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I swear this truck hates me.

The Griff

The Griff

High drag, low speed
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(sorry I keep making these threads of my problems/ignorance)

Well, today was my first day of my senior year of high school. I figured I would drive the Blazer with the top off, take some people out to lunch, you know, high school stuff.

This morning It started fine, idled fine and ran fine, I got to the school and shut it off without problem.

Came out for lunch, started it and let if idle for a few minutes before we took off, put it in gear and it dies, the same thing happens again, but the third time it keeps running, so I think I just didn't give it enough time to warm up, so I just chock it up to my stupidity. Then we get to burger king and waiting at the light I notice it is idling quite rough, sounds like a hell of a cam, but it freaks me out. We pull into the parking lot of BK and right as I pull into the parking spot it dies, everybody hops out and starts going in, I mess with the truck and it won't idle at all on it's own, I turn it up a couple turns, no change, I just get pissed off and go in too.

On the way back I have to hold the brake with my left foot and the gas with the right just to keep it running.

We get back I decide not to mess with it until after school.
So after school I start it and keep it running for a solid 10 minutes, and it keeps running on it's own, so I go to pull onto the road, and the S10 Blazer infront of me pulls out, and what happens? T-boned by a Focus.
While that's happening, my Blazer died again. So I decide "B*tch, your going to run whether you like it or not!" and crank the idle up about 6 turns, and it runs alright, still idling rough, but running fine on it's own.

And for the cherry on top, on the stretch of highway home, I go to pass a slower car, and notice it has a terrible spark knock, "well that's lovely"


Then I get home and start looking things over, and notice that it smells very hot, (checked the antifreeze later, completely full). After that in an attempt to take care of the spark knock I back the timing off even more than it already is, and it doesn't fix it, just neutered the power.


Well that was my spiel, Think the old 350 is just about done? Supposedly the 305 went bang, and a 350 and TH400 with over 100K went in, and the truck has 74,000 Gov't documented, and the engine was changed in 92.
 
Sounds like you just need to start going over things. Check vacuum lines, choke, timing set correctly, blow out fuel lines, carb filter..... good quality time checking everything. Probably end up something simple and stupid, something you weren't going to see at school while frustrated.
 
From the symptoms it does sound like your most likely culprit is a bad vacuum leak. Mine had similar symptoms, wouldn't idle without help, idled rough, ran hot, etc when I had an intake gasket leak.

To test for vacuum leaks, spray carb cleaner or brake cleaner around the carb gasket, intake, hoses, etc while idling. If your idle speeds up you've found the leak. Don't run it too hard until you find the issue, vacuum leaks cause a lean running condition. Of course check all the other factors like timing, fuel, spark, etc.
 
I agree --vacuum leak sounds like suspect #1 in his case...have to be a fairly large one for it to stall or lope at idle that bad.like the hose going to the PCV valve or power brake booster maybe...or carb base gasket,intake,etc..

The lean mixture resulting from the extra air getting in the engine will make it want to spark knock and reduce power,also raise cylinder temparatures..if it has an EGR valve make sure its closing fully at idle,that can cause the same symptoms..

Also check the choke ,if its not opening fully it'll run rich,choke pull off failing can make it lope at idle,but you'd see black smoke from the exhaust and smell raw fuel too if that were the cause..

I've had a distributor rotor make a engine run weird like this before too--it would start up perfect,but snuff out or want to die as soon as you went to put it in drive and take off...drove me batty till I tried swapping a known good used one in its place and it cured it!..could see no cracks or carbon tracks on it either..:dunno:
 
Well, I considered it being a vacuum leak, because I had a vacuum gauge hooked up next to my tach, and it was running off the vacuum line at the base of the carb, but about 3 months ago it slipped off and sealed itself shut on the exhaust manifold, but it didn't seem to hurt anything so I left it alone, So I know it has a vacuum leak but it wasn't hurting anything.

Although I'm not ruling out the possibility of it developing another one.


I started it up today and it idled fine, I put it in gear and it stumbled but kept running.
 
Well today I spent some time messing with the truck, it seems that on high idle, (before the kick-down) it idles fine, but that's around 900-1100 RPM, after kick-down it's a rough idle around 250-350 RPM, and sometimes so low the whole truck shakes like hell. I'm amazed it's even running that low. It's worth mentioning that the idle screw really has no say on the idle speed on the engine anymore.

I got the vacuum gage hooked back up, though I'm not sure if it's working, or if the vacuum leak is really, really bad, at it's rough Idle it just bounces zero to 2 In.Hg.

Also every time I start it, there is a huge blue-ish cloud, It's always burned some oil, but I never new it was this bad.


EDIT, just found the paper my dad got after he bought the truck.
The old 305 went away when the truck had 26,671 miles, and a 350 came out of a 131,081 mile 1981 GMC K30, So now it has roughly 200,000 miles on the engine, and that's a lot of miles for a carbed small block. And it was put in in 91.
 
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That engine does sound like it is a bit tired, although it that wouldn't explain some of your symptoms.

Have you looked at the carb? As the means of fuel and air delivery it could be the culprit if you've come up empty on the simple stuff.

900-1100 is way too high on a stock motor/cam combination, and a typical small block is going to pull 16-20 inches at idle. Smoke at start up could be leaking valve seals, but given your other problems, I'd say its probably mixture-related. Do you have a known good carburetor you can swap on there to test? If not, check and make sure yours is tuned properly and not malfunctioning.
 
You really need to find your vacuum leaks. 900-1100 is fine for high idle. The sticker on my radiator support says 700 normal idle, 800 w/ AC on, and 1600 fast idle(Which seems really high to me so mine is set at 900).

Assuming a Quadrajet? Also not to be a dick, but are you sure you're adjusting the correct idle screw?
 
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It has a 2 barrel Rochester that my dad rebuilt years ago.

I have a milk crate of carbs, but they are all 4 barrels, even a brand new 600 CFM Holley from the early 80's, I also have the 4 barrel intake that was on it when we bought it, but I'm really not in a mood to switch intake manifolds.


And I know that I screwed something up when I was trying to get it to stay running Wednesday, I half assed got it back around normal, but nowhere near where I had it.
 
The Rochester? no, one Idle and one mixture, Idle on the left mixture on the right.

Wow. I've got a Jeep I've been trying to sell and I just got an offer to trade, for an 85 6.2 K5, sitting on 33 inch Falkin wildpeak A/T's and a 4 inch lift. Supposedly the 6.2 and TH400
 
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Hmm..guess he couldn't wait to finish posting to go make that trade?..:dunno:..

I've never seen any 2 bbl carb with ONE mixture screw,there should be one for each barrel...maybe one fell out?..that'd make it run crappy for sure!..
 
No, I just thought I should share that, waiting to hear back from him.

If it does have two, I sure can't find it, unless I'm really bass-ackwards with my understanding of this carb, and have been thinking one of the mixture screws is the idle.
 
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