NAXJA Forums -::- North American XJ Association  

Go Back   NAXJA Forums -::- North American XJ Association > NAXJA Unibody Jeep Technical Forums > Jeep Cherokee XJ (1984 - 2001) > OEM Tech Discussion
HOME Member FAQ Sponsor Info Rules Bylaws E-Mail

OEM Tech Discussion Forum for OEM (Original Equipment) or stock XJs and MJs.

Reply
 
Thread Tools Display Modes
  #1  
Old July 29th, 2021, 15:43
Cvldwell Cvldwell is offline
NAXJA Forum User
 
Join Date: Aug 2015
Location: 805
Posts: 7
92 High Fuel Pressure/Stinks/Runs Rough

Hey gents. 1992 XJ 4.0 with an interesting and long one for you. I have done research on all forums, etc until my eyes bled and I can't figure it out. Any ideas would be much appreciated.

TL;DR - Jeep stinks and won't smog, abnormally high fuel pressure for a 92, lots of replaced parts previously, runs pretty well at all ranges with a slight misfire at idle probably vacuum/exhaust leak related. Ready to throw a new head, new sensors again, and the new fuel pump in.

Facts and Issues:
- Recently started running with a strong typical "smog" smell, can't pinpoint the exact timeframe of when it started. This mostly happens when the e-fan kicks on and brings the temp down, but it the smell is becoming worse as the days go by, now stinking all the time. Before it would only happen after idling for 20 minutes and once the fan brought the temp down from 210-185.
- Fires up immediately when cold, like second rotation.
- Long cranks if firing once warm, but doesn't exhibit symptoms of heat soak as it doesn't stumble or run poorly, it just cranks 6-7 rotations before firing like its trying to bring fuel back up (but the fuel is already there per the gauge).
- It has had a myriad of parts replaced recently as I'm a "throw everything at it" kind of guy. I've replaced injectors with Ksuspension 4holes, walker muffler, IACV, air charge sensor on the TB, coolant temp sensor in the thermostat housing, fuel filter, exhaust manifold as it was cracked, o2 sensor, MAP sensor, plugs/wires/cap/rotor, throttle body gasket, probably forgetting some things. I have reset it every time after replacing parts.

Here's where things get interesting.
- I checked the fuel pressure at the rail and its 40psi+ with key on/not running and the same while running, and 50psi+ when running with FPR vacuum line disconnected.
- I checked the return line from rail to tank and don't see any kinks that may cause a high pressure.
- From what I understand, this year should be around 31psi at the rail.
- I can't tell if its rich or lean, but it stinks like all hell and runs a little rough at idle. No indication of either on the plugs, they're completely clean and were replaced before this all started.
- It does leak down from 40psi to 25-30psi after about 20 minutes after shut down, though I haven't waited longer to see if it drops further.

I thought maybe tank check valve leaking down or injector bleeding, but the results of the rail pressure test show the exact opposite? Spark plugs are neither black nor white.

Is there anything in the sending unit/pump that can cause high pressure? I have a new unit, just don't want to replace it if I don't need to. Can anything in the head cause this like a stuck valve? Can it throw some kind of loop when the temperature drops back down from 210 that causes it to run rich or lean? I think it's on the OEM catalytic converter, but unsure how it would cause high fuel pressure. I haven't compression tested or vacuum tested for exhaust restriction.


I'm at a loss. Thanks in advance!
Reply With Quote
  #2  
Old July 29th, 2021, 15:54
Cvldwell Cvldwell is offline
NAXJA Forum User
 
Join Date: Aug 2015
Location: 805
Posts: 7
Re: 92 High Fuel Pressure/Stinks/Runs Rough

Also just wanted to throw it out there, it's a one owner, never been off-road, and has been meticulously cared for. I have a 3" binder full of service records going back to the purchase invoice. No chance of "abuse" or anything that could be causing this other than a parts failure that I'm not understanding. Pic for proof that it's not a hack job, lol.
Reply With Quote
  #3  
Old July 29th, 2021, 17:20
tech1001 tech1001 is offline
NAXJA Forum User
 
Join Date: Oct 2016
Location: Los Angeles
Posts: 237
Re: 92 High Fuel Pressure/Stinks/Runs Rough

The 1st thing it could be the fuel pressure regulator , change that and recheck the fuel pressure .
Reply With Quote
  #4  
Old July 29th, 2021, 17:41
Cvldwell Cvldwell is offline
NAXJA Forum User
 
Join Date: Aug 2015
Location: 805
Posts: 7
Re: 92 High Fuel Pressure/Stinks/Runs Rough

Quote:
Originally Posted by tech1001 View Post
The 1st thing it could be the fuel pressure regulator , change that and recheck the fuel pressure .
Thanks. Forgot to mention, it has a new FPR. I'll try another one but I'm thinking it's deeper than that. Or I have a poor understanding of how the regulator works, haha.
Reply With Quote
  #5  
Old July 29th, 2021, 18:56
tech1001 tech1001 is offline
NAXJA Forum User
 
Join Date: Oct 2016
Location: Los Angeles
Posts: 237
Re: 92 High Fuel Pressure/Stinks/Runs Rough

Also use a air hose and blow out the return line just to make sure it not plugging up . The fuel pressure regulator has a spring loaded needle and seat with a vacuum diaphragm that pulls on the needle so when vacuum is applied it pulls on the spring and lowers the fuel pressure .
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
87 renix 2.5 - high fuel pressure, is that bad? oldskoolsleeper OEM Tech Discussion 3 November 16th, 2010 17:07
High Fuel Pressure XJunky OEM Tech Discussion 1 June 17th, 2009 08:13
Fuel Pressure too High. ajporter03 OEM Tech Discussion 0 April 8th, 2008 18:15
Fuel pressure too high? alky350 OEM Tech Discussion 2 February 22nd, 2006 12:19
Fuel pressure too high my65289stang OEM Tech Discussion 4 January 14th, 2006 03:24


All times are GMT -7. The time now is 16:21.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014