lhpdiver

Our check engine light has been pretty much on for the last 7 years or so. I have purchased one of those sensors to turn it off long enough to get through emissions testing. I have purchased a $100 or so smoke test gizmos on ebay. I and my mechanic tried it out for 15 minutes or so a while back. We found nothing - but I could not swear we used the thing correctly...

So my question - is there an alternative way to isolate the possible source of the error ? What happens if I disconnect the two hoses on the solenoid purge valve ? Can I drive the Jeep ? Can I put some duct tape over one of the ports and drive the Jeep to see if the error is thrown ? and then switch the test to the other port ?

Any thoughts appreciated.

awg

name the year and engine size of your vehicle

identify what code is being thrown

use that to identify the failed parts and replace them

Cummins93

The leak detection pump as a large S bend hose coming off it. I have capped it before. This basically makes the LDP pressurize just the piece of hose in a short time with a low number of contacts counted as the rod moves up and down. The ECU can be fooled.

lhpdiver

2001 Cherokee 4.0L
Code is 456 (from memory) small evap leak
As I understand it that could be anything anywhere in the evap system.

Visually everything is fine. Not the fuel cap, New MOPAR solenoid purge valve and that little cylindrical exhaust gizmo (evap canister ?).
When we put it on the smoke machine smoke was only seem at that canister.

But perhaps someone can answer the questions from my original post ??

lhpdiver

Thanks for that - that is probably why even in our little world they are smart enough to pop the hood and have a look before performing emissions testing :-) ?

Thanks for helping my aging memory. We also replaced the LDP with a 'genuine' MOPAR part from ebay. The mechanic (who is great and has a similar Jeep) swears that even though I purchased a MOPAR part it might have been a clone and I need to purchase the part directly from the Chrysler dealer $$$ ???

Thanks for your patience - so are you suggesting if I cap the hose from the LDP I can then play with the hoses coming from the solenoid purge valve independently ? As I understand it one port goes to the rear and the other the front ?

Patman

Spray a little starter fluid over your vacuum hoses. If your engine revs, you found your leak..

dave1123

Yeah, but! The leak only occurs when the LDP cycles to test the system. It's a small leak because of the time required for it to leak down. The small leak on my 2000 WJ was the test port itself. The schrader valve in the port was leaking. I got several from a junkyard and the first one I tried fixed it. You can try eliminating the "T" the port is in to see if that's the cause.

Cummins93

Capping the hose and still throwing the code cuts down where the leak/defective part can be. It can also get you through emissions and back on the road in a pinch.

lhpdiver

Apologize for bringing this topic up yet again.

Our mechanic - who also has a 2001 Cherokee - happens to have another 2001 Cherokee in his shop at the moment which does not have an evap problem. That jeep will be in his shop for at least the next 3 weeks (owner travelling). So our mechanic's suggestion is to one by one start rotating components out of the working Jeep into our 2 non-working Jeeps. Problem is he has already swapped the evap leak detector into HIS jeep and it still threw the fault. Now he is suggesting swapping out our pump to see the results. I'm no mechanic - but that just seems silly.

I came across a video on youtube today which (I can't find the link to at the moment) where the (very entertaining guy from NC) touched on things I had never known before. For instance - he used his code reading computer to put the Jeep into "evap testing mode" - which I guess means closing the purge valve to properly pressurize the system. It seems that my scan tool can do the same. In the past there was yet another guy on the internet that said you had to stick a screw driver into the throttle switch to allow the smoke to flow through the system. I'm not sure that is good advice.

I read the manual for my scanner and it says - consult your service manual as to how to take your evap system out of test mode. I have no such manual but am hoping that if I detach all probes etc and restart the car it will be out of test mode ???

Take it to a pro you might suggest - but I would almost bet you that my simple $100 smoke machine is the ONLY such device within 100 miles or so.

In the case of the video I mention - he needed to drop the fuel tank to solve the issue and that is something an old man such as myself will not attempt in the driveway.

This can't be rocket science. I already have like $100 invested in a smoke test thingy. We have replaced all the big ticket items - not all the rubber hoses yet I don't think. On the internet they get a fortune for little adapters that attach to the evap test port - and replacement test ports are not cheap either if you can find them.

At one point 2 or 3 years back our A/C was only blowing air down by our feet. The shop had to pull the dash and 'rebuild' some sort of box (using glue) to fix the issue. At that time they said they also noticed that there was a vacuum hose behind the dash that was not properly attached. I want to believe that for months after that we had no check engine light issues.

Sorry for the ramblings...

downs

I know if i was the owner of that other Jeep and I came back to find out my Jeep had been canablized for parts for troubleshooting without my knowledge or permission I'd be highly pissed.

If permission was given then disregard.

downs

You could have built a smoke tester for about 50 dollars but 100 isnt bad either.

Vacuum leaks are a common cause of HVAC issues. Id be leary of a shop that told me they had to rip apart the dash (not quick job) to "rebuild a box with glue" then magically found a disconnected vacuum line "behind the dash"

Id start manually pulling and checking hoses visually.

lhpdiver

I have known our mechanic for years AND he has known the other owner likewise.

That is not an issue (but the thought had occurred to me also). But I believe the goal was not to cannibalize but merely 'isolate' and the restore.

awg

One of our gents finally resolved his issue by replacing a faulty purge solenoid,,, after a lengthy process

What code is being thrown ?

I think a smoke test is a wise idea, cant hurt

after that, substituting parts while you have the opportunity also sounds sensible, (that is one reason I have a spare 59 VIN off my DD)

if an XJ-owning mechanic is stumped, that isnt encouraging, but it will probably be something simple in the end

lhpdiver

Well that tester might have cost me closer to $50 if we lived in the US ...
When our 'shop' pulled the dash it was because the A/C was only blowing down at our feet. After they pulled the dash and fixed some box that (I am assuming) helped direct the air flow as desired (but I'm sure you know better than I) - they noticed a disconnected hose.

We (thankfully) live in a world where whenever possible things a repaired rather than automatically replacing them.

The honesty/sincerity of our mechanic is not open for discussion.

tech

I also have a 2001 xj and I had the same code . The way I fixed it was to remove all hoses and cleaned the hose and fitting at the charcoal canister and adding a Nylon Tie Wrap around each hose to add some sealing to it because the hoses felt a little loose and that was 5 years ago and the code never came back .