Studder/cutting out on heavy gas pedal

[Zhowardfzj80]

Alright I've read more than I can imagine the last 2 weeks on this issue. Tried many of the tips and help from what I've read. Issue still exists.

The two noticeable symptoms are cutting out on heavy acceleration, and a quick jerk while at stop lights or at a stop/not rolling or accelerating (like just in my drieway or parking lot) and rpm drop of only 100 or so rpm very quickly when it's in drive or reverse. The rpm drop is very quick, drops for a millisecond and right back to normal rpm. It's almost a jerk, entire truck shakes but it's very quick. And it will do it randomly. No consistency to it and might go 1 or 2 minutes without doing it at all, but then it might do it 4 or 5 times in 20 seconds. In park or neutral it does not it at all. Idles perfect. So far I've done this list of stuff.

Spark plugs
Plug Wires
Distributor cap
Rotor
Fuel filter
Found couple vacuum hoses off (someone said it likely clogged my catalytic converter??)
Cleaned butterfly valve
seafoam in gas tank and vacuum line at brake booster.

 

[Zhowardfzj80]

Alright I've read more than I can imagine the last 2 weeks on this issue. Tried many of the tips and help from what I've read. Issue still exists.

The two noticeable symptoms are cutting out on heavy acceleration, and a quick jerk while at stop lights or at a stop/not rolling or accelerating (like just in my drieway or parking lot) and rpm drop of only 100 or so rpm very quickly when it's in drive or reverse. The rpm drop is very quick, drops for a millisecond and right back to normal rpm. It's almost a jerk, entire truck shakes but it's very quick. And it will do it randomly. No consistency to it and might go 1 or 2 minutes without doing it at all, but then it might do it 4 or 5 times in 20 seconds. In park or neutral it does not it at all. Idles perfect. So far I've done this list of stuff.

Spark plugs
Plug Wires
Distributor cap
Rotor
Fuel filter
Found couple vacuum hoses off (someone said it likely clogged my catalytic converter??)
Cleaned butterfly valve
seafoam in gas tank and vacuum line at brake booster.

Also want to explain at times when I'm accelerating it has no symptoms. Like it is great. It's all so random and at different speeds. The 02 sensors are very rusty and I don't even think I could have them changed. They look like they would snap off and break out of the pipe. They are not thread in style they look like they have two post studs to mount look in terrible shape.

 

[BILT4ME]

Alright I've read more than I can imagine the last 2 weeks on this issue. Tried many of the tips and help from what I've read. Issue still exists.

The two noticeable symptoms are cutting out on heavy acceleration, and a quick jerk while at stop lights or at a stop/not rolling or accelerating (like just in my drieway or parking lot) and rpm drop of only 100 or so rpm very quickly when it's in drive or reverse. The rpm drop is very quick, drops for a millisecond and right back to normal rpm. It's almost a jerk, entire truck shakes but it's very quick. And it will do it randomly. No consistency to it and might go 1 or 2 minutes without doing it at all, but then it might do it 4 or 5 times in 20 seconds. In park or neutral it does not it at all. Idles perfect. So far I've done this list of stuff.

Spark plugs
Plug Wires
Distributor cap
Rotor
Fuel filter
Found couple vacuum hoses off (someone said it likely clogged my catalytic converter??)
Cleaned butterfly valve
seafoam in gas tank and vacuum line at brake booster.

The description of symptoms points to electrical issues.

Could be a wire grounding out or a poor connection.

Could be a bad ground at the coil.

What brand of Cap/rotor/wires/plugs did you use?

These are sometimes finicky and don't like aftermarket parts.

Wiggle the plug connection on top of the distributor cap.

No, it didn't clog your cats.

Did the proablems happen pre-Seafoam?

 

[SmokingRocks]

Yea I agree with electrical. Does it happen when the rig has gone through water? Rain etc?

 

[SmokingRocks]

also download your factory service manual from the link in my description. It'll help you deal with whatever this issue is.

 

[Zhowardfzj80]

The description of symptoms points to electrical issues.

