[2.5L TBI Jeep YJ Wrangler Running Rich and Won't Idle]

Hello Moses,

 

Finally I ended up buying both and installing both. I was not able to obtain 13 PSI with none of them. Not the 18-20 I was getting originaly but slightly above 16. From what I have learned in this process it seems it is not fuel pressure related.

When I crank the engine and it first start it, the RPM are normal for the first 5 seconds. Then somehow a fixed 1000 rpms are commanded. You can tell from the iddle motor that is spinning in order to adjust that iddle. 

In the process of replacing the fuel pump and the fuel sender unit my fuel gauge droped to zero regardless of the fuel quantity. 

Just an observation, both pumps are louder than the one I had before. 

Thanks again and please let me know your thoughts on the matter. 

[2.5L TBI Jeep YJ Wrangler Running Rich and Won't Idle]

Thanks again Moses for your kind and fast reply. I don t remember the fuel capacity of my tank. Is there any way of knowing it by means of the VIN number. (2J4FY29E0KJxxxxx). 

I did find the Crown pump 83502995 but it is only the puel pump. I think the best would be to change te whole fuel sending unit. There is another item on eBay that seems to be compatible: "Fuel Level Sending Unit For 1987-1990 Jeep Wrangler 2.5L 4 Cyl 1989 1988 Crown" link: https://www.ebay.com/itm/295255257536 manufacturer part number does not match those you gave me: 83502990. 

Also, as you mentioned. I will check the return line for obstructions before buying it.

 

Thanks again!!!

[2.5L TBI Jeep YJ Wrangler Running Rich and Won't Idle]

Thanks a lot Moses!!! After a couple of months and various thread sizes error on the purchase of the adaptor I finally got the correct one. Your guess was absolutely right. I was not able to test it with the "T" method. The fuel pressure is higher than it should be: between 18-20 PSi. 

I will check the return line. In case the fuel pump is incorrect and wrongly replaced in the course of the las 30 years. Do you know the correct part number? Thanks again.

[2.5L TBI Jeep YJ Wrangler Running Rich and Won't Idle]

On 11/28/2022 at 10:23 PM, Julio said:

Thanks again Moses. I remember the pressure regulator because I replaced it when I bought a kit to rebuild/refresh the TBI. All the gaskets and rings where there and that triangular shaped membrane was the pressure regulator. 

Do I need a special gaude to check the fuel pressure or a 40 USD tool from amazon is enough?  How is that adjustment performed on the pressure regulator? I do recall something like a sloted screw in the midle. 

Hello Moses. I finally received the pressure test kit. Unfortunately, none of the fitting included fit into the "pressure test port plug". I had to remove the fuel supply tube and attach it there, hence, I was not able to test it with the engine running. Nevertheless, the readings  of the fuel pump where normal. 

 

Without removing the TBI I jumped into the other possibility, the “fuel pressure regulator”. I noticed the illustration you sent me depict a “pressure regulator screw”. Mine in the contrary seems to have a flushed or slim bottom. It there any protective cap underneath there? Thanks again!

[Jeep YJ Wrangler 2.5L TBI Troubleshooting]

On 12/4/2013 at 3:21 PM, Moses Ludel said:

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

This forum is very helpfull. I'm having similar problems. I was searching on how to test the pressure and adjust the pressure regulator and HERE IT IS! 

[2.5L TBI Jeep YJ Wrangler Running Rich and Won't Idle]

22 hours ago, Moses Ludel said:

Julio...You're welcome.  I thought you needed to focus on the pressure regulator.  The unit is at the throttle body.  There is some adjustment possible with the balance spring/diaphragm design.  The diaphragm and mounting gasket can weaken, leak or be misfitted.  This is a source of fuel leakage, poor mileage and enriched exhaust for emissions tests. 

