'98 Grand Cherokee, 5.2, po455, comes and goes

Joined
Sep 7, 2007
Messages
7
Likes
0
Points
0
#1
Hi guys,
hope there is someone out there that can help with this. I've got this po455 large leak purge code that keeps coming on. But it is sort of weird. Unlike most leaks that I've ever heard of, it is not an all the time leak. Since I repaired the one obvious bad vacuum hose, smallest of three by the charchol canister, this code can stay away for days. And them BAM, when the Jeep is starting from a cold start, there is it. And never just sitting in the driveway, but only after you start to drive away a bit, but still fairly cold. By the way, this is a NYS car which means it has a California type emmissions package on it, and so I believe a different purge set up than the federal ones, if that helps anyone diagnosis or understand this issue better.

I've thrown a Stant replacement gas cap at. No better. I read the one other thread on this and that mechanic seemed to think the Mopar, OEM cap was better than most aftermarkets. Does that seem to ring true here? I've seen this before with replacing the radiator. Only a Mopar original has returned this car to it's perfect temp behavior both cold weather and hot. He also spoke of putting a vac gun on the Vapor Line and seeing if it can hold a vacuum, Yes purge valve passed, if not it's bad. Questions: should this be done with the Jeep, on, running, off, hot or cold, or does none of that matter??? I think it might, but I'm not sure. Also of all the small vacuum looking like connections on my valve which one is the one this other person was refering too??? The Vacuum Line, the one to the and from the manifold vacuum source??? The one I'll explain down below that I think send vacuum to the charcoal canister? Some other line.

Yesterday, while I pulled out, cold, Coolant Temp 111, I backed out of my driveway and barely throttled to the stop sign no more than 25 feet or so away and braked. Somewhere in that time, the code came and the light, lite. When I retrieved the freeze frame data it said the car was traveling at 38 mph!!! No way. I cleared the code and this moring I got it again and this time it said I was going zero miles per hour while I was driving modestly thru the local streets, 20-35 MPH probably. I'm almost sure it do NOT happen while sitting still at any of the stop signs. Meanwhile the data I get hook up and watching real time seems to be just about on target when I can glance at it and not drive off the road, so that's confusing too. If it helps here is the last freeze frame data that I recorded from this mornings trigger: po455; RPM: 832; Calc Load%: 5.5; MAP 10.6; Coolant temp: 111, LT FTRM1% 0.0, ST FTRM1% 3.9; Speed MPH 0; Fuel Sys 1 clsd, Fuel Sys2 N/A. I understand everything but the LT and ST FTRM1% ones. What are they talking about?

Soooo, Might I have a totally different problem, like bad computer connections, the ECM itself, the speed sensor in the T-Case, or something totally different that is making something here misbehave? My other thought is might a vacuum leak somewhere else, feedback into this system some how and make it think I have a leak here? My vacuum seems much improved since that above memtioned repair, but??? It is a Mopar with the standard vacuum operated HVAC Duct work and I was working in there, replacing the evaporator this past spring, and all the diaphrams are going on 9 years old, brake booster too.

I was messing with the Charchol canister, bumper removed to install a new, heavy duty radiator support both as an up grade and this one becomes a great, strong tow point that is connected across the framerail, hitch style, with D rings. I just thought I'd be safe and get the thing out of the way while I was wrenching. But two of the four studs that attach it, upside down to the cross member were frozen so the studs in the plastic just spun without loosening up. This is when I first pulled on, probably starting the issue of the vacuum leak, found that cracked hose that I replaced it too. Like I said that helped vacuum symptoms a lot and I thought I should be done, but no. I was installing this rad support to go modest off-roading, first time for this jeep. My group took all the modest trails, only one or two bumps to speak of for the skid plates, lots of bounce but really not very bad. But I guess enough bouncing around could have shaken something loose or dirty something up. So it was when I returned home a few days later (a week after messing with the canister by the way) this is when the code started to show up. Could something be dirty like the purge air filter? Could the charcoal canister have a small leak by those studs that I tried to wrench on. I was gentle with a quarter inch drive reaching thru that small slot between the grill backing and the cross member. Didn't beat on the thing.

Its really the on and off nature of this that has me stumped. If I had a real "large Leak" wouldn't it be ever day, and pretty much ever re-start hot or cold, or do I misunderstand the system and how and when it works? Does the system only check itself on those first really dead cold re-starts? Could I have a slowly dying component like the purge valve itself, much like in that other thread. Or some other intermidiant, working, misbehaving component elsewhere that is messing with the electrical side of this issue???

