hey guys, i think i used to belong to this site ....... if ls1tech used to have a truck room, think i used to be ETC ... anyway.

i have three codes ;

p0102 - maf low input

p0443- EVAP purge valve

p0449- EVAP vent valve

truck- 02 chevy 1500hd 4x4 , 6.0 with whipple compressor, 8.1 marine inj's, nelson tune. 88k miles

basically these codes all hit a couple weeks ago on the highway doing about 80. the truck seemed to jump out of gear for a second and then right back, codes set immediately. cleared itself on the drive home then did it again [gear thing] taking off from a light. now if i clear the code it resets right away.

car idles fine and runs fine, seems to shift hard when the light is on [harder than normal, i have the shift firmness bumped]. showing stable 19 psi vacuum at idle.

cleaned the maf, checked the plug, checked the wire/ route, seems fine. still get the code. might need a new maf but, not sure if it's related to the other two codes so.........

checked the lines for the EVAP system, all are in good shape, disconnected blew air through them, all clear. no obvious leaks [don't have smoke machine]. pressurized canister, seems to hold pressure. plugs at both solonoid and vent valve are connected. solonoid on manifold has some voltage when idleing but it is very low. swapped the gas cap with one from another car that doesn't have any issues- didn't help.

wondering if anyone has had this issue and what the culprit was.

as far as the EVAP my guess's are:

purge solonoid

vent valve

tank pressure sensor

line leak i can't locate.

MAF ;

if not related to the other codes i guess i need a new one, don't have an ocilloscope so the only tests i can do are voltage and resistance [going to try that tomorrow]. also going to see if my efi live program still works and if that helps pinpoint anything.

if anyone has any thoughts before i either break down and go to a shop or start throwing parts at it, i'd appreciate it.

thanks,

 

bump.

 

I've scanned these same codes on an 04 silverado. I changed the purge solenoid and everything is fine now. Do you know someone who will let you plug their solenoid in on your truck? Takes about 10 minutes to pull it off and try it on yours.

 

noone close but i can go buy one, that was going to be the first part i threw at it as it's the easiest to replace.

so you had a 102 code that cleared after you changed the purge solenoid ?

doesn't seem like it should be related but ..... you never know with vehicles these days.

 

got home too late to locate a solenoid today, the dealer was the only one who had one in stock and get this ......... it's $6 cheaper than autozone huh ?

anyway, too late to get one so i pulled the old one off and ran 12v to it and it opened every time. not sure if that means it's good as i don't know what the actual delivered voltage is but .......... any input ?

tried to log it with efi live but for some reason my program keeps telling me it's an un registered interface and keeps prompting me to input registration info. checked my files all info is correct but i can't get it to work, only limited functionality with no real time monitering. guess i have to email paul again.

wanted to see what the actual hz was on the maf and see if i can monitor the evap system, looks like it's a supported pid so i just need to get it working.

thinking of reflashing with edit to see if i have some glitch that's developed.

 

FWIW, the MAF can cause the trans to operate different depending on how messed up it is.

 

yeah i know, everything effects everything and what the cars says isn't always the root cause of the issue.

i've looked around and seen people replacing the front solenoid, rent vent valve, tank pressure switch and still throwing the codes.

i've seen where the tps doesn't throw a code but the computer thinks it's open more or less than it is and blames the maf for the problem.

that's why i'm trying to log the maf and see what's what but i guess i have to wait to see if i can get the program up and running.

what's weird is the codes are all simultaneous , i can't see an immediate connection between the evap and the maf circuit but i don't doubt it exists ........ somehow. unless they were on the same circuit ....... but even if i blew a fuse i should get no signal to the maf at all ..... right ? and the truck does run, doesn't seem like it's in limp mode.

think i'll reflash tomorrow just because it's free [ unless my edit program doesn't feel like working ;]

thanks for the replies, keep em coming if you have any ideas

 

I wonder if somehow you ran over something. I know it sounds farfetched, but if your harness got messed up somehow then that could definitely cause some problems.

I'm assuming your tune is setup to run speed density as well with the whipple. Set the fail freq. to 0 and see how the motor runs. Also, see if those codes pop up while in SD.

If you can log the long term fuel trims it might show you if the MAF is freaking out.

Wouldn't hurt to replace the EVAP solenoid though

Hope you figure something out soon, I know what it feels like to have crap like that happen.

 

doesn't appear to be any physical damage to anything, but, with a harness wrapped up tight ........ who knows.

honestly don't know if my tune is set up to run in sd mode, what in edit would show me that it is ? the whipple crap is all offline, the add on inj's as well as the electronics.

wouldn't setting the fail freq to 0 just cause the pcm not to throw a code but still reference the maf ? that's not exactly speed density but would stop the pcm from recognizing there is a fault.

have to research it a bit more, read somewhere that the maf should be reading 3000hz @ idle. of course i have to get efi live going. if i can log it should already be set up for ltft and stft and i'll check the maf and all the sensors i can.

never had this code before, i have read that the evap test is 5 or six different tests of the solenoid, rear vent valve, line vacuum etc. seems like it would be able to differentiate between a vac problem and a part failure, seems odd that both front and rear parts are coding at the same time.

tried to get a gas cap at autozone ...... once again they didn't fail to fail ....... none in stock. this is just in case the cap i used wasn't compatable, seemed to fit but it wasn't for my truck. sure the dealer has one as well as the solenoid, just hate to replace stuff that's might not be broken, at $40 a shot it adds up quick.

 

Yeah i hear ya.

Setting the MAF fail freq to 0hz tells the PCM that the MAF isn't working and to operate in SD. Reason to leave it plugged in is because your IAT sensor is built into the MAF itself. When you open the tune and look at your primary VE, if it doesn't look stock then most likely the VE has been tuned. It shouldn't be stock anyways.

I'm not familiar with the whipple system at all unfortunately. Where does the EVAP mount to with that setup?

I think you're right on the idle at 3000hz, or 1lb/min. I do remember my buddy throwing only a few EVAP codes when his solenoid was bad. He replaced it and the codes went away. Still doesn't explain the shifting out of gear though. Maybe the EVAP failed and threw junk into the intake?