Randomly goes lean, off idle, cruising, boost

[boosteds10]

Not sure whats going on but my truck randomly goes lean. Almost every time sitting idle i give it a tiny bit of gas, it hesitates, goes lean and then goes back to normal and drives fine. Cruising around it randomly goes lean, also when slowing down for a stop.

Idk whats going on. This is on the stock chip and two bar, not using the ostrich in my sig, thought that could be the case and I took everything out but its still there.

What gives?

 

[WyoSyclone]

Re: Randomly goes lean, off idle, cruising, boost

Have you checked all of your vacuum lines? The MAP and FPR are tied into the tee off of the rear of the plenum. Vacuum leaks can cause a variety of issues.

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

ill take at look at it in the light tomorrow....I did the bike tube test a few days ago and found the TB was leaking. I got that rebuilt and its better now....doesnt leak down as fast. is it supposed to stay pressurized for a while or just for a little bit?

 

[WyoSyclone]

Re: Randomly goes lean, off idle, cruising, boost

ill take at look at it in the light tomorrow....I did the bike tube test a few days ago and found the TB was leaking. I got that rebuilt and its better now....doesnt leak down as fast. is it supposed to stay pressurized for a while or just for a little bit?

I'm not real sure how fast it is supposed to bleed down... you'll get leakage past any open valve anyway... the important thing is to listen for leaks, and/or spray things down with soapy water and look for bubbles.

...Just thinking out loud.....with the check valves in place in the vacuum lines we really aren't doing a valid test are we??? We're testing pressure, which is stopped by the check valves. When we go into vacuum the check valves open - the leak could be on the other side of the check valve. Correct?

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

very true....could just spray around the intake or those check valves when idling tho and see if the idle raises. Idk I dont think its a vacuum leak..i went over all of it several times and sprayed around the intake

 

[Don W.]

Re: Randomly goes lean, off idle, cruising, boost

Mine does this also. Although not as bad. What's interesting is I can sorta change it by changing base FP. Are you using the PLX to drive the narrow band to the ECM?

I wish I had two 02 holes in the DP, one for the stock o2 and one for the PLX. I sometimes wonder if the PLX reacts slow on the narrow band side. This winter I think I'll weld in another hole and put back the stock o2.

Just thinkin' out loud...

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

yeaup I am using the plx to drive the stock narrowband signal...I had the issie before the PLX install...I thought my O2 sensor was going out...and i was planning on the wideband anyway

 

[WyoSyclone]

Re: Randomly goes lean, off idle, cruising, boost

I guess it could be an IAC hanging up and not following the ECM's outputs, or a clogged orifice.

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

IAC is brand new, Im gonna screw with the fuel pressure a little bit to see if it makes it change at all...maybe its similar to Dons

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

Ok so I went out and checked for vac leak, cant find any. The base fuel pressure is 38psi. I went out and took a video of my A/F gauge. If you check it out when i give it a little throttle it goes lean, if I push it a little more its normal. Once I left off it stays rich for a few seconds then goes back to its normal spot.

This video is all at idle.

http://media.putfile.com/Typhoon-Fuel-Problem

I went out and at half throttle it doesnt break up under boost but at full throttle it breaks up.

Maybe run some injector cleaner through it? think of could be getting stuck or opening and closing slow?

 

[Don W.]

Re: Randomly goes lean, off idle, cruising, boost

At idle that's what mine does just not as bad. As to a cause I'm baffled. But like I mentioned, I can control it a bit with fuel pressure. Also I don't have cutout issues once I'm off idle. Whither cruising or FT mine runs pretty good. It's just does this little dance at idle. It's worse on a cold start BTW. If I don't touch the throttle on a cold start it will prolly die once or twice, if not it comes very close.

Sorry none of that is much help... If you figure it out let me know.

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

Don, you are right about the cold start it wants to die at first without even touching the throttle....once its warmed it gets better but its still pretty much undrivable. I'm going to run some injector cleaner through it and see what happens. I have no clue what else to do. Im baffled myself.

