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1990 Jeep YJ Wrangler 2.5L TBI Engine Dies

repairs

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5 replies to this topic

#1 n7kme

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Posted 03 April 2014 - 06:47 AM

Hi, all.  I'm a new member from Bullhead City AZ.  first post is with a problem that my 90 YJ base 2.5 is having.  The engine seems to be running fine for anywhere from 5 to 15 minutes, then a very slight stumble (misfire) begins and within about three to five minutes it starts to act like it's starving for fuel and then dies.  As soon as it dies, I can start it right back up (no delay) and it repeats the same thing over again.  It seems to me if it was a plugged fuel filter or a loose connection, that it would not necessarily start right back up again.  The thing that is weird is that there is NO delay when I start it up.  It dies, then fires right back up and is fine for a few minutes. At first I thought maybe the vacuum air restrictor in the air box was closing down and starving it for air, thereby choking it out, but I'm not sure if that's it and when it starts to die I can't get out to the air box to open it up before it dies. It does not seem to do it if I just let it sit and idle in my garage.  It only does it when I'm on the road.  Any thoughts? ideas?  Crank position sensor? TPS? Injector? vacuum leak that I am not hearing?  Any Ideas on where to start looking would be welcome.  Thank you.

 

2.5 TBI 4 cyl  (110,000 miles)

5 SPD AX5 Trans

NP231(?) Transfer case

 

Craig

Bullhead City AZ

 


Craig

Bullhead City Arizona


#2 Moses Ludel

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Posted 03 April 2014 - 09:11 AM

Hi, Craig, and welcome to the forums!  We're very pleased to have a new Jeep Wrangler member and happy help with your engine problem. 

 

One of the most popular and heavily trafficked articles at the 4WD Mechanix Magazine website is the piece I did on troubleshooting the 2.5L TBI Jeep four-cylinder engine.  I suggest you read that for openers.  I also did an in-depth exchange in the old "Q&A" column days with a Jeep Wrangler 2.5L TBI owner from Alaska.

 

Here are the links to each piece:

 

http://www.4wdmechan...p-TBI-Four.html

 

http://www.4WDmechan...ion-System.html  [See the Q&A exchange titled, "Stumbling 2.5L TBI Four and a Long List of Solutions!" in this article format Q&A...Q&A is now all at these forums.]

 

There is also the discussion right here at another 2.5L Jeep four-cylinder engine tuning topic:

 

http://forums.4wdmec...roubleshooting/

 

Please let us know if this helps solve your issue.  If not, we'll consider the next steps!

 

Moses



#3 n7kme

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Posted 06 April 2014 - 07:24 AM

Moses, thanks for the reply.  I finally dug out my Jeep Owner's Bible, and along with your articles I have been ever so slowly putting my Jeep back together.  It is one of those Jeeps that was pieced together from multiple sources by the previous owner and not everything lines up where it is supposed to go.  The wiring harness has been butchered and pieced together with scotch-locks and butt splices in multiple places (really!) and it looks like several of the suspect sensors were thrown into a vat of acid and mud prior to being put in.  I am no longer surprised at what I find in this poor little Jeep, so I think the best thing at this point is to start reconstruction of all the wiring and sensors and get it back to square one. I'm betting once I get everything back to where it is supposed to be, with wiring that isn't in multiple pieces, most of my issues will go away.

Love your site, and your books!

 

Thanks,

Craig

Bullhead City AZ.


Craig

Bullhead City Arizona


#4 Moses Ludel

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Posted 06 April 2014 - 02:13 PM

Craig, thanks for the compliments!  The links I provided cover a lot of ground with the troubleshooting and understanding the functions and identities of the various Jeep 2.5L TBI components.  Our forum exchange was a hands-on like yours, and some wading through the materials should provide insights.  Of course, I'm pleased to go further if you exhaust the details offered and haven't solved the problem!

 

You mention the wiring harness splicing and butt connections, and that is a concern.  For EFI sensors, the important signals for the ECU are dependent upon wires with integrity and the correct resistance.  Butt crimp connectors are terrible when resistance is critical:  There is no assurance that all strands of the wires will make contact.  There's also the risk of moisture wicking into the connector and up the wire insulation, a problem that worsens with humid climates, 4x4 water fording and even the occasional clean up at the car wash!  Crimp connectors work for trailer light wiring and other tasks where resistance loads are not critical—just step up wire gauge and use the right fuses!

