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Old 04-11-2019, 08:58 AM   #1
shifty
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P0446 mil

I feel like I'm being noisy on the forum since coming back. Sorry. Lots of stuff hitting at once and I have a rare increase in free time which can end any second!

Truck: 1998 Sierra, 5.7L, 90k miles, throwing P0446 code alone.

Recent mechanical work done (last 8 months):
  • Stant locking gas cap installed (September 2018)
  • SeaFoam top-end cleaning (January 2019)
  • A/C compressor and serpentine belt replaced (April 2019)

Let me say up front:
  • Gas cap seems the obvious culprit to me here although that was 7 months ago ...
  • Still, last night I cleared the DTC and reinstalled the OEM gas cap just in case ...
  • But strange it started shortly after AC work, being the compressor is next to EVAP can and all ...
  • So I checked hoses to EVAP can, hoses attached to intake top-end plastics, airbox, all look OK
  • The truck was never really driven in overly dusty environments during its life, if someone is headed down that path.

I'm thankful GM's EVAP systems seem pretty simple. Sadly, I don't have a diagnostic tool that will allow me to watch tank pressure sensor output or jigger any valves so I'm flying blind here.

I'm curious how often do the EVAP cans or tank pressure sensors go out? Seems like they're cheap ($120 combined) to replace.

Anything else I should be looking at? Which hoses should I absolutely check, other than the two attached to the EVAP can and the ones attached to black intake plastics?

Any thoughts on where to start with testing, knowing all I have is a cheap Ancel AD410 ODBII tool?
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Old 04-11-2019, 10:24 AM   #2
95 S_Trucker
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Re: P0446 mil

That code sets when there is a vent malfunction.

Check the vent valve mounted to the canister and check the wiring for it.

The pcm will open the purge valve and pull a vacuum on the entire evap system, and then the purge valve will close. If it holds vacuum for a certain amount of time, it verifies there is not a leak anywhere in the system. Then the pcm will open the vent valve, and vacuum should drop. A P0446 will set when the pcm doesn’t see a vacuum drop.
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Old 04-11-2019, 10:57 AM   #3
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Always scan twice

Not knowing how many times this code popped up, my advice is always clear a code and look for it to return.

Nearly any code can be a result of a glitch. I've had several over the 20 years I've had mine, come up once to never return again. Also in that 20 years, I've still got the original hardware for the EVAP system.

I had an evap code once about 10 years ago to which a new cap cured the problem. I am the only guy in my neighborhood with a good scanner so my neighbors have me scan their vehicles for them. ALL of my many neighbors that had an EVAP code have cured it with a new cap.

I don't like locking caps because they never feel "cranked" down tight to me. It requires a tight seal to keep from leaking.

Another point of contention with regard to leaking. I ask customers at my store that have an evap leak if they recently did a fuel pump replacement. It's highly important the seal for the pump be good to not leak vacuum.

The other thing to remember is things like a body lift where the fuel pipe has to be extended. Yet another place to leak vacuum.

Last i don't believe in coincidence. I feel that you or the shop leaned on something too hard while doing the compressor work. Start with a thorough inspection of the joints and hoses nearest the compressor and work out in perimeter from there.
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Old 04-11-2019, 11:40 AM   #4
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Re: P0446 mil

P0446 is a vent malfunction. It’s not a leak code. You would have a P0440 or a P0442 if there was a leak somewhere.

It’s definitely not the fuel cap.


Also, the evap monitor is the toughest one to set, it may take 50+ miles of mixed driving for it to set.
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Old 04-11-2019, 04:00 PM   #5
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Re: P0446 mil

Thanks for the discussion guys. Appreciate it.

Quote:
Originally Posted by 95 S_Trucker View Post
P0446 is a vent malfunction. It’s not a leak code. You would have a P0440 or a P0442 if there was a leak somewhere.