The only thing that was changed from when it ran good untill now was that I heat wrapped the downpipe and put a turbo blanket on it. After a few days of runnin fine like that the O2 sensor started freakin out on me and makin the truck run like shit. At a stop the O2 mV would drop down to 4.4 and then upon givin it some gas it would stumble a bit and the quickly jump up to 600mV and climb from there. Now at the lowest the plx is readin 100mV narrowband so I assume that it is ok. Would a half clogged cat give me intermittent problems? My silverado had issues like this and then just one day finally gave out. clogged cats.

Very frustrating, out of the whole time I have owned the truck ive only been able to keep it running and enjoy it for 5% of the time.

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

I put the ostrich back in and used a 33lb $59 starter bin. Now the thing idles perfect but still does the same stuff when i give it some gas and still breaks up a bit in high boost.

I watched today though and when I feel it break up above 10psi the tach is steady and doesnt jump around or anything. If im cruising around like half throttle in 5psi of boost it feels perfect. So awkward that its only touchy in some spots and not others and the fact that the two areas that are the worst are on the complete opposite ends of the spectrum, right off idle and anything over 10psi.

Could extra heat kill anything in the exhaust? Truck has a crappy flowmaster ive been meaning to get rid of. This all started happeneing shortly after the DP wrap and turbo blanket.

 

[Don W.]

Re: Randomly goes lean, off idle, cruising, boost

Ya might trash the Flowmaster. To my knowledge they don't make a straight through muffler which, IMHO, any turbo vech should have. I like Flowmaster most of the time, they're even made here, but I don't think they're good for our trucks. Any back pressure is gonna raise heck with WOT performance. The there's the cat issue which you've mentioned. I have a 3" on mine, and I have a source for "racing" cats if I can find it.:rotf:

 

[WyoSyclone]

Re: Randomly goes lean, off idle, cruising, boost

Run it through Autotune a few times and you'll probably be on your way to a pretty good tune.... That off idle/low rpm stuff was what I had to deal with when I started on my 40lb BIN.... 4 or 5 logging sessions later it was totally drivable. Then you need to set your boost/fuel grade target and work on tuning for boost and timing.

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

I ran through 3 autotunes, eac time gettin like 10,000 datapoints....didnt seem to do anything. Im gonna take the catback off later today and do a quick drive and see if that helps a bit. I know Autotune is where its at and will be using that once this little issue gets resolved because I dont think its a tuning thing.

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

......aaaaaand the starter is actin up and probly on its way out :rant: :tdown: :roll:

umm yeah.. maybe ill spring for a test pipe and do some other stuff while im at it. Ill revisit this thread once everything is good to go again

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

Ditched the muffler for a straight pipe....sounds cooler but still no change. Then i went to go pull all the plugs i had just put on a month ago. Two of the boot wires looked like they were dry rotted and were cracking and chunking off all over the place. I swapped in a new set of wires and the truck was perfect for ten minutes and now its back to its old off idle hesitant self.

The only good thing is im not having the higer end stumble anymore.

 

[Don W.]

Re: Randomly goes lean, off idle, cruising, boost

If it's JUST a slight hesitation right off idle, like mine, I stopped worrying about it. For one thing I rarely operate right there. Mine, for example, just skips a couple of cyls and then continues to run normally. Part of my problem, if that's the correct word, is my Sy is the only one I've ever driven so I have no real comparison. Glad to hear the stumble is gone, now you can work on the tune.

 

[boosteds10]

Re: Randomly goes lean, off idle, cruising, boost

Don im pretty sure mine is exactly like yours and the plug wires were just making it worse. Did some more autotunes tonight and by the end I was cruisin down the highway at 25% throttle 10psi like a dream. You are right about the hesitation though, just give it a little more gas and you are through the hesitation almost instantly.

If I ever figure out wth it is ill be sure to report back

Thanks buddy