Could be a wire grounding out or a poor connection.

Could be a bad ground at the coil.

What brand of Cap/rotor/wires/plugs did you use?

These are sometimes finicky and don't like aftermarket parts.

Wiggle the plug connection on top of the distributor cap.

No, it didn't clog your cats.

Did the proablems happen pre-Seafoam?

Ngk plugs, blue wires and not sure on cap and rotor. Happened way after seafoam. Like maybe multiple months. Even after the plugs wires etc were changed it was a week before issue started. And at first....it was just the 100rpm pulse. It wasn't cutting out at all. Then multiple weeks after that the cutting out and studdering started then.

 

[Zhowardfzj80]

Yea I agree with electrical. Does it happen when the rig has gone through water? Rain etc?

Doesn't matter rain or shine. Also, usually doesn't happen right away after a cold start. Almost seems like it needs to warm up slightly first.

 

[BILT4ME]

Ngk plugs, blue wires and not sure on cap and rotor. Happened way after seafoam. Like maybe multiple months. Even after the plugs wires etc were changed it was a week before issue started. And at first....it was just the 100rpm pulse. It wasn't cutting out at all. Then multiple weeks after that the cutting out and studdering started then.

I would be willing to bet you have a plug wire or three shorting out while running. They could be crossing to each other or to the head.

Run the engine up to temp, remove the spark plug loom cover, take it someplace VERY dark and let it run when you open the hood and look for the light show. That is a quick easy way to tell. Don't stick your hand in the fan.

 

[ZackR]

What happens when you run it with the 02 sensors disconnected?

My ancient 02 sensors caused a handful of drivability issues like you are describing, hesitation when slightly warm but not cold, etc..

Once disconnected (during troubleshooting) the CEL came on (as expected) but it ran much better. New 02 sensors solved the issue in my case.

 

[Zhowardfzj80]

What happens when you run it with the 02 sensors disconnected?

My ancient 02 sensors caused a handful of drivability issues like you are describing, hesitation when slightly warm but not cold, etc..

Once disconnected (during troubleshooting) the CEL came on (as expected) but it ran much better. New 02 sensors solved the issue in my case.

My CEL is already on but the 02 sensors look so bad of shape I'm afraid they'd snap off. Maybe I should try it still. What could it hurt?

 

[ZackR]

What codes does the CEL show?

 

[SmokingRocks]

Nvm I was thinking this was a different RTH thread

 

[Zhowardfzj80]

So to this point I have done the list of stuff listed on my original post comment, and now have replaced the intake hose with new, added 2 missing vacuum lines to the vacuum modulator, found a loose ground wire (cleaned and tightened) rechecked my D-cap and just ordered my oem o2 sensors. If the o2 sensors don't help the situation I believe I'm going to have to tear in to the intake and IAC for cleaning/replacing.

 

[Malleus]

Cleaning the IAC is free. Just takes time.

 

[Zhowardfzj80]

Cleaning the IAC is free. Just takes time.

Yea having trouble removing the bottom Phillips screw

 

[Malleus]

Yea having trouble removing the bottom Phillips screw

You have to remove the throttle body, first. Or, you can use very small vise grip pliers and replace the screw.

I had to do both.

 

[Zhowardfzj80]

You have to remove the throttle body, first. Or, you can use very small vise grip pliers and replace the screw.

What year is the LC you have?

 

[Halfpint]

did you wiggle the intake tube? mine would stutter too on heavy wot- bc the tube was flexing more on acceleration and it was worse in reverse.

 

[SmokingRocks]

IAC wouldn't cause issues at heavy throttle. I suspect there's a wiring issue, possibly injector wiring. I'd probably break out my oscilloscope and start dataloging the injectors during a pull.

I had a similar situation documented here: Calling all you Diagnostic Gurus

 

[ozarkmud]

I'm suspecting your fuel filter or fuel pump sock is clogged. Would explain the heavy throttle and make sense after Seafoam in the gas tank, if it lifted up a bunch of debris.

If you managed to get a fuel pressure monitor setup, it could help debug this.