Lastly, this car does have one of those test ports for the system, but the lable on the valve talks about only 1 psi pressure for testing. I gather this is not something the shadetree mechanic can test with his own vac gun and shop compressor??? Or is it. I've seen you guys talk about smoking a system and I gather that is with one of those special test set-ups. Are there modest priced ones that us shadetree guys might not find too expensive that would do a good job and help us get to the bottom of such issues? I don't mind spending some money of good tools, for cars I will own for a long time. Like my snap on Mopar boltless fan pully holder tool. I've got to be able to access the nose of my own motors, right? It cost a few bucks but I've used it a number of times now and it was well worth it. Could you suggest a few if they exsist? Do big national tool rental houses rent such things??? What would be the name or type of test system I am shopping for?

Lastly, Many of the hoses on this purge system seem to be odd sizes, no less what is one size on one end, does not terminate at the same size at the other end. So regular vacuum and fuel line hose doesn't work well if at all. Do you professionals have an aftermarker suppier, other than Dorman (I've looked there already) for these things, these nipples and fittings and the like so as to be able to replace a bucks worth of hose and not a fifty dollar harness of tubes and connectors. I like the old cars, at least 7/32's was 7/32's on both ends of a run of hose. But not these modern ones.....

I know that this has been a really long post and I appoligize for that. But I wanted to give you all that has happened and that I already know so as to hopefully make it easier for you to help me get to the bottom of this and not waste your time on the other end of this issue. Thanks ever so much. You guys are great. It really is nice of you to share your knowledge and expertise like this so readily. Have a great weekend....
Paul ;)
 

Transman

Receptionist & Complaint Dept.
Joined
Nov 14, 2006
Messages
2,953
Likes
0
Points
0
Location
New Jersey
Website
www.edsofvineland.com
#2
The canister, in my opinion, would be the likely candidate. They are problematic at best. Yes, a smoke test would be a good thing and you may need to have a shop do that, compared to the price of buying a smoke machine, unless you are willing to get trained on the use and are going to do lots of car so you can pay for it. You can do enough damage by doing it without training, that fitting you spoke of has left hand threads.
The reason it is intermittent is probably because the computer needs a bunch of things to happen at the same time before it will even run the test. Outside temp, level of fuel in the tank, how long the vehicle has been off, etc.
Please don't be concerned about how large your post is, we usually get "my car don't start whats wrong with it" for a post.
I do agree with OEM for the fuel cap also, Stant is a popular manufacturer but I have had many problems with their components. Post back, Transman
 
Joined
Sep 7, 2007
Messages
7
Likes
0
Points
0
#3
Was just about to go home for the night. Thanks for getting back so fast. So start with cap, then with a canister? New or would a boneyard be a crapshot? I just don't want to "throw expensive part at it". I don't mind throwing modest priced parts sometime, but expensive ones, with no real incling of what is what, that's another story. When you say that the canisters are prblematic at best would you mind expanding on that. Are Mopar, Jeep canisters a poor design? Are most or all cansisters a problem. It's funny I still think of the old canisters on my '70's Darts and Scamps. Are there really working guts or valves and check thingies in these things these days? Or is it just that plastic and glue of so-so quality, after rattling around for 8-10 years and exposed to fuel vapors ever day will eventually develop a leak somehow, somewhere???

It's funny, I'm convinced that it is a cold in the morning thing, like all those parameters that you layed out in your reply. So I guess these things aren't checking all the time then. I just figured that the purge system would operate more, not less, when hot because that is when fuel tends to vaporize more.... FYI, in the really cold weather up here in Syacuse, you can hear the thing(purge valve and pump) clicking away pretty loud, especially when she first starts up. I've been told by a few different people that this is normal? I guess at 9 years and 182K miles I'm way outside my federal emmissions warrentee lol.... Any leads on all those weird vacuum hose ends and nipples??? The rubber stuff that wants to fail.