It’s definitely not the fuel cap.
This is what I was wondering. I know P0446 has been caused by cap on both our Toyota Highlander and a friend's Camry. Granted, that's Toyota, different beast.

Is my understanding correct on the EVAP system?

I believe: My model has the EVAP canister and solenoid mounted up front between aux battery tray and AC clutch. That has two lines coming off it - one to the intake for re-burn, one back to the tank, which is expected to be sealed. For the PCM to understand whether vent/purge is necessary there's a 3-wire pressure switch on top of the tank, next to the fuel pump, which the PCM uses to monitor vapor and pressure levels, decide if it's necessary to open up the solenoid on the canister, releasing vapor into the intake for re-burn, or throw a code in case of malfunction (leak, high pressure, etc.)

Is this accurate?

What I don't necessarily understand is what specifically is causing vacuum on the tank - Full pump sucking gas out of the tank? Then the solenoid is releasing pressure? Does the gas cap not at all act as a high-pressure limiter on the tank side of the system?

I swear my '03 Sierra had a vent valve towards the rear, had mine replaced under warranty before selling the truck, was clogged. Is the solenoid on the EVAP can the equivalent in this case?
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Old 04-11-2019, 04:08 PM   #6
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Re: P0446 mil

PS - may or may not be related. Over the last couple of weeks I've noticed two sounds from behind my glovebox area.

One is almost like ... when you're trying to unlock power doors on a foreign car and they're already unlocked. Or maybe forcing a kids toy with plastic gears to roll foward and backward really fast.

Additionally, the other sound is ... it sounds almost like there's a piece of plastic in an empty glove box, and any time I step on the gas, I hear a 'clack' sound, almost as if I have a piece of plastic is sliding back or forth into different sides of the glovebox.

The gear-like sound happens most often when turning left or right, but not exclusively.
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Old 04-12-2019, 09:24 AM   #7
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Re: P0446 mil

Quote:
Originally Posted by shifty View Post
PS - may or may not be related. Over the last couple of weeks I've noticed two sounds from behind my glovebox area.

One is almost like ... when you're trying to unlock power doors on a foreign car and they're already unlocked. Or maybe forcing a kids toy with plastic gears to roll foward and backward really fast.

Additionally, the other sound is ... it sounds almost like there's a piece of plastic in an empty glove box, and any time I step on the gas, I hear a 'clack' sound, almost as if I have a piece of plastic is sliding back or forth into different sides of the glovebox.

The gear-like sound happens most often when turning left or right, but not exclusively.

I wish I could remember it's name, but there is a small controller under the glove box that controls the heat and AC valve/flapper thing. That is a common issue and they are easy to replace.
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Old 04-12-2019, 10:59 AM   #8
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Re: P0446 mil

Not on a pickup but on my car I get this code all the time. I just clear it and move on.

Everyone who lives out here on these dusty MT back roads cusses GM all the time for this "problem".
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Old 04-12-2019, 03:54 PM   #9
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Re: P0446 mil

The vent valve is the solenoid mounted on the canister. That is what you need to check. And check the connector and wiring too.
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Old 04-27-2019, 02:57 PM   #10
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Re: P0446 mil

For what it's worth, an update and a couple of things I'm confused about in case anyone here can answer (thanks in advance)

I pulled the Stant locking gas cap the day of my last reply and replaced with the factory gas cap. I cleared the MIL/CEL. I've driven around 150 miles of mixed city/highway driving (mostly city) and still no new code.

Honestly have no idea if it's just because these systems randomly throw P0446, or if it was genuinely the gas cap not allowing the closed fuel system to keep any vacuum on the tank. Or if I just haven't driven enough for the system to complete EVAP test (150 miles seems like plenty).

Nonetheless, I pulled a clean looking vent valve at the JY that, with basic 9v battery testing, appears to be a working unit, so I may swap it out in the near future.

I'm really confused on a couple of things though.

GM says there's a vapor purge solenoid for my square vapor canister (ACDelco 214-640), it's a little round unit, but I cannot for the life of me figure out where that thing lives! Anyone know?

Finally, when shopping for new vent valves, I found something. ACDelco part number for the vent valve with strap is 214-2214 ($93!) and shows as the right part for my L31, but I'll be damned if ACDelco p/n 214-633 ($19) isn't EXACTLY the same vent valve without the strap. What the hell?

It looks like the Tahoe, Yukon and Suburban in '98 also had the L31. I've found a few in the JY with round EVAP canisters instead of my square. Weird?

If it's not cracked, is it ever necessary to re-pack or replace the vapor canister? If nothing else, I'd like to clean it off, it's dirty as hell up top.
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Old 04-27-2019, 04:16 PM   #11
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Re: P0446 mil

I dunno, but my former neighbors said they spent a fortune repeatedly at a shop to fix this problem on their Tahoe, so much so that they traded it in for a Ford! And then they finally sold out and moved to town so maybe they had the problem with that, too?

The old fellow at the former GMC dealership in town (lost his franchise under the great bail out) said there was no permanent fix and to just delete the code but keep checking it when the light comes back on just in case it's something else more serious next time.
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Old 04-27-2019, 07:41 PM   #12
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Re: P0446 mil

Quote:
Originally Posted by shifty View Post
For what it's worth, an update and a couple of things I'm confused about in case anyone here can answer (thanks in advance)

I pulled the Stant locking gas cap the day of my last reply and replaced with the factory gas cap. I cleared the MIL/CEL. I've driven around 150 miles of mixed city/highway driving (mostly city) and still no new code.

Honestly have no idea if it's just because these systems randomly throw P0446, or if it was genuinely the gas cap not allowing the closed fuel system to keep any vacuum on the tank. Or if I just haven't driven enough for the system to complete EVAP test (150 miles seems like plenty).

Nonetheless, I pulled a clean looking vent valve at the JY that, with basic 9v battery testing, appears to be a working unit, so I may swap it out in the near future.

I'm really confused on a couple of things though.

GM says there's a vapor purge solenoid for my square vapor canister (ACDelco 214-640), it's a little round unit, but I cannot for the life of me figure out where that thing lives! Anyone know?

Finally, when shopping for new vent valves, I found something. ACDelco part number for the vent valve with strap is 214-2214 ($93!) and shows as the right part for my L31, but I'll be damned if ACDelco p/n 214-633 ($19) isn't EXACTLY the same vent valve without the strap. What the hell?

It looks like the Tahoe, Yukon and Suburban in '98 also had the L31. I've found a few in the JY with round EVAP canisters instead of my square. Weird?

If it's not cracked, is it ever necessary to re-pack or replace the vapor canister? If nothing else, I'd like to clean it off, it's dirty as hell up top.
The purge solenoid is mounted on the engine. The vent solenoid is mounted to the canister.

97 and earlier had the round charcoal canister. 98 and newer have the squarish charcoal canister.
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Old 04-27-2019, 09:31 PM   #13
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Re: P0446 mil

If you live in very dusty areas plumb the air intake side of the vent valve to.the clean side of the engine airbox or put a filter on it.
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Old 05-01-2019, 11:16 PM   #14
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Re: P0446 mil

Spoke too soon. MIL returned today on the way to work.

My handheld code reader supports an EVAP test while engine is off, which appears to just toggle the vent valve open/closed 3x. Pretty noisy.

I noticed my vent valve was missing its cap totally, but that has nothing to do with its vent function. I ran EVAP test on it anyway, it opened/closed the valve three times (6 clicks), seems to be working. "Test passed" according to the unit. Maybe it's just periodically failing and that's causing the MIL?

Still, I swapped it out with what looked like a brand new one out of a '98 Tahoe I found at the JY a week or two ago $8 vs. 10x that. Ran EVAP test on that one after install, 6 clicks sounded exactly the same as the old. "Test passed" according to the unit.

I don't think it's the vent valve in this case. All of my hard lines look good too - no cracks I can see.

