4.3 vortec V6 running terrible

[straight6chevyguy]

Hi guys, been working on another project truck I picked up. It's a 2002 Chevy S10 4x4 with the 4.3 vortec and automatic transmission.
It starts and Idles fine and reves fine for the first couple minutes or so but after that and you give it some gas it runs really rough. it will rev up but is misfiring really badly.

I had trouble codes for maf sensor and O2 heater circuit malfunction.
I replaced the maf sensor but no change.
On my scan tool the O2 sensors seem to be working.
I have checked the tps and it checks good.
Also got a code for random multiple cylinder misfire after revving it a bit but disconnected the battery and came back today and it's gone ran the truck a bit misfire code has not came back. May not have ran it long enough I don't know. Funny though I drove the truck home and never got a misfire code until I ran it the other day.

Fuel pressure is 50-60 psi
I have also tried a new distributor cap. It also has new spark plugs.

I have done a little research on other forums but haven't really came up with anything other than what I've already checked.

I'm hoping someone here with more knowledge then me can point me in the right direction as what to check next, as I'm kinda lost at the moment.

[D13]

Stolen from the web...One of the first symptoms of a problem with the ignition module are engine performance issues. If the ignition module fails or has any problems it can lead to performance issues with the vehicle, such as misfires, hesitation, loss of power, and even reduced fuel economy.

Don't buy a cheap one and be sure to use the grease to insure heat transfer.

Fought this for months on my old truck. Kept popping modules, poor running and finally no start. Eventually traced it back to a bad Accel plug wire that was shocking the module.

If it has a bazillion miles check the distributor shaft for being sloppy too. Not normally an issue but if it starts hitting on the pickup coil weird things will happen.

[Bigdav160]

Do you know your fuel trim numbers?

[straight6chevyguy]

Originally Posted by Bigdav160

Do you know your fuel trim numbers?

So I must admit that I'm not knowledgeable as to what exactly fuel trims are but
When I read your post I was like, "fuel trims, my scan tool does that!"
For some reason looking at my scan tool I'm not finding any such thing.
Not really sure what I was thinking?

[TATE228]

years ago my dad had a 96' throwing a bunch of codes. The cat fell apart inside, somehow it would run fine cold when it got warm it would start to miss and eventually just die.

[straight6chevyguy]

Originally Posted by TATE228

years ago my dad had a 96' throwing a bunch of codes. The cat fell apart inside, somehow it would run fine cold when it got warm it would start to miss and eventually just die.

So I'm curious how was this resolved? Did you replace the cat?

[straight6chevyguy]

So here's the video...
The first minute or so engine is running ok then I hold it close to 2k rpm and after several seconds it starts misfiring.

https://m.youtube.com/watch?v=NhHTgc...ature=youtu.be

[chevyguyase]

It sure sounds like you have a clogged or restricted exhaust. When your converter came apart a piece may have came loose and and clogged your muffler/exhaust. If you can get a hold of a vacuum gauge (they are very inexpensive) hook into manifold vacuum, I prefer using the vacuum at brake booster hose if you have one. Watch the vacuum at idle and rev it up to about 2000 rpm if the vacuum readings start dropping off your exhaust system is highly suspect. You can also check for exhaust gas pressure by removing an 02 sensor and hooking up the vacuum/ fuel pressure gauge to the O2 bung hole. Running, the pressure should not be over 1/2 lb. Also leaving the Y pipe on and the 02s connected remove the rest of the exhaust and test it that way. Be aware that Cat. converters don't die, they are murdered, meaning something else caused the converter to fail. Rich mixture, spark plugs, wires. etc. Good luck.

[straight6chevyguy]

Thanks everyone for the comments so far.
I should have mentioned it sooner but my cat is bad, that is it was broken up inside and was rattling really bad. Yesterday I actually took the complete y pipe off and shook the rest of the cats contents out so it's gutted now. I actually started the truck with the exhaust off and it actually ran with just the open manifolds super loud lol.
Still misfiring though it seemed a little bit better but kinda hard to tell.

I will try to get the fuel trim numbers later to day.

