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mechanic help please.

Started by ely, October 05, 2009, 04:29:13 PM

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ely

working on a 94 chev. pickup with 350 engine and 4 speed auto tranny in it. the engine is newly rebuilt say less than 3000 miles on it. trans . newer still.

truck used to run fine. had the tranny disenigrate on it. got that rebuilt. the truck sat for about 3 months in the mean time. got it all put back together but the truck seemed to have no power at all. at times it would backfire, pop, cough. all while running down the road. on hills you will lose speed and have a tough time ,making the next hill.

i first checked the fuel pressure,12 pounds. book says 11-13. checked filter nice and clean. replaced it anyway. truck gets worse to the point it only goes 35 mph and gets hot on the gauge,a little over 210. 

i then clean out the cadelettic converter, thinking it may be stopped up. truck makes a little improvement, stops heating up, runs at 195. still no power.

i have changed dist. cap. and rotor . no change. changed ing. module, seemed to help some so far with the popping and backfireing, but it still does not have the power it needs.imo.

also in the mean time i have put new plugs and wires on the engine.
this truck now uses alot of gas when we drive it. not at all what we were accustomed to.

ely

truck will run and shift out fine and will get on up to speed now. but on the lower end it just has no power.  from a standing stop on gravel it will barely scratch the tires. on pavement forget that.

anyone dealt with this sort of thing before that knows what i am over looking.
any ideas....i mean besides the buy a ford joke. im not really tired of pushing this chevy yet. :-X

karl

Timing?
vacuum advance?
Bad gas?
"I ask for wisdom and strength, Not to be superior to my brothers, but to be able to fight my greatest enemy, myself"  - from Ojibwa Prayer.

Bruce_A

Vacumn leak, electrical to trans not hooked up properly?  Downshift linkedge?

Slabs

What kind of Carb?  Rochester?

Check the float set and clean the float needle and seat.  Is the needle the right one?

Oh 94!  May be injected.  Disregard above if so.
Slabs  : Offloader, slab and sawdust Mexican, mill mechanic and electrician, general flunky.  Woodshop, metal woorking shop and electronics shop.

mcfcfan

Hi ely,
From experience i agree with Karl, as i was reading your post i kept thinking to myself must be timing.
I am ex diesel mechanic 15 years.
Glad i got out of it though some 10 years ago.
Hope you get it running smooth.
Good luck
Lee
Life isn't about how to survive the storm,
but how to dance in the rain."

Coon

Hold on guys........ don't get your undies in a bunch.  :D  I know the problem quite well.  Have had this problem a couple of times as well as diagnosing the same kinds of problems.  The typical problem in this case would be the oxygen sensor.  Typically one would disconnect the positive battery cable and leave disconnected for twelve hours.  Next put the new sensor in and reconnect the battery cable.  Now drive the vehicle for 30-40 miles fast, slow, accellerate hard, brake hard all while the computer reboots itself.  Most of all don't just pussyfoot around or the vehicle will be guttless and have no power much like it is now.

Brad.
Norwood Lumbermate 2000 w/Kohler,
Husqvarna, Stihl and, Jonsereds Saws

rebocardo

I think Brad hit the target.

> i then clean out the cadelettic converter,


How did you do that? Do you mean you hollowed it out?

In the FWIW category, the Chevy cats. are known for clogging up.

The other thing I have to question is the fuel pressure at 12 pounds. Does this mean you have the single TBI injector over the carb? If so your problem might be the TPS built into the carb.

Coon

In a '94 as he states it is that vehicle should have an actuall fuel injection system and not the Toilet Bowl Injection (TBI) :D    12 lbs pressure is more than adequate. 
Norwood Lumbermate 2000 w/Kohler,
Husqvarna, Stihl and, Jonsereds Saws

moosehunter

ely,
Take the distributor cap back off and check the distributor shaft for play. That vintage GM engine was prone to wearing out the bushings in the distributor. This would cause the timing to be very erratic.
Timing is a very distinct possabilty. Checking the cam timing would be a good idea.
Did you see any signs of the cat coming apart before you "cleaned it out"? (your'e killing our grandchildren) Pieces of the cat can plug up the muffler.

Coon,
No need to leave the battery unhooked for 12 hours. Disconnect the negative terminal. Wait 10 seconds, touch the negative cable to the positive post, then reconnect. That will clear all memory from the computor.
Also an actual fuel injection system has 40 + psi. 12 psi is correct for a TBI.

mh
"And the days that I keep my gratitude
Higher than my expectations
Well, I have really good days".    Ray Wylie Hubbard

ely

the timing was my next adventure. thanks for all the input.
it is a throttle body injection system.
not bad gas as i have ran three tanks thru it so far. bought at different places.

the converter was not broke up before i cleaned it out.

the tranny may have a wire or set of wires not hooked up. but i know it does shift out thru all the gears properly.

will check for slack in the distrib. also

moosehunter

ely,
Another thought I had is the fuel presure under load. If your filter is plugged or the pump is going bad it would cause the symtems you decribe.
Put the fuel guage on it and drive it, make sure presure stays up.

Computor grounds can also cause a lot of problems. Make sure every wire you see that is attatched to the body or engine is clean and tight.

mh
"And the days that I keep my gratitude
Higher than my expectations
Well, I have really good days".    Ray Wylie Hubbard

ely

ok thanks, i just checked the pressure while it was running in the shop.