I'm suspicious this came on within 50 miles after my swapping my HVAC compressor and serpentine belt, compressor is right next to the vapor canister and vent valve.

Can anyone tell me how to test the vacuum/pressure on the EVAP line(s) using the inline test port?

Any way to test if the purge solenoid is functioning, or test the tank pressure sensor to confirm it's sending valid pressure data? Or would that toss a diff't code?

EDIT: Full disclosure, I guess this happened within 200 miles of doing a top-end SeaFoam cleaning on the truck too. In case that's somehow relevant.

EDIT2: Forgot to say - thanks for all y'alls help so far, I'm learning a lot. Emissions testing is coming up in less than 10 weeks and my funds and time are both on the thin side right now. Stealership or a shop would really hurt
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Old 05-02-2019, 09:14 AM   #15
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Re: P0446 mil

Oooh hey, I found a diagnostic page on the GM website which pertains to the L31, lists a bunch of diag codes and technical details on expectations.

https://gsi.ext.gm.com/gmspo/mode6/p...t57R_HD_yE.pdf (see page 33/40)

It mentions this exact error code with a bunch of diag info. Specifically says it points to a "restriction" in one of the following. I wonder if my vapor canister is just clogged?

When I popped off the vent valve, I took a whiff on the nipple and it smells pretty heavily saturated. I looked in the hole, it looked like the canister was just full of foam. I've heard others say there was cotton packing and charcoal in there. I guess this box isn't serviceable eh, if it needs to remain sealed.
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Old 05-02-2019, 09:24 AM   #16
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Re: P0446 mil

Your tool should cycle the vent closed and the purge open to pull a vacuum on the fuel tank to allow you to look at the tank pressure.
I can individually command the purge and vent valves with the Tech 2 and command an evap test with a specific purge duty cycle % to watch the effect on the tank pressure PID.
If your tool can command the vent it shroud be able to command the purge valve as well. It should also let you view the tank pressure data PID. The evap test should allow you to specify a purge duty cycle but 100% is good enough if you can view the tank pressure.

You can test the purge valve for a gross leak by checking for vacuum through the valve when it's supposed to be closed with the electrical plug disconnected... there should be zero vacuum with it unplugged and the engine running. You need to command it open to check for vacuum when it's open.

If you suspect a vent blockage... command the purge to 50% and vent open. The tank pressure shouldn't drop much since there should be a path through the evap can and vent valve to the open air.
If you overfilled the tank and saturated the carbon in the canister with fuel it may not purge very well if at all.
Mud daubers and spiders like to make nests in the vent intake hoses for some reason. Check there before changing parts.

If you drive in dusty conditions or have critters making a home in the vent hose opening you can either run an SAEJ30R7 hose up to the clean side of the air filter or install a 19208702 vent filter from the GMT900 trucks on the vent hose.
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Old 05-02-2019, 11:59 AM   #17
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Re: P0446 mil

Thanks, hatzie

I don't think this cheapie Ancel AD410 unit I have supports anything beyond basic. It gives a limited list of menu items, one is "EVAP System Test". You select it, it triggers the computer to add/remove voltage to the vent solenoid, and if it works "test passed!"

Not very helpful.

After seeing how useless this is and watching videos on YT on diagnostics, and reading about using tools to bleed and do other things, I'm interested in returning this Ancel unit. Tech2 is a good unit? I had trouble finding anything that would fill the void between what I have currently and the $600-$4,000 smaller shops use. Cen-Tech 60794 seemed to get closer, at least it can read tank pressure and reset ABS stuff. Would love something that allows what you're saying, ABS, SRS and bleed functions would be nice.
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Old 05-02-2019, 01:01 PM   #18
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Re: P0446 mil

The Vetronix Tech 2 was the GM dealership tool from the mid 1990's til around 2010ish.
The reasonable quality Chinese knockoffs are sufficient to the task at hand. I own one with a case, CAN-DI and all of the adapters that cost around $350 shipped from Guangdong, China about 7 years ago. It's about $290 without a case.
The knockoffs are not without problems.
  • I had to change the DC-DC Converter when it arrived requiring soldering skills and tools beyond a lot of folks skill set.
  • Some of the super cheap versions have issues with the VCI module so you get to send it back or replace the VCI.
  • I will not use any Tech 2 for ECM updates because any Tech 2 requires a fully RS232 compliant serial port on the PC doing the work. USB-RS232 will not cut it.

