Weird Engine Stumble

[fishsticks]

I'm throwing this out there to see if anyone has had a similar issue. I've had this problem twice now over the last 2 weeks. The first time I thought it was a fluke.

Start the truck from cold. Drive it and almost immediately it lacks power. Trying to give it more gas results in stumbling and popping from the exhaust. Can't seem to rev it over 2500ish RPM when in gear. Maybe 3000-3500 in park.

No codes are set, and the engine has no trouble holding idle when this happens. If I shut the truck off and restart it, the problem immediately goes away.


Checklist:

Plugs are <20K (They are not Delcos but this doesn't seem like a plug issue)
TB cleaned when plugs done. I've had it off again recently and it looked good. Will check again today.
Recent Thermostat
Recent Fuel Filter
Recent 02 sensor (it's a Bosch... maybe a lazy O2 sensor?)


I'm usually good at this stuff. The problem not setting a code, being fixed by restart, and being very intermittent have me stumped though. I'd rather fix it now than live through it a few more times before I figure out what it is.

Ideas?

[bartonmd]

Fixed by a restart = electronic...

Could be computer, or could be a connection issue causing the computer to see something that's not the case... Much like the computer sees a dead/disconnected coolant temp sensor as reading -40F, so it adds a bunch of fuel, and floods out on startup...

Still thinking...

Mike

[fishsticks]

Thinking out loud...


The last major thing I've changed on the truck is the body lift... this never happened before that.


I'll check for stretched wires later today.

[djthumper]

Which O2 sensor? If it is the front one that is where I suspect.

Just thinking as there is where I have had the most problem with that kind of stumbling.

[Regulator1175]

Interesting to hear this, I am experiencing similar issues. I have just chalked it up to cold starts and the fact that I have 225k miles. After a bit of warm up it seemed to go away. I am currently running through the list of potential fixes now, replaced the fuel filter, next up is O2 sensor, air filter, and plugs. I got a bit sidetracked with my trip to MI though, and my repairs got put on hold.

I will be looking forward to you finding a solution.

[fishsticks]

So far it's happened to me once more since I last posted.

I was driving down the road...so I simply popped it into neutral, shut off the truck and immediately restarted it... problem solved.

Seems like "resetting" the ECM by shutting the truck off fixes the problem. I'll probably go pick up a spare at the local scrap yard to add to the ever growing collection of spare parts I carry with me.

[Zero]

Did you try disconnecting your battery for a half hour, and let the pcm, ecm and bcm reset? Do you have someone near by that you can switch computers with? (I guess you would have to have access to HP tunners for that)

[BSalty]

That sounds like possibly a cat going out or a primary O2. I had a similar problem on another GM vehicle where the muffler was full of rust/gunk causing it to get too much back pressure but only intermittently.

[fishsticks]

That sounds like possibly a cat going out or a primary O2. I had a similar problem on another GM vehicle where the muffler was full of rust/gunk causing it to get too much back pressure but only intermittently.

Cat is new... so is the O2. I thought maybe the new O2 was lazy/defective but the problem is totally random and unrepeatable.

Going to pull the battery leads for awhile today. It's worth a shot. Right now it's an occasional annoyance... but I'd rather not end up with a big problem on the trail.

[BSalty]

You checked for the infamous Ex stuffed the potato in the tail pipe right?

Yeah if you got a new cat I would suspect a bad connection or a slow O2. If its only in cold start, do you have a tune done on your PCM? If your getting it in closed loop I would suggest looking at a scan tool to watch your IAT vs 02 readings.

[Zero]

Any chance a dirty cam shaft position sensor could cause this? I know it caused some rough idle issues for some people. A common problem is sludge buildup on the screen, it can be cleaned to help fix the problem.

[bgwolfpack]

Any chance a dirty cam shaft position sensor could cause this? I know it caused some rough idle issues for some people. A common problem is sludge buildup on the screen, it can be cleaned to help fix the problem.

Good info Z.

I had a intermittent miss in mine a while back and changed many parts until I found the culprit. It was in fact a bad cam shaft sensor. Although this doesn't really sound like the same miss. This sounds more like starvation than electrical.

2 cents

[fishsticks]

No signs of it for going on five days now...

My fuel purge valve is finally deciding to die though.... or maybe I just have a bad fuel cap.

[bgwolfpack]

No signs of it for going on five days now...

My fuel purge valve is finally deciding to die though.... or maybe I just have a bad fuel cap.

So it did throw a code? #?

[fishsticks]

Update.


It's gone. Hasn't happened since last time I posted about it.



CEL comes on now and then... then goes out after a couple starts... usually after I get gas. I'm 99% sure it's throwing an EVAP code, but since I bypassed the Class 2 adapter for my stereo, I haven't been able to scan the truck. There's a new one sitting on the dining room table, I just need to get off my butt and put it in.

I should probably by a new gas cap too...

[irishboy02]

Iv actually just started experiencing this within the past week as well. The temp is starting to drop so i have an auto start that i let warm the truck up before i get in. I typically will get in with water temp around 140 and trans temp around 55 (as per scangauge). When i start to drive i have a little hill i need to get up and i can feel the truck bog down around 2k-2500 and i can actually feel the truck shaking - similar to the feeling of not letting the clutch out if i was driving stick. I have 7k on this trans and now 37k on this motor. A new cat with all new 02 sensors and a new exhaust. K&N intake with a clean filter, however i do have a dirty throttle body - not terrible but its there. Have about 3k since my last oil change, ill be doing one more soon. Today i got in it at 158wt and 60TFT, put it into drive, hit the gas and my truck just completely stalled not moving me an inch. Yesterday I had the battery disconnected for about 25-30 min.

If i drive for a little bit it tends to go away but before the truck is at water temp 180+ and its typically between 2k and 2500.

Any takers?

[Trail X]

No codes?

My first thought was a bad sensor - but that should show in a code.

[irishboy02]

I have 2 codes- one is P0410 ( secondary air recirc - i disconnected this about 10 months ago ) and the other is P0528 ( circuit for fan clutch , my fan blades sheered the wires because they were not in the fan shroud properly)

These codes are both per scangauge.

[Trail X]

Your codes could possibly be masking another code. Some DTCs check to see if other DTCs are enabled before enabling itself -- although I don't see that the codes you posted mask anything per the diagnostic parameter sheet published on this site.

I can't imagine a dirty throttle body doing this, but might be a good place to start.

Will it die in neutral while revving the engine?

How old is your fuel pump?

[irishboy02]

Today was the first time it actually died, but then it started right back up. Iv had these codes for a while, but thats exactly what i thought that maybe it wasnt reading it right. Yesteday i disconnected for about 30min if not more and the system reset itself and is not showing any new ones. While in park or neutral i can rev it up to the comp limited 4k and hold it there with no issue. Its my OEM fuel pump so its at about 69k on it, but dont forget its a new motor(to my truck). Im thinking about doing a little fuel injector cleaner and new spark plugs since i did get the motor out of a junkyard.

I really cant figure this one out.