GM Vortec Swap: PO441 (Incorrect Purge Flow) Repair

[Taylorious]

Howdy Mud:

Got myself a 'interestingly maintained' L31-Block (Series 1) 350ci Vortec FJ60 last summer... and have been slowly working the bugs out.
...all kinds of fun things have happened:
Burned plug wires on Block-hugger headers, cooked a distributor, cooked cats running lean, replaced entire harness with a Howell EFI, newer spider injectors, etc.

New problem: OBDII code PO441.
GM's VCM labels this as "Evaporative Emissions Control System: Incorrect Purge Flow"
Which, by my estimation, means the flow from the charcoal canister into the intake manifold is either too much, or too little.

I've made a diagram of how my FJ60's OEM emissions system is hooked to the GM engine bay:

(The highlighted YELLOW in the above image is where I believe the potential problem to be.)

Here's what I've found as potential causes/repairs:
-Bad Gas Cap
-Bad vacuum switch
-Broken or damaged EVAP line
-Broken or damaged Charcoal Canister
-Open in VCM purge command circuit
-Open or short in Voltage feed circuit to Purge Solenoid
-Faulty purge solenoid Restriction in EVAP solenoid, line or canister
-Corrosion or resistance in purge connector
-Bad VCM

As such, I'm going to start with the stuff on the green list.

If anyone has experience with these old Vortec's, or knows likely culprits in the "Octopus Wah" of vent hoses from the separator through the body... please let me know! I've heard, also, that placement of Emissions components (e.g. the Charcoal canister) could definitely affect the performance of the system, as could the lean-running conditions that cooked my cats last fall. Anyone got 411 on that?

Thank you.
I'll post updates as I go along...

 

[spotcruiser]

I've been running an L31 since 2011 without issue. I purchased a used OEM cannister during the build, expecting that I'd need it, but tried it first with the original FJ40 cannister and that worked great so I've never changed it. I left the system upstream of the cannister stock.

 

[spotcruiser]

Looking at the diagram, your purge circuit is not controlled by the ECM? You have it drawn by a simple switch.

 

[Taylorious]

Looking at the diagram, your purge circuit is not controlled by the ECM? You have it drawn by a simple switch.

Hey there!

I'm sorry! It's connected to ECM. Apologies. Took me way longer than needed to draw this out, and there's obvious mistakes haha.

 

[spotcruiser]

How does the ECM measure flow? It doesn't. I think all it's looking for when it calls for purge, is that the valve opened. It can only tell that the valve is opened by current flow through the circuit. Have you verified that the valve operates?

 

[Taylorious]

...I purchased a used OEM cannister during the build, expecting that I'd need it, but tried it first with the original FJ40 cannister and that worked great so I've never changed it. I left the system upstream of the cannister stock.

So; you're saying that your L/C canister worked in place of the GM hardware? I know my canister is GM... and thought I'd inspect that first, since it's literally bolted to the radiator support. However, the lines all the way up to the tank are long since it's so far from the OEM upstream (e.g. headed to the separator) hardline which is on the firewall.

 

[Taylorious]

How does the ECM measure flow? It doesn't. I think all it's looking for when it calls for purge, is that the valve opened. It can only tell that the valve is opened by current flow through the circuit. Have you verified that the valve operates?

So, if I'm understanding, ECM only opens the purge valve when the truck is in motion? I thought this circuit opened when the vehicle was at highway RPM's and speed sensor was registering high. I could be totally wrong though...

 

[spotcruiser]

Yep. I rerouted the 1/8 line from the location of the GM cannister (by front headlight) to the original FJ40 cannister (rear of passenger fender). It just runs from the purge valve back to the OEM cannister.

So; you're saying that your L/C canister worked in place of the GM hardware? I know my canister is GM... and thought I'd inspect that first, since it's literally bolted to the radiator support. However, the lines all the way up to the tank are long since it's so far from the OEM upstream (e.g. headed to the separator) hardline which is on the firewall.

 

[spotcruiser]

I think if the engine conditions call for purge (off-hand I don't know exactly what those are) and a vacuum switch doesn't sense flow, it sets the code.

