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Where did my POWER go!?

gm29chev

gm29chev

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I have a 86 Blazer and it has pretty much stock everything at the moment. The only real change that has been made prior to me owning it was an electic fuel pump. Anyways, I hoped in the truck the other day and after letting it warm up I took off. The engine runs great going down the road but when I really hit the gas the truck lags bad. It even died on me a few times. After a long trip the other day, about 50 miles, I checked my engine temp and it only read 120F. And even after 50 miles of interstate driving the engine still lagged at about 70%+ peddle to the floor. This problem started rather suddenly as the day before when I drove it it was fine.

Do I have 2 problems here? One being the low temp and the other being the lack of power? or do I have one problem with two outcomes. Either way...how do I get my POWER back?
 
How long since a full tuneup?

First thing i would do is check timing, plug condition, look for obvious vacuum leaks, etc.
 
We did a full liquid change on it about 300 miles ago or so. Timing is currently at 8 and I know it needs to be about 4. Plugs actually look pretty new and it has some vacuum leaks. The thing I wonder is this...when we were looking at the throttle the other day it seems like the flap wont open all the way (sorry just getting in to this and not sure what thats called) when we really hit the throttle. Could this be a vacuum problem or do I need to replace something in there?
 
I have not replaced the fuel filter. Would this cause the lag though?
 
That was by the temp probe. My guage actually reads 250F or above.
 
I have suspicions that you might be right about the vac leak? What can I do to fix this? I will get some hose and just start replacing hoses but it cant be that easy right?
 
gm29chev said:
We did a full liquid change on it about 300 miles ago or so. Timing is currently at 8 and I know it needs to be about 4. Plugs actually look pretty new and it has some vacuum leaks. The thing I wonder is this...when we were looking at the throttle the other day it seems like the flap wont open all the way (sorry just getting in to this and not sure what thats called) when we really hit the throttle. Could this be a vacuum problem or do I need to replace something in there?
Click to expand...

that flap you're talking about is the choke and it must be closing on you.
 
Chevy305 said:
that flap you're talking about is the choke and it must be closing on you.
Click to expand...
Yes it is the choke. Do I replace this piece or could it be the vacuum leaks and hoses that are causing that not to open?
 
gm29chev said:
Yes it is the choke. Do I replace this piece or could it be the vacuum leaks and hoses that are causing that not to open?
Click to expand...

the choke can opperated a number of different ways, disconnect it and wire it open *when the engine is warm* that is. Then see if it still gives you problems.
 
Chevy305 said:
the choke can opperated a number of different ways, disconnect it and wire it open *when the engine is warm* that is. Then see if it still gives you problems.
Click to expand...
Good idea. I will give that a shot tomorrow.
 
it seems to me like it would obviously be a stuck open thermostat causing it to run cold making it run like ****, But im guessing this cant be the case since noones mentioned it?
 
You know we thought about that as well on Sunday when we were trying to figure this thing out. Im not counting that out but I havn't done it yet cause were just not sure its that. I am going to try some of this other stuff first and then if I have to tear in to that bad boy...well that will suck.
 
Now if it were the thermostat the engine would not necissarily run cold though would it? Like I said the engine after 50 miles of 75 mph only read 120F.
 
gotblazers said:
it seems to me like it would obviously be a stuck open thermostat causing it to run cold making it run like ****, But im guessing this cant be the case since noones mentioned it?
Click to expand...

oh i missed that part, that could actually be holding the choke closed partially... :doah:
 
gm29chev said:
You know we thought about that as well on Sunday when we were trying to figure this thing out. Im not counting that out but I havn't done it yet cause were just not sure its that. I am going to try some of this other stuff first and then if I have to tear in to that bad boy...well that will suck.
Click to expand...
it took me 30 minutes to change mine out my first time doin it with my dad guiding me so its probably not as bad as you think not to mention its like 8 bucks as i recall :dunno:. I'd probably do that just to rule it out as its a incredibly important and cheap piece but i understand that time and money can be at a premium so you gotta decide how to spend em.

gm29chev said:
Now if it were the thermostat the engine would not necissarily run cold though would it? Like I said the engine after 50 miles of 75 mph only read 120F.
Click to expand...
I was thinkin this also, I would tend to think that a fully open thermostat would keep it cold no matter what you did with that 350 just because thats alot of focking fresh coolant being circulated non stop. But i really couldnt give you a definite answer either way.

It sounds like your carbed still since as i recall tbi didnt start till 89. I actually had a very similar problem to you the other day. The night before i was pissed off and i put the pedal to the floor and held it there all over town and ive never floored it all the way down because i know its likely to throw a rod in that 175k mile 34 year old 6.6 motor. Well nothing broke and i got home fine. The next day i went to go to work and the truck could barely hold an idle, I had to idle over to my dads house which is next to my work and walk from there. I got home and figured i would play with the carb idle screws which on my q-jet i have one for eachside of the carb and they control how much fuel/air gets through. Turns out they were supposed to be 1.5-2 turns to the left for normal useage and somehow my angry lead foot the night before had caused them to open up to a full 5 turns left. I backed them both off down to 2 turns, Played with my idle control screw which determines how far back the throttle can go therefore determining where the gas is when my foots off it and the truck ran better than it did before. Have been drivin it 2 weeks now without a problem
 
Great. Thats exactly the info I was looking for. Thanks to everyone for the info. Looks like a I have a few things to play with before the weekends rolls around.
 
gotblazers said:
it seems to me like it would obviously be a stuck open thermostat causing it to run cold making it run like ****, But im guessing this cant be the case since noones mentioned it?
Click to expand...


Nope your probably right. I'm gonna guess open thermostat = low temps = choke not opening = no power.
 
I'm planning on replacing all the vacuum lines on my 87 5.7. What sizes do I need to do this? They re all pretty hard and crusty other than the ones that are away from the motor and they are cracked very bad.
 
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