My Max at times struggles to maintain an idle .


Heres the deal.


I have seen it lop from near a 1000 RPM to idle low and stumble.In addition the injectors can be noisy and knock when it stumbles or so it sounds.


I hook up my Tech II and monitor data to see Injector command but yet when you scroll to Balance rate the will not scale.When the truck stumbles it will flash Injector balance rate and the are all over the place and out of GM spec.At the same time the FRPCV reading is bouncing up and down.Unfortunately I know longer have a complete Helms manual in my grasp to trouble shoot properly.


At other times ,normal idle ,the Balance rate is with in GM spec.


All of this is sporadic at best ,unable to duplicate at will ,snap shots will show probably in their eyes a Scan Tool malfunction. I haven't made contact with the dealer as I hate bringing it in.The thought of their grubby lil paws all over drives me insane not to mention I just had the nose repainted and Oh My God does it look sweet.


My last horror story with the Saab and a 15,000 mile service LED to grease smears all over the interior of a Leather off white interior front to back as they needed to fix rear arm rest. This isn't over yet two weeks later I'm still reeling pissed.


What controls the idle beyond FRPCV and Injectors? Will the FRPCV skew injector balance rates? Is it the FRPCV sticking and going south?Is it just ideling to low to show balance rates?


The lop tells me so but the stumbles and lack of idle and injector "knock" also makes me think injectors.


The FRPCV I can do myself in order to maintain my anal attention to preserve my trucks interior exterior appearance.


WTF is happening Diesel Gods???


Mac





I forgot to add if I bump it up to the third stage high idle for a minute or two or three ,it will settle down the idle to normal. I'm pretty sure it's the FRPCV valve sticking but I'm looking to rule out injectors,atleast till I get my first stone chip. http://www.dieselplace.com/forum/smileys/Embarrased.gif


Edited by: Mackin

Mac, first, you do have an 01 truck and that is the trouble year for the sticking FRPR.


As far as finding it, the best way to describe a faulty FRPR is it will have a fish bite idle. If you go to data display and engine data 1, (F0) click the soft key that says 'live plot' it will bring up a screen that lists the data to watch, no values. highlight and enter on the actual fuel rail pressure and desired fuel rail pressure, then plot it. The two lines should lay nearly on top of each other with maybe a little variance in the actual. you may have to reset the graphs to a smaller scale to see it well. I think I normally use 4000psi for the low side and 8000 psi for the high side. If the truck is acting up, this is the best time to do it. A faulty FRPR will show a shark tooth pattern on the actual side. Also you could look at your FRPR flow rate, this is found in fuel system data (F2). Watch your FRPR flow rate at idle, should be 600-1000. More then that and the regulator is seeing to much fuel. Usually high injector return is to blame for high numbers here. The LLY trucks run higher here.. usually in the 1400 range.


You also mention that the balance rates do not show. Anytime the truck is sitting at steady idle, meaning no throttle input, the injectors should balance. If it dont, then something is not letting it get to that point. If it runs bad enough, it wont balance as its too far of baseline. As for the knock, if you can catchit happening with the scanner hooked up, then go into output controls and fuel injector balance test. You can kill each cylinder in there. If you kill a cylinder and the knock goes away, you can about count that injector as junk. Also, killing one cylinder may smooth out the idle. Again, if that happens, that injector is junk.

Thanks Eric I'll see what I can find out. Think I may have to go to Tech II school,too. http://www.dieselplace.com/forum/smileys/Geek.gif


Maybe Geerhead can bring me to work on "Bring your kid to work day". Problem is I'm older,we look nothing a like,but we can pull it off.


I'm the red headed step child.


Mac http://www.dieselplace.com/forum/smileys/HiHi.gif