Stinger87

Jeep YJ Wrangler 2.5L TBI Troubleshooting

107 posts in this topic

Just want to add my 2 cents worth to this thread. THIS WHOLE THREAD IS GREAT! I have had all these issues with my 90 YJ 2.5 TBI. I will be taking my tablet out to the garage with me and start walking through each of these steps. Thank you Moses for all you do and all your patience. And thank you stinger87 for staying with it long enough to see it through. I see hope for my little desert rat in the near future..

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You're welcome, Craig...Let us know what your find...Glad you find this resource valuable.

 

Thanks!

 

Moses

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OK, so my Jeep ran great for about a year.  Then it began to stall out randomly.  I replaced the CPS and it ran great for another month or 2.  

 

Now the relays are clicking again.  But only sometimes.  Sometimes it will fire right up, but sometimes it will just click click click.  

 

Tried cleaning up the grounds at the firewall. No change.

I went to clean up the grounds near the dipstick tube, and the connectors broke and are currently disconnected.  Still starts and runs with them disconnected so they cant be connected to the relays.

Is it possible I have a bad ECU?  Anyone have a good used ECU for my 89 2.5? Or are there any other donors i can use from a junkyard?

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Adam...A poor ground on the ECU circuit, poor connections at the ECU, or corrosion on ECU terminals could be an issue.  Especially if your YJ is in a humid climate, poor connections due to corrosion could be a problem.

Before tossing the ECU (which could in the end be defective), try disconnecting the ECU plug and cleaning the contacts on the plug and ECU.  Use an electronic contact spray cleaner.  Do not scrape with a sharp tool, not even a screwdriver tip.  If you see what appears to be a black coating, this is oxidation and should be removed.  

If you have room for reaching the contacts, use ScotchBrite pad (fine or medium grit) then flush debris with spray contact cleaner.  Make sure the ECU's grounding is good.  Repair that ground connector at the dipstick tube.

Think of clicking relays as poor current flow or a weak ground that increases resistance.  Check the ohms resistance of grounds with a volt-ohmmeter.  A quick check is to check the resistance from the battery negative post to the end of the circuit, which could be a relay's ground terminal.  If there is resistance, look for corrosion, a wire with damage or an open.  On a ground circuit, insulation resistance testing is not as critical as it would be on a positive wire's insulation.  If you have a quality meter with insulation resistance test capacity, you can check for wire opens and shorts.

There is too much resistance somewhere.  This could include an ECU printed board with weak solder circuits. 

Moses

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As a footnote, Adam, you shared that the engine ran fine for 2 months after changing the CPS.  Then the troubles returned.  Have you checked the new CPS for oil on the contact point or poor plug connections?  Is resistance (at the grounds or poor insulation integrity) within specification on the CPS wiring circuit?  Is the new CPS's ohms resistance reading normal?

One item that comes up is oil from a rear main seal leak that spatters on the CPS and makes for poor contact.  Is your CPS getting smudged with seeping engine oil?

Moses

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I replaced the CPS again with no change.  Everything looked fine when I took it out.  

Would the CPS cause the relays to click when I turn the key, before cranking?

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Adam...Back to the original premise:  Clicking relays mean that the voltage/amperage to a relay is inadequate or being interrupted.  12VDC takes both the hot (+) leads and grounds (-) into account, either can have too much resistance with the same impact.  Too much resistance (positive or negative circuits) causes a voltage drop or open.  Too much resistance can be caused by poor ground contact(s), wires that are deteriorating or fraying, corrosion, and so forth.

On the Jeep YJ Wrangler, there is much talk about poor grounding, apparently an epidemic problem.  Corrosion, painted surfaces and loose connections can cause excess resistance or ground interruptions.  

One overlooked obvious is poor contact at the battery itself.  If the posts are corroded or making poor contact with the terminals, this can wreak havoc.  Periodic cleaning, and if necessary, scarfing the corroded lead at the posts and/or battery terminals to achieve fresh contact, can help prevent issues here.  (An inexpensive four-way cutter is available for cutting and re-shaping the posts and battery terminals; go lightly here, just enough to clean up the posts and terminal ends.)  Use of a spray or brush-on battery terminal protectant has some benefit once quality contact has been restored.  

Other common points of resistance are a worn ignition switch or the junctions of wiring from the battery to the main chassis feeds.  The power lead (second, smaller gauge positive battery feed) can have too much resistance.  Often, an aftermarket replacement positive battery cable has a poor crimp connection on the lighter gauge pigtail lead.  This would be something to check.

Of course, a relay can be defective and ratchet away.  I'm sure you've checked that possibility, but if not, try substituting another relay in place of the clicking one.

Moses

 

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