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 October 14th, 2010, 20:55
theallpowerfulme theallpowerfulme is offline
NAXJA Forum User
 
Join Date: Oct 2010
Location: knoxville, tn
Posts: 4
Strange starting/no start problem - ECU questions - video

I have a '96 XJ with no modifications to the drivetrain. I recently experienced a no start issue in which the engine would turn over and never make an attempt to fire. The following were replaced: crankshaft position sensor, dist cap, rotor, plugs, wires, TPS, IAC all with no change in the problem. I then replaced the ECU (top picture below) with one from a '97 (second pic below). The jeep fired right up, but ran like it had a cylinder or two misfiring. This would not change with throttle position. Noticing that all numbers on the ecu were different, I assumed a different year model my have different settings so I bought another 96 ecu (third pic below). On the 96 ecu, one of the numbers is the same as the original that came in my jeep, but all the other numbers are different. After installing the ecu, the jeep fired right up and ran great on several occasions. Then, it would fire up, but not idle. Now, it tries to fire... but rarely runs (note this is different than the original problem in that it actually tries to run, but doesnt). It will start on occasion and idle for about 1 min, but them usually dies on it's own (I am giving it zero throttle position during this). I can put the '97 in it and it will fire right up, but again, will run like it has a misfire on two or more cylinders. Help a noob out! TIA! :cheers2:

EDIT: I'd like to add that there is no CEL during any of this. Except the '97 which has a CEL and the gen light on.







***VIDEO ADDED***

Here is the starting/idle issue with the 1997 ecu:
1997 ECU starting on Vimeo

Here is the no start issue with the replacement 1996 ecu:
1996 ECU starting on Vimeo

Last edited by theallpowerfulme; October 14th, 2010 at 21:15.
Reply With Quote
  #2  
Old October 15th, 2010, 14:44
theallpowerfulme theallpowerfulme is offline
NAXJA Forum User
 
Join Date: Oct 2010
Location: knoxville, tn
Posts: 4
Re: Strange starting/no start problem - ECU questions - video

bump
Reply With Quote
  #3  
Old October 15th, 2010, 15:12
gradon's Avatar
gradon gradon is offline
NAXJA Forum User
 
Join Date: May 2006
Location: DC
Posts: 3,115
Re: Strange starting/no start problem - ECU questions - video

I have a 96 M/T and had to use a 97 M/T pcm as a back-up when I blew the original pcm(heater wire on o2 sensor harness kissed the Borla and blew the pcm). I too had the check engine light(though no codes stored)and the gen light was like 1/4 on when I used the 97 pcm, so there are definitely harness differences between the 96 and 97 obd2 systems(I haven't verified by fsms yet, but the question has arisen multiple times if all obd2 pcms are swappable, so I'll do my homework and report back w/ the differences). I'm inclined to say use 96 pcms for 96s and 97-99 are interchangeable and 99.5-01s are interchangeable. I'm curious if the replacement 96 would work great again if you disco'd and reco'd power to it and then once it relearned parameters, acted up again. Basically people are going to recommend that you clean and tighten your grounds and disco and reco all sensors.
Reply With Quote
  #4  
Old October 15th, 2010, 15:13
birchlakeXJ's Avatar
birchlakeXJ birchlakeXJ is offline
NAXJA Forum User
 
Join Date: Jan 2008
Location: Melrose, MN
Posts: 2,779
Re: Strange starting/no start problem - ECU questions - video

I'd look at a couple of options....

1. Start your own testing to see whether you have a poor spark or a marginal fuel or even something as simple as a marginal battery (yes, it can happen and be strong enough to start the engine). Visually check spark on a few cylinders, get a fuel pressure gauge on the schrader valve and watch it, etc.

2. Get it on an engine analyzer to get some higher tech help here.....
Reply With Quote
  #5  
Old October 16th, 2010, 13:55
theallpowerfulme theallpowerfulme is offline
NAXJA Forum User
 
Join Date: Oct 2010
Location: knoxville, tn
Posts: 4
Re: Strange starting/no start problem - ECU questions - video

Quote:
Originally Posted by gradon View Post
I have a 96 M/T and had to use a 97 M/T pcm as a back-up when I blew the original pcm(heater wire on o2 sensor harness kissed the Borla and blew the pcm). I too had the check engine light(though no codes stored)and the gen light was like 1/4 on when I used the 97 pcm, so there are definitely harness differences between the 96 and 97 obd2 systems(I haven't verified by fsms yet, but the question has arisen multiple times if all obd2 pcms are swappable, so I'll do my homework and report back w/ the differences). I'm inclined to say use 96 pcms for 96s and 97-99 are interchangeable and 99.5-01s are interchangeable. I'm curious if the replacement 96 would work great again if you disco'd and reco'd power to it and then once it relearned parameters, acted up again. Basically people are going to recommend that you clean and tighten your grounds and disco and reco all sensors.
You are the third person that has talked about the O2 sensor, was it the upstream that gave you problems?

