91 Cherokee rough idle, stumbling acceleration, fuel pressure drops fast - Page 2 - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Cherokee & Comanche Forums > XJ Cherokee Technical Forum > 91 Cherokee rough idle, stumbling acceleration, fuel pressure drops fast

WJ Shackle Tabs: Tow-Hook Replacements2014 Spartan Locker Special - While Supplies Last! Dana 3FS: 2007-2013 Jeep Wrangler "HALO" Angel Eye Kit

Reply
Unread 05-09-2012, 05:24 PM   #16
Reptile
Web Wheeler
1991 XJ Cherokee 
 
Join Date: Feb 2011
Location: Bakersfield, CA
Posts: 1,297
Quote:
Originally Posted by noir View Post
I'm not sure exactly. When he sends me the quote today I'll give them a call and ask more questions about it. This was a line from the email:

"Yours has proven to be quite frustrating and difficult to diagnose. *You had covered all of the easy stuff, but we still had to double check some of it. *Bottom line is we have proven the problem does NOT lie in the ignition system, or fuel delivery system. *We have isolated that the majority (if not all) of the problem lies in the #4 cylinder. *What I believe we are dealing with is a sticking intake valve on # 4 cylinder."
This seems too far fedge. A sticking valve would cause severe internal damages. Let's put it this way; I dont think you could have driven it to the shop. I would be very cautious about a diagnosis which points to a very specific alleged cause, purely based on a "belief". Why dont you open the valve cover and see for yourself? It really isn't that difficult.

Reptile is offline   Reply With Quote Quick reply to this message
Unread 05-10-2012, 08:37 PM   #17
noir
Registered User
1991 XJ Cherokee 
 
Join Date: Jul 2006
Location: Seattle, Wa
Posts: 51
...still haven't heard back from the shop. No quote or anything. Kind of frustrating that it's taking so long to even quote me on a valve job; and they're closed tomorrow.
__________________
'91 Jeep Cherokee 4door 4.0L HO, 5" homebrew, diced fenders

Last edited by noir; 05-10-2012 at 08:39 PM.. Reason: Spelling
noir is offline   Reply With Quote Quick reply to this message
Unread 05-10-2012, 11:09 PM   #18
Reptile
Web Wheeler
1991 XJ Cherokee 
 
Join Date: Feb 2011
Location: Bakersfield, CA
Posts: 1,297
Quote:
Originally Posted by noir View Post
...still haven't heard back from the shop. No quote or anything. Kind of frustrating that it's taking so long to even quote me on a valve job; and they're closed tomorrow.
That's the thing about taking it to a shop, you're at their mercy. Mechanics are crooks, they might be trying to sell you an engine... Ask them how they determined the problem was in cyl #4, to see what they say. So you know the only way to find out is to do a compression test.
Reptile is offline   Reply With Quote Quick reply to this message
Unread 05-11-2012, 10:26 AM   #19
noir
Registered User
1991 XJ Cherokee 
 
Join Date: Jul 2006
Location: Seattle, Wa
Posts: 51
Quote:
Originally Posted by Reptile View Post
That's the thing about taking it to a shop, you're at their mercy. Mechanics are crooks, they might be trying to sell you an engine... Ask them how they determined the problem was in cyl #4, to see what they say. So you know the only way to find out is to do a compression test.
Got an email back this morning. It gave me a quote and his recommendation was to probably just find a new jeep on Craigslist.

When I pick it up on Monday morning and pay the $140 for diagnosis I'll ask for exactly what they did.
__________________
'91 Jeep Cherokee 4door 4.0L HO, 5" homebrew, diced fenders
noir is offline   Reply With Quote Quick reply to this message
Unread 05-12-2012, 12:03 AM   #20
Reptile
Web Wheeler
1991 XJ Cherokee 
 
Join Date: Feb 2011
Location: Bakersfield, CA
Posts: 1,297
Quote:
Originally Posted by noir View Post
Got an email back this morning. It gave me a quote and his recommendation was to probably just find a new jeep on Craigslist.

When I pick it up on Monday morning and pay the $140 for diagnosis I'll ask for exactly what they did.
Okay, sounds like he could be a descent guy who gave his best shot at it. Beware, still. Ask him what he did, but don't try to steer the conversation in any directions, all you want is an unbiased opinion, and take it from there.

Remember, if you have compression on all cylinders (within specs), that's good news. If he hasn't done the test, you can do that yourself. If the problem's intermittent, that tells you it is very likely electrical in nature. Electrical issues are by far the most difficult to diagnose. How many times do you hear people say 'my car is acting up, but the shop guy couldn't find anything wrong...'. The problem is you have to recreate the very particular conditions that trigger the symptoms; and factors such as temperature (as engine gets warm), outside humidity, etc. will affect electrical. You can always have that one component that is borderline failing.

