Stinger87

Jeep YJ Wrangler 2.5L TBI Troubleshooting

102 posts in this topic

I just cross referenced the two numbers and the pump for the 89 is the one that i got from Napa. I even cross referenced the Chrysler number for the 91-93 to see if the same pump came up and a different one did come up. A different pump did come up so as long is Napa is correct on their number then i do have the correct pump for a 89 TBI. Something happened to make the jeep run like this all of a sudden because Friday after work it was running terrible too and the engine sounds about the same as it does now. Only difference is i didn't open the tbi cap to see the amount of fuel that it was using on Friday. I am not sure if i am having a complete ECM/ECU failure of some sort. The emission shop that i took it to did say that the jeep was going in and out of Open closed loop erratically and they couldn't pin point the issue. They said it was dumping about 5x the normal amount of fuel and only going into closed loop for about 3 seconds and then right back into open. Right now it is running so rich that it floods the motor and will not allow it to start until the fuel in the intake evaporates. I have changed every sensor on the jeep except the oil pressure sensor. I have never had this many issues with any vehicle and i have been a mechanic for about 7 years now (heavy equipment so i guess this doesn't really help my cause haha). Back to the fuel pump, i dropped the tank and took the old pump out and the sock was not attached to it and it was laying at the bottom of the tank. Also the old pump had so much gunk and grim clogged up in it i swore the new pump would fix it but it didn't. One other thing that i will fix in the morning and i just thought of is the fuel tank vent line was just dangling before i dropped that tank so i don't know if that is the culprit or not. I know it is supposed to be linked to the evap canister but i will find the loose hose and hook it up in the morning and retest everything. Something that still doesnt make sense is how none of my sensor have any affect on how the jeep runs now. MAP, MAT, CTS, TPS i can have them all unplugged and it just runs like it does even if they are plugged in.  :huh:

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could contamination have jacked up my fuel pressure reg? Once i installed the new pump and saw the sock was not attached i replaced the filter as well....

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I was about to ask if you changed the filter...The sudden stalling and inability to start could have been a filter issue at that point.  If the filter was bad enough from sucking debris off the tank bottom, it may have disintegrated and clogged the pressure regulator.  Recall, you did have one point where the removal of the regulator and reinstalling it seemed to help...I commented that the pressure regulator may have had a clogged passage that cleared. 

 

Debris like you describe, from either the sludged tank or a filter coming apart, could create fuel flow issues or clog the TBI fuel inlet, pressure regulator or ports/passageways within the TBI unit.  As professionals, we don't like to borrow trouble, right?  So, my approach is always systematic and aimed at eliminating immediate symptoms.  Here's what I would do now:

 

1) Confirm fuel pressure from the pump, making sure it is within the 27 PSI or so maximum.

 

2) If the pump pressure is correct, I would verify fuel pressure past the regulator.  It must be limited by the regulator to 14-15 PSI.

 

3) Once you have uniform fuel flow at the regulator in terms of volume and pressure, turn to the passages in the TBI unit, between the pressure regulator and flow nozzles.

 

4) An often overlooked sensor that can create a lot of trouble is the crankshaft position sensor at the back of the engine on the upper bellhousing. Oil and debris can cause this sensor to malfunction or work intermittently. Many overlook this as a trouble spot and chase after other issues.  It takes only minutes to access this sensor, remove it, and clean it thoroughly with spray carburetor cleaner and a rag.  If in doubt, do an ohms resistance test on the device. 

 

Make sure you do not have too much fuel pressure past the regulator.  If pressure is high, determine whether this is a pressure regulator malfunction or a fuel pump with excess output pressure.  You had many times that the engine ran well then suddenly went into some form of fuel flow failure: too little, too much, etc. 

 

Note: At this point, with all of the flooding, the oxygen sensor and catalytic converter may be overloaded.  You may need to clean that up to restore a normal idle and closed loop functions.

 

Overall, though it costs for diagnostic equipment, you likely could benefit from a search for DTCs.  A DRBII or aftermarket scan tool (Snap-On or OTC Genesys) with hook-ups for the Jeep TBI era could prove helpful.  Any code reader that would hook to your diagnostic plug could at least retrieve stored codes from the ECU.  Look for an inexpensive code reader for your pre-OBDII era Jeep.

 

I'd be surprised if you have no stored codes at this point.  I would clear the codes and get a fresh read, as there could be several sets of stored codes with some problems already remedied. 

