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Discussion Starter · #1 ·
Hi All,

I have a 2007 Jeep Grand Cherokee. 125k miles with a new 4.7L engine installed at 112k. (That's a whole other story).

After the last few fill-ups, it will run fine for a short period (10 min?) then will begin to buck/lose power when trying to accelerate. I notice this happening only after filling up and then getting on the highway. This is not a rough running engine or cylinder skipping, it feels like a full power loss that occurs only for a second, runs again for a few seconds then bucks again. Will repeat as long as I accelerate or call for power. It fires and idles fine in these situations (between bucks). Problem goes away after I burn off a few gallons of gas, runs fine after that. It did kick a PO205 code last time, but I do not believe this is an injector problem because it does not skip just one cylinder, it fully shuts down for a mil-second (i.e. the bucking feeling).

I read on a search about a Vapor/Liquid separator valve in the fuel system. In the gas tank itself? That can fail, and shoot fuel into the intake manifold which floods the engine for a second causing it to stall? This valve is intended to burn the vapors in the tank, but when fails shoots liquid instead of vapor which overwhelms the intake?

Has anyone heard of this problem? Or had similar symptoms after fill up? Any idea what is wrong and what repair is required?

Many Thanks
 

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90grandoneer
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You're pretty much correct above. In many cases, when stalling occurs after fill up and goes away after burning off a few gallons, the problem is related to the fuel purge system. A good quality diagnostic scanner can check the purge solenoid, but the problem could also be with the charcoal canister. It's my understanding that problems can occur when the vehicle is repeatedly overfilled (adding more fuel after fuel nozzle shuts off) or the valve you indicated above allows fuel to enter and contaminate it. According to the Chrysler folks, what happens is, "an engine stall condition just after filling the fuel tank. There is an integral multi-functional control valve that may allow liquid fuel to enter the evaporative emissions system causing a rich fuel condition when the purge system is initiated."

A couple thing you may want to do:
---Try to not fill it completely full a couple times and see if it still stalls. If it doesn't, this is likely the issue.
---Another thing you could try is to disconnect the purge vacuum hose at the intake manifold and cap both the fitting on the intake manifold and the hose and then see if it happens. You'll almost certainly get a code when the hose is disconnected that will have to be cleared after your "experiment" is completed.
 

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i was thinking the same - an EVAP issue.

I would scan for codes- I do not trust key on off code displays.
Do not top off tank.
Does the pump kick off often during refueling?

The p0205, is a WIRING or circuit prblem with that injector. Maybe a quick check the inj
connector to start.
 

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Discussion Starter · #4 ·
Thanks for the help. The auto shutoff works fine when filling the tank, and I don't try to add additional fuel once it shuts off. So that piece works. But filling the tank to full seems to be the culprit. I drove it all week and had to fill it twice, but did not fill above 3/4 of a tank. No problems at all this week, so I think I have proven to myself that if I don't fill the tank I don't have the problem.

Last year I had the check engine light coming on with evap codes. Had to do a smoke test and they finally figured out that there was a vacuum leak at the charcoal canister o-ring. Once replaced that problem was fixed and the check engine light has not come on again. The charcoal canister and purge valve (up front) were replaced at that time. So I am guessing this problem is internal to the tank and exactly as you describe, fuel is getting purged into the intake manifold when it should only purge vapors. Problem is I cannot find any part called a liquid/vapor separator valve or anything like it listed anywhere as a replaceable part.

Do you know if that part is replaceable? I have heard that it is not, and the only way to fix this is to replace the gas tank. I don't want to do that on a 2007. $$$ But I really would like to be able to fill up the tank for those longer drives.

Thanks
 

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Discussion Starter · #5 ·
I will take a look at that injector connector.



The code only kicked once during the surge problem and has not returned. So I kind of concluded that this was kicked as a result of the bucking.



Not filling the tank beyond 3/4 seems to have solved the problem, but I really would like to get the problem fixed.
 

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90grandoneer
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I believe that valve is in the tank. On the early LX vehicles (300, Magnum, Charger) they extended the warranty on the fuel tank to lifetime because of this exact problem. I had the problem with my 300 and after they replaced it, I've never had a problem again. It had about 170K on it when it started acting up. My Magnum has just over 90K on it and I've not had any problems with it......yet.

As I said, you may want to fill it up and, at the same time, disconnect the purge solenoid hose (either at the solenoid or at the intake manifold) which will render the purge system inoperative.....but probably also give you a DTC. Then drive it as usual and see if the problem occurs or not. This should confirm if it's somewhere in the evaporative system or not. I'd also check the purge solenoid again, even though it's been replaced. If it's good, then go back to the charcoal canister and if it is again contaminated, the problem is most likely in the tank. Not much else left??
 

