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"Stumped": 1990 YJ Wrangler Running Rich


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I have been trying to figure it out for about a year now on and off, Here is the story, Its the 2.5L

I bought the jeep for $150 because it had been sitting for about two years prior to my purchased, the reason it was parked was because it would not start, I figured I can fix it, great deal. Two flat tires too shouldn't be hard.

So... I first replaced the plugs and wires, rotor button and cap, didn't start. Replaced the ICM and it started...Yes I thought I did it....but...it was sputtering and blowing black smoke out exhaust, running rich, so I started replacing sensors, Map, O2 Sensor, CTS, Injector and CPS  also the intake gasket..not in that order and not at all the same time. still ran horrible. So I did a compression check and found low compression in #1 and #2 cylinder. I pulled the head and found holes in the side of those pistons, I ordered pistons and ring set, when I pulled the pistons to replace the rings on #3 I found the groove where the compression ring was widened so I replaced #3 piston along with 1&2 also replaced rings on #4. Now I have good compression on all four cylinders. Replaced Head gasket and assembled tested and it still ran rich, then water pump went out so I replaced it. I replaced the fuel pressure reg but the new one ripped with the original spring that in the presser regulator so I put my old one back in with the smaller spring and it ran better but still rich, I tried to test fuel pressure but the gauge reads 0. and it is still running so I wasn't worried about it cause it ran better. It doesn't sputter or bog down when I drive it but there is definitely black smoke out exhaust and smell of richness. I also checked vacuum lines.. I  replaced the four going into the TB and Map sensor and some others. Sprayed cleaner around hoses and no change, Did a vacuum test and I have about 11 or 12 Hg on the gauge. I can also unplug any sensor and it stills runs the same.

I was wondering what else could be wrong and could mechanical parts be causing this problem? I did read this very informative page that did help a lot I have checked everything mention on this page    http://www.4wdmechanix.com/Tuning-and-Troubleshooting-the-2.5L-Jeep-TBI-Four.html

There might be some things I missed so if there is any questions please ask. I am thinking there could be lots more wrong with it and I am getting tired of it not getting any better.  I just am going crazy trying to fix it.

Oh I also checked the Cat converter and it is not plugged.

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I followed your comments closely.  One distinct concern is the 11 or 12 in-hg vacuum.  If that is at an idle, the vacuum is very low.  This could be lean mixture, valve timing or valve sealing issue.  Valve issues usually mean a loose timing chain or valves that do not seat properly, which creates a wavering vacuum gauge needle.  The other issue is low or no fuel pressure reading, which could be causing a lean condition that gets compensated by an over-rich mixture setting.  Lastly is the possibility of an EGR valve leak, which would drop vacuum and create a mixture issue.

 

There are two tuning measures to explore.  There has been much discussion about the 2.5L TBI here at the forums with good points brought up.  Read the exchanges here at the forums related to 2.5L TBI troubles.  Also, in the general repair section, I did a forum topic on how to quickly check for valve timing chain wear.  Do a timing chain test. 

 

We can discuss this further after you've pored over the 2.5L TBI remedies made by several forum members...

 

Moses

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Thank you for your response,

I was hoping it might not be a valve sealing problem but I was thinking it might... when I found the holes in the sides of the pistons there were also part of the ring that was gone, the valves looked OK but could have been scored when the ring broke up and just not sealing. The reason I didn't have it checked when I had the head off was the person I got it from had a lien on the jeep for unpaid child support, I had my name added to the title so I am an owner but not sole owner, They could take the jeep anytime they wanted so I was just trying to not put that much money into it but get it running. 

I did check the EGR and found it needs a new on but I haven't replaced it because I wanted to make sure there weren't any other issues that I would find that would make me just want to cut my losses and just park it. I took off the EGR valve and put a piece of metal tape over the hole and reinstalled it and plugged the vacuum line going to the EGR. I read that the engine does not need the EGR at idle so in doing this I would see if it would correct itself, but it still runs the same. 

I was wondering why can I unplug any of the sensors and it not change one bit, It seems to me that it goes into an open loop and doesn't bother reading any of the sensors. Does it do this to compensate for another issue or could one of my new sensors be bad? I really didn't want to waste time checking all the sensors again when it could be a mechanical issue.

I will do the timing chain test as you suggested.

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Frankly, I wouldn't do anything with this engine until after running a cylinder leakdown test.  This would unearth telltale issues like leaking valves, poor ring seal, cylinder wall issues or head gasket and casting issues.

 

You must be running in "open loop".  Do the mechanical tests before aiming for a sensor fix.  Anything from a clogged exhaust system to poor oxygen sensor readings could force the system into open loop.  We can address that after you confirm the basic condition of the engine.

 

Moses

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