If you have a laptop or an old desktop PC that you can use in the shop the WiFI MDI clones are $200 and they work just fine over USB using Bosch MDI drivers. They're workable with hacked copies of Tech2WIN. GM-VXDIAG at around $140 is another choice again with hacked Tech2WIN and special drivers on the PC.
Tech2WIN is essentially a Tech 2 running on a PC using the MDI or VXDIAG as the interface.

The Launch PROS X431 Mini is around $800. It's from Launch Tech China not Launch Tech USA so you don't get support from Launch USA... Corporate and international politics I believe similar to buying a Malibu in Buffalo NY and not being able to get GM warranty in Toronto ONT... but it may be stolen tech by another Chinese company... the whole story ain't out there.

The Autel Maxdas DS808 is around $700 on sale right now. You won't find a better deal on a full function scanner that doesn't have intellectual property issues. Eric O uses these in his South Main Auto Youtube videos on customer cars.

One of the guys on the Impala Forums just bought a Vident iLink400 handheld that is supposed to do ABS Bleed among other bi-directional functions for around $160. He says it works but it's not super intuitive.
http://www.videnttech.com/product/item-79.html
https://www.amazon.com/VIDENT-Multi-...07FVMQ9TK?th=1
https://www.ebay.com/itm/322824891739?ul_noapp=true
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Old 05-02-2019, 01:36 PM   #19
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Re: P0446 mil

I'm probably out $150-300 on labor just rolling this into a shop to do the exact same tests (then add on parts/labor) and I enjoy DIY so I'm thinking hard on this one.

Quote:
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The reasonable quality Chinese knockoffs are sufficient to the task at hand. I own one with a case, CAN-DI and all of the adapters that cost around $350 shipped from Guangdong, China about 7 years ago. It's about $290 without a case.
The knockoffs are not without problems.
  • I had to change the DC-DC Converter when it arrived requiring soldering skills and tools beyond a lot of folks skill set.
  • Some of the super cheap versions have issues with the VCI module so you get to send it back or replace the VCI.
  • I will not use any Tech 2 for ECM updates because any Tech 2 requires a fully RS232 compliant serial port on the PC doing the work. USB-RS232 will not cut it.
This is what I was checking out online, minus the case I'm seeing $270-330 shipped, and they definitely look grey market to me. My concern is whether it's garbage or not. Nothing is sacred anymore, no doubt the plans for the unit leaked or were stolen 10+ years ago so these are probably roughly the same without the same QC of the original (QC/QA costs $$) so buyer gets to deal w/all the bugs and defects.

I work with two EEs and know my way around an iron, multimeter, o-scope and other misc related tools myself, so I've at least got some pro level support nearby.

Quote:
Originally Posted by hatzie View Post
If you have a laptop or an old desktop PC that you can use in the shop the WiFI MDI clones are $200 and they work just fine over USB using Bosch MDI drivers.
You know, I have a stack of SSD-loaded Dell E6230s I was just about to sell locally on the cheap. I think they have a serial port on the chassis, too. If not, there's a snap-on mini dock which hooks into the databus on the bottom that seems to operate way better than USB->RS232 adapters.