 

Also, you described the sensors looking like mud and acid.  Shorts to ground or voltage leaks to ground can result.  Like a dirty battery case, if the sensors are encrusted with conductive material, and that can include soil with minerals, there could be voltage leaks to ground.  The terminal of a sensor could be shorting mildly to the brass or metal shell of the device and creating resistance or voltage changes.  Even minute voltage changes can throw off a sensor signal to the ECU.

 

If you cannot find harnesses or a harness change-out appears daunting, you can repair wiring properly and get good results.  I like to use rosin core solder and seal the solder joints with multiple layers of heat shrink tubing. 

 

First, I place fresh heat shrink tubing, cut to the right lengths, well up the cut wires and away from the soldering heat.  Take the stripped, opposing wire ends and interlace the bare wire strands together—facing toward each other.  Minimize the diameter of the bare wire joint; mimic the diameter of the insulation if possible. 

 

Now you can solder the braided strands together, using rosin core (not acid core) solder.  Add rosin paste as desired to assure solder flow through the bare wire strands.  A finished solder joint around 5/8" in width works well, using a smaller soldering iron or a soldering gun.

 

After the solder joint cools, slide the heat shrink tubing over the bare soldered joint and insulate the section.  Shrink the tubing carefully to the wire insulation without melting the insulation.  The tighter the tubing against the insulation, the better seal.  You can double up with a couple of heat shrink layers...Done correctly, heat shrink can prevent shorts and moisture wicking.

 

Note: To shrink tubing, I use a heat shrink gun, heat gun or even wooden kitchen matches with the flame passed quickly around the tubing without melting the wire insulation or burning a hole through the tubing.  Practice on an old scrap of wire. 

 

Soldering takes time but can save wiring and make permanent repairs.  Unless the current damage is extreme, avoid replacing harnesses.  I like your approach:  Restore known wiring issues first.  Later, the troubleshooting will be accurate and reliable—like you want your Jeep Wrangler to be!

 

Keep us posted and share interesting developments.  Troubleshooting will be straightforward once the wiring is in good shape.

 

Moses



#5 m3out

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Posted 05 May 2014 - 04:26 PM

Hi Moses,

 

I'm having an annoying ignition problem with my 89 Wrangler 2.5 TBI. It wil start without any problems, but after a few minutes (sometimes after a day of good driving) the engine backfires and the tachometer jumps up and down at the same time. The engine dies, but from time to time keeps firing in the distributor (with ignition switch still in on position). I changed the CPS and the ignition module, but the problem remains. I've read your tuning and troubleshooting page, but still can't figure out how to isolate this problem. The only thing I can think of is the ECU, or a short in the wiring going to the ICM. All wiring looks good (very good even). Is there a way to find out if the problem is in the ECU, without first buying a new one?

 

Kind regards,

 

Martijn.



#6 Moses Ludel

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Posted 05 May 2014 - 06:51 PM

m3out...Welcome to the forums, Martijn! 

 

The 2.5L is a popular topic at present...Your thorough description of the problem may hold a clue: The ignition is obviously involved, as the tachometer is watching for a #1 cylinder spark signal from the ECU.

 

Before condemning any more parts or chasing down areas of concern, please check out the ground connections.  We just covered this issue with another '87-'90 circa TBI YJ Wrangler 2.5L.  The trouble spot was the firewall and oil dipstick ground connections.  Proper ECU circuit grounding or faulty connections could be an issue.

 

On these Jeep vehicles, electrical connections are now aging and corroding.  On any 12V D.C. system, grounds are as critical as hot leads, although problems seem more prevalent on the positive side because the ground is often the body or frame on metal bodied vehicles.  Grounds are critical between the engine/alternator and the frame, the frame to body, and the body to engine.

 

Check out the grounds, they could be creating too much resistance.  Look closely at the ground connection junctions, inspect the battery terminals for corrosion (check for a battery short or defect, too), and make sure that circuits like the ECU get a proper ground.  Under hood heat can raise resistance in wiring circuits, and vibration can create "opens" at loose or corroded connections.  This might account for your trouble while driving the Jeep.

 

My diagnostic tool of choice for this kind of troubleshooting is a volt-ohmmeter.  You can test ohms resistance over short and long wiring circuits very quickly with this tool.  Even the grounds can be tested this way, using the probes between the body, frame and right at the primary ground terminals and junctions. 

 

Let us know how this works out...If the grounds are not the issue, we'll take the problem to the next level!

 

Moses





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