'93 GC running very weak, code 51 - JeepForum.com
Reply
 
LinkBack Thread Tools
post #1 of 54 Old 06-18-2010, 09:27 PM Thread Starter
groovon
Registered User
1993 ZJ 
 
Join Date: Jun 2009
Location: Oakland
Posts: 53
'93 GC running very weak, code 51

My '93 Grand Cherokee Laredo (automatic transmission) has always seemed to lack power in the year I've had it, but over the last three days it's gotten so bad it won't climb more than a moderate hill, even in 1st/low range.

When you put your foot down hard, it feels like it's choking - like there's a rag stuffed in the throttle body, or a blocked exhaust pipe or something.

The air filter is OK. Starting is normal. Idle is normal. Engine runs smooth enough, i.e. no missing, and revs OK under no-load conditions. Temp. gauge doesn't show over-heating even when engine has been pushed.

A mechanic checked the fuel rail pressure at 34 psi. I guess that's OK.

The diag. code says '51' which is the O2 sensor saying that the engine is running lean. Might it be simply the O2 sensor is out, or else it's OK and telling me I need new injectors? A vaccuum hose off I haven't spotted yet? A cracked intake manifold? I can't see anything like that so far...

What do I do next? Try to check/clean the fuel injectors? Spend $70 to change th O2 sensor?
I'm just an old fashioned carburetor and manual transmission kinda guy, so I'm pretty much in the dark here.

Thanks for any help!
Dave

groovon is offline  
Sponsored Links
Advertisement
 
post #2 of 54 Old 06-18-2010, 09:36 PM
ratmonkey
R.I.P.
 
ratmonkey's Avatar
1997 ZJ 
 
Join Date: Dec 2006
Posts: 19,804
What motor do you have? Fill out your profile! It matters for diagnosis.

Is the cat plugged?

Unplug your o2 sensor and see if anything improves.

Reset your computer after that test and see if anything improves.

'97 zj 5.2, some stuff, some other suff, and some things that even work sometimes.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

ratmonkey is offline  
post #3 of 54 Old 06-18-2010, 10:01 PM
stmprnch
Registered User
 
Join Date: Mar 2005
Location: Dallas, Oregon
Posts: 125
And More Info

Quote:
Originally Posted by ratmonkey View Post
What motor do you have? Fill out your profile! It matters for diagnosis.

Is the cat plugged?

Unplug your o2 sensor and see if anything improves.

Reset your computer after that test and see if anything improves.
I agree with Rat, knowing what motor your dealing with will help but so will more general information.
How many miles on which components, has the engine or tranny had any major service or replacement that you know of?
How many miles on the clock?
Have you done a compression test?

I'm a fan of finding the problem before I throw money at parts. But I'm also in the process of tearing down my '93, obvious contradiction. Today I pulled the intake and exhaust off the motor, the long block is still in the ZJ. The engine would start and run fine with no noise, all seemed just fine. Today with the manifolds pulled I can tell that two of the six holes are not healthy. On mine the tranny broke, something in the overdrive, so I'm doing both to put it back on the road healthy.

'93 GC (ZJ) Selectrac
4.0L I6 BORED & BALANCED @ 225k; AW4 Auto; NP242 TC
PROTHANE IN CA's & TA's; DAYSTAR URETHANE COIL SPACERS & BUMP STOPS; HOTCHKIS SWAYBARS
stmprnch is offline  
 
post #4 of 54 Old 06-18-2010, 11:33 PM Thread Starter
groovon
Registered User
1993 ZJ 
 
Join Date: Jun 2009
Location: Oakland
Posts: 53
4.0l il6

Thanks for the replies, guys. Sorry, I forgot to say it's the 4 liter inline 6.

I haven't done a compression test yet, will probably have it done on Monday.

The cat is only a year old, but I spose I'll get it checked. (I don't think the exhaust is plugged up - it just feels like it.)

I disconnected the O2 sensor plug to see if there might be a bad connection. No such luck.
I might check the voltage output from it tomorrow according to the manuals.
(According to the manuals, the O2 sensor doesn't come into play until it reaches operating temp, and the lack of power is apparent before then.)


I'm still kinda hoping it'll be something simple. What are some likely causes? (Start with the cheap ones(!)

8>)

PS - About 140k on the clock as far as I remember. Yeah, it's a bit of an old beast, and has had minimal maintenance on my part, I'll admit. Oil change at 3k, check fluids, etc. Plugs once in awhile. Early history of vehicle is unknown to me.
Burned out coils like crazy at first, until by chance I put a coil in that worked. Been no such problem since - reliable as heck (though under-powered), until now.

...Oh, just now and again, will get a loud clicking on a cold engine - I take it a sticky cam follower. Always clears up after a few minutes and runs smooth again.

Dave

Last edited by groovon; 06-18-2010 at 11:58 PM.
groovon is offline  
post #5 of 54 Old 06-19-2010, 06:47 AM
littlefdl
Registered User
1994 ZJ 
 
Join Date: Mar 2009
Location: High Point, NC
Posts: 160
Might be a exhaust manifold leak. That affects your power. look into it, i have a big crack in mine and it has the exact same symptoms as your jeep.
littlefdl is offline  
post #6 of 54 Old 06-19-2010, 11:04 AM Thread Starter
groovon
Registered User
1993 ZJ 
 
Join Date: Jun 2009
Location: Oakland
Posts: 53
Thanks. I don't think it's that, as there's no sign of popping or backfiring etc

At the moment I'm going by the fault code #51 'O2 says running lean', looking into checking the sensor Voutput, disconnect it and see what happens; then maybe look for a vaccuum leak, or check the injector system.

