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Unread 08-19-2013, 12:55 PM   #61
Always2L8
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Hope I'm not butting in here. Just now skimmed through this thread. Not a FI expert but have gone through some trials and tribulations with mine. From what I understand you have a 98 4.0 OBD II XJ engine. My simple mind keeps me in the OBD I era, but principles are the same.

For a 98 XJ, the injectors should be putting out 23.2 lbs/hr @ 49 psi. Your latest posts indicate you are getting 60 to 100 psi at the fuel rail? I don't want to sound preachy, but a rail pressure difference can be signifigant. Information reference - http://jeep4.0performance.4mg.com/tech_specs.html .

My very simplified explanation: The computer/software uses the related base rail/injector psi (49 psi) and fuel flow rate (23.2 lbs/hr) as a primary unchangeable constant value (among others). It is acted upon by multiple variable inputs (i.e. TPS, MAP, O2, H2O TMP, IAT, etc) in order to maintain a fuel/air (F/A) ratio of 14.7:1. The computer code also uses the fuel flow rate as a basis to determine fuel injector pulse rates. The computer has no way of knowing if you changed the rail/injector pressure/flowrate. Therefore it will use the factory assumed flow rate setting to adjust/learn/compensate (via O2 Sensor) to maintain the desired A/F ratio.

Does the MOPAR software compensate enough for this increase? I don't know, maybe someone on here does. If outside those parameters, it will never run right. Can you change the software? It's been several years, but as far as I know, hacking/changing MOPAR codes is difficult but may be out there. As suggested, you may be able to use an earlier model year fuel rail with an adjustable pressure regulator (look up HESCO $$). IMHO you may need to get the rail pressure regulated at 49 psi if using the stock injectors, or change injector size to flow at 23.2 lbs/hr at whatever pressure your running at the rail. First option much preferred.

Example (and if you don't mind a little math):
- Given factory fuel injectors (23.2 lbs/hr @ 49 psi), @ 60 psi those same injectors will put out (60/49)^0.5 * 23.2 = 25.7 lbs/hr. An 11% increase in flow rate.
- Given factory fuel injectors (23.2 lbs/hr @ 49 psi), @ 100 psi those same injectors will put out (100/49)^0.5 * 23.2 = 33.1 lbs/hr. A 43% increase in flow rate.

A Big question is - What will the Peoples Republic of Kalifornia allow you to do with your vehicle?

Good Luck

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Unread 08-19-2013, 01:35 PM   #62
SLO_Ken
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Agreed that I need to get the rail pressure down closer to 49psi. Although, as you point out, at 60psi the flow rate is only about 10% higher than stock, which (i think) the computer should be able to compensate without much difficulty. It might run a bit rich, but I would think that it should run smoothly. I have a feeling that there is more going on here than just the high fuel pressure, which is why I need to get a code reader.

As for what is allowed by the State, here's a link to the California Bureau of Automotive Repair guidelines for engine swaps.
http://www.bar.ca.gov/80_barresource...uidelines.html

I plan to document and report here my experience with the BAR certification process.
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Unread 08-20-2013, 12:49 AM   #63
Always2L8
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Big agreement on checking engine codes. This may be information you are already aware, and if so sorry. You can get engine codes through the CEL. Check this link http://www.xjtalk.com/showthread.php?t=11574 . It's clunky and relatively low tech. It works for my OBD II Grand Cherokee. It took me several tries to get the hang of it, but its cheap.

Godd Luck
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Unread 08-25-2013, 11:56 PM   #64
SLO_Ken
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I tried getting the codes by switching the key on and off... no luck. I found a decent code reader on eBay, it should be here sometime this week. In the meantime, I've been searching a bunch of forums for anyone with similar problems. I found a bunch of threads describing exactly this problem, but not many with solutions. Most of the "helpful suggestions" leaned toward the distributor being off a tooth one way or the other, clogged exhaust (cat, muffler, etc.), TPS, or CPS.