Well, perhaps I can swing by the dealer and get a new cap and price out a canister tomorrow morning. I love your your assistant there. Have a great weekend...
Paul ;)
 

Transman

Receptionist & Complaint Dept.
Joined
Nov 14, 2006
Messages
2,953
Likes
0
Points
0
Location
New Jersey
Website
www.edsofvineland.com
#4
The purge system does work all the time but the test does not. The reason I pointed at the canister was you seemed to think it was physically damaged. What we find in damage to the canisters is the fact that gas jockeys gotta get that extra dollar in the tank to top it off, this causes raw fuel to enter the canister which destroys the charcoal inside. If you have physical damage to the canister then it needs to be replaced even if it is not helping set the code. If the rounding screws are not into the canister then pass on replacement until you KNOW it to be bad.
As for the special hoses and ends, Dealer only. I do hear that Dorman is starting to make these so a trip to a good local parts house might be in order. Dorman makes good quality OEM style parts. Transman
 
Joined
Nov 14, 2006
Messages
4,878
Likes
52
Points
48
Age
118
#5
A large leak has been detected in the evaporative system. See TSB 25-001-02. Also, possible faulty or loose gas cap. Note: The respective Powertrain Diagnostic Procedures Manual will direct the technician to determine if the vehicle evaporative system has an external system leak. Examples of some external system leaks are: a loose gas cap, a disconnected evaporative system hose, or a loose hose connection. Remember that the evaporative system may also have an internal system leak. This internal leak may be caused by an intermittent or permanently stuck open Duty Cycle Purge (DCP) valve. This leak source is considered to be internal because any escaping emissions enter into the engine system and not directly into the atmosphere, unlike an external leak. An internal leak may cause one of the above DTC?s. Possible causes of a stuck open (intermittent or permanent) DCP valve are: 1. Corrosion due to system moisture or possible water intrusion into the system.


2500102A - MIL ILLUM., DTC P0442, P0455, OR P0456 - LEAK DETECTION PUMP, LEAK DETECTED

Details: MIL illumination with one of the following DTC:
P0442 EVAP Leak Monitor .040 Leak Detected (Medium Leak)
P0455 EVAP Leak Monitor Large Leak Detected
P0456 EVAP Leak Monitor .020 Leak Detected (Small Leak)
If one of the above DTC’s are present, perform this diagnostic test first before proceeding with the diagnostic procedures in the appropriate Powertrain Diagnostic Procedure Manual.

Raise the vehicle on an appropriate hoist. Locate the LDP vent valve. Remove the vacuum hose from the top of the vent valve (Fig. 1). Attach a hand vacuum pump to the vent valve and apply 20” Hg. vacuum. Observe the vacuum for 10 seconds. If the vacuum holds between 15.5” Hg. and 20” Hg., refer to the appropriate Powertrain Diagnostic Procedure Manual, MDS2, or the Leak Detection Pump Operation and Diagnosis booklet (Publication No. 81-170-000606) for further diagnosis. If the vacuum drops below 15.5” Hg., obtain the appropriate LDP vent valve using the Mopar parts catalog and perform the Repair Procedure.

Repair procedure:
1. Remove the left rear wheel.
2. Remove the wheelhouse splash shield (five plastic rivets P/N 34201631) to gain access
3. Remove the hose at the top rear of the evaporative canister to ease vent valve removal.
4. Remove all clamps and all hoses attached to the vent valve.
5. Install new vent valve. Ensure all hoses, clamps and the vacuum hose to the top of the vent valve are securely attached.
6. Attach the hose at the top rear of the evaporative canister.
7. Install wheelhouse splash shield using five plastic rivets.
8. Install left rear wheel (WJ only).
9. Lower vehicle.
10. Use the DRBIII® to erase the DTC.

Parts required:
4669865 LDP vent valve
 
Joined
Sep 7, 2007
Messages
7
Likes
0
Points
0
#6
He guys. Thanks for both replies. I'm very curious about this TSB. Is there a good place that you folks recommend us regular folks can go and get answers to and search for our TSB's??? I'm gonna do some google, but I gather that you guys have a "better" place to get the dirt on these things. Are there good ones for the general public?

BTY, all of my control stuff, both purge valve and the leak detection pump are on the driver's side inner fender and my canister is upside down on that crossmember I spoke of in the earlier posts. I gather that little write up was from like that monthly Mopar publications and was "general" to a number of cars sharing similar equipment, yes? i've heard of the little XJ Cherokees having some equipment behind the splash shield, but not my ZJ.

Don't you just love TSB's??? Thanks for that lead.....

