stumble/hesitation on 2005 6.0 gas motor

Chuckman

Chuckman

Well-Known Member
Joined
Oct 9, 2005
Location
Huntersville
so after running the old gal REALLY hard at extended RPMs last time we went and had fun, cranked her up yesterday and runs great then stumbles hard on acceleration

edit; for awhile, its been back firing upon deceleration but until now no stumble

what I got:
cable pull TB
front 02's only
no codes set
nothing cleaned / cleared yet.

where to start?

intake gasket leak?
TB gunked up?
 
Last edited:
You could start by checking the intake gaskets and cleaning the throttle body...couldn't hurt. I'm kinda leaning towards a misfire from a bad coil pack or perhaps a fuel issue.
 
I'll check fuel sat. how do I check gaskets unless I completely remove them? never really had good luck with the propane trick. what exactly are we cleaning in the TB and how?
 
I have a random misfire on my truck from time to time. Same motor as yours. I think mine just needs a general tune up, but from what I have read the fuel pump is common to start going bad and lose pressure. Apparently these engines need 55+PSI. Check the fuel pressure at idle and at WOT.

Also, take what I say with a grain of salt. I’ve only had my truck for a month and been researching a lot, just sharing what I read elsewhere.
 
Spray some carb cleaner down the sides of the intake, it'll let you know if they're leaking...but if they were bad enough, it would have codes set for Bank 1 & Bank 2 too lean. If you pull the throttle body off, you'll see the oil build up inside the bore where the IAC motor goes. Unbolt it and spray some cleaner all up in there and you can even clean the plunger on the IAC while you're at it. If nothing else, that'll help it idle a little better. I'd check the fuel pressure for Ss&Gs.

If you haven't done it within the last few years, plugs and wires would be good. I usually go ahead and fork over a few bucks and get the 8.5mm MSD wires and some eBay special heat socks to cover the plug boots. NGK or Delco plugs only for me. I've had factory sized wires crap out on me after a year or two and all of the random misfires I've had have never set a code, but with some RPMs/good load on the motor OR cruising at like 70mph I could feel it every 10 seconds or so. I kept after it until I tracked down the offending coil pack and replaced it.

I think you can check them with a multimeter...they should register so many ohms from this pin to that pin or something...I had to look it up last time I did it.
 
this is a fall on your face stumble, not a misfire
 
Ahhhh...then yeah, check the fuel pressure.
 
just FYI IIRC this is the corvette filter setup, with only a pressure line to the motor, the return is in the filter right at the tank
 
fuel pressure at idle is 55 or so. revved it a little and it didnt drop. replacing the filter in the AM.
so far. removed mass air flow and cleaned, removed TB stripped and cleaned, intake removed and inspected. nothing apparently bad/broken/leaking.
bummer. after I get manifold and filter changed, then time to start in on the injectors/wires/coils etc. any good advice as to where to look how to troubleshoot?
 
I fixed my 6.0 with a crank position sensor. Thought it was the transmission at first but it was a whole lot of miss fires.
 
I'd be interested to see fuel trims, calculated load, maf values, and oxygen sensor values at idle, under load, and snap throttle.

Sent from my SM-G955U using Tapatalk
 
got fuel filter changed. still 50 psi max. looking for a pump now.
 
update.
new fuel pump and filter. holds 65+ at idle. still stumbles. still no codes. after warm up Im getting
+19 degrees timing, 0.449 v at 02's, 38 kPa MAP, 1.2 MAF at 571 RPM

how does one go about checking for injectors no good?
 
Chuckman said:
update.
new fuel pump and filter. holds 65+ at idle. still stumbles. still no codes. after warm up Im getting
+19 degrees timing, 0.449 v at 02's, 38 kPa MAP, 1.2 MAF at 571 RPM

how does one go about checking for injectors no good?
Click to expand...

Are the o2s switching? Or stuck at .449? 1.2 g/s or lb/min. If its g/s that's extremely low, you've either got air entering the engine behind the maf or a bad maf. 11.2inhg of manifold vacuum is also low, what condition was that reading under? Does it use the map to calculate baro? Under WOT what are oxygen sensors doing? What is ltft at the RPM the stumble occurs?

Sent from my SM-G955U using Tapatalk
 
I'll have to check again later on O2's and WOT.

1.2 lbs/min MAF

this is a stock 6.0 2005 motor with only rear 02's deleted by Jims performance. No tune and all stock parts. data gathered at idle after heated up.
as mentioned before, properly cleaned TB (cable pull) and MAF and new intake gaskets. Not to say that any or all of it was bad or not still bad.
 
Chuckman said:
I'll have to check again later on O2's and WOT.

1.2 lbs/min MAF

this is a stock 6.0 2005 motor with only rear 02's deleted by Jims performance. No tune and all stock parts. data gathered at idle after heated up.
as mentioned before, properly cleaned TB (cable pull) and MAF and new intake gaskets. Not to say that any or all of it was bad or not still bad.
Click to expand...
Retake the readings while the stumble is occurring that should give better information!

Sent from my SM-G955U using Tapatalk
 
gotcha. just crazy storm today and no top on this ride.
 
ok went out and stuck my foot in it.
data looks weird.

fuel trims steady at 0 - all the time
calculated load is 3% constant
02s vary 0.440 to .455 or so

it runs great at WOT but getting there and under load at 40mph and 4th gear its not happy
 
Last edited:
Chuckman said:
ok went out and stuck my foot in it.
data looks weird.

fuel trims steady at 0 - all the time
calculated load is 3% constant
02s vary 0.440 to .455 or so

it runs great at WOT but getting there and under load at 40mph and 4th gear its not happy
Click to expand...
If load isn't increasing that's certainly odd - fuel trims rarely sit at 0 and oxygen sensor movement should have a much wider "swing". What tool are you using to record the data?

Sent from my SM-G955U using Tapatalk
 
O2s should be switching above and below that .450 constantly between .1 and .9v Fuel trims will go to 0 when in power enrichment, which in that truck is most likely above 90% throttle, otherwise the LTFTs should be moving around +- 10 ish
 
Back
Top