NVLD Evap tricks

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Redtruck-VA

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Became curious when an overseas member asked about removing the entire EVAP system from his 03. Since most if not all Hemi models are NGC they have the Natural Vacuum Leak Detection (NVLD) system. This is actually a very simple system with only three wires attached to it.
1. A ground wire.
2. A switch sense wire (normally open).
3. A solenoid valve (normally closed unpowered).
The evap test actually occurs when the engine is turned off and is centered around a change of pressure (vacuum) within the sealed tank due to any temperature change. If the tank is NOT sealed then there is no vacuum to close the switch.

Upon engine startup the switch sense (open or closed) is sent to the PCM to indicate if the tank is sealed or not. If the switch sense is “closed” this indicates the tank has held a vacuum and the system is functioning. The solenoid then opens the valve allowing the tank to breath for remainder of run time. If the switch sense is open then this indicates the tank is not sealed and the PCM moves to the next test which has the solenoid close the valve (no power) and looks for the switch to close indicating vacuum. If this test fails (switch sense open) then a DTC is set.

I see is a direct relationship between switch sense and solenoid being “powered”. So using a standard 12vdc relay with the normally closed (NC) contacts wired to the switch sense indicating “switch closed” every time the engine was started the PCM would see the tank is sealed. And the solenoid would then be powered to open the valve for normal operation and the switch sense would then open. My conclusion is a simple relay can replace the NVLP/ evap system with no codes.

Inputs are always appreciated.
 

03MopaRamman

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draw it out on a Napkin please and what switch to buy and where to cut and splice, this has been a pain in my **** since I bought the truck and in summer I clear the P0440 at least once a week. That would be real cool Buds DIY, Carry On.Thanks Danny.

PS. Greg is an 03 Genius and well I just Play with Ammo in the Hot Sun.
 
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Redtruck-VA

Redtruck-VA

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draw it out on a Napkin please and what switch to buy and where to cut and splice, this has been a pain in my **** since I bought the truck and in summer I clear the P0440 at least once a week. That would be real cool Buds DIY, Carry On.Thanks Danny.

PS. Greg is an 03 Genius and well I just Play with Ammo in the Hot Sun.

Danny, you make a old Chief blush.
I'm just a retired machinist that's still has all his fingers. lol

Like my other tricks I have to test them to find out how they work in real life.
 

03MopaRamman

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Chiefs don't work in the Army anyways just carry a Pace stick and look mean (a broom knows no Rank for sure), but all Navy guys from the Swain down help everywhere.....I been to Sea once on a Msl Shoot, anyways I am seriously interested in this Mod and the Idle up. I am subscribed. Are you back home yet if I may ask.

I did some work on the EVAP and for a while had it sealed pretty good but now my homemade hoses are cracked in the bends, etc and I also replaced the cannister midway under the truck.

Edit: Oh ya keeping the fingers is Important......I got all Mine Too, and,,,knock on wood never had a Misfire!
 
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Redtruck-VA

Redtruck-VA

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Danny, I'm wrapping up here and should be home in a few weeks. The high idle works great so that'll be easy to set up. If I can get the Megasquirt running I'll pull the mod off of my truck for you. But seriously it is dirt simple.
 
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Redtruck-VA

Redtruck-VA

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I got nothing to draw with, maybe this will work.

This is what I see is needed for a part list to replace the NVLD.
Initially I would leave everything in place and just wire up the relay to see if it works. The system will continue to work as the purge solenoid is still functioning but shouldn’t be able to throw codes. This might be the solution for those nagging codes that keep popping up. Next step if satisfied with the electrical bypass would be to bypass the NVLD itself for those of you running off road.

12vdc automotive 40a relay NC or 5 pin SPDT
1 Resistor, 130 ohm. 5w to be safe, connected to pin 87a, other end connected to Grd BK/PK
12vdc source wire is OR connected to pin 85
Grd wire is BK/PK connected to pin 86
PCM “Sense” wire is WT/DG connected to pin 30
Maybe someone can draw up a diagram. But it’s simple.
 
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Redtruck-VA

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Thinking about what would happen if the PCM attempted to do a “Small/Large leak test”. As I see it the Purge Valve itself is dumb, meaning it in itself cannot throw a code if operating. The PCM monitors it’s voltage state which would throw a code if it was simply unplugged, but as long as it is functioning it is good. This is how the Small/Large leak test is accomplished; The PCM logic signals the Purge valve to run and Monitors the NVLD sense switch condition, if it closes it is indicating vacuum. Determined by Purge valve run time it then determines if a leak is present and if it is small or large. A code is only thrown if this test fails.
The NVLD in it’s simplicity relies on the single sense signal from the switch within the NVLD to indicate if there is vacuum or not regardless if it is caused by a temperature change within the sealed tank or from a Small/Large leak test done by the Purge valve. Part of this test includes removing power from the NVLD solenoid closing it’s valve. This is the same power now used to operate the bypass relay and with the power removed the sense switch will close indicating vacuum and the test should pass as the PCM logic has the Purge Valve open with a clock running and is expecting the NVLD sense switch to close showing a vacuum. The length of time it takes the PCM to sense vacuum determines the size of the leak if a leak is indicated. No leak indicated, no codes…
Well this is where my research has lead me to this point.
Inputs are welcomed and no doubt needed.
 

03MopaRamman

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I'll hunt down the parts and find the NVLD and see what I can do with your recipe thanks. Gotta crawl underneath to fix my First Gear Cable adjustment then I'll jump into this. Tommorrow. 100 Mile Weekend road trip with the Big RV trailer and to see how the truck handles with latest tweaks. I'll report back on the NVLD progress (Its under the Fuse Box Drivers side, I think).