 

At this point, I'm thinking a dirty crankshaft position sensor, high fuel pressure or a fuel pressure regulator malfunction.  Functions of the ECU typically work or they don't; seldom do they work intermittently, which makes me think in terms of a "mechanical" device rather than electronic.  (I would, however, check wire connectors for corrosion and contact integrity.) 

 

 As you share, you've exhausted a variety of sensor possibilities, not to mention your wallet, chasing this around.  Onboard diagnostics and fuel pressure tests can demystify and at least confirm or eliminate trouble spots.  Stop the flow of money over the parts counter until you're absolutely certain you have a malfunctioning part...

 

Unless you've exhausted your tools or patience, there's much to be gained by following through.  Be systematic like your heavy equipment repairs and troubleshooting.  When you do find the culprit and fix it, you'll have far more trust in the Jeep.

 

Moses

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Alright so here is what I got. Took the tbi off the and the regulator is wrecked. The regulator has a bubble and tiny rip in it. There was also a little debre in the regulator bowl. Hopefully with the new regulator it should be good getting tired of replacing the regulator haha. I took some pictures for everyone to see and I'll load the picture of the gunked up fuel pump

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Oh, boy!  Did you flush out that fuel tank?  I've seen more "troubles" with fuel tanks and gunk since the ethanol era.  Left to its own devices, ethanol damages plastic screens, dissolves things like pickup socks, clogs motorcycle (and automotive) carburetor jets and passageways, you name it!  Maybe corn farmers made it big on the ethanol bonanza, consumers certainly didn't...

 

So, you're back on the repair trail and narrowing the fix here.  Good job, Josh!  Thanks for sharing the photos, quite graphic!  Looking forward to the next update...

 

Moses

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I didn't flush the tank because it is less than a year old and I don't really have the resources to do so where I currently live (apartment). I am sure there is some gunk in there but I hope this will do for now. I got the new pump and pump sock on. New fuel filter and a new regulator and tbi gasket coming here soon. I probably won't have another update until after thanksgiving but I'll keep you posted once I get everything in.

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Happy Thanksgiving to you, friends and family, Josh!  You're going to have a very reliable '89 Jeep YJ Wrangler 2.5L four-banger when this is all done...

 

Moses

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Good afternoon,

 

Thanks for the holiday wishes and i too hope you and everyone had a good time during the holiday. Today i installed the new fuel pressure regulator and the jeep runs but it sounds like its getting to much fuel. Im not sure if something went up and is holding the injector open or not but i can actually unplug the injector while the jeep is running and the jeep runs better..... I didnt do to much digging into it today other than the new fuel pressure regulator and tbi gasket then fired it up. Alot of smoke came out of the tail pipe and the engine was rocking pretty hard like it was missing but it just looks like way to much fuel is spraying. And im not sure why the injector still works when unplugged.

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changed the fuel pressure regulator spring and fired up the jeep and it seems like it was running rough but better so i checked the spray pattern and it was spraying and it had a drip too so i pulled the injector out to clean it with carb cleaner. Cleaned it up and just did what i could to clean and install it. Fired up the jeep and it was running good so i started cleaning up my tools and then i reved the engine a little about 2-3k rpms and then it stalled and wont fire back up. When you crank the engine white smoke comes out of the intake. Gonna let it sit outside in time out for a while to think about its actions.... ill do some more research later and see what i can figure out. One more thing alot of black soot blew out of the tail pipe too and covered the side walk.

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Has been running very rich, and the oxy-sensor may be sooty, too.  Could pay to remove the O2 sensor and clean it a bit, at least inspect it and wipe off soot.  The engine has been through the ringer with over-rich mix, you're likely sorting out the impact of all that fuel flowing through.  Spark plugs could also be sooty at this stage...

 

As for the "injector still works when unplugged", that's a good one.  Makes me want to run a pressure check of incoming fuel pressure to the regulator.  If this over-fueling persists, the regulator may be unseating from too much incoming fuel pressure, which I hinted about earlier.  Time for an actual fuel pressure test on that inlet pressure to confirm the fuel pump output?

 

I'd check the spark plugs and oxygen sensor for soot...

 

Moses

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I will check harbor freight or rent a fuel pressure tester from auto zone. Something I was thinking earlier, I traced the old fuel pump to a 91-95 fuel pump and I have no clue about the old regulator because the springs are totally different. The old regulator had a heavy duty spring and the new regulatory was a very easily compressed spring. Today when I installed the new regulator I used the old regulator spring and it ran like hell and was pouring fuel even with the injector unplugged. I installed the new spring with the new regulator and it ran better but I didn't test to unplug the injector which I will do in the morning. In earlier posts I mentioned none of the sensors worked either but that I think is because I had so much fuel pressure that the sensors could not cause the engine to cut off because of the fuel air and spark ratio. I will post again tomorrow with some more info about all this. Attached are the new and old springs for the regulator. The old spring Is the large one and the new one is the small one which seemed to help with the fuel pressure. The second photo is the black soot that blew out the back.