Be patient, persistent, take ownership, and you'll eventually find your way out of this... and learn a bunch in the process.
Reptile is offline   Reply With Quote Quick reply to this message
Unread 05-14-2012, 05:50 PM   #21
noir
Registered User
1991 XJ Cherokee 
 
Join Date: Jul 2006
Location: Seattle, Wa
Posts: 51
Picked it up today. He said that the cranking compression was good across all cylinders (~170 lbs), but the running compression on #4 was low. The running compression on all the other cylinders tested good. They checked all the standard stuff (basically the thing I replaced) and didn't find any issues. They also swapped #3 and #4 injectors to see if it was an injector issue and no change. So he said he wasn't sure if it was an intake or exhaust valve issue but that either way its a valve problem.
__________________
'91 Jeep Cherokee 4door 4.0L HO, 5" homebrew, diced fenders
noir is offline   Reply With Quote Quick reply to this message
Unread 05-15-2012, 01:49 PM   #22
Reptile
Web Wheeler
1991 XJ Cherokee 
 
Join Date: Feb 2011
Location: Bakersfield, CA
Posts: 1,297
Quote:
Originally Posted by noir View Post
Picked it up today. He said that the cranking compression was good across all cylinders (~170 lbs), but the running compression on #4 was low. The running compression on all the other cylinders tested good. They checked all the standard stuff (basically the thing I replaced) and didn't find any issues. They also swapped #3 and #4 injectors to see if it was an injector issue and no change. So he said he wasn't sure if it was an intake or exhaust valve issue but that either way its a valve problem.
A weak valve spring can cause a low compression on dynamic test. This is something that is fixable if you're up to the task and prepare well enough for it. You're going to need a valve srping compressor and an air compresssor that can produce 100 psi. Anyhow you're first step is going to open the valve cover...
Reptile is offline   Reply With Quote Quick reply to this message
Unread 05-15-2012, 11:23 PM   #23
noir
Registered User
1991 XJ Cherokee 
 
Join Date: Jul 2006
Location: Seattle, Wa
Posts: 51
Quote:
Originally Posted by Reptile View Post
A weak valve spring can cause a low compression on dynamic test. This is something that is fixable if you're up to the task and prepare well enough for it. You're going to need a valve srping compressor and an air compresssor that can produce 100 psi. Anyhow you're first step is going to open the valve cover...
Ok I'll do some reading. I saw valve springs on rock auto pretty cheap. I should probably order the overheigth ones right? One set is 1.834" and one is 2.016"
__________________
'91 Jeep Cherokee 4door 4.0L HO, 5" homebrew, diced fenders
noir is offline   Reply With Quote Quick reply to this message
Unread 05-15-2012, 11:40 PM   #24
Reptile
Web Wheeler
1991 XJ Cherokee 
 
Join Date: Feb 2011
Location: Bakersfield, CA
Posts: 1,297
Quote:
Originally Posted by noir View Post
Ok I'll do some reading. I saw valve springs on rock auto pretty cheap. I should probably order the overheigth ones right? One set is 1.834" and one is 2.016"
No clue. I did the job on my wife's Liberty and it required a dealer only tool because the engine uses rocker arms, so I bought a universal one and grinded the hell out of it... was a PITA. But I'm assuming it would be a lot easier to do on the 4.0 and a standard valve compressor would work (I found mine at Pepboys for like 20 bucks). See my thread.
http://www.jeepforum.com/forum/f28/b...pring-1163721/

The real big deal when do this type of procedure is to make sure you don't drop the valve, or you'll pretty much have to tear the whole engine apart. This is why you need to set the piston (cyl #4 in your case) at TDC and apply 100 psi of air pressure inside the combustion chamber. If it holds pressure, then you can remove the valve keepers. In my case the valve wouldn't hold pressure, so I had to find a way around, but I don't think it would be a problem for you, since you do have compression.

Make sure you get familiar with the procedure before you get started and get the tools and supplies needed. Let us know if you run into issues.
Reptile is offline   Reply With Quote Quick reply to this message
Unread 04-29-2013, 10:20 PM   #25
deadpool1597
Registered User
1994 ZJ 
 
Join Date: Apr 2013
Location: weaverville, ca
Posts: 1
Just to interject...If you do not have access to a compressor or the valve won't hold pressure; you can remove the plug, feed sturdy nylon rope in the hole while the piston is at the bottom of it's stroke until the cavity is full. Turn the crankshaft and Viola! the valve won't fall into the cylinder when you take the keepers and springs off. Just reverse the direction you turned the crank and pull out your rope. BOOM, done.

Oh, just my 2 cents but if your valve won't seal, you are better off doing a head job. I know, I know but if you take the time and money and get a head job when you determine it's an upper engine problem you won't regret it. The 4.0 6 is an easy one to work on. It's an old motor with old school heart even if it has new tech bolted to it. Your Mom probably warned you about listening to a guy that speaks in absolutes but, without fail, every motor I did a head job on, ran stronger, cooler and more efficiently. Period. Anyway, good luck, hope it works out. I loved my 91 Cherokee limited, had everything....went anywhere.
deadpool1597 is offline   Reply With Quote Quick reply to this message
Reply

Tags
fuel , idle , injector , rough , stumble

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.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.


Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.