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This is my first post here so I’d like to introduce myself briefly and then post some info about my vehicles condition.

I recently purchased a 1989 Cherokee 2.5 TBI that has ~115k miles on it. It’s my first Jeep and if all goes well, my last. I’m looking forward to the journey of owning an old busted up Cherokee for as long as possible. 
 

So I read a few threads in this forum that were related but could not find my specific issue. Here is a rundown of what happened/what was been done:

Slow cranking(slower and slower til no start)

Tested battery, low cranking amps, replaced

Checked starter wires, oil compromised hot wire to starter, replaced both hot and ground on battery/starter

Replaced starter

Tested coil, seemed ok

Replaced plugs

Changed distributor cap and rotor

Tested compression (95, 95, 115, 95)passable?

Replaced main ground strap

Tested CPS, ok

Cleaned TB and injector. Fuel pooling in intake manifold

I had one major problem through this. Had cylinder 3 and 4 plug wires reversed and blew the valve cover off. Replaced that and performed 90% of previous checks after the misfire problem.
So basically I am getting a good crank, decent spark and fuel but no combustion. Any suggestions to help me get this thing running again would be greatly appreciated!

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AngeloM...Let's break this down.  My comments are in red:

20 minutes ago, AngeloM said:

This is my first post here so I’d like to introduce myself briefly and then post some info about my vehicles condition.

I recently purchased a 1989 Cherokee 2.5 TBI that has ~115k miles on it. It’s my first Jeep and if all goes well, my last. I’m looking forward to the journey of owning an old busted up Cherokee for as long as possible. 
 

So I read a few threads in this forum that were related but could not find my specific issue. Here is a rundown of what happened/what was been done:

Slow cranking(slower and slower til no start)

Tested battery, low cranking amps, replaced

Checked starter wires, oil compromised hot wire to starter, replaced both hot and ground on battery/starter

Replaced starter

Still does not turn over at a normal speed after each of the above steps?  Or does it crank without starting and eventually run the battery down?  Or is cranking speed now okay?

Tested coil, seemed ok

Replaced plugs

Changed distributor cap and rotor

Tested compression (95, 95, 115, 95)passable?

This is low compression.  I don't place much stock in compression gauge cranking tests.  An engine can have a good deal of cylinder taper, and the compression will still pop upward.  Your compression is low even for a cranking compression test, which begs a cylinder leakdown test.  Search here at the forums for "leak down" and "leakdown", you'll see why I prefer a leak down tester.

Replaced main ground strap

Tested CPS, ok

Cleaned TB and injector. Fuel pooling in intake manifold

Fuel is still pooling after cleaning the TB and injector?  Or did this straighten out?  Is the fuel pressure in specification when tested at the TB test port?  Have you changed the fuel filter to assure adequate fuel flow volume?  See 2.5L troubleshooting exchanges here at the forums for details on the 2.5L TBI-related fuel pressure and regulator issues.  

I had one major problem through this. Had cylinder 3 and 4 plug wires reversed and blew the valve cover off. Replaced that and performed 90% of previous checks after the misfire problem.
So basically I am getting a good crank, decent spark and fuel but no combustion. Any suggestions to help me get this thing running again would be greatly appreciated!

See below comments...

Assuming that you have "a good crank, decent spark and fuel but no combustion", I would suspect one of three things:  1) cylinder seal is weak (valves or rings leaking, gasket issues, etc.), 2) there is a valve timing issue or 3) the ignition timing is off.  If valve timing is late, this could be a stretched timing chain or on the 2.5L engine a worn chain tensioner

Late valve timing would read low manifold vacuum (directly read at the intake manifold, not ported vacuum) when the engine idles.  A simple vacuum gauge can be used for this test.  The gauge will also pinpoint leaking valves, which will show as a jumpy gauge needle.  Since the engine picks up its top-dead-center (TDC) signal from the CPS, the ignition timing should be on.  I would still verify the distributor's rotor position with #1 piston at TDC.  Make sure that the distributor and rotor are indexed properly with the camshaft and crankshaft position.

A thirty-one year old, 1989 XJ Cherokee with only 115K miles on it is most unusual.  (Our 1999 XJ has 181K miles on it.)  Do you think your Jeep's odometer is reading the original mileage?  If so, the engine has set for long periods or perhaps the XJ was only used for short, local runs.  Do you know the vehicle's history?  When you had the valve cover off, was the rocker area sludgy or relatively clean?

Moses

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Thank you Moses. I will answer each reply as best I can

Cranking speed seems to be within standard range. The battery, wires and starter straightened that out. I haven’t been able to get a second pair of eyes on the spark since initially when I started investigating it was yellowish-orange in color. 
 

I briefly looked into the leak down test information posted in your Honda motorcycle article. I would perform this test but it looks like I will need a leak-down test unit? 
 

I have not tested for actual pressure or flow. I removed the test port plug and placed a rag beneath the port, turned the key to engage the fuel pump and had fuel on the rag. I do not have the proper adaptor to test the pressure at this time. Fuel pump engages, fuel is delivered but I don’t have data on pressure and flow yet. There seemed to be less flooding after cleaning the injector nozzles. I have not done the filter yet either. 
 