P.S/ Cleared a P0440 today and one yesterday as the temp hit 30 Degrees Canadian! Working Downrange in Cotton Coveralls!
 
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Redtruck-VA

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Danny the NVLD is located in front of the gas tank next to the evap canisters. With my flr shifter I used the OEM lever with a hole drilled off to the lower corner. I'll see if I can find a picture. I stuck mine in park (shifter) disconnected the cable, left the trans lever in Park and adjusted the cable length until it slipped into the hole. Then shifted the shifter to drive which should also have shifted the trans to the drive position and adjusted the cable length again to slip into the lever hole. This should have been a very fine adjustment if it was needed at all.
 

03MopaRamman

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Was having troubles keeping it in park last winter and quick adjusted for that and downside lost 1st. Pretty sure I just need to pull my homemade pin and then turn the threaded pin a few times around to allow for a better rearword reach, but the cotter pin I put in behind the pin is a *****, just need some real good Light under there and I should be good. So the electrical pins you speak off are back under the truck and not under the hood?
 
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Redtruck-VA

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Was having troubles keeping it in park last winter and quick adjusted for that and downside lost 1st. Pretty sure I just need to pull my homemade pin and then turn the threaded pin a few times around to allow for a better rearword reach, but the cotter pin I put in behind the pin is a *****, just need some real good Light under there and I should be good. So the electrical pins you speak off are back under the truck and not under the hood?

The three wires are the connector plugged into the NVLD at the Evap Canisters. You are thinking the purge valve under the hood.
 

03MopaRamman

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Ok Got it, Too easy, All I remember is all the tubing and a round cannister jigger, never realized there was a plug, Thanks will have a look!
 
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Redtruck-VA

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Let us know...
 
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Redtruck-VA

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P.S/ Cleared a P0440 today and one yesterday as the temp hit 30 Degrees Canadian! Working Downrange in Cotton Coveralls!

Being temperature sensitive now makes some sense to me, if the NVLD pop off valve (part of main valve) is stuck and doesn't relieve as it should the tank will build excessive pressure from the increasing heat and the tank is unable to over come the pressure and recover to a vacuum state and then throws a code for a leak. When there may not actually be a leak but just too much pressure to develop a vacuum needed not to throw the code..
 

47cj2a

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I got nothing to draw with, maybe this will work.

This is what I see is needed for a part list to replace the NVLD.
Initially I would leave everything in place and just wire up the relay to see if it works. The system will continue to work as the purge solenoid is still functioning but shouldn’t be able to throw codes. This might be the solution for those nagging codes that keep popping up. Next step if satisfied with the electrical bypass would be to bypass the NVLD itself for those of you running off road.

12vdc automotive 40a relay NC or 5 pin SPDT
1 Resistor, 130 ohm. 5w to be safe, connected to pin 87a, other end connected to Grd BK/PK
12vdc source wire is OR connected to pin 85
Grd wire is BK/PK connected to pin 86
PCM “Sense” wire is WT/DG connected to pin 30
Maybe someone can draw up a diagram. But it’s simple.

Hello,

I would like to thank you for this!
A little back story, I recently installed a 5.9 Magnum engine in my 1998 TJ. The problem was that the truck was a 2000 so I kept getting a p1495 code for the pressurized fuel tank pump being missing. The TJ never had it and I had no good way of installing the truck one. Finding a computer is near impossible because the truck was a manual. Its quite difficult finding a 1999 or older 5.9 truck with a manual computer. After looking over the wiring diagram for the truck I noticed that the pump looks like its nothing more then a relay. This led me to do some research online where I bumbled onto this thread. Even though the wires are a little different I was able to combine a few things a trip to the junk yard for some factory wires, drill out and install them onto the Jeep C3 plug a quick test and now the check engine light is gone!!

So thank you. All thats left is to clean it up a bit and solder some connectors.

35949104_10101586558032173_5657884827043495936_n.jpg


28795315_10101502210350603_5888749827893142150_n.jpg
 
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Redtruck-VA

Redtruck-VA

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I'm glad it was able to help. Sounds like you have an interesting swap going on. Nicely done..
 

47cj2a

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Thank you.

Honestly its much easier, cheaper to install a Magnum in a TJ then and LS or any other engine. You use the factory Jeep fuel pump. all your gauges work. You just have to splice some wires from the truck engine harness to the factory jeep harness. but its much cleaner and nicer then trying to make a chevy computer talk to the jeep things or having to get different gauges and fuel pumps.

where the engine ends up and the NV4500 being 3 inches longer I didnt even have to shorten/lengthen my drivelines.
 
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Redtruck-VA

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Thats sweet, I installed a 46rh in my 03 ram hemi and it used the original cross member and driveshaft. There are swaps available that are really easy... I'm surprised more folks aren't doing them.
 

47cj2a

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After coming back from a work trip and having some time with the jeep it would throw the code just going around the block.
A little more research and some wires getting moved around its been about 75 miles with no codes thrown.

87a on relay I wired to #20 wire on the C3 plug. Its the Evap Emission Solenoid wire.
85 on the relay I wired to #10 wire on the C3 plug. Its the leak Detection Pump Solenoid wire.
30 on the relay I wired to #14 wire on the C3 plug. Its the Leak Detection Pump Switch.
86 on the relay I wired to positive on the battery. I also installed a 10 amp inline fuse. Not sure if its actually needed though.

Just an update if someone else some day is searching the internet and runs into this thread.
 
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