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what to do? I bought a 1985 GMC Suburban ¾ TON 4x4

morrisammo

morrisammo

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Question for you folks in Gear head land?
I bought a 1985 GMC Suburban ¾ TON 4x4, , it’s in good shape. Little or NO rust.
The motor, well it starts and Idle’s, but it is rough, I have changed the plugs, distributer, wires, checked the timing. And did a compression check, but it still runs rough. And is not drivable.
This is the twist, someone whom owned it at some point in its life, had a Camaro motor put in it; I don’t know what year motor it is. And it has TPI injection from the now out of business Arizona TPI, at one time I do believe it ran well, but when I bought it, it had been sitting in a garage for 3 years.
So I’m weighting out what to do. Or what to get done to it. Seeing getting it running well, has stepped out of my skill/ knowledge range, and I need to bring it to a shop.
My goal is to have a super dependable vehicle that runs and runs, change the oil, do a tune up now and again and get 150,000 out of the motor, be able to drop in a re-build and run it another 150,000.
So the opinion I’m asking for is?
Should I have the shop fix the TPI and keep it as is?
Or should I have the shop, change it back to factory TBI?
OR another option?
 
First,congrats on your purchase!..I also have an '85 Suburban ,but its a K10 and a diesel..

First I would have the engine looked over good for any vacuum hoses unplugged,cracked or leaking..any air getting into the intake will screw with the idle quality..it might have a valve or two sticking if it sat a long time,or a stuck lifter ,it might get better as its run more--adding a little seafoam or marvel mystery oil to a fresh oil change might help it some..

Sure all the plug wires are on the right plugs?..firing order might be wrong,if you put them back where they were,someone else may have messed up when they put the wires on before you got it..

I dont know much about fuel injection,other than its beyond my ability to diagnose or repair it much--only know what I have seen friends deal with on newer vehicles...

A compression test will tell if a cylinder has low compression,which will reduce power a lot and make it skip or run rough--when you took the spark plugs out,you should have looked good at each one and put them in order so you know which cylinder they were in,often you can tell just by looking at the deposits on the plugs which cylinder has not been firing or has low compression..(I poke them thru a hunk of cardboard when removing them so I can keep track of which cylinder they came out of)..

Since the truck had a different engine installed,it could be someone just used the original computer from the truck,and its not "matched" to the engine,being a different year or application?--I assume it has a computer if its fuel injected...also I dont know if the aftermarket EFI is compatible with a stock GM computer--I would assume so,but it might require a certain one..that I cant help you much with..
 
diesel4me said:
First,congrats on your purchase!..I also have an '85 Suburban ,but its a K10 and a diesel..

First I would have the engine looked over good for any vacuum hoses unplugged,cracked or leaking..any air getting into the intake will screw with the idle quality..it might have a valve or two sticking if it sat a long time,or a stuck lifter ,it might get better as its run more--adding a little seafoam or marvel mystery oil to a fresh oil change might help it some..

Sure all the plug wires are on the right plugs?..firing order might be wrong,if you put them back where they were,someone else may have messed up when they put the wires on before you got it..

I dont know much about fuel injection,other than its beyond my ability to diagnose or repair it much--only know what I have seen friends deal with on newer vehicles...

A compression test will tell if a cylinder has low compression,which will reduce power a lot and make it skip or run rough--when you took the spark plugs out,you should have looked good at each one and put them in order so you know which cylinder they were in,often you can tell just by looking at the deposits on the plugs which cylinder has not been firing or has low compression..(I poke them thru a hunk of cardboard when removing them so I can keep track of which cylinder they came out of)..

Since the truck had a different engine installed,it could be someone just used the original computer from the truck,and its not "matched" to the engine,being a different year or application?--I assume it has a computer if its fuel injected...also I dont know if the aftermarket EFI is compatible with a stock GM computer--I would assume so,but it might require a certain one..that I cant help you much with..
Click to expand...

A buddy of mine and I checked all of those things, vacuum, and the old spark plugs, I do know the TPI was put on by a company that, did TPI for a living, they did the fuel pump, the new distributor.
New wire harness, and the computer that went with it. The guy that owned it has a window tinting business and did move it around his lot, from time to time, so it did not totally sit for 3 years.
I see your from Mass!! I grew up in Squantum! Retired from the Army, and Stayed in Texas!
 
If it had ethanol gas in it for 3 years,it will likely have to be run thru several tanks of fresh gas with some injection cleaner in it to hopefully clean all the stale gas and residue ethanol leaves behind--it corrodes metal parts badly due to water it absorbs and it makes aluminum parts get all white and fuzzy..

I'd run it awhile after changing the fuel filter with some additive in the fuel and see if that helps..and I agree about checking the fuel pressure,thats critical on injection..

Squantum huh?...I thought I knew where every town in MA was,the name sounds familiar,but I'll have to google map that one...near Boston I think?..
I'm originally from Fitchburg...now living near Middleboro..
 
I would learn as much as possible about the tpi see if I could get that running tbi is great but its a step down from tpi imho
 
4xcrazy said:
Replace the fuel filter and check the fuel pressure.
Click to expand...

THIS!!!

I don't know if you've jumped to the conclusion yet that this is some complex EFI problem, but without steady fuel pressure at spec. during cranking / running you won't ever make it run. That's one of the first most basic things to easily check too.

blazinzuk said:
I would learn as much as possible about the tpi see if I could get that running tbi is great but its a step down from tpi imho
Click to expand...

And I agree with this too. I had a TPI setup in my IROC-Z and did quite a bit of tinkering with the basic run of the mill mods most guys do on those systems. It is very user friendly, and easy to work on. Plus it is superior to TBI for sure. You can make a lot of midrange torque with the TPI setup, that's where that system shines.

If you find that fuel pressure is within spec, I'd figure out how to look at DTC codes. Did somebody install a check engine light or LED or something capable of flashing the DTC's?
 
Light is present and I believe its actually on right now. As soon as we can we'll pull the code.
 
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