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Originally Posted by hatzie View Post
The Autel Maxdas DS808 is around $700 on sale right now. You won't find a better deal on a full function scanner that doesn't have intellectual property issues. Eric O uses these in his South Main Auto Youtube videos on customer cars.
His video was the first I found when diagnosing this exact issue - where he finds the TPS is the problem. Then I ended up over at another YouTube channel he referenced during that video who went into a longer explanation with a different tool. That's what led me to buy my cheap Ancel unit, $800 was hard to swallow at the time. I could tell it was using Android and it seemed to be crawling to a halt thru that video, so I had some concerns.

I have a Samsung Note 2 new, unopened box (inventory leftovers) and one of the 1st Gen Nexus7 tablets too ... surprised there's not some readily available conversion kit out there for old tablets, that would be awesome!

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Originally Posted by hatzie View Post
One of the guys on the Impala Forums just bought a Vident iLink400 handheld that is supposed to do ABS Bleed among other bi-directional functions for around $160. He says it works but it's not super intuitive.
http://www.videnttech.com/product/item-79.html
https://www.amazon.com/VIDENT-Multi-...07FVMQ9TK?th=1
https://www.ebay.com/itm/322824891739?ul_noapp=true
Honestly, the interface looks scary like the $30 unit I have now. It does lots of stupid **** and a lot of the information is gibberish. I'm attaching some screenshots.
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Old 05-02-2019, 02:10 PM   #20
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Re: P0446 mil

Un-translated data is the problem with the cheap ones. My guess is the Vident is similar.
Raw Mode 6 etc data is not good without the ability to interpret it. It's why I use Torque Pro for some of that.

My bet is they're being produced by the same Chinese factories that Bosch and HP were using when they ended support for the Tech 2. The only real bad thing about the decent gray market units is the power supplies available to us can't withstand a re-start cycle so they don't help diagnosing a tow-in no-start situation.
My Tech 2 wasn't that bad. I changed the power supply to a known pedigree DC-DC converter more because I didn't like the look of the unknown source converter that was installed in mine. Datel and Mornsun make decent trustworthy DC-DC bricks that fit the board and run at about 8vdc. The originals ran down to @5v IIRC.

If you have a few garage grade laptops available I'd think about going the Gray Market WiFi MDI route. The one I purchased in January is $229 with an SATA HDD with Tech2Win supposedly installed and working. I wouldn't connect to the internet with that drive but it's just fine for a garage PC with the network drivers removed or just never installed.

If you use the AC Delco TIS web applet to program a controller you can just use a different PC with a known pedigree OS along with the MDI.
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1969 Dodge Polara 500 B383, A833 SOLD
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1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


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Old 05-17-2019, 02:19 PM   #21
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Re: P0446 mil

So ... How hard is it to drop the tank in a GMT400?

Got my Tech2 and problem seems clear. Tank pressure sensor always reads an outrageous vacuum level whether truck is running or not, gas cap on or off. Bad FTPS, I'd guess?

Tech2 won't even run EVAP tests "Too much fuel tank vacuum Test Aborted". Here's a short video of test attempt and longer video of evap/fuel readings of Tech2 display while truck is running if interesting.

Fuel pump has been buzzing like a MF for at least a year now. Guess I might as well swap both at the same time while tank is dropped?

Looks like tank just has two straps and a frame brace holding it in. Guessing 15mins + jack to drop it. Any tips/warnings? Like, ground cables to remove, wires or lines to loosen, etc?
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Old 05-17-2019, 02:43 PM   #22
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Re: P0446 mil

Since you're in Hotlanta you probably don't have much rust to deal with...

TPS commonly refers to Throttle Position Sensors. FTPS is the acronym you're reaching for...

I'd remove the bed bolts with a ratchet and lift the bed off with a buddy and set it on sawhorses or slide it back on 4x4 timbers til you can reach the sender. It's 8 or 10 bolts, a ground strap or two, and unplugging the tail lamps.

Option two is take the LH bed bolts out and unscrew the RH bed bolts about 1" then tilt the bed and support it very very very well.

Liberally coat the bed bolt threads with never seize before you screw em back in.
I usually coat the fuel line ferrule threads with never seize and slide the ferrule back on the line so I can coat the outside of the line as well.

