Stutter between 2500 and 3500 rpm

[Kittamaru]

My truck has recently developed a stutter... speed doesn't matter as much as engine RPM and pedal depth. When it stutters, if I push further down on the accelerator it gets worse, let up on it (but still accelerating) it gets slightly better. I think it could be running VERY rich... but I don't know.

 

I ran injector cleaner, recent oil change and a recent fuel filter change. Air filter is a K&N with only a few thousand miles on it.

 

Any ideas or info you'd need?

 

PS - when it passes 3k the power picks up, and after 3500 rpm the truck surges and the stutter disappears. It doesn't seem to happen at ALL when the truck is cold, and is more prevalent in 2nd and 3rd gear without OD/TC lockup.

[adamzan]

Check your o2 sensor. You can unplug and see if it runs better, it's on the passenger side of the engine bay. Mine had 2 white wires and 1 black. Common problem on older vehicles.

[Nismojunky]

thats your coolant temperature head sensor mine did that untill i unpluged it and replaced it

[Nismojunky]

heres where its located

 

http://z.about.com/d/autorepair/1/0/s/9/42331543.gif

[Kittamaru]

Would make sense - my engine seems very cold as of late and my heat sucks... heh. Thought it was just cause it's been cold as balls.

[Nismojunky]

accually it has nothing to do with the temperature is there a heavy smell of gas comming from the engine when this happends?

[Kittamaru]

Not always... but my truck has been smelling of fuel for a little while now (I know she's running a bit rich, but I haven't had time or money to get her serviced ) it's only recently started to stutter... could it be that running rich is clogging sommat?

[Kingman]

This is what mine did when the temp sensor already noted freaked out. It was telling the ECU it was in the antarctic, so whenever throttle was given, the ecu would DUMP gas into it, and flood it, causing it to sputter and what not. At higher RPM's, the engine could keep up, because naturally it was requiring more fuel. Think of it as the engine is idling, but the ECU thinks it's floored, so it's dumping way too much fuel in there.

 

Though this could be a multitude of things really, vacuum, ignition, fuel issues, LACK of fuel, too much fuel, o2 sensor (likely), MAF sensor, etc.

 

Also, what's the temperature outside? That's what threw the towel in on my sensor finally, being going from 68* to 35*

Edited December 11, 2008 by kingman92010

[Kittamaru]

This is what mine did when the temp sensor already noted freaked out. It was telling the ECU it was in the antarctic, so whenever throttle was given, the ecu would DUMP gas into it, and flood it, causing it to sputter and what not. At higher RPM's, the engine could keep up, because naturally it was requiring more fuel. Think of it as the engine is idling, but the ECU thinks it's floored, so it's dumping way too much fuel in there.

 

Though this could be a multitude of things really, vacuum, ignition, fuel issues, LACK of fuel, too much fuel, o2 sensor (likely), MAF sensor, etc.

 

Also, what's the temperature outside? That's what threw the towel in on my sensor finally, being going from 68* to 35*

 

 

Well, it dropped from approx 40 to around 10-20 for a few days... now it's back up to 40's again *rolls eyes* damn weather round here is crazy

[adamzan]

Things I would check:

 

-o2 sensor

-maf

-clogged catalytic converter (it made my stutter worse and smell of gas)

 

for the smell of gas, is it up front or in the rear, or at the tail pipe?

 

If its up front there are some fuel line hoses that have little screw clamps, check those and tighten them if need be. If it's in the rear, there is a seal on the top of the gas tank that leaks, even if you can see fuel dripping, it seeps out. If it's at the tailpipe, then you know its something with how its running, and not leaking.

[Kingman]

Well, it dropped from approx 40 to around 10-20 for a few days... now it's back up to 40's again *rolls eyes* damn weather round here is crazy

 

Did your truck start acting up before that or suddenly with the temp change?

[Kittamaru]

With the temp change.

 

And as for where the smell is - no clue. My nose is plugged pretty well due to a sinus infection... not sensitive enough atm to tell where, just that it's there.

[Kingman]

With the temp change.

 

Coincidental, or we're on on to something

[Kittamaru]

Dunno... there is a smell of gas for sure - is it possible to tweak the engine myself for the cold weather? Thing that worries me is, normally, my temp guage sits at about the 1/3 - 1/2 mark. As of late, it sits more around the 1/4 to 1/5th mark...

[Kingman]

Dunno... there is a smell of gas for sure - is it possible to tweak the engine myself for the cold weather? Thing that worries me is, normally, my temp guage sits at about the 1/3 - 1/2 mark. As of late, it sits more around the 1/4 to 1/5th mark...

 

Don't really know what would make the engine run colder, unless your guage is mis-reading. The temp sensor only deals with how much gas to give the engine.

 

As far as I know, there isn't anything electrical that deals with the engine temperature its self.

 

Oh, and it could be possible your choke is sticking a little because of the cold weather...

[Kittamaru]

Didn't think of that...

 

I think it's running way rich, so I'm guessing O2 or Temp sensor? Considering it's the ORIGINAL sensor from 18 years ago

Edited December 11, 2008 by Kittamaru

[adamzan]

kingman just remember his truck is MPFI not TBI, I don't know if that makes a difference. Kitt, just unplug the o2 and see if its better, if not plug it back in, then try the temp sensor. Trial and error my friend.

[Kittamaru]

*nods* I'll try that when I get home today

 

O2 is in the exhaust system - have any pictures handy? not gonna have long to look (it's pouring here)

Edited December 11, 2008 by Kittamaru

[adamzan]

You don't unplug it underneath, I don't have a photo handy, but I can tell you, its one of those 4 plugs near the power steering resevoir. There are 2 white and 1 black wire.

[Kittamaru]

rgr, will check - I'll be able to do it round 6

[Kittamaru]

I guess I'm not going to be able to look tonight - still raining like crazy, plus it's cold and windy now... god I wish I had a garage here...

[Kittamaru]

Redfinder, problem - I don't HAVE any plugs with 2 white and 1 black wire... o0; Not that I can see. I have 3 groups of plugs - two with 3 (one behind and one beside the steering fluid tank) and one near my throttle body.

 

Update - it ONLY happens when it's warmed up... and it's getting worse. Happens from 2k - 3,750k now...

 

Update #2 - I discovered the clamps holding the hoses onto my fuel filter were loose... so I tightened em up. no idea why that'd make a difference... but going to test it. There is a group of plugs near it covered in... something. Either thin oil or fuel or fuel and oil... don't know what. I dried them the best I could, tightened the clamps, and, as said, am going to test.

 

Also - I have a plug near my Throttle assembly that's got 2 wires going into it... the plug is busted beyond all hell and looks corroded. I'll get pics when my fiance gets home so Ic na use her camera (don't know how to use it tbh)

[adamzan]

That last one you mentioned could be part of the Throttle position sensor...

[Kittamaru]

I took the plug apart... the plastic is slightly melted and the metal (if that's what I'm looking at... it's that bad) is pretty fskced up on both sides of the connection...

 

Problem is... the truck runs EXACTLY the same with that plug disconnected... no CEL or anything... GAH!

 

What all can I safely start unplugging? the thing is, this doens't stutter at all when in park or neutral... just under load So I have to get out, drive it, let it warm up, and then see if the stutter is gone.

[adamzan]

If it only does it when warmed up, that would indicate a sensor most likely. This is because before it warms up the truck runs in open loop, which means its just doing what it can to keep the motor running. When it goes into closed loop it uses sensor input to adjust the air/fuel mixture.