We have discussed the fuel pressure regulator here at the forum many times, so you will find details by simply using the search keyword(s) "pressure regulator", "2.5L TBI", etc.  Here is just one example below.  Note that I also mention the throttle position sensor voltage, which I would highly recommend checking.  The TPS can also create an enrichment issue or emissions test failure.  The TPS voltage and test procedure are described in detail within the factory workshop manual (FSM):

I have also shared a trick that's useful for determining the spray pattern of the TBI regulator and the injector.  You move the air intake horn aside from the top of the TBI unit.  Using your induction timing light, hook the pickup to #1 spark plug lead, and run the engine at an idle while shining the timing light at the TBI unit's throat.  The injector relies on TDC for #1 cylinder as a signal.  This gets picked up with the crankshaft position sensor and flywheel position. 

You will see the spray pattern of the fuel plus any leakage, bad flow or fuel dripping that shouldn't be there.  I did this with GM TBI as a dealership tech in the eighties.  A decade ago, I photographed the injector pulses on a Corvette Cross-Fire Injection (1982-84) 5.7L V8 engine for Corvette Magazine to illustrate a normal spray pattern.  The timing light was the light source in a dark room...It's a very cool and quick diagnostic method.

As for tools, I also have written to that subject in our forum exchanges about the 2.5L TBI system.  There is a plug at the TBI test port where you hook up a fuel pressure gauge.  You're looking for 14-15 psi at this test port.  This is a quick and easy test if you have the right gauge and fittings/adapter for the TBI port thread.  The port adapter fitting was a Chrysler tool.  You can improvise with the correct thread pitch fittings and a common fuel pressure gauge that reads in this range (0-30 psi would be fine, higher will work, you need an accurate 14-15 psi).  

There are CD versions of the factory shop manual (FSM) available for 1987-90 YJ Wranglers.  Specifications, tools and test procedures are covered.  You can get a CD or even a download (PDF format manual) at eBay.  This would be a sensible investment.  I rely on genuine FSM print copies in my library.  Actually, the CD or downloads are much easier to navigate or copy/print out pages for work in your shop.  I highly recommend that you get a copy if you plan to work on this Jeep® much.  Make sure it's a copy of the actual FSM.

Here is an example.  Bishko uses the factory FSM, and this is a CD version.  There are often download copies available for less, so shop a bit.  This is the manual that you want, it's discounted but still higher priced than in recent years.  (It could be that popularity is driving up demand.  Shop and find out.)  1987-90 YJ Wrangler manuals will work.  My print copy set is 1989 and works well for these model years.  If you find a 1989-90 FSM for less cost, it will work:

https://www.ebay.com/itm/152798258131

Let us know how this works out, Julio...

Moses

 

Thanks again Moses. I remember the pressure regulator because I replaced it when I bought a kit to rebuild/refresh the TBI. All the gaskets and rings where there and that triangular shaped membrane was the pressure regulator. 

Do I need a special gaude to check the fuel pressure or a 40 USD tool from amazon is enough?  How is that adjustment performed on the pressure regulator? I do recall something like a sloted screw in the midle. 

[2.5L TBI Jeep YJ Wrangler Running Rich and Won't Idle]

On 11/25/2022 at 1:49 PM, Moses Ludel said:

Julio...I took your images into my photo edit software then rotated and sharpened them for viewing.  They are very helpful, and below each picture, I have make observations about obvious issues:

 

RPM normal; Fuel Trim short term looks okay; LT (long term) fuel trim very high:  total for fuel trim high.

Nothing of obvious concern here...

Exhaust rich...

For a quick observation, the rich exhaust and high LT fuel trim hint that either the fuel flow is enriched or the exhaust is restricted.  The catalytic converter could be clogged or not functioning properly—or both.  The idea is to find the issue and not replace parts until you know they are defective.

First, I would check the fuel pressure at the TBI fuel test port with a fuel pressure gauge.  Run the test at idle and 2,500 rpm.  (Stay away from the engine driven fan, do not lean over it when revving the engine.)  Make sure the pressure is normal or 14-15 psi.  If pressure is high, that could be the cause for running rich.  If pressure is high, the issue could be 1) the TBI pressure regulator, 2) leaking regulator gaskets or 3) a restricted return line from the TBI unit back to the fuel tank.

The pressure regulator can be adjusted if slightly out of range.  If defective, the regulator needs to be replaced.  You want the pressure to be a constant 14-15 psi at the TBI test port.  Another cause of high fuel pressure can be a fuel pump that has been replaced with a 1991-up MPI fuel pump instead of the lower pressure output 1987-90 style TBI type.