NEVER EVER use impact tools on the bed bolts. The cage for the bed nuts gets wallowed out by the impacts til the nut is loose and then it just spins.

If the fuel lines weren't so miserable to R&R with the bed in place I'd think about dropping the tank but...
The FTPS is a push in deal just like a MAF sensor. Same location as the T800 trucks. Right through the top of the sender. Get a Delphi fuel pump and pressure sensor. Not worth the headache of using the aftermarket crap in this location.

The full set of 1998 service manuals are in my signature. Vol 3 & 4 has the FTPS troubleshooting info.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 05-17-2019 at 03:12 PM.
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Old 05-17-2019, 03:14 PM   #23
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Re: P0446 mil

Totally understand. Well, in that case I'm going to do the fuel pump at the same time. It's damn impossible to reach up/around the tank to pop out the sender.

FWIW, Summit Racing is having a sale. Most place list the pup AC Delco MU1745 (19331272) for $170-190, Summit Racing has a special offer on it for 150.99 right now. I took off an extra $15 with coupon code: ALWAYS

So, heading down to McDonough to grab my $146 pump now... and I guess my weekend will either be filled with taking a bed off or dropping a tank...

Lucky enough I had some spare $$ in my PayPal from selling misc old crap on eBay, so the Tech2 only "actually" cost me $80 out of pocket. I'd have rather spent the other $220 PayPal balance somewhere else but whatever... such is life, I guess...

Thanks again everyone for your help on this one. I'll report back when all this gets done in the next couple of weeks just to confirm all is good after replacing the TPS.
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Old 05-19-2019, 08:05 PM   #24
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Re: P0446 mil

Problem solved.

Good thing the AC Delco pump came with a pressure sensor. I'd picked up a pressure sensor off fleabay, was apparently bad, reading pressure while the truck was off, before digging into the pump replacement, I figured I'd swap it in to confirm my evap CEL was tied to that and proved it was.

After two trips to the store to buy three different quick connect tools that wouldn't fit in the tight space of the feed/return lines, the pump and sensor are installed with new 4-pin harness (ACDelco's heat shrink butt splices suck ass).

Pump and sensor work great, no more buzzing from the pump, Tech2 evap shop test passed with flying colors thanks to the new genuine sensor, things function as you'd expect on purge/seal which it wouldn't before (video).

Still have a little bit of a stumble at idle, but I seriously expect that has something to do with the stock fuel spider more than anything.

hatzie, you were a great help with this whole situation, thanks so much for lending your knowledge.

Quote:
Originally Posted by hatzie View Post
It's 8 or 10 bolts, a ground strap or two, and unplugging the tail lamps.
Glad I took your advice here too. I have always been told to drop the tank. Taking the bed off wasn't exactly a walk in the park, but it finally gave me a chance to clean and wax the bed-cab gap while I was at it and clean up the frame a bit.

For the record, exact count on fasteners for a '98 extended cab with 6.5' bed is:
  • 8 bed bolts
  • 2 bolts and a plastic clip for the filler surround
  • 3 hex head screws to pop off filler cover
  • 4 screws to pop out the two lights
  • 1 ground strap near the filler neck
  • Tailgate
  • All the plastic clips holding the rear lighting looms in place.

Came off no problem, standard ratchet, no breaker bar, what you'd expect for a truck that lived in GA its whole life. Want to keep it that way so took your advice of plopping some anti-seize on the 8 main bed bolts too.

So, I guess this is case closed. 6 hours work total with all the extra stuff piled on and 90 minutes of trips to the store to inevitably cut off the return/fill nipples on the old pump to gain access to use the tools I already had. Meh.

Should be able to pass emissions next month, no problem!
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Old 05-19-2019, 08:06 PM   #25
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Re: P0446 mil

Last but not least ... money shots of cleaned and waxed bed and cab gap metal, new pump installed.
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