Paul
 
Joined
Sep 7, 2007
Messages
7
Likes
0
Points
0
#7
Guys,
My OEM gas cap just came in. So I just got it and put it on, and then cleared the codes. Let's see what happens, fingers crossed, it should only be so simple.
If you don't mind I've got a few questions about this subject. First off. Since I just installed the cap, Jeep was hot when I changed caps, but so far no codes thrown. Does the system test on most or all re-starts, or just cold ones? FYI, now I can feel the purge valve clicking away, again on hot re-start to drive back to work from dealer. Good sign, or do I have to wait for a good, cold re-start tomorrow or late tonight?

As a good old analog kind of guy. Aren't there, shouldn't there be ways to tests these two things. Sort of like the procedure Kev wrote up. Kev it sounds like this set of tests was written in general as a basic release by mopar to cover a number of cars, yes? I gather I could try and duplicate this and apply it to the pump on my Jeep if the new cap fails. I might want to do it anyway, just for the heck of trying it and seeing what happens. Would there be anything wrong with applying a little battery power to the correct contact while grounding the other and seeing if these things can go thru their paces? i don't think they get stepped down voltage.

Like apply 12 volts to this contact and watch for vacuum to either like pass thru or to hold a vacuum, Power on and off and watch for a change in vacuum, jump contacts. Just to make the things cycle thru their paces and obverve whether or not they can and do. Almost all other sensors, relays, solinoids and the like have a nice little test procedure like this. But my MOPAR published factory service manual has none. My dad always taught me when you buy a car new, buy the darn FSM. Years later when people don't want to know, you'll know and just when you really need it. But there was no basic test procedures like that in the FSM. It would seem to me, that being able to test them for blocking and hold vacuum when in closed position and passing vacuum and the like when in an open position would just be common sense and clearly outlined in a FSM. Run some basic tests on the purge vavle and the LDP before getting into the whole "smoke test" thing and other things. On my Jeep they are both fairly accessible right there on the fender, pretty easy really....Only the silly canister is buried behind the front bumper for some "great" engineering reason. is there a good book on manually testing these components??? I'm starting to wonder, was there a separate emmissions Manual published for each vehicle or group of cars by Mopar?

I found another similar, no test laid out in the FSM. I've got an old SJ, the full size cherokee with the viscous coupled 229 T-Case. In the old FSM, they clearly have tests to determine if the VC is good or shot. It's based on using a torque wrench and seeing how much torque it takes to spin a front wheel. And that obviously shows how well the VC is holding, and transfering torque around. But on this '98 ZJ Grand Cherokee, for the 249 Quadra-trac t-case there is no mention of anything like this. The Diagnositic run down list even talks as though the thing is some locked-up, part time only t-case. "Driving too much on paved roads, in 4wd" Where did that come from, the 231 Dx chart? No test procedures at all, just replace if VC proves to be defective. Not on a bench or in the vehicle. Sorry about mouthing off, but this is the type of hard info that I buy a full blown FSM for... And that way I don't have to bother har working guys like you. Instead I can answer most of my own questions myself, right?
Anyway, fingers crossed and I'll let you guys know. Thanks for all your input and ideas and have a good night.
Paul ;)
 

jay

Hero Member
Joined
Nov 14, 2006
Messages
445
Likes
0
Points
16
Location
NC
#8
Transman said:
The canister, in my opinion, would be the likely candidate. They are problematic at best. Yes, a smoke test would be a good thing and you may need to have a shop do that, compared to the price of buying a smoke machine, unless you are willing to get trained on the use and are going to do lots of car so you can pay for it. You can do enough damage by doing it without training, that fitting you spoke of has left hand threads.
The reason it is intermittent is probably because the computer needs a bunch of things to happen at the same time before it will even run the test. Outside temp, level of fuel in the tank, how long the vehicle has been off, etc.
Please don't be concerned about how large your post is, we usually get "my car don't start whats wrong with it" for a post.
I do agree with OEM for the fuel cap also, Stant is a popular manufacturer but I have had many problems with their components. Post back, Transman
And to add to what Transman said, the fuel tank had to be between 3/4 and 1/4 full or the EVAP test will not run. There are other items as well.
 
Joined
Sep 7, 2007
Messages
7
Likes
0
Points
0
#9
Unfortunatly the code has returned even with the OEM cap, so I guess it is either try a canister or go to a dealer and let them run a better Diagnostic with possible smoke test to boot. The canister is about $93 bucks. I know it has to be done, but I just don't like not being able to test, diagnosis and probably fix things myself. It just doesn't sit well with me. I like being able to at least figure it out so I am going in prepared and informed. Will keep you all in the loop and thanks again one and all for your advice and time.
Paul