The concern is pinpointing the cause of high fuel pressure.  If pressure is normal at the test port from an idle to 2,500 rpm, I would consider an exhaust restriction.  Flow out the tailpipe can be measured.  A simple test is to feel the actual pressure at the end of the tailpipe.  Have someone accelerate and decelerate the engine during the test.  Use a glove to protect your hand.

You did not share the engine's cranking compression.  I would run a compression gauge test for a quick overview.  Disconnect the coil high tension wire to prevent an engine start.  Hold the throttle open...If there is more than 10% difference between the highest and lowest cylinder psi, the engine balance is off.  If one or more cylinders have low compression, run a cylinder leak down test on the low cylinder(s) to see whether the valves, rings or a blown head gasket are at fault. 

Vacuum circuits do need to be correct.  At these forums, I have posted the vacuum circuit diagram(s) for the 2.5L TBI engine bay if you need to check the hose routing.  Search the forum with keywords "vacuum", "2.5L" or "2.5L TBI" to find one of the exchanges that includes YJ 2.5L vacuum diagrams.  Usually these are PDF attachments that you can open.

As for tachometer readings, I would trust the Snap-On scanner.  Be aware that the tachometers were different for 2.5L fours and six-cylinder engines.  Did you install a 2.5L (four-cylinder) tachometer?  If your diagnostic scanner or another tool has an induction pickup that clamps over the #1 spark plug lead and provides a tachometer signal, you can get the most accurate rpm reading that way. 

The reading you get on the Snap-On scan tool is simply information/data from an ECU/ECM/PCM.  An rpm signal is usually data  from the crankshaft position sensor.  The only way the information could be inaccurate would be a problem with the CPS (sensor) or the ECU.  Does it sound like the engine is idling at the speed displayed on the scan tool?

Let us know the TBI test port fuel pressure reading...

Moses

Thanks a lot Moses for your kind, complete and fast reply. 

The catalytic converter is not clogged yet. I replaced a couple of month ago to rule out that theory. I have routed and checked the vacuum lines several times. I believe they are ok at this point. 

I will explore the fuel pressure theory. It sound very solid. Either the pressure regulator, the fuel pump or the return line. That's uncharted territory for me. Where is the pressure regulator? and how it can be adjusted? Do you know about any tool to check the pressure?

The new tach is for the 2.5 L TBI. 

Thanks again Moses, have a great weekend!

[2.5L TBI Jeep YJ Wrangler Running Rich and Won't Idle]

14 hours ago, Moses Ludel said:

Julio, what does the smog shop say is the cause for the failed test?

Moses

Thanks a lot for your message.

I dont remember the numbers exactly. Mixture was too rich and the jeep was spitting gas and black particles from the escape. This was May 2021. Eversince I have changed everithing that I have read and watched on forums and videos. (TPS, IAC, MAP Sensor, 02 Sensor, TBI gaskets and Coolant T Sensor, distributor cap, sparks and wires, air and fuel filter, even a new TACH. The las thing I ve replaced was the injector.) Nothing happens, iddles evenly at 1.000. Like it was programed to do that. Besides that the jeep runs great. 

I tried what I read in one of your posts about disconecting the egr solenoid and watch for a reaction. It makes a difference.

I have looked around the vacum lines not thoroughly. But havent fount any parent leak using wd40 and cigarete smoke. There is one line missing on the font axle. The one that goes into the dashboard line. Also, the in the same 4wd harness there is a blue cable (I believe is vent) plugged with an iron ball. 

 

 

IMG_9048.HEIC IMG_9047.HEIC IMG_9045.HEIC

[2.5L TBI Jeep YJ Wrangler Running Rich and Won't Idle]

I have a very similar issue with my 2.5 TBI YJ. Mine idles at 1000 fixed rpm. Smooth. Changed every possible sensor including a NOS tach and a new CAT. I'm unable to pass the emission test. Altough the tach is showing a steady 1000 rpm, the SNAPON scanner shows 730 rpm.