the misfire continues! any ideas?

[bama16]

I had/have what seems to be a standard 3.4 misfire or stumble. I am not getting any CEL, plugs checked, plug wires replaced, and coilpack resistance checked and within spec.

The car starts and runs fine on startup, once it warms up a bit the misfire begins.

It will drive fine when not under heavy load. No miss if a gently roll onto the throttle and will rev to 6000 without miss.

car sputters in the mid rpm range ~2000-4500 and then clears up from there

car misfires initially when opening throttle body from the engine and then smooths out. after the initial stumble at tb opening, it smooths out.

any ideas on what may be causing this? The three injectors on the passenger side are ticking, i can't get the the driver side while running.

thank you for any help...it's driving me crazy!

 

[giovannie23]

I would check the throttle body sensor
See if that helps

 

[Philz]

Had same issue also miss feel in cold weather warmup.
New o2 sensor helped lots but TPS sensor was the main culprit.
I replaced sensor problem solved for very little $$

OEM Part check model year compatibility
http://www.amazon.com/gp/product/B00736D76S/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

.

 

[wc11]

Happened to me 2 summers back and it was injector #2.
Truck almost sounded like a Subaru

 

[Que]

had same problem recently. turned out to be #6 injector.

 

[jstim]

I just recently had cylinder 6 misfiring. I replaced the plugs, wires, cleaned the throttle body, replaced the idle air control valve, and the PCV valve. I did all the extra because after I replaced the plugs and wires it was still a little wonky. I would look into some of that as well, but if it IS an injector....good luck my friend.

 

[bama16]

thanks all...i really wish it would throw a CEL. I have 6 injectors on the way. i'm going to replace and go from there. i hate throwin money at it, but i figure while i'm pulling it apart i will just go ahead and replace.

 

[vipergrhd]

Crankshaft bolt

It may not be even related but it would be a good idea to check torque on the Crank bolt (210 Ft lbs i think) hope you find the true culprit soon.

 

[absalom]

If you get sick of throwing money at it, I got a cherry motor for you

 

[Paperjam]

This can also be caused by a restricted fuel filter or fuel pump believe it or not. A stumble under sudden load changes may be indicative of that. You could hook up a scanner and check your fuel trims while the stumble happens, or throw a fuel pressure guage on it while running. See if it dips below 30psi (spec is about 42), you can also do a fuel volume test, Google that one. But if she stalls you aren't getting enough volume.

Fuel pumps don't often go on our trucks, but they do get tired and provide less than ideal volume. A restricted fuel filter too, it's a Maintenence item everyone seems to forget about.

 

[BrianSD_42]

It seems very odd that you don't have a CEL.

Does the CEL bulb work? When you turn the key it should light up before starting the engine.

Misfire and power loss but no codes ..... Hmmmm?

 

[96LTDrus]

Happened to me 2 summers back and it was injector #2.
Truck almost sounded like a Subaru

I had the exact same issues, also with injector #2. Truck would cut out a little at times, then straight up died as I was driving on the highway.

 

[gamefreakgc]

Sometimes when there's no codes, it's a sensor being wonky because it's the ECU itself causing the miss by cutting fuel back or retarding timing. I know you already ordered your injectors, but it would not hurt to also test the TPS, MAF and other keys sensors (O2 even).

 

[bama16]

This can also be caused by a restricted fuel filter or fuel pump believe it or not. A stumble under sudden load changes may be indicative of that. You could hook up a scanner and check your fuel trims while the stumble happens, or throw a fuel pressure guage on it while running. See if it dips below 30psi (spec is about 42), you can also do a fuel volume test, Google that one. But if she stalls you aren't getting enough volume.

Fuel pumps don't often go on our trucks, but they do get tired and provide less than ideal volume. A restricted fuel filter too, it's a Maintenence item everyone seems to forget about.

I forgot to mention I replaced the fuel filter. I did get a couple a backfires in the intake while driving. which leads to me believe it's a lean fuel condition

It seems very odd that you don't have a CEL.

Does the CEL bulb work? When you turn the key it should light up before starting the engine.

Misfire and power loss but no codes ..... Hmmmm?

I pulled the plug on the TPS just to see if there was a difference. The CEL came on, but went off when i plugged it back in.

Sometimes when there's no codes, it's a sensor being wonky because it's the ECU itself causing the miss by cutting fuel back or retarding timing. I know you already ordered your injectors, but it would not hurt to also test the TPS, MAF and other keys sensors (O2 even).

I cleaned the MAF, but didn't change. I debated on the TPS, but it doesn't miss under light load, but miss as the same throttle position under heavy load. I have valve cover gaskets going in at the same time as the injectors. If these don't change it i'll just chalk it up to peace of mind with new parts under the manifold.

Thanks you everyone for the help!