There was oil residue buildup in the rocker/spring assembly. One thing I noticed in attempting to pinpoint the timing was that the distributor rotor blade was at its tail end of its contact for each pistons’ top-out stroke. I only confirmed this by eye as I rotated the engine through all four strokes by placing the cap on the rotor and removing when each piston topped-out. Is this a concern to investigate further? I’m unsure of whether spark occurs at top-out or just before.

I will not be able to perform a vacuum test that requires the engine to be running. 

The Cherokee came from the Nantucket area possibly originally where I believe it had two separate owners then I bought it from a guy in Syracuse who had it for about 2 years. I believe that the mileage is correct. The body shows holes from rock chips turned rusted nickel-sized holes on the hood and passenger rear roof corner which have cause various rot issues beneath the vehicle but the rockers and pillars are solid while there are the usual rot spot in the floor pans. Other issues for another time. I think it was driven intermittently and possibly garage kept for periods of its life. It is a second vehicle for me so I drove it once a week or so but started it at least twice a week. The cranking speed was slowing with each startup for about 3 weeks before it would not start. 
 

 

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Hi, AngeloM...See my comments below:

On 5/10/2020 at 8:09 PM, AngeloM said:

Thank you Moses. I will answer each reply as best I can

You're welcome, Angelo.

Cranking speed seems to be within standard range. The battery, wires and starter straightened that out. I haven’t been able to get a second pair of eyes on the spark since initially when I started investigating it was yellowish-orange in color.

A strong spark is important as is the base ignition timing...If the spark jumps the gap at 0.035" with vigor and consistency, you're good.

I briefly looked into the leak down test information posted in your Honda motorcycle article. I would perform this test but it looks like I will need a leak-down test unit?

There are many leak down testers available at Summit Racing and Amazon.  Prices range from $45-$120...These devices will last for many years and pay for themselves.  You do need an air compressor, it doesn't need to be a large unit, even a portable 10-15 gallon unit would be enough volume:  https://www.summitracing.com/search/department/tools-shop-equipment/part-type/leakdown-testersThe OTC tester is a good buy;  shop around on that item.  I've seen this unit around $55-$60.

I have not tested for actual pressure or flow. I removed the test port plug and placed a rag beneath the port, turned the key to engage the fuel pump and had fuel on the rag. I do not have the proper adaptor to test the pressure at this time. Fuel pump engages, fuel is delivered but I don’t have data on pressure and flow yet. There seemed to be less flooding after cleaning the injector nozzles. I have not done the filter yet either.

A fuel test gauge is relatively inexpensive, ranging from the Harbor Freight test tools to more expensive types.  This is a very basic test kit, they go up from here:

 https://www.harborfreight.com/Fuel-Injection-Pump-Tester-62623.html

There was oil residue buildup in the rocker/spring assembly. One thing I noticed in attempting to pinpoint the timing was that the distributor rotor blade was at its tail end of its contact for each pistons’ top-out stroke. I only confirmed this by eye as I rotated the engine through all four strokes by placing the cap on the rotor and removing when each piston topped-out. Is this a concern to investigate further? I’m unsure of whether spark occurs at top-out or just before.

This forum response is helpful:  https://forums.4wdmechanix.com/topic/900-setting-the-valve-timing-on-a-25l-jeep-four/?tab=comments#comment-5980.  If you have low manifold vacuum at idle and valve timing is the issue, your distributor rotor will also be out of sync with the crankshaft/piston position.  Below is the link to a lengthy article I did at the magazine, which is helpful if you suspect that the problem is the distributor/rotor position and not necessarily the valve timing:

https://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four?r=1

I will not be able to perform a vacuum test that requires the engine to be running.

Understood...This test is valuable when you get the engine to run. 

The Cherokee came from the Nantucket area possibly originally where I believe it had two separate owners then I bought it from a guy in Syracuse who had it for about 2 years. I believe that the mileage is correct. The body shows holes from rock chips turned rusted nickel-sized holes on the hood and passenger rear roof corner which have cause various rot issues beneath the vehicle but the rockers and pillars are solid while there are the usual rot spot in the floor pans. Other issues for another time. I think it was driven intermittently and possibly garage kept for periods of its life. It is a second vehicle for me so I drove it once a week or so but started it at least twice a week. The cranking speed was slowing with each startup for about 3 weeks before it would not start.

Primary ingredients for a viable engine:  1) sufficient compression, 2) proper valve lift, 3) proper valve timing and 4) normal oil pressure.  The remaining issues are ignition or fuel related.  Make sure the engine is viable, that spark and ignition timing are on spec and that the fuel pressure and volume are correct.  There a many exchanges at this forum covering the troubleshooting of the TBI fuel injection, fuel supply and pressure, the ISA motor, the ECU, the sensors and other functions.  Take time and use the search box with keywords related to each of these subjects.

It's a process that begins by making sure the engine is viable...Tune, sensors and other issues follow your verifying the basic engine condition:  seal for each cylinder, valve lift, valve timing and such.

Moses

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