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Hello all,

I am having some issues that have become more perplexing than my knowledge has the answers for so hopefully someone can steer me in the right direction. 

I started off by trying to improve the rough idle my Jeep has had for years. I rebuilt the TBI, new O2 sensor, new ISA, TPS, coolant temp sensor, MAP sensor, spark plugs, distributor, plug wires, battery, fuel and air filter and installed new vacuum lines wherever I could (minus the hard lines which are difficult to find replacements for). 

After this, the Jeep was running great for a week or so, idling smooth and better throttle response. However, few days ago it started stalling and dying after I would put it into gear and apply any gas to it. I started digging through old forums here on this site and working through the EGR system and cleaning up grounds. Now it actually won’t fire up at all, or will for a second and then die. Before this it would idle fine for a while then choke out and die. 

I have an inkling that the progressive nature of this may help figure out what’s going on... I’m thinking fuel pump, EGR, something electrical; but I honestly am lost at this point. My mechanical knowledge is pretty novice and I just work on my Jeep in my garage as a hobby so I have no electrical testing tools. Any help or thoughts would be much appreciated! Thanks in advance!

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jcbbgator...Does sound like a fuel supply issue from the sequence and progression of the trouble.  Before doing anything else, check the fuel flow on the engine side of the fuel filter.  Observe the fuel flow volume when the pump runs;  fuel should flow forcefully and steadily.  If not, try another fuel filter and test again.

If this hasn't solved the problem, check the TBI regulator pressure, simple enough at the TBI check port.  The best way to perform this test is with a pressure gauge at the check port.  You want pressure within range (14-15 psi at an engine idle).  You also want a steady flow of fuel here, and that can be checked at the port or the fuel return line near the tank.  Fuel return flow should be steady—with normal fuel pump pressure and volume, there should always be a steady flow of fuel returning to the tank. 

Note:  Do not stop the flow of fuel to the tank or pinch the return line for more than a few seconds!  Fuel pressure will spike up dramatically under full fuel pressure from the pump.  You're looking for return flow volume.  Do not restrict this return line with a gauge.

If flow volume or pressure is off, consider a clogged fuel pump pickup or a defective fuel pump.  The fuel pump motor can actually be analyzed with the pump still in the tank.  However, this requires a wave form oscilloscope that can calculate the amperage draw of the pump motor, the running voltage wave form, the condition of each commutator segment plus the pump's running rpm.  I'm guessing you do not have an oscilloscope (Pico, Autel Maxiscope, Hantek, etc.).  The mechanical tests I suggested are useful and practical alternatives.  They will work.

Should you need to replace the fuel pump, make sure the new pump is for the TBI 2.5L four.  Operating pressure is much lower than the inline 4.0L six or the 1991-up MPI engines.  There is a difference between TBI/EFI and MPI/EFI fuel pumps.

Other possibilities for the trouble you describe would be the MAP sensor or the Crankshaft Position Sensor (CPS) at the flywheel end of the engine.  Check the MAP sensor against the factory specs and verify the vacuum to the sensor before replacing the sensor.  (You've purchased plenty of parts already.)  The CPS can get oil on it from rear main seal oil seepage.  That can lead to trouble and intermittent misfire or no-start.  Also check the wires to the CPS, make sure they're not cooking against the manifold.

Places to start...Let us know what you find.





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  • Moses Ludel changed the title to 1989 Jeep Wrangler YJ 2.5L TBI Stalling and No Start

Moses, thank you so much for the detailed reply. I cleaned up the CPS which didn't seem to help but was an easy starting point. I tried disconnecting the engine side of the fuel filter and there was nothing except some initial dribbling of what was in the fuel filter... so I am going to start by replacing that again (even though it was barely used - maybe it sucked up some crap from the tank) and I think i'm going to drop the tank just to make sure the sock is on and the pump isn't clogged so I don't do the same thing to the next filter. I have a feeling the pump/sending unit may be clogged defective because my fuel gauge is also not giving a reading at all either. 


Thanks again for the advice - it is very much appreciated. I am going to work through this in the next day or so and see if I can figure out the cause and I will post here what I find in case it helps someone else with a similar issue in the future. Thanks for all you do


Have a great day everyone

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