[straight6chevyguy]

So I guess I should ask the question does anyone else think that the cat would be my problem? Does it need the cat for it to run right? I know very little to nothing about fuel injection engines. But I'm trying to learn lol

[straight6chevyguy]

So I just swapped the ignition coil/module from my 98 1500 on to this truck.
It still runs the same no change.

I guess that rules out the ignition module.

[straight6chevyguy]

So everything I have read so far leads me to believe the truck should run fine without the cat. Yes one can argue about performance and the check engine light and all that but from what I have came up with I don't think it would cause it to misfire. Unless someone can tell me otherwise. Also I do understand that a clogged cat will cause an issue but since my cat is now gutted that's out of the picture.

I'm gonna be posting a video of the truck running so you all can hear exactly what I'm dealing with.

[straight6chevyguy]

I have already disconnected the muffler.
In the video I posted it is running with just the y pipe and now gutted cat
So pretty much straight piped.
Thank you for the reply though.

[vince1]

I had a 90 that used to leave me stranded in intersections when the coil would quit but I got used to carrying a spare and one time got it swapped out before AAA arrived. I think I went through about 4 in close to 400k kms.
I suppose yours would have a different coil setup though.
Have you changed the fuel filter and spark plug wires?

[straight6chevyguy]

I have already tried the coil from my other truck. Didn't fix it.
Just today I tried some different plug wires still no change.
Have not changed fuel filter but fuel pressure readings seemed good. I may still change it anyway.

[straight6chevyguy]

Just remembered to post this...
I found it poking around... Screwdriver bit plugging off a vacuum line.
No clue where it plugs into...

Sorry the picture is sideways

[chevyguyase]

I think it goes to a vacuum reservoir. It is a round black ball looking thing about 6-7" in diameter that stores vacuum that your hvac system uses to open and close blend/defrost doors in the dash.

[straight6chevyguy]

So I'm reviving this old thread to see if anyone out there has any new suggestions. Quite some time ago I got fed up trying to figure out the trucks problem and parked it. And it's been sitting since. I'm thinking about tinkering with it again and hopping I can actually figure it out this time.
If anyone has any new advice please comment as I'm still as lost as when I started this thread.

[vince1]

I watch South Main Auto and Pine Hollow Diagnostics on Youtube. You might get ideas on how to diagnose your problem after watching some of their videos.
They are pretty good with those diagnostic scanners or whatever they are called.

[Dead Parrot]

Fresh Gas. For that matter, any chance that bad gas could have caused the original misfires?
Couple of old school suggestions:
Run it in a really dark place with all lights off and your eyes adjusted to the dark. Look for any ignition electrical juice escaping wires. Or any other sparks from a loose connection.
After a bit of running, pull the plugs and examine. If 1 or 2 look different then the rest, give everything about those cylinders a close look. Plus check the plugs for an obvious way lean or way rich condition.

Verify your voltage is proper. Computers really don't like out of range voltage.

[Grounded63]

How many miles are on it ?

[leegreen]

you said it had 50+PSI fuel pressure, but does it hold that pressure for 5 minutes after you turn the key off? The injector spider is a known source of leaks on 4.3

I'd also find out what your long term fuel trims are, they will indicate what the computer thinks is happening. If you scanner does not do it, get a Bluetooth OBD2 dongle off amazon and a copy of torque pro for your phone.

plugged cat sounds like too much fuel, if the computer is trying to trim lean but not getting there a leaking spider could be the culprit

[straight6chevyguy]

Thanks everyone for the comments.
The truck has been sitting a while and a few of the details are missing from my memory on everything I did and didn't check.
In the next couple or so days I will be looking at it again and I will post updates.
I believe fuel pressure was holding but my memory could be wrong. I will be rechecking that.
Can't remember the exact milage I think somewhere just below 200k. 180k Maybe?

[Grounded63]

At nearly 200k. I wouldn't be surprised if the distributor is just plain shot. Not necessarily cap, rotor, stator, module . . . But the actual body/shaft/bushings.

A loose timing chain can also cause erratic timing issues.