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I didnt do a fuel pressure check on the jeep but everything is working as it should now after putting the new regulator and spring in. The injector no longer fires when unplugged. Im thinking it had excessive pressure and forced it to open and fire. So as of right now the jeep fires up and runs pretty good i didnt get to take it out for a drive but tomorrow i will get some fuel and i think im going to seafoam the vacuum lines again to clean all the sensors. I also think im going to get a second bottle of seafoam to run in the crankcase because i have a squeaky lifter which does go away after its warmed up. I also think this will be a good idea just because of how rich it was running to help clean out all the carbon build up. ill post back again tomorrow and let you know the results. As of now i am thinking that my issues is resolved but i want to run it for about a week to make sure.

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Wow, that spring comparison is graphic, thanks for the photo!  The wire size on the smaller spring must be 1/4th the apply pressure...Apparently, there was excessive fuel pressure, and the leaking or by-passing regulator was "force feeding" the injector without the normal electronic opening and closing of the fuel flow. 

 

Good observation, and good solution...Let's see where this leads now that the engine is flowing a more moderate amount of fuel.  We'll see if the sensors are all back on line with normal closed loop function and air-fuel ratios.

 

Moses

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well back to the drawing boards...jeep now idles decent until warm then bounces from 500-800 rpms. also bucks really really bad when driving! maybe look at timing again tomorrow or when the engine cools down. This little guy is a nightmare haha

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Lean or like a timing issue?  Possibly, Josh...However, I'd check the TPS voltage reading.  This device is adjustable on the 2.5L four.  Unstable idle and bucking could very well be remedied by a simple TPS adjustment or repair.  Don't rule out the ISA motor adjustment.  Might as well check the WOT adjustment, too!

 

To demystify this, I've copied the 1989 factory manual information on adjusting each of these devices for a 2.5L TBI.  Open the PDF for details!

 

Jeep 2.5L TBI TPS ISA WOT Adjustments.pdf

 

Moses

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thanks for that Moses, tomorrow morning i will run those tests to make sure the adjustments are in spec. one more thing i forgot to add is other than the slightly rough idle it runs and revs fine until i put a load on it/ drive. it was still dropping the rpms really low when coming to a stop.

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Try the TPS and other tests, this could narrow it down.  With all of the changes in fuel pressure, a new pump and regulator and so forth, there could be room for a TPS adjustment or ISA setting...WOT is simple to confirm.

 

We always like it when there is something concrete to address.  You've found several sources of trouble lately, Josh, on the right track!

 

Moses

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Alright it seems like my tps sensor is bad. The most voltage I can get out of it is 1.7v unless I fully open the butterfly valve then it goes up to 4.1v. The book doesn't say to test with a wide open throttle or just sitting there as if it were idling so I'm not sure if it is bad or I'm just testing it wrong

 

i tried adjusting it but the voltage would only go lower down to like .5v

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The factory method looks for a percentage or ratio as indicated in the PDF...If you followed the steps, you're getting useful feedback!  The TPS (Throttle Position Sensor) is like a rheostat or potentiometer: as the throttle valve opens, the voltage goes up proportionately, engine idle being a specific baseline voltage.  This signal is crucial for the A/F ratios, idle performance and to achieve a balance throughout the EFI system. 

 

Since the TPS gets a real workout (consider the switching cycles here!), this is often a trouble spot on higher mileage EFI engines!  If you can narrow this to a defective TPS switch by accurate testing, you've hit the mark!  If you confirm the TPS failure, you have a very tangible source for the trouble you describe...Sometimes, the TPS can be adjusted, but if it is finicky and not holding an adjustment, it's defective.

 

This is what I like about mechanical things.  There's always a reason why they work or don't.  (Human beings are more complicated.)  Keep us posted, Josh! 

 

Moses

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im going to say that it is worn out then. It is very old looking and was covered in dirt possibly causing to much resistance on the inside causing the low voltage. im going to purchase a new one hopefully get it today from the Napa distribution center up the road then i will compare voltage and post the readings that i am getting.