Don_Papenburg

The computer module could be going bad also . If none of the above helps go to a junk yard and get a good used one with the same numbers as yours . try it if it works buy it .  A used one might be better than a new one that might be bad and cost a lot more . Buy a new one if you can't find a used one .  Had to get  a computer for my S10 it was simular problems only it never smoothed out .  Got a good used computer module at the junk yard and drove away with a happy truck.
Frick saw mill  '58   820 John Deere power. Diamond T trucks

DanG

If all else fails, just wait until Captain finds this thread. ;D
"I don't feel like an old man.  I feel like a young man who has something wrong with him."  Dick Cavett
"Beat not thy sword into a plowshare, rather beat the sword of thine enemy into a plowshare."

Chico

Have you changed both filters theres one in the back and one on the drivers side either under the drivers door area or on the bottom of the firewall on the drivers side also I would make sure that the entire ex. system was clear even tho you cleaned it it may sytill be the prob diconnect it  at the front of the conv tie it up drive see what it does if it doesn't make a diff reconn and goe to tailpipes to make sure you have flow It could be the module inside the dist under the dist plate also I would replace entire dist cap rotor module etc this will prob solve you prob if the ex wasn't stopped up
Chico
My Daughter My sailor MY HERO God Bless all the men and Women fighting for us today If you see one stop and thank them

SamB

My GUESS ??? would be you either had more than one problem to start with or you created a new problem while trying to fix the original problem. Have you verified the firing order and checked for possible crossed wires? Not that I've ever done anything like that  ::) :).....

Captain

I found it.  Just waiting to see some more test results.

Captain

Corley5

Burnt Gunpowder is the Smell Of Freedom

ely

still keeping up with this thread. my dad is driving it now. but i did have him to remove the battery cable to reset everything. he just has not drivin it enough yet to see if it helped.

chico you say there are two filters, i know about the one about the drivers door inside the frame. changed it when all this started and checked it more recently. where is the other filter you speak of. in the tank?

samb yes the wires are correct and in the correct place.

have not checked the distrib. for slack yet.

Captain

When checking the distributor, pay close attention to the magnetic pole piece under the rotor affixed to the shaft.  It is on a set of splines.  If this pole piece becomes loose, your set of symptoms is similar.

Captain

Warbird

I'm going through something very similar with an older Chevy.  Interested to see what your troubles end up being.  So far, I've checked and rechecked the timing, even turning the distributor 180, thinking maybe the guy I bought the old thing from had messed it up. 

That wasn't it.  The thing had backfired on him so big that it blew the muffler apart.  We checked all sorts of things.  I bought a refurbished Rochester and put that on (strangest thing, a 4 bbl carb on a V6.  That was from the factory, tho!).  Definitely helped but now we have to keep pumping the gas pedal to fill the carb and when that gas runs out, the engine dies.  We checked the fuel pressure and it was pretty high for a carbureted system (I think it was about 30).

Just worked on it again last night.  It has been so long that I have no idea at this point.  We're going to try again next week by running a fuel hose down to a gas can and feed the engine off that, just to make sure it isn't bad gas, clogged filter, etc.  If that doesn't do it, I'm really at a loss.

I did find a wire bundle that runs through a metal tube from the back of the starter up to the back of the block and to the top of the engine.  That metal tube was directly up against the exhaust manifold, so I was thinking maybe the wires melted inside.  They all seem to pull through the tube okay, though.

In other words, I feel your pain ely.  If you ever figure it out, let me know would you?  My truck is an 82 or an 86 (would have to look again).  I'm a hairs breadth from just scrapping the entire thing.

Rockn H

Like Captain said, I would check the magnetic pickup in the distributor.  It is right under the rotor.  If it has any cracks or the seams show seperation, it is bad.  This was a common problem in those year models.  The pickups in new and reman distributors have been redesigned and look nothing like the originals.  This is your timing pickup for the ecm and it can cause very eratic timing signals to the ecm.  A quick visual inspection and you can move on.

The next thing that sounds possible from your earlier discription would be the Electronic Spark Control.  It's usually located on the passenger side next to the throttle body.  It's flat, has two sets of wires plugged in and one maybe two vaccum lines.  There's a rubber breather sticking out that looks like it should have a vaccum line, but it should'nt.  Check the vaccum lines and make sure they are not cracked and still connected to the intake.

Hope you've already found the problem, if not, maybe this will help.

JJ

I am sure you have looked, but is air cleaner clogged?

I just had similar problem with my toyota and found the entire air box plugged up with about 1000 acorns (double DanG chipmonk).

I check my ford, and same thing; chock full of nuts.

          JJ

ely

here for an update.  it may not be the problem but we think it may be.
there is a fuel return line that runs along with the fuel line. when it goes up the back of the engine the hard line turns in to rubber for a foot or so. these connections are squeezed like hyd . lines.

dad has discovered that the return line is actually leaking. we think it may have happened when the tranny blew up and turned a bit sideways. most likely hit the line then.

he checked his milage and said he was getting 10 mpg and something had to be done. thats when he noticed that hose was wet.

so when weather permits we will get that taken care of.

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