I'll be searching and reading here on and off all day, probably.

Thanks guys. I'll let you know what I find.
Dave
groovon is offline  
post #7 of 54 Old 06-19-2010, 11:30 AM
Unka-Boo
Registered User
1993 ZJ 
 
Join Date: Nov 2006
Location: Milwaukie, Oregon
Posts: 260
When was the last time you changed the fuel filter?
Unka-Boo is offline  
post #8 of 54 Old 06-19-2010, 11:32 AM
phitmein
Registered User
 
phitmein's Avatar
1995 ZJ 
 
Join Date: Feb 2009
Location: Columbia
Posts: 3,418
I would be leaning towards the O2 sensor. Read the following link and see if it sounds simular.

https://www.jeepforum.com/forum/f13/l...-speed-812083/

P.S. I am old school too, see my profile.

Phit
phitmein is offline  
post #9 of 54 Old 06-19-2010, 11:56 AM Thread Starter
groovon
Registered User
1993 ZJ 
 
Join Date: Jun 2009
Location: Oakland
Posts: 53
Thanks. Will be checking fuel filter today. As well as O2 sensor, if I can. And whatever else is recommended.
groovon is offline  
post #10 of 54 Old 06-19-2010, 12:02 PM
-Joe-
Registered User
 
-Joe-'s Avatar
1995 ZJ 
 
Join Date: Jan 2005
Location: Lexington, KY
Posts: 4,634
If you are getting code 51 and the sensor is fairly old then the fix seems simple. Not sure why you would look elsewhere.

If the o2 has been acting up awhile it could have affected the plugs as well. So a tuneup would not hurt things.

- Joe -

'95 Jeep Grand Cherokee Laredo I6 4.0L
242TC - Extreme Engineering 2" Front Lift/1.75" Rear Lift - ES9000 Shocks + JKS BPEs
Moog Cargo Control Springs
Magnaflow Converter - Dynomax Muffler
235/75/15 AT Uniroyal Liberator Tires
-Joe- is offline  
post #11 of 54 Old 06-19-2010, 12:12 PM Thread Starter
groovon
Registered User
1993 ZJ 
 
Join Date: Jun 2009
Location: Oakland
Posts: 53
Thanks Joe. Guess if I was feeling very lucky I would pay up and just change the O2 sensor. I wasn't expecting it to be that simple, but maybe it is.
There's still a few (easy) things I want to check yet, then probably I'll be looking for a new sensor.

Do you know where I'd be best to get one from (in N. CA)? Best brand? Is a generic one liable to be OK, or not?
Thanks
groovon is offline  
post #12 of 54 Old 06-19-2010, 12:17 PM
phitmein
Registered User
 
phitmein's Avatar
1995 ZJ 
 
Join Date: Feb 2009
Location: Columbia
Posts: 3,418
In the link I sent Ron's fix was his O2. He and I have PM'ed many times about it.

Rockauto.com is a very good parts connection.
phitmein is offline  
post #13 of 54 Old 06-19-2010, 12:30 PM Thread Starter
groovon
Registered User
1993 ZJ 
 
Join Date: Jun 2009
Location: Oakland
Posts: 53
Kragen Auto here says they have an 'original fit' (OEM Jeep?) O2 sensor for $58.

Mine is old I think, so it's probably not a bad bet.
groovon is offline  
post #14 of 54 Old 06-19-2010, 01:05 PM
phitmein
Registered User
 
phitmein's Avatar
1995 ZJ 
 
Join Date: Feb 2009
Location: Columbia
Posts: 3,418
I would make sure to stay OEM and "original fit" smacks of not being OEM too me.

Here is what rockauto list for my 95 4.0 GCL.

RockAuto Parts Catalog
phitmein is offline  
post #15 of 54 Old 06-19-2010, 02:57 PM Thread Starter
groovon
Registered User
1993 ZJ 
 
Join Date: Jun 2009
Location: Oakland
Posts: 53
It's a Bosch 15704 - seems like it should be OK. The old one, as expected, was burnt a light tan and looked pretty old.

Unfortunately, the new one made NO difference whatsoever to engine performance. I put in a bottle of injector cleaner just for good luck, too. (ha-ha)

What next?

[Edit: BTW, this morning she overheated really bad for the first time. (As you might expect anyway, if it was running lean.) But it hadn't, so far, and I dunno why it would do this out of the blue, on just a short trip. Until this morning she hadn't seemd to run hot with this current problem.]

I don't have the facilities to do much work on it this weekend and what basic tools I have are at my construction site. I'll probably have to take it into the shop on Monday and leave it with 'em, see if they can find what's up.

I'm gonna to study my Chiltons and Haynes the rest of the day... Any other ideas?
Thanks
Dave
groovon is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Jeep Forums Replies Last Post
95 zj code 41 and running rough. Barbless ZJ Grand Cherokee Forum 18 12-13-2009 01:07 PM
weak oil pan cloiselle ZJ Grand Cherokee Forum 3 07-26-2009 08:29 PM
94-4.0 code 51 running lean petey156 ZJ Grand Cherokee Forum 0 01-07-2009 05:56 AM
A/C weak kmroxo ZJ Grand Cherokee Forum 3 09-25-2006 04:29 PM
Threw a code today... Running BAD ! wild4stangs ZJ Grand Cherokee Forum 10 03-22-2006 05:38 AM

Posting Rules  
You may post new threads
You may 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
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome