresh, readily available replacements down the road, but nooo, I guess they need to be different for the sake of being different...

54.gif
Not hard to find a battery at all.


Yeah, most batteries come with BOTH terminals and fit just fine in GM cars.
 
Originally Posted By: Jonny Z
Why the GM side terminal batteries that are prone to be stripped (over-torque) or come loose (under-torque)? You mean you really can't repackage the space under to hood for the extra 1 inch of headroom? Using a common size battery will ensure the customer to be able to get fresh, readily available replacements down the road, but nooo, I guess they need to be different for the sake of being different...


I prefer them to top terminal batteries, the connections are sealed better. Put some grease on the terminal, don't get carried away with the torque and usually that's the last time you need to mess with them.
 
As long as the battery does not have a leak, side terminals stay corrosion-free since they are not exposed to acid fumes venting out from the top of the battery. This was the reason for the switch to side terminals, not clearance issues for top terminals.
 
Originally Posted By: 38sho
Originally Posted By: opus1
My first instinct is to respond "why not?"

I'm guessing this was an interim step by GM to allow them to remove carbs and buy some time while redesigning engines to take sequential systems.

My '89 S-15 Jimmy had it and I never had a problem.


I highly doubt that, as they had sequential fuel injection on other engines before this setup even came about..........

perplexes the H out of me that they made this setup, I have only heard bad about them. Also the intakes are prone to leaking and are a serious job to do compared to removing an intake off a LSx or such.....


I think the key phrase is "other engines". The 4.3, at least in the vintage I had was a 350 with 2 cylinders lopped off. Having owned cars with 350's before the S-truck, I know that they were carbureted so I stand by my guess that this was GM's "quick fix" to replace a carb and be able to say the engine was fuel injected while they worked on making a "real" FI engine.

I can't dispute what you've heard, but I can tell you that in my personal experience, I got 160,000 miles out of this wacky set-up, with the injectors being original throughout. The reasons I scrapped the truck had nothing to do with any fuel/drivability issues.
 
Originally Posted By: Corvette Owner
Originally Posted By: ls1mike
Originally Posted By: Jonny Z
Why the GM side terminal batteries that are prone to be stripped (over-torque) or come loose (under-torque)? You mean you really can't repackage the space under to hood for the extra 1 inch of headroom? Using a common size battery will ensure the customer to be able to get fresh, readily available replacements down the road, but nooo, I guess they need to be different for the sake of being different...

54.gif
Not hard to find a battery at all.


Yeah, most batteries come with BOTH terminals and fit just fine in GM cars.


As of now, that's true; not the case when they were first introduced. In my book the negatives still far out-weight the positives (pun intended).

Something simple like a car battery, there is no need to introduce unnecessary complexity. N/S versions sized for 4/6/8, and two 8's for diesels trucks. Imagine if your local AZ only stock 3 sizes, what their burn rate would be and how much more likely you are going to find a fresh one and not a sulfated one that has been collecting dust for a while.
 
I just realized that I'm not talking about the same thing after all. My S-truck had TBI, not central port.
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So I now bow out of any further contributions to this thread as I really have nothing of value to add.....
 
Originally Posted By: Jonny Z
Why the GM side terminal batteries that are prone to be stripped (over-torque) or come loose (under-torque)? You mean you really can't repackage the space under to hood for the extra 1 inch of headroom? Using a common size battery will ensure the customer to be able to get fresh, readily available replacements down the road, but nooo, I guess they need to be different for the sake of being different...



They went back to top terminal batterys. Those side terminals sucked - never could keep them tight and when you tried you stripped them out. Warranty costs were high too.
 
Originally Posted By: GMBoy
Originally Posted By: Jonny Z
Why the GM side terminal batteries that are prone to be stripped (over-torque) or come loose (under-torque)? You mean you really can't repackage the space under to hood for the extra 1 inch of headroom? Using a common size battery will ensure the customer to be able to get fresh, readily available replacements down the road, but nooo, I guess they need to be different for the sake of being different...



They went back to top terminal batterys. Those side terminals sucked - never could keep them tight and when you tried you stripped them out. Warranty costs were high too.


Thank God. I see brighter days for GM ahead.
 
Nothing wrong with CFI/TBI systems other than they are not as modern as sequential FI systems. They were a simple and reliable replacement for the carb, and easy to work on! A lot of the domestic cars were using this in the 80's while the imports were still using carbs.
 
Originally Posted By: dishdude
Nothing wrong with CFI/TBI systems other than they are not as modern as sequential FI systems. They were a simple and reliable replacement for the carb, and easy to work on! A lot of the domestic cars were using this in the 80's while the imports were still using carbs.


Yes, the term "central point fuel injection" includes the use of a typical throttle body with an injector mounted above the throttle body opening.

What I am wondering is (other than cost) why GM designed a system that uses a manifold similar to a port injected system, but it uses a single injector with poppet valves at the ends of tubes to spray fuel into the intake runners above the intake valves.

I found a descriptive article. Like the article reads, this system is NOT easy to work on in the typical sense of the word.

http://www.underhoodservice.com/Article/..._diagnosis.aspx
 
More time for the fuel to atomize? Less heat troubles for the injectors? Maybe there was a space issue with fitting injectors into the intake manifold where they'd normally go. It does seem silly, but there must be a reason for it.
 
I know that GM has had problems for years on the Vortec engines with regards to the fuel spider. I know it has been revised several times because they would get leaks, etc and cause all kinds of problems.
 
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