94 Silverado not running right ?????

[slightlybent47]

I have a 94 Silverado with a 350 and four speed automatic.
It had a slight miss and would kind of bump every 5-10 seconds.
It has 140,000 miles so I changed the plugs, plug wires, rotor and rotor cap, but it still has a slight miss.
I resurfaced the heads and did a valve job on it at 100,000 miles so the top end should still be good.
It also has the same miss in it when under power and will sometimes when sitting at a light it will bump so hard that it will shut off.


Also it just passed a state inspection with no cods showing up and emissions were fine.
The check engine light dose NOT come on.


Any ideas ????????

[fastredrider44]

Fuel filter or check that coil wire again.

[Titanium]

Whats your fuel pressure? Have you checked your timing? Sometimes bad MAP sensor will act like this too

[CJM]

timing, fuel pressure, injectors.

[mxduner]

is that still a tbi? does it do it all the time? or just when hot? fuel psi i would check as mentioned. as well as the other rec's above

[slightlybent47]

Yes it has the old tb1
I also took it to pep boys but they didn’t have a tester for that year.
It dose it al the time, I checked the timing and it was off a little, I found a vacuum line lose. But it still has a miss in it. I had to stop working on it cuz it started raining.
I’ll look at it again tomorrow.
I did put in a new fuel filter some time back but I can’t remember how long it’s been.


Anything else I should check?

[Heatpump#4]

run a can of either sea foam ( follow directions on can) i thinks its a third in gas a third in oil an a third threw your vacume line.. My friends truck had that problem an i used the sea foam like that an its doesnt miss or anything now also the lucas intjection cleaner does wonders also.... hope this helps

[chucked]

Running injector cleaner through an engine wont help a bad problem like this. I think I know the problem you are having, I had the same problem in my v8 s-10, which had a tbi 350 in it. Does it have a check engine light? You don't need a tested to check it, just a paper clip. my problem was a leaking injector o-ring. If you take the air cleaner off, you can see the injectors shooting down into the throttle body, if you can see anything but a nice fan spray mist of fuel (dripping) you have a leak.

[Heatpump#4]

Originally posted by chucked
Running injector cleaner through an engine wont help a bad problem like this. . then i guess the little gremlins in the truck fixed my problem. an it could be the injection o ring but nine times outta ten its not

[CJM]

Originally posted by Heatpump#4
then i guess the little gremlins in the truck fixed my problem. an it could be the injection o ring but nine times outta ten its not \\Sometimes you get lucky, soemtimes you dont.

If it has a 350 or 305 tb has one mounted near the air cleaner on the older trucks with 2 injectors in it-they can be bad. I cant recall if this is the case with the 94 tho.

[chucked]

Originally posted by Heatpump#4
then i guess the little gremlins in the truck fixed my problem. an it could be the injection o ring but nine times outta ten its not

Please provide me with some evidence of this? I've owned about 10 chevy TBI vehicles. Most of them had the same exact TBI unit he has on his 350.

[slightlybent47]

Thanks for the suggestions.

Well after doing everything I can myself to no avail, I took it to a local shop and had them do a full diagnostic on it.
They checked the compression on all cylinders and that was all good.
Then they checked the timing and it was fine, they checked the fuel pressure and that was good. they found a crack in a vacuum line and fixed that and they did find on of the new spark plugs I had just put in had a low resistance on it, so they replaced that.
They checked the injectors and said they were fine.
And I had them readjust the valves and it dose run somewhat better at idle but under a load it still sputters and sounds like it has a miss in it.
All the parameters on the diagnostic check out fine, so WTF?

Something is not right somewhere but i just can't seem to find it.

[CJM]

Leak down test maybe. They put air into the cyl/head and then you can see if the head gasket is leaking.

Could be carbon deposits in say the throttlebody, or even the plenum, the truck is older.

It still sounds fuel related to me tho. Hey try seafoam in the brake booster line got nothing to lose.

[slightlybent47]

Originally posted by CJM

It still sounds fuel related to me tho. Hey try seafoam in the brake booster line got nothing to lose.


what dose that do and why would i do that?

[CJM]

Originally posted by slightlybent47
what dose that do and why would i do that?

it will put the seafoam into the engine, seafoam is basically a concoction of mostly kerosene and some other junk. But what it does is it cleans out carbon deposits and gummed up carbs, injectors, etc, and trust me it does work.

Back in the day we used to add a bit of atf to the oil, let it run for about 15-20 mins and flush the stuff out-cleaned the engine quite well. Cleaning carbs you could break up carbon deposits by pouring (VERY SLOWLY) a glass of water straight into the carb-and it does work. I did it to an 86 grand wagoneer 2 years ago after the kid gave it to a buddy of mine and said it was totally shot.

