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87 K5 TBI Falling on its face... no power

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badbowtie03

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Hey yall, so my k5 just started out of the blue having hardly any power under acceleration.. it will start and idle good... it will even rev perfect. You can hit WOT at an idle without any hiccup all the way up to 4,500 rpm... but if you put it in gear and drive off with light throttle it seems kind of normal at first... but then. If you give it maybe more than 1/4 throttle it kinda seems like its running out of gas... if you WOT then... it will spit/sputter and randomly have power but then wont really get over 3-3,500rpm... it makes me think it might be a fuel issue? Or possibly something electronic Like a sensor? I wouldnt think its spark because it revs perfect at idle... any ideas? What do yall think? Thanks a lot!!
 
Could be a lot of things:

bad or too little gas (Bad regulator or filter)
Ignition related
Bad sensor

Have a code reader?
 
I had a similar issue with a motor I swapped in a truck, timing was way off. Maybe something in the distributer or the timing itself, like bent said could be a lot of things.

Also you don't need a code reader, just a paper clip
 
I'd just add, does your check engine light work properly in the first place? If it doesn't, the ECM could be spitting out codes and you wouldn't know it. Doesn't always, sometimes there will be an issue without a CEL, but it helps to make sure it works.

Without jumping too far into diagnoses, I'd also check fuel pressure pretty early on. Not knowing the rig, the hose used in the past (and up to who knows when on replacement stuff that's sat on the shelf for a long time) inside the tank is not ethanol compatible, and will split in time. I chased a problem with intermittent poor running/sputtering/backfiring/loss of power for quite some time until I put a fuel pressure gauge on it. Often it may run better with a full tank in these cases. But that isn't a way to test, if the rip is large enough, the resistance from the fuel in the tank won't matter as much like it would if there was a small hole.

Autozone should have a fuel pressure test kit with the right adapters for the GM fuel line. I tested it at the fuel filter, because it's about the easiest to access. TBI is very tricky at the engine side, I'd leave that alone. If the hose is long enough, you can put the gauge in the cab and test while driving even with the adapter at the fuel filter.
 
Check for a clogged catalitic converter if it still has one too..they can have the catalyst come loose inside and block exhaust flow,and not do it all the time too...
 
It doesn't take nearly as much fuel to rev an engine in neutral since there is no load on it, as compared to actually out driving the vehicle. As said above put a fuel pressure gage on it and do some base level diagnostics.
 
black dawg said:
By your description, fuel filter would be my first try.
Click to expand...
I am a big fan of k.i.s.s., keep it simple, stupid. A fuel filter is cheap, easy, and you could probably use one anyway. Don't make it harder than it has to be. Ask me how I know. Good luck, tell what you find out.
 
Weak spark can crap out under load,but let it run ok in neutral also..
Seen a bad rotor or distributor cap do it too,on older engines that used them..
 
Other than usual tune up stuff, plugs, rotor, cap, air/fuel filter etc....

X2 on the catalytic converter. I drove My 95 z28 to work a few years ago- went from 275hp to about 150 hp on the ride home. Not long after that it would idle, and rev up fine in neutral while the car was still warming up. After it was warm, if you tried to let the clutch out and give it gas, it would die. I Could barely move and park the if i slipped the clutch enough. The cat was bad- melted and plugged up.

I have a tundra with a bad cat right now- it drives pretty normally but is showing a code for catlyst efficiency. When the truck is warmed up, if you get on the road and get the RPMs over 3,000, and keep rolling your foot into the gas, the engine will stall.
Pretty sure theres something loose in the cat, but most of the time the truck runs normally.
 
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