Sticky Long term fuel trims (+18%)

I've been slowly doing some of the maintenance work to make sure the Jeep is ready for my commute. 

2 weekends ago I replaced the spark plugs, boots, and cleaned the throttle body as part of getting the maintenance to a known condition. My younger son decided to help, so it was a good project for him to get his hands dirty and use a torque wrench and plug gap tool.
 

I had disconnected the battery while we did the work, and for the first tank of gas after the new plugs I saw fuel economy jump up to 17-18 mpgs in mixed driving. That was great compared to the 15 MPGs I had been seeing before the new plugs and TB cleaning.  Unfortunately it was short lived and economy dropped off with the next tank. 

I replaced the water pump a couple weeks ago and temps are good (207 at idle w/203 degree thermostat). I have all driveline fluids and trans filters to replace (suffered sticker shock getting that from the dealer).

I have an exhaust leak to fix. Not loud enough to hear with windows closed, but I can hear it when driving with the windows down. Some of it is from a sloppy weld the used car lot made when replacing the muffler. It also sounds like it "sneezes" when fired up cold. 

Now I've also had a few weird things happen:

- when driving on the highway at a steady cruise it had bucked like the ignition cut out and then quickly came back. It did this about 5 times, maybe 30 seconds apart. Not long enough to stall, but enough to make me think I was rear ended, or broke something serious in the driveline. It did this again once today. Both days this happened were after about an hour on the road. 

- code P0507 cleared last week after the first instance of the cutting out, and returned again today. 

- STFT bounce around but are only a couple percent away from zero when idling for both banks.

- LTFT seems to be stuck at +18% for both banks.

- O2 sensor 1 for both banks is moving across a range of 0.1-0.9v and seem to be working as expected 

-O2 sensor 2 on both banks stay around 0.1-0.2 v

- Not sure if it's related, but the muffler was replaced when I purchased the jeep and noticed that within a few weeks it looked like it was changing color from heat (starting at inlet and moving towards outlet), but at the time figured it was just a cheep muffler  

So other than needing to fix the exhaust leak, what else should be on my to do list to try and trouble shoot the fuel trims and get my economy to improve since even small improvements will have an impact (94 miles a day round trip).

Plus 18 on both banks implies a vacuum leak,  bad maf or map, low fuel pressure, something on the intake side. Something that affects both banks.  O2 out of range would be one bank, a weird injector the same.

A vacuum leak will usually have trims trend higher at lighter engine loads and speed.  A maf can do lots of things, but will often transition from plus to minus through the load range.

If it's not flex fuel, 20 or 30 % alcohol in the fuel can do the same thing.  

I'm betting you have a cracked hose/intake, p0507 is an excessively high idle code.

As to the other, ditch the muffler for something else. Sounds like excessive back pressure to me because it's installed backwards.

Streetwiseguy and Ranger50, thank you for the info and suggestions. 

The funny thing about the code is the idle speed is around 625 rpm, so I'll need to look and see if the code returned, or if it was some weird side effect of the bucking. 

As far as I can tell the Hemi doesn't use a MAF, but instead uses a MAP sensor. I'll have to take a look at the live data for it to see if it's behaving correctly. After seeing the build up on the TB I wouldn't be surprised if the MAP was misbehaving.

I'll check for vacuum leaks and also check the fuel pressure this weekend.

I may just replace the MAP if the cost isn't too bad at the dealer. 

I filled up at a different station and checked the LTFT after a 50 mile drive and they were still stuck at 18. 

Check trims while driving.  Compare idle,  cruise and wot.  That will tell you much more.

Don't know hemi's well but when LS engines do this it is usually an intake gasket leak or a hose. 
 

try sprAying brake clean around hoses, intake connections etc while watching the trims. 

So I took some more time to check readings today.

Also, something I forgot to mention, but I'm thinking may be relevant is that I had a "check gas cap" message come up on the information display. It had shown up Monday, and went away Tuesday morning. I had loosened and retightened the cap. I've gotten the message a few times and have replaced the cap twice (the seal on the first replacement tore in a month). It seems to only occurr when the fuel level is above 3/4 of a tank, and sometimes will persisted even if I loosen and retighten the cap while the tank level is high.  No stored or pending code though, even when the message shows up. 