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Discussion Starter · #7 ·
Thanks, I will do as you suggest and see how she operates. I am betting the charcoal canister is toast again :) All the best.

"you may want to fill it up and, at the same time, disconnect the purge solenoid hose (either at the solenoid or at the intake manifold) which will render the purge system inoperative.....but probably also give you a DTC. Then drive it as usual and see if the problem occurs or not. This should confirm if it's somewhere in the evaporative system or not. I'd also check the purge solenoid again, even though it's been replaced. If it's good, then go back to the charcoal canister and if it is again contaminated, the problem is most likely in the tank. Not much else left?"
 

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I have a very similar issue. I'm going to have to "play" with the gas tank level to see if it's related. Seems mine only does it when it's 90+ outside and after it get it p to running temp and turn it off for a while. Say go in a store for a while and return to drive it again. Only code I've gotten is P0300, random misfires. Sometimes solid CEL and sometimes it flashes, but usually gone the next day after it sits over night. I'm still watching things to try to narrow it down.
 

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Discussion Starter · #9 ·
Funny, My problem appeared mostly when it was really hot outside 90s. And even after I stopped filling it full it kept up with the problem for a while. I did have a few times when I had the same experience as you, stopped at a store, then it started bucking again once back on the road and up to running speed. I have yet to do the test suggested above, but drove it another 250 miles in the last 4 days, 3/4 tank fills, and no problems now at all. I have added three containers of "heat" brand dry gas over the last fills too. I still think this is related to the purge valve or solenoid but so far so good with the problem not coming back this week. But try filling to 3/4 full and do that for about 500 miles of driving before concluding thats not going to resolve the symptoms. It took a few tanks to lose the symptoms. That said, it has been alot cooler here the last week or so, so I dont have 100% confidence that the 3/4 fill solution is the fix.
 

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Nothing major to report back but filled up this morning, normal station and same octane. Rounded off 13 cents after it clicked off full. I did notice something last night though. I checked the electrical connection on the purge solenoid and all kinds of stuff came out - dirt, ect when I unhooked it. I cleaned the plugs on both ends, added dielectric grease and put back on after several on and offs to possibly clean off the prongs. Now let's drive it and see. Doubtful right now because the weather is cooler.
 

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Discussion Starter · #11 ·
I am beginning to get clarity on when this is happening. Turns out it is not necessarily related to filling the tank, and may be related to stopping in the middle of a trip, shutting off the vehicle then starting up again. So for example. I drove 100 miles or so, and stopped for an hour at a mid point. Started the vehicle again and got the bucking. At this time the tanks was about 1/3 full. Yesterday I drove 120 miles, filled up to 3/4 of a tank, drove across the street to a store, shut the vehicle off, then started up again, and then it started bucking again right away. I have had 2-3 instances where the vehicle has had less than half a tank, but was running and hot, then shut off for a short period, then started again and started bucking. None of these times was the outdoor temperature over 80 so I no longer think outside temp is necessarily part of the problem. I am beginning to think that when I drive the vehicle and let it sit overnight I dont get the bucking again the next day. Just when it is warm, run for a while, shut off, and then restarted. The bucking has been less severe in the recent weeks and tends to pass within 10 miles of driving or so. I still suspect this is related to the EVAP system and the purge process since it feels like and intermittent fuel problem. All other times the vehicle runs well and consistently well so I dont think it is electrical or fuel pump related. Those problems would show up more often and not just in this pattern of hot, stop, run, buck. Will keep you posted on my symptoms and suspicions.
 

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Discussion Starter · #12 ·
Well I figured it out. It was in fact the ECM. I ended up ordering a replacement ECM/Computer from www.fs1inc.com, it was literally plug and play, took me 10 minutes to swap out the computer. I have now driven it about 1000 miles in both warm and cold temps and the failure is gone. I have to say I was a bit skeptical that FS1 could provide me a computer that would work out of the box, but they did. I would recommend calling them and talking to someone if you place an order. If I had simply ordered on-line I would have ordered the wrong part, but the service rep figured out what I needed and it only took about a week to receive it.

Out of frustration with the intermittent nature of the problem i took the vehicle to the dealer, they could not figure it out and frankly i dont think they spent much time trying. They quoted a bunch of other work that did not need to be done and returned my car. I think they were hoping I would just trade it in. So I figured for $300.00 bucks what did I have to lose. It was a cheap fix given the cost of used Grand Cherokees these days.

All the best. Bob
 

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90grandoneer
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Glad you finally got it fixed, Bob. That's a good price for a rebuilt PCM/TCM too. Don't you just love the "stealers"? Take it in for one problem and they tell you a hundred other things are bad but can't fix the problem you took it in for. That's why I do all my own work, except for front end alignments and only take it to the stealer for recalls or warranty work. They've even screwed a recall up once.
 
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