Stinger87

Jeep YJ Wrangler 2.5L TBI Troubleshooting

102 posts in this topic

Pleased to add comments and assist...Checking the timing by the factory method might help, it's electronically controlled, so follow the official Mopar procedure for setting the base timing.  Good you're getting the pressure testing equipment, you'll demystify the regulator and other issues, Josh, and Harbor Freight seems like the cost-effective tool source in this case...

 

The source for the PDF on the TBI adjustment is a 1989 Mopar Service Manual for Jeep.  Should be reasonably accurate on all counts.  Check under the regulator bowl for signs of an adjuster screw, a mirror might help.  If possible, avoid the need to unbolt the TBI unit again.

 

Moses

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Good evening I hope everyone had a good weekend. haven't done anything with the jeep this weekend waiting to get a line made tomorrow so I can have a leak free fuel pressure tester for the jeep. Once I get it I'll get some readings and post some pics just wanted to give a heads up and that I didn't give up on it yet haha.

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Thanks for checking in, Josh...Please upload some pics of the pressure test (800 pixel width photos work nicely), many 2.5L Jeep folks will benefit.  Thanks for following through on this troubleshooting step, you won't regret it, the info will be conclusive!

 

Moses

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ok so here is what i got so far. I got a line made for the fuel pressure tester to hook right up to my tbi unit but it appears that i have a faulty gauge. I know i have a good amount of pressure to the gauge because when i disconnect the gauge and turn the key fuel shot about 4-5ft. I shouldn't be shooting fuel everywhere but working solo and having to reach in turn the key while keeping an eye out for pressure this seemed to be the only way. Anyway the jeep does fire right up but the spray pattern coming out of the injector now is horrible. I'm going to check to see if i can take it apart and clean it and if not ill just get a new one because it looks to be clogged with contamination from the tank.  I have two picks of how i set up the fuel pressure line if anyone needs more pictures i can grab more.

post-93-0-68469800-1386630202_thumb.jpg

post-93-0-51715000-1386630205_thumb.jpg

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Josh, is this gauge hooked up to the return line to the fuel tank?  If so, the effect is like a kink or obstruction in the return line: The gauge is a stopping point with no "T" back to the tank.  You do not want to check pressure on the return line, regardless.  The pressure check is at the small port plug opening (threads into the TBI unit) shown in the factory shop manual PDF illustration I supplied earlier.  Locate the test port and removable plug in the PDF picture.  Zoom into the PDF, this can be done in Acrobat or Adobe Reader, simply pull into the illustration to get a better view of the test port location. 

 

Also note in the factory manual that it says a restriction in the return line will cause the pressure to spike very high, which may be what you're experiencing at the gauge.  The test port pressure, by comparison, will only reflect the regulated pressure at the TBI unit (if correct, 14-15 PSI). The fuel supply and return lines would be independent of the test port pressure.

 

To test incoming pressure to the TBI from the tank, make a "T" for the inlet pipe connection.  The gauge becomes one leg of the "T", the other two legs would be the fuel flowing from the pump into the TBI unit.  This should be actual, unregulated fuel pump pressure.  Again, do not restrict or attempt to test pressure on the return line, this line must be unrestricted all the way into the fuel tank.

 

Let us know what you discover...

 

Moses

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In my picture i have a bass fitting connected into the test port near the return line thats the only reason it looks slightly different. From what i can tell i have it set up exactly how the books pictures for a TBI engine has it set up. It looks like a fuel line but its just the brass fitting i used in the test port to hook up my gauge. I then ran a line to my gauge from that port. I turned the key on heard the fuel pump turn on but the gauge had 0 on the reading. That is when i removed the gauge and hit the key to make sure pressure was getting to it and a powerful line of fuel shot out. I also took the gauge to work and used our shops fuel pressure set and hooked it up to a MPI engine and it still had zero psi. im going to see about borrowing a gauge from work or purchasing another one.

