Misfire on idle after fixing code 42

[IsaakMooar]

Could easily be a valve-sealing problem.

Cranking compression test, perhaps a cylinder leakdown test. If you've got the leakdown tester connected, it'll be easy to find TDC #1 to verify the timing pointer/damper alignment.

So this could be the issue causing the miss?
Still confused on why it would run fine on base timing if it was a motor issue. Unless it not sealing so messing with the sensors?

 

[Schurkey]

Sure. It "could" be.

There's half-a-dozen things it "could" be. Test. Find out.

 

[Scooterwrench]

Start with ignition timing,I think it's too far advanced.

 

[Petey Mack]

I'm having a very similar issue with my 4.3 V6.
It will idle fine without a miss when the advance is unplugged. When it's plugged in it has a miss.
My issue goes forward to driving and missing enough to stall at a stop light.
In the last 3 months I already went through the laundry list with new parts(IAC, MAP, Coil, Distributor, Control module, wires 2 times, plugs 3 times, distributor caps/rotors,
Temperature sender/temperature switch/pigtails on each).

Plugs are even and evenly clean
Maybe too clean.
I can't see the TDC with timing lights(tried 2) when it's running.
If it's not running perfect by Friday it's for sale.
Thanks for any help!
Pete.

 

[Petey Mack]

I'm fed up with it all. Please send any info. I'm posting it for sale next Friday, August 11 if I don't have it perfect again.
When it's perfect, you would never know it's a V6 because it accellerates effortlessly and cruises at 75 MPH getting 19 MPH with the A/C on full blast.
I bought it from my best friend, he bought it new.
It's never seen snow or salt.
I've owned it for the last 15 years and it's not a work truck, it's a go around truck.
NO RUST! None. A/C, power doorlocks and bench seat. Everything works.
Trailer package.
The pictures say it all.
The one dent was done by someone texting going 15 miles an hour into my right bumper/fender.
The only paint you see that is not original is the passenger side door where I rubbed a low pole backing out of a parking spot.
Every inch you see is original paint other than that.
I'm near LAX/Santa Monica area in CA.
Without this frigging miss, it'll drive across the country without a problem.
New Goodyear A/T tires 2 months old.

I'd rather fix and keep it but I'm fed up.
Thanks!
Pete.

 

[Schurkey]

I'm having a very similar issue with my 4.3 V6.
It will idle fine without a miss when the advance is unplugged. When it's plugged in it has a miss.
My issue goes forward to driving and missing enough to stall at a stop light.
In the last 3 months I already went through the laundry list with new parts(IAC, MAP, Coil, Distributor, Control module, wires 2 times, plugs 3 times, distributor caps/rotors,
Temperature sender/temperature switch/pigtails on each).

WHAT YEAR? WHAT VEHICLE?

What is the fuel pressure at idle, and under load? When it's acting up? How old is the fuel filter?

What does the magnet on the distributor shaft look like? TBI distributors are infamous for cracked magnets.

Connect a scan tool, find out what the computer wants you to know. Codes "can" be helpful, the real diagnostic power is in the data stream and bi-directional control.

I can't see the TDC with timing lights(tried 2) when it's running.

How can you verify initial ignition timing then? You NEED to verify ignition timing.

WHY is it that you "can't see the TDC..."? Do the timing lights not flash? Do you not know where to point 'em? Missing timing pointer? Something else?

If it's not running perfect by Friday it's for sale.

I'm fed up with it all. Please send any info. I'm posting it for sale next Friday, August 11 if I don't have it perfect again.

Threaten it. That's sure to help.

The pictures say it all.

They say it's a TBI, which narrows down the year range.

 

[Scooterwrench]

Nice clean,solid truck. I'd fix it. Maybe pay a good mechanic to figure it out.

 

[Petey Mack]

So this could be the issue causing the miss?
Still confused on why it would run fine on base timing if it was a motor issue. Unless it not sealing so messing with the sensors?

Thanks for the reply, I'm just figuring out responding and using the forum. It's a 94' Chevy C1500, 4.3 V6, automatic.
Started out a year ago with hard starting when cold(Not really cold at 60 deg. at the lowest.
It progressed to lackluster accelleration in the midrange to falling on it's face during anything other than moderate pedal into it.
Changed the basics(Plugs/Cap/Rotor) with no change.
Plugs looked good BUT number 1 was almost too easy to remove. Loose in my mind.
No good results or changes.
Then I pulled out the parts cannon.
IAC, TPS, MAP, Temp sensors, EGR, O2 sensor, pigtails for all with the exception of the IAC.
2 years ago, rebuilt the TBI with new injectors just to do it. Overmaintain it.
The IAC...
If I unplug it while idling, nothing changes by even a hair.
The resistance measured on the bench is 52-54 ohms.
Never checked the pigtails going to the new IAC. for power/resistance or however you check it.
Changed the Distributor. No start. Crappy distributor now I found out the hard way (A junk Amazon "MOSTPLUS" brand).
No start, I had to change the ignition module from the get go to get it to start.

Had the shroud off as well as the fan to easily get into the engine bay.
I could time it at that time because the timing mark wasn't crowded with the fan or shroud in the way.
FYI, the truck won't overheat in 65 deg. weather without the fan installed which seems odd.
It closes loop at 195 when the thermostat opens and never got hot unless it's 90 deg. out with the AC on at a stop light with the fan/shroud installed.
I check temps with infrared temp gun on the thermostat housing as well as the instrument on the dash.
With the ignition advance wire unplugged I kind of got it TDC zero deg. advance.
Timing mark jumping around and never steady.
This is why I say "kind of" hit 0 deg. advance.
It's not idling consistent and missing so it's not steady by a long shot.

Changed the rotor for the 4th time in 3 months and the cap is #3 just to be certain.

Another thing;
I had an IAC. code a couple of years ago and changed it.
Solved the code issue.
Changed it again when it started running bad.

I'll check fuel pressure(filter is 2 month old and the one before that was a year ago).
No fuel leaks or smell.
Fuel pump in the tank is 10+ years old.

Never checked compression because plugs are always dead even light brown.
I change the Plugs/wires/cap/rotor every season.
I gap the plugs at .035 per Factory specs.
All ACDELCO maintenance parts.
I'm on timing light #2 just to confirm it's not the light missing the mark.
Forgot;
It idles and starts better with the ignition advance wire unplugged.
Still a miss at idle and it's inconsistent not on the same beat.
Exhaust is rich.
I removed the Cat a long time ago.
This was a long reply but everytime I look at that old boy, I remember it running 100% top notch just back in Feb!
I mean top notch.

Thanks for reading all of this!!!
Pete.

 

[Schurkey]

Check fuel pressure.

Connect a scan tool, look for "codes" and review the data stream. Verify EVERY sensor including the O2 sensor when it gets hot enough.

 

[Scooterwrench]

You say it ran good in Feb.,when did you change the dist.? You said you had to change the Ign. module to get it to fire up,have you changed the dist. since?
Is the timing bouncing around with the base timing connector unplugged?
Lot of new junk parts being sold right now,you get what you pay for and even then just because you're paying for a quality part doesn't mean you'll get one.