I've got an extra CPS on the shelf, so I may just swap that out to see if it makes a difference.
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Unread 08-26-2013, 06:11 AM   #65
gmakra
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http://www.hesco.us/products/7973/fu...r#.Uhs3qz9mNh4
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Unread 08-26-2013, 06:30 AM   #66
Matt1981CJ7
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Ken,

Wouldn't the condition of the plugs be a good indication if your problem is too much fuel?

Matt
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Unread 08-26-2013, 12:00 PM   #67
SLO_Ken
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Quote:
Originally Posted by gmakra View Post
Ooo... spendy! I'm using the OBDII fuel rail, without a regulator, so this would not work for me... unless I go to an earlier fuel rail.

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Originally Posted by Matt1981CJ7 View Post
Ken,

Wouldn't the condition of the plugs be a good indication if your problem is too much fuel?

Matt
Yes, yes it would. Although, I'm not sure how much I will learn from brand new plugs that haven't been run over idle for more than a minute or so... I'll pull the plugs this evening.
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Unread 08-26-2013, 10:29 PM   #68
SLO_Ken
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Here's a couple shots of the plugs. As I said, they are brand new, and have not been run over idle for more than a minute or so. I'm not sure that there is any useful info here...

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Unread 08-27-2013, 03:53 PM   #69
Matt1981CJ7
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Ken,

As I understand it, the color change should be at the apex of the curve in the ground strap.

Yours appears to have too much timing, which could explain the backfiring.

Matt
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Unread 08-27-2013, 05:59 PM   #70
SLO_Ken
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Scott, could you throw a timing light on Clay's engine and let me know what his base timing is? I find it hard to believe that mine could be off so much as to render my Jeep undriveable, but I've been wrong before...

edit: my timing at idle (~700rpm) is currently 12* BTDC
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Unread 08-27-2013, 08:07 PM   #71
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Quote:
Originally Posted by SLO_Ken View Post
Scott, could you throw a timing light on Clay's engine and let me know what his base timing is? I find it hard to believe that mine could be off so much as to render my Jeep undriveable, but I've been wrong before...

edit: my timing at idle (~700rpm) is currently 12* BTDC
Will do, but I can't get to it until Thursday. Working my PT job tomorrow afternoon, and I won't be home until late. I can catch it Thursday afternoon when I get home from my REAL job!

It was my understanding, through reading, that the 4.0 dizzy only went in one way. You can't insert it wrong, and you can't turn it... if I understand correctly. Total timing is determined between the crank and cam sensors via the puter.
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Unread 08-27-2013, 08:13 PM   #72
SLO_Ken
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Got my code reader today. Pulled the codes... a couple were expected (batt temp sensor, TCM, etc...) and P1391 - Intermittent loss of CMP or CKP. Loss of the Cam Position Sensor or Crank Position Sensor has occurred. So, I'm gonna swap out my CPS and see if that makes a difference.
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Unread 08-27-2013, 08:15 PM   #73
SLO_Ken
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Quote:
Originally Posted by Skerr View Post

It was my understanding, through reading, that the 4.0 dizzy only went in one way. You can't insert it wrong, and you can't turn it... if I understand correctly. Total timing is determined between the crank and cam sensors via the puter.
Right. I just want to verify that I got my CPS in the right spot. You and Clay seem to have gotten it right Just checking my work...
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Unread 08-27-2013, 09:28 PM   #74
SLO_Ken
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Originally Posted by SLO_Ken View Post
Got my code reader today. Pulled the codes... a couple were expected (batt temp sensor, TCM, etc...) and P1391 - Intermittent loss of CMP or CKP. Loss of the Cam Position Sensor or Crank Position Sensor has occurred. So, I'm gonna swap out my CPS and see if that makes a difference.
Oh, that made a difference alright!! Woohoo!!! I'm so happy!

Next up: new exhaust (need to find a cat)

Also, I still need to find an adapter for my VSS, and an air cleaner. And, I should probably try to get my fuel pressure down a bit closer to 50 psi. Then I should be ready to go see the referee
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Unread 08-27-2013, 09:38 PM   #75
Matt1981CJ7
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Ha, so it was timing related.

The plugs rarely lie.

Glad you got her running.

Matt
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