Quote:
Originally Posted by birchlakeXJ View Post
I'd look at a couple of options....

1. Start your own testing to see whether you have a poor spark or a marginal fuel or even something as simple as a marginal battery (yes, it can happen and be strong enough to start the engine). Visually check spark on a few cylinders, get a fuel pressure gauge on the schrader valve and watch it, etc.

2. Get it on an engine analyzer to get some higher tech help here.....
1. I have spark, seems to be in the proper intervals. Also fuel pressure was tested and is a hair under 40psi. Battery was load tested and is A-OK

2. With the replacement 96 ecu there are no codes or CEL, on the 97 there is a CEL but no codes. I do not have a DRB.
Reply With Quote
  #6  
Old October 16th, 2010, 16:02
gradon's Avatar
gradon gradon is offline
NAXJA Forum User
 
Join Date: May 2006
Location: DC
Posts: 3,115
Re: Strange starting/no start problem - ECU questions - video

Fuel pressure is supposed to 49psi+/-a couple. If you're getting 40 at idle and then when you put a load on it and it drops even more. . .maybe that's why it isn't running right. When was the last time you changed the fuel filter? Might be time to drop the tank and inspect hoses and filter sock on pump too. Last week I had to change out the clogged external fuel filter on my buddy's 96: the pump couldn't push the amount of gas through the filter that it wanted to, so the hose was leaking. Took off the filter and held it vertical and saw all the nice rusty crud that came out.
Reply With Quote
  #7  
Old October 16th, 2010, 16:06
carl.vaughn carl.vaughn is offline
NAXJA Forum User
 
Join Date: Sep 2010
Location: Illinois
Posts: 1
Re: Strange starting/no start problem - ECU questions - video

How long did you drive it with the replacement 96 ECU? I am kind of new to the XJ seen, but have been working on vehicles most of my life. I know that on most vehicles, when you replace a computer, it will be in learn mode for at least 3 drive cycles. A drive cycle is from cold to normal operating temperature. Just a thought.
Reply With Quote
  #8  
Old October 20th, 2010, 20:45
theallpowerfulme theallpowerfulme is offline
NAXJA Forum User
 
Join Date: Oct 2010
Location: knoxville, tn
Posts: 4
Re: Strange starting/no start problem - ECU questions - video

Quote:
Originally Posted by gradon View Post
Fuel pressure is supposed to 49psi+/-a couple. If you're getting 40 at idle and then when you put a load on it and it drops even more. . .maybe that's why it isn't running right. When was the last time you changed the fuel filter? Might be time to drop the tank and inspect hoses and filter sock on pump too. Last week I had to change out the clogged external fuel filter on my buddy's 96: the pump couldn't push the amount of gas through the filter that it wanted to, so the hose was leaking. Took off the filter and held it vertical and saw all the nice rusty crud that came out.
Well it was a hair under 40 and fluctuating while starting. It never actually ran. I will pull the pump and check that stuff out.

Quote:
Originally Posted by carl.vaughn View Post
How long did you drive it with the replacement 96 ECU? I am kind of new to the XJ seen, but have been working on vehicles most of my life. I know that on most vehicles, when you replace a computer, it will be in learn mode for at least 3 drive cycles. A drive cycle is from cold to normal operating temperature. Just a thought.
Starting has been attempted with the new 96 ecu a hundred times. It rarely starts and runs, but when it does, it dies quickly.
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
88 strange no start skyaugen OEM Tech Discussion 5 January 10th, 2009 10:53
very strange starting problem.. DeadHead420 OEM Tech Discussion 7 April 12th, 2008 11:01
Strange Noise when starting/Cutting Off Cherokeekid88 OEM Tech Discussion 2 June 29th, 2007 19:30
Strange Starting issue OCMI_Teddy OEM Tech Discussion 8 April 22nd, 2007 15:00
Strange Problem when Starting boise49ers OEM Tech Discussion 8 March 11th, 2005 06:12


All times are GMT -7. The time now is 04:46.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014