Edit: I'll look into it.

 

[Taylorious]

I think if the engine conditions call for purge (off-hand I don't know exactly what those are) and a vacuum switch doesn't sense flow, it sets the code.

Now we're getting somewhere... I think that your first comment about we weirdly drawn diagram reflects that the cause might actually be a poor purge valve OR a poor charcoal canister vent control valve... if it has one. I'll need to look tonight.

 

[spotcruiser]

Schematic. It has a Purge Valve and Cannister Vacuum Switch. I think your issue is there.

 

[Taylorious]

YES!

We L31 guys gotta keep the flame burning from all the new shine on the LS platforms!

Thanks!

 

[spotcruiser]

Just noticed that yours is a 99, so looked for the schematic (mine is a 96). It's a little different.

1999 Schematic

 

[Taylorious]

A question: Where are you pulling these FSM's from?

 

[spotcruiser]

LT1Swap.com
These are the schematics for a 99. http://www.lt1swap.com/1999_vortec_5.7/engine_schematics.htm

 

[spotcruiser]

Did you solve the issue?

 

[Taylorious]

I'm still digging through this... and of course, taking a vacation starting this evening that will put me out of action of repairing this until the 30th of the month.

HOWEVER:
I've not solved the issue quite yet, but your digram helps massively!

From what I can figure, the problem lies in this area (see image), and there's a particular piece that I'm confused about... (see photos)
(Image #1)

(Image #2)

Based on what I can tell, and from the parts fiche, the "Canister Purge Valve" and "Canister Purge Solenoid" are the same thing. That's what's depicted in Image #1.

However, I can't identify what the piece is in Image #2. Based on the diagram above, I believe it'd be the "EVAP Canister Vent Control" Or, perhaps, a "EVAP Vac. Switch?"

And, to make matters even more confusing.. my harness is a Howell Dynamics harness, and I don't know if the wire colors are accurate representations of the OEM system's color code.
The 2-plug wire to the "Canister Purge Valve" in Image 1 is labeled "CANISTER PURGE VAC" and the 2-plug wire to the unknown part in Image 2 is labeled "CANISTER PURGE."

Whatever that unknown part is is my first suspect. I know that my lines are clear, as they were pressure tested with a smoke pump recently.

Any thoughts?

 

[Taylorious]

Hi all. Updates....

Had to do the lovely Intake Manifold gaskets on my L31 over the return from my trip on the 30th, so truck's been down until yesterday... but still have the P/0 441 code!

Here's my learnings from what I've been digging up so far:

1) There are differences in EVAP systems between 1996-1999 Chevrolet L31 Vortec engines. (Thanks @spotcruiser for this help so far too!)

2) One of the differences is the EVAP "Canister Purge Valve Switch" which seems to be a unique part for the 1996-96 5.7L engines
(AC Delco Part # 12556357)

3) I have some strange/unknown type of Canister Purge valve, as seen in the pictures above as "unknown part."
I believe this to be a 1989-1998 "Fuel Vapor Canister Purge Solenoid", which is AC Delco part # 1997201.

4) When doing the intake manifold work as mentioned above, I noticed my Canister Purge Solenoid had oil in it when I removed it from my upper intake manifold and let it sit on the bench. ...this could have fowled the solenoid, I suspect, and is creating my PO code.

5) I am increasingly sure that my current wiring set up is correct, and that the Purge Solenoid is not mis-wired to the Vac switch and vice versa. (Confirming with Howell Dynamics now.)

Below is my current summitracing shopping cart. I think the issue is one of these parts, as seen in the image above...
None of the local parts stores stock AC Delco, but Durlast and Everstart parts instead which... I've had issues with.

Any thoughts?

 

[Taylorious]

Final thought... perhaps the 1996-97 diagram is what I should seek to replicate!
(Using above AC Delco parts 12556357 and 1997277 only) See below for diagram:

 

[spotcruiser]

So, your ECM seems to only have two things by which it can judge "Purge Flow". I assume it needs to see current flow in both of those solenoid valves shown in your photos. Do both valves have continuity?