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I am soooo frustrated ! ! ! ! ! ! !

Uncle Fester

Uncle Fester

1/2 ton status
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Mar 23, 2006
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Cheyenne
Okay, here is the deal, I changed from 33" tires to 35" tires on my suburban, and lost some power...expected that as I only have 3.73 gears....no problem, still ran fairly well. Well, in the last few days, power has dropped off more, now the truck does not really make power untill I get her up to 2600 or more RPMs :mad: :mad: :mad: from 2600 on up to 4000...power is fairly good, for a stock 350 w/quadra junk.
I have set the timing to 10* with vacume disconnected and plugged off. I have checked for vacume leaks using eather at base of carb, and all vacume lines hooked to the carb, no leaks found. Truck has 160K miles SHOWING on the motor, I say showing because I found out the truck used to be a state fish and game truck, and then a sheet metal company truck, so I am betting mileage is higher....but do not know.
Anyone have any ideas what might be wrong with my poor truck? Could it be the timing chain getting loose? ? ? ? Also, gas mileage has dropped off BAD in the last few days, I used to drive to Denver (100ish miles one way) and back on 1/2 a tank with the 35s, tonight it took me 1/2 a tank to drive to Ft.Collins and back (45-50miles oneway).:eek1: :mad: :mad: :mad: :mad:
 
Have you thought about checking out the tranny also. It may need a tune up as well.
 
Have you checked to see if the secondaries are actually closed at lower rpm/idle?
Have you done a leak down or compression check? Could be bad valve seating/ring blow by(is it breathing heavily?)
Also check that the rotor arm turns against it's spring weights. A siezed advance unit will kill power. Why disco the advance vac anyway?
 
Okay, guess I have a few more things to check....
Also the tranny is a SN465 with a new clutch, so I doubt it is the tranny, but it is possable I guess, how do I check it?
I do not have the ability to do I leak down check. at least I do not think I do, how is it done?
I had a friend suggest doing a vaccum test at the intake and see what kind of vaccum the motor is making...
I am also going to test the vaccume advance unit to see if it is working right.....lots of work to do tonight....:doah:
 
If its a manual that's not your problem. Vacuum leaks will be most noticeable at idle and would not affect your mileage much.

My bet is your fuel filter is clogged or your carb needs to be rebuilt. Its possible the float (in the carb) sunk as well.
 
:doah: I forgot to say that the biggest power loss came after changing my fuel filter that mounts inside the Quadrajet, right where the fuel line enters the carb... sorry about that:doah:
 
How are you calculating the distance between two given points? Are you using the odometer? If you're using the odometer and you have not had the speedo re-calibrated then right there is your gas mileage issue. The change in tire size will have made the odometer not read correctly now so you can't use it as a tool anymore to judge mileage. Now if you know the distance between the two given point by means of a map or other means then forget about what i just said.
 
The odometer innacuracy addresses his mileage issue only. It's still running like crap too. Tires won't cause that problem..

I'd pull the plugs and get a good idea of what's going on. Are they fuel fouled? Oil or coolant fouled? It could be that it needs plugs, wires or both.

I know mine uses oil due to a couple of valve stem seals leaking. When they get fouled the 350 still runs ok, but the power is way down when the engine is under 2000 rpm. I'll usually notice the popping from the exhaust (raw fuel and glasspacks) and yank the two offending plugs to find them nice and cruddy.

Takes 20 minutes or less to pull the plugs. I'd pull them and see what you got.
 
Definitely do a wet/dry compression test. That will help diagnose all sorts of problems.
 
Okay, thanks for all the ideas and help guys, I think I found the problem.... I did a vaccum test at that vaccum port between the carb and the distributor, anyway, at a steady 2000 RPM (I like my throttle lock) I have a steady 12 inches of vaccum. Accourding to my Peterson "How to trouble shoot you car" book, that is late valve timing, and adjusting the timing did not bring the vaccum up, so that, according to the little book, is a timeing chain going bad.

That is a fairly easy fix, and cheap one too, thank god! :bow: I will have it done sometime this weekend....:waytogo: :waytogo: :waytogo:
 
Vacuum between the carb and distributor won't tell you anything as it is a ported vacuum source. There is no test that will tell you that your timing chain is bad or stretched. Anyone or any book that tells you that is incorrect.
 
sorry you misunderstood me, or that I didn't state it clearly, there is a port on the intake, between the carb and distributor that I used to do the vacume test. and what the book says about the low vaccum reading is that the valve timeing is late....the main thing that controls that, to my knowlege is the timing chain.
 
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Uncle Fester said:
sorry you misunderstood me, or that I didn't state it clearly, there is a port on the intake, between the carb and distributor that I used to do the vacume test. and what the book says about the low vaccum reading is that the valve timeing is late....the main think that controls that, to my knowlege is the timing chain.
Click to expand...
late valve timing as in a tooth or two out, yes that would cause low vac but a worn chain? No way. A big cam can cause low vac, burnt or worn valves/seats, worn cam lobes, ignition timing out..........
There isn't enough room in the timing cover for a chain to have that much slack. Unless ofourse you have the nylon gears and they are FUBAR'd and have jumped a tooth or two.
 
When trying to diagnos using vacuum as your source you need to be on a full manifold vacuum source not ported vacuum.
 
4X4HIGH said:
When trying to diagnos using vacuum as your source you need to be on a full manifold vacuum source not ported vacuum.
Click to expand...
I think I know where he means, it's a take of directly into one of the runners and it exits between the carb and dizzy so it is full vac but the diagnosise is still wrong I think.
 
After re-reading his post now i may have misunderstood him. Sounds like he is using the full manifold vacuum right behind the carb. This vacuum will start dropping when a hotter cam is installed. On a stock engine the vacuum should be somewhere between 17-21 inches. Once you start changing cams to a hotter grind the vacuum reading will start to drop. The hotter the cam the worse the vacuum reading.
 
lets back up to the tire change for a minute. You got a heavy vehicle, and if you put on a 35 tire on, you now have dropped your rpm range by a couple hundred. If its like mine that engine don't make real good torque until your in the 2500-3500 range, right where the heavy vehicle likes it. If you've went from a semi aggressive tread pattern to an aggressive one, and the tire construction is more resistant to rolling that could be a significant contributor. The contact patch of the tire may be up to 25% higher with the new tires, and therefore causing more drag.

The engine problem, since it started with the filter change...did you get the filter put in, in the right direction? Did you check your fuel pressure? I would look for something that you may have touched recently before noticing the problem. Eliminate the simple stuff first.
Keep posting up
 
Fester, you need to take into account that you are at higher altitude than sealevel which is usually where those books set vacuum pressure at. Try advancing your timing a little.
 
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