I still say you should do a leakdown test.

[slightlybent47]

Originally posted by CJM
it will put the seafoam into the engine, seafoam is basically a concoction of mostly kerosene and some other junk. But what it does is it cleans out carbon deposits and gummed up carbs, injectors, etc, and trust me it does work.

Back in the day we used to add a bit of atf to the oil, let it run for about 15-20 mins and flush the stuff out-cleaned the engine quite well. Cleaning carbs you could break up carbon deposits by pouring (VERY SLOWLY) a glass of water straight into the carb-and it does work. I did it to an 86 grand wagoneer 2 years ago after the kid gave it to a buddy of mine and said it was totally shot.

I still say you should do a leakdown test.

None of that makes any since, why would you ever want to pour water in the carb? That’s sounds like some very bad advice to me. And what dose the break buster have to do with the motor?

[CJM]

Originally posted by slightlybent47
None of that makes any since, why would you ever want to pour water in the carb? That’s sounds like some very bad advice to me. And what dose the break buster have to do with the motor?

Pouring water in does work, its a very old mechanics trick. Gotta keep the rpms up tho and its not something i would recommend unless you got a clue. http://answers.yahoo.com/question/index?qid=20080807085324AAh9uX0

you can also use ATF, it has a similar effect to seafoam

Brake booster is a vacuum line that feeds into the engine, it will suck the seafoam up. Could also put it in your pcv valve hose too iirc. The brake booster house goes straight to the cylinders in most vehicles tho..

But really all of that is old school mechanic tricks that do work even tho they sound insane.

[slightlybent47]

Ok now I have done the atf trick in the past but the water thing is a new one on me.

[slightlybent47]

Ok I see the concept but that just sounds weard!

[CJM]

I know right, it sounds insane-but it does work.

[BakerRacing40]

have any cats on it? EGR on it? might try looking there. looks like you've check all the other usual suspects...

also.. if my memory serves me right... there is a little rubber hose in your fuel tank that can be bad. to check it, hook up a fuel pressure tester and clamp off your return fuel line to your fuel tank. it pressure goes up, you should be good. if the pressure doesn't change, wa-la, problem found.

hope this helps!

[slightlybent47]

I would think the egr would show up when it was inspected or when the diagnostic was done. I had to replace it about 5 years ago when I got it inspected and it showed up then.
Still doesn’t mean it hasn’t gone bad again though but I think that would have already shown up on the test.

I hate it when something is wrong but I cant nail it down.

[slightlybent47]

Ok I found a small leak in the muffler so that may be where I’m hearing the funky sound coming from.
And of course I can’t find my receipt for the muffler that has a lifetime warranty on it. I just hope they still have me in there computer.
I’ll see what I can do about it next week, it’s time to go ride!!!

[slightlybent47]

Ok I had a new muffler put on today and it sounds 100% better. The sputtering is gone and it’s running much smoother. It still has a slight bump every now and then but nothing like it did. I may try some new injectors and see if that dose the trick, I’ve replaced just about everything else.

Thanks for the input.

[CJM]

Ah exhaust leak was letting to much back pressure go out. Glad your mostly fixed now.

[slightlybent47]

Originally posted by CJM
Ah exhaust leak was letting to much back pressure go out. Glad your mostly fixed now.

You may have a point there about the exhaust.
Now on to the A/C, I just replaced the compressor, drier, orifice, flushed the whole system and vacuumed it down and charged it up and it worked great for about a month then the compressor went out again. It sounds like the bearings keep going out in the compressor, I did put in the oil when I installed the compressor but the only thing I did not replace was the condenser coil.

What could be making the compressor go out?

[slightlybent47]

oh and i used all new parts, no rebuilt crap.

[mxduner]

is it the clutch thats out or the comp.? i'm assuming you switched to r134?

[CJM]

Sounds like you didnt add enough oil perhaps-but if the only thing that isnt new is the condenser then maybe it has built up corrosion and its seeping into the compressor?

[slightlybent47]

Yes I converted it to 134 and I put an 8 once bottle of oil that was for a/c unit when I put the compressor on. It’s fine until you turn on the a/c and when the compressor kicks in it knocks real bad. And doesn’t cool anymore even though it shows a full charge.

Could the orifice get plugged up and that would keep the fluid from circulating and maybe that is what made the compressor go out? I’m just guessing at this point.

The last one did the same thing. So this makes twice it’s done the same thing.

[beastlywarrior]

hmm funny my 93 was having the same problem, so i checked my plugs and it turned out one was bad even though i just replaced them

[CJM]

Did you change the orifice filter thingy (forget the real name)?