Now back to the fuel trims. I was driving home so wasn't able to really look closely at the meter, but there were some trends.  Today on the drive home the LTFT moved between -4 and 12 on both secondary roads and highways. Most of the time the LTFT moved in the opposite direction of the MAP signal. Light cruise the MAP was showing 6-8psi and LTFT was 8-12, but moved based on load as well as throttle. Coasting down hill under light throttle would result in the LTFT going high.

Seems like I need to check for vacuum leaks, especially around the purge canister and hoses. I'll also check fuel pressure, and see if there are any leaks around the intake. 

There was still a bit of roughness at idle and steady cruise. Something that is uneven enough for a car person to pick up on, but not something your average driver would notice. 

Seems like more inspection and testing is on the agenda for the weekend. 
 

On Edit: I wonder if the purge solenoid is the source of the "sneeze" when starting the engine, especially after sitting overnight? Something to check. 
 

Two things I learned about Chryslers working on them at the dealerships...

1.- they can't build a hose or bearing to last more than about 23 minutes.

2.- they are still speed density, so no maf ever unless it's some rebadged pos.

Unplug the purge solenoid, disconnect the hose going from it to the tank, start engine and check for vacuum.  With it unplugged, it should be shut and therefore no vacuum.

If it is sticking open, this is a large source of your issues.

if you find little chunks of black dust in there, like bits of charcoal, that is because it is the charcoal canister coming apart.

Latest update:

The jeep behaved going to and from work. The drive home was about an hour and then the jeep sat for about 20 minutes while I changed before taking my son to hockey practice. I had gotten gas on the way home from work and reset the fuel economy display (I know, not accurate but a reference point). Interestingly the fuel economy was better on the 20 miles of 30-40mph secondary roads than on the 65 mph highway section that was approx 20 miles.

Approx. 15 minutes into the drive to practice (almost all highway) the engine start to cut out for a split second and then recover. This happened probably 6-8 times and once it started it seemed to be linked to slight changes in throttle position or load. This was probably a mile before the exit and then a mile to the rink after getting off the highway.

After getting off the highway it was still acting up and felt flat with slight throttle changes. Pulled into the parking lot and it stalled but fired right back up with the idle staying high (1200) for about 60 seconds and then dropping back to 600. While it was running I checked and no codes. 

Before I went into the rink I checked the evap valve per Pete's instructions. No perceptible leak but I did end up with an evap code which wasn't surprising. 

While I didn't want to take a shotgun approach, I picked up a MAP sensor and Crankshaft position sensor on the way home. I installed them after eating a late dinner and then checked for vacuum leaks by spraying carb cleaner along the intake manifold/injectors, some of the vacuum lines, and around the throttle body.

I only moved it from the portable garage in the backyard to the driveway.  I'll have to see how it does tomorrow. 

Well, replacing random parts didn't fix it, but did help me change my focus.  

It was fine on the way to work, but acted up on the way home, to the point I thought I might need to get my son to call AAA for me. 

I had the scanner with me, and noticed when the engine cuts out the light for the security system flickers and the throttle body light flickers, the tach drops but no other lights. So I plugged in the scanner and started graphing the pcm voltage. When the hiccups happen the voltage drops to 0, and then jumps back up to 15ish. I didn't capture any of the screenshots on the drive, but voltage is a bit flaky even idling.  Here a couple photos:

So based on that I'm thinking I have a power problem. A quick check in the driveway didn't reveal any overheated relays, battery felt cold, pcm was cold, and wiggling grounds and wires didn't cause it to stumble or stall.

I'll check the voltage in the morning when it's cold, and also take the belt off and see  if the voltage is more stable without the alternator turning. 

I don't want to throw any more parts at it, but need to get it sorted out this weekend. I don't trust it even around town at this point. 

Any thoughts?
 

Ugh.... power problems in a Chrysler.

I forget if your vehicle has the TIPM or not, but they have a lot of internal failures.  Sometimes you can get lucky and pop them open to find corrosion that you can fix.

According to my googling, it has a TIPM and it appears that there's enough failures there is a strong market for repaired units. 

Tomorrow or Sunday I will be digging in to see if I can identify any issues.

So I just cleaned up ground at the body and both connections at the battery.

Nothing looked bad, but the body side had paint so all contact was through the little points on the ring terminal. I cleaned the body side down to bare metal where it contacted and reinstalled. 