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The book says i need to be around .935 or 93% and with my output reading of 1.7 and my input voltage of 5.1 volts i was no where near that. 1.7 divided by 5.1 gave me .33 repeating or 33%. I am determining that this is a faulty tps sensor so i will get a new one and retest and adjust to put the tps within factory settings.

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Well i installed the new TPS sensor and the max that i could adjust it to was 1.9 volts but under wide open throttle it is at 4.7 volts which does cross over to .92 when divided by my input voltage of 5.1 is almost spot on. Fired up the jeep sounds really good reved good with no issues so i took it out for a drive. It was doing decent seemed to be lacking on power and about half way around the neighborhood it started sputtering/ bucking not as bad as before and coming up to stop signs it would still drop to about 500 rpms and bounce around. 

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went back outside to tinker around and noticed with the key on engine off the injector drips and i don't think this should happen and its a new injector so i hope it didnt get ruined from all the debris that ran through the system from bad pump. that's all i got for now

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You're taking a scientific approach, Josh!  Good troubleshooting and observations.  Sounds like a new TPS was necessary, and you're in the ballpark on its configuration. 

 

There were many overlapping issues here, and you have done a terrific job of working through the maze.   Your experience is a gem for others.  Started with a dirty fuel tank and displaced sock, many replacement parts thrown into the mix along the way, plus problems that crossed paths and caused real confusion.  You inherited a "nightmare" by some estimations, I think this is all worthwhile in the long run, as you'll end up with a much more reliable and predictable Jeep Wrangler.  You're now replacing defective parts without "guesswork", and this is way up the learning curve.

 

Your engine's current running condition sounds much easier to troubleshoot, Josh. You may have a clogged fuel filter at this point, and the dripping injector is a concern.  I'm confident that you'll nail it this round.  I'm still of the opinion that a fuel pressure/volume check at the inlet to the TBI would be useful.  Your Harbor Freight tester idea makes perfect sense, you don't plan to use the tool day in and day out, so this would be the right approach for the current project.

 

We haven't discussed the TBI pressure regulator setting.  This is adjustable, and I have provided the steps in the PDF below...The test and adjust does require a pressure tester, so again, the Harbor Freight kit makes sense.

 

You want the right fuel pump pressure and volume of fuel flow.  You want the correct regulator pressure setting (14-15 PSI tested at the TBI regulator test port shown in the PDF.)  The injector needs to flow fuel on closed loop commands.  The cold start/warm-up enrichment needs to work, the system needs to drop into closed loop at the right stage...If the fuel filter is clogged, you might get sufficient pressure without volume, so volume is important, too. 

 

On that note, you would be able to check volume more safely at the regulator test port, as the pressure is much less than the fuel pump supply pressure.  Be careful here, this is gasoline!  A "T" into a large coffee can or gas can could be helpful, with key on/engine off during the test.  Set regulator pressure before checking volume flow.  Adjusting the regulator pressure might solve the fuel drip from the injector.

 

2.5L TBI Pressure Settings.pdf

 

Thanks for having the patience to push through on this—especially in an apartment workspace!  If you had sublet the project to a shop, you'd be unsure of the long-term prognosis and would be out a good deal of money by now.  By fixing this yourself, you are very aware of 2.5L TBI troubleshooting, and others are benefitting from your experience and gained knowledge!  I'm sure they are appreciative of your efforts, findings and strategies...

 

As a footnote, Josh, if you find that the inlet fuel pump pressure is too high for the regulator's range, there are inline fuel pressure regulators available from Summit Racing and others to drop down the incoming pressure—without restricting flow. 

 

Another concern with the TBI system is the return line to the tank.  If the return line is pinched, clogged, kinked or otherwise restricted, the fuel pressure at the regulator and port will soar.  If you have normal inlet pump pressure and very high test port pressure that cannot be dropped by adjustment of the regulator, suspect a restriction or obstruction in the TBI return line to the fuel tank. Check hose routings!

 

On your TBI system, the pump pressure goes directly to the TBI pressure regulator, and the TBI regulator has to buffer whatever incoming pressure exists.  Incoming pressure, therefore, is very important, and we discussed the pressure range for the pump earlier.  Test to confirm...

 

Moses

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Yeah I think tomorrow after work I will go ahead and get the set to add to my tools. I was reading the PDF file you attached and the only thing is my regulator does not have a screw to adjust the pressure. Maybe it is old and got sheared off. I will keep you posted again tomorrow hopefully with some pressure readings that I am getting. Sometime this week I'm going to inspect the timing again since I've made a lot of changes to the electrical side. Thanks again for all the help so far Moses you are filled with knowledge and I appreciate you taking time out of your day to help.

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