 

This here is kind of getting ahead of myself but on the bowl that the fuel pressure regulator and spring sit in, at one time it did have the adjuster screw in it but looks like someone cut and ground it off so no more adjustments are able to be made if need be. With that being said any ideas on where to get a new one because i cannot find a part number and i hope i wouldnt have to buy a new unit.

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ok new discovery, my gauge does work. Now that i know my gauge is working that leads me to think the jeep's fuel pressure is pretty much at zero. Yes the pump is pushing fuel but i am thinking it has to do with the regulator and that small spring that i installed. What i will do is reintall that old spring that was larger and then check my fuel pressure. Earlier i was saying that the large spring was causing too much pressure but i need to be able to get some sort of reading. If my pressure is too high i should be able to either find a new spring or get an inline regulator. I am not 100% on all of this but it sounds like a good direction to go in. My symptoms right now sound directly to being a fuel problem. Idles good with the fuel its getting but once you put a load on it and accelerate it doesn't have enough fuel to compensate for the amount of air coming in.

 

Currently we are in the middle of a rain/snow storm so hopefully i will have some more updates soon.

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Exciting development, the pressure gauge is telling us something!  Interesting that the fuel shot out of the port but the gauge reads zero.  Something is "bleeding off" the pressure or there is no "column" of fuel in the system.  This could be a mechanical issue with the fuel regulation and/or passageways, either not adjusting pressure properly or bleeding fuel off and redirecting it to the tank.  The latter would explain why there is fuel spurting from the port but no pressure. 

 

The regulator must hold the pressure at the TBI unit, enough pressure and volume to provide a continuous, 14-15 PSI flow of fuel to the engine.  By design, any excess pressure/volume simply redirects to the return line.  When not restricted, the return line is an immediate bleed.  The return line has no backpressure, and the fuel simply runs back into the tank.

 

You're on the right track.  Either the fuel gets rerouted when the plug is in place (pressure builds) or there is no pressure, as you suspect.  I would still take a quick read on the pressure line coming into the TBI from the fuel pump to establish a baseline/reading for the fuel supply pressure.  I would check the supply pressure two ways: 1) connect the line directly to the gauge, bypassing the TBI unit altogether, and 2) make a "T" into the TBI and to the gauge.  If #1 is a success story (showing a nice, continual pressure reading on spec) but #2 is not (pressure drops when fuel moves into the TBI unit), then the pressure regulator is defective and returning all fuel to the return line, which drops the fuel pressure to "0".  If that is the case, there's not enough fuel to run the engine...Make sense?

 

If the incoming fuel pressure by itself (#1 test) is erratic, there's something preventing tank fuel from reaching the TBI unit under pressure.  This could be a pressure or supply problem (unlikely the pump, as you installed a new fuel pump that presumably works well) or an obstruction in the fuel supply between the pickup point for the fuel pump and the TBI unit.  A restriction could be anything from a clogged fuel filter to a kink or packed debris in the supply line, a clogged pickup in the tank, or even a vacuum/tank pressure issue caused by the evaporative emission system (unlikely but possible if someone has tampered with the EVAP hoses or there is a defective EVAP canister).  You've ruled out a lot of these possibilities, they're still worth mentioning. 

 

     Note: EVAP system issues were highly prevalent with carbureted engines and their low fuel pump pressures; however, this is near impossible with high volume/pressure submersible fuel pumps. Normally, I would not suspect the EVAP on a TBI system and would take that system into account only if you cannot pass an emission tailpipe test or if you smell gas fumes with the engine shut off.

 

Restricted fuel flow will not impact pressure, but it will get a "0" reading if no fuel is moving into the fuel gauge.  Again, you need both pressure and fuel volume from the tank to the TBI

 

This is all very taxing when working outside in freezing weather, that's why the pressure tests help so much.  You can more quickly isolate the trouble area.  Josh, you'll be an "expert" on 2.5L TBI before this is over, and your Jeep will be reliable and predictable.  Sorry that you have to perform this work in the freezing weather...

 

Moses

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Today I didn't do a whole lot with the jeep but I yanked the tbi off the top of the motor to thoroughly clean and go through it. I'm going to replace the 4 vacuum lines on it and inspect all the ports to make sure