I remove the TIPM and it appeared to have been opened before based on what looked like hot glue sealing it on the side where the BCM connects. I disassembled it and couldn't find any visible issues with corrosion, but the boards were soldered together so not much I could check. I did spray it all down with electrical cleaner (no residue), and then reassembled with dielectric grease on all connectors and RTV to seal the BCM side of the housing. 

So far voltage looks better, staying around 14-14.2v slights rise with rpm's, but  much more stable. It will take a longer drive to figure out if there's improvement in the stumble, but that will have to wait until tomorrow.

While I was dirty, I took out the welder and took car of fixing a few leaks in the weld from the dealers installation of the muffler. I double checker the number and they used a direct fit Walker quiet flow and installed it in the correct direction.  

So no joy...

Still had it cut out a couple times on the way home, although it seemed less harsh.

The voltage still dropped to 0, then recover to 14.2, but except for the sudden drop to zero it was smoother when graphed. 

Any ideas on what to do next?

I'm thinking I should clean all the connections at the alternator, clean all the plugs at the PCM, and then I'm not sure.

If it wasn't so jarring to the driveline I would wait until some failed and then it would be easier to find where power was going in but not coming out.

You said you had an alarm system?  I can see that being the issue.  Like randomly cutting power to the pcm. Can you temporarily bypass power directly to the pcm to see if that solves it?  

I have an 08 GC with the 5.7 also. I had issues with the car randomly cutting out and/or stalling. No codes in my case, but online I saw lots of issues with cam and crank sensors. They were cheap, so I did both and that fixed that issue. 
 

I also had huge exhaust leaks from both manifolds due to broken studs on the heads. I replaced both manifolds with new studs and no more exhaust leak. The first tank after the manifold fix was 18mpg, then back down to 15mpg ever since. 

dean1484 said:

You said you had an alarm system?  I can see that being the issue.  Like randomly cutting power to the pcm. Can you temporarily bypass power directly to the pcm to see if that solves it?  

It's the factory system, and I see a flicker of that light (simple round dot) and the throttle body light flicker when power cuts out. I don't think there is a way to bypass the factory module to test if it's the culprit.

I think it might be an artifact since when I turn the key on (without starting the engine) and wait long enough, all the lights except those two go out. Once I start the engine those also go out. 

In reply to Spoolpigeon :

I replaced the crankshaft position sensor and map sensor last week, but didn't do the cam position. I'll give that a try and see what happens. 

It may be the stumble is causing the power drop, and not the other way around. 

It definitely seems to be something breaking down with heat and time. This morning I hit more traffic than normal in the morning and I had it happen just as I was getting off the highway. 

One last thought....

Could it be something in the alternator causing the problems? 

Maybe a shorting diodes or caps when getting hot?

Im thinking that may start to explain the pattern seen in some of the scans:

or do those live in the PCM on something from the 2000s?

New info:

The counters for miles since codes cleared reset when power cuts out. Run time since start also resets. 

I drove 47 miles home without shutting it off and it ended up taking about 80-90 minutes to get home. 

Sitting in my driveway the miles since codes cleared showed as 7 miles, and run time was 2 minutes when I pulled over along the way home to check live data.

There seems to be differing levels of severity in the cutout, sometimes it's smooth and the engine just goes flat, other times is very harsh.  

It happens in normal and tow mode, so it seems like MDS isn't the cause.

Everything sounds like the PCM is getting its keep alive memory power cut.

I have had to bypass various internal circuits on TIPMs before.  Ma Mopar has had enough problems that they have a part number for an external relay kit, with instructions on how to bypass certain internal relays.

In reply to Pete. (l33t FS) :

That makes sense. I'll have to find a wiring diagram and try bypassing the TIPM for the constant 12v lead to the pcm. 

I have the wiring diagrams from alldata, now I just need to decide where I want to feed power into the circuit. 

I'm thinking that I can make up a test lead using some wire with an inline fuse holder and a ring terminal on one end and a spade on the other. That will let me run a lead from the positive side of the battery to the output side of the fuse in the under hood fuse panel (not TIPM). If the problem persisted then I can run a longer jumper to the factory splice in the wiring harness near the PCM. 

That reminds me, I should inspect the factory splice while I'm under the hood. 

Hopefully the problem is in the wiring and not a failing solder joint for the connector  inside the PCM. 

I bypassed the TIPM with a jumper from the battery to the output side of the fuse slot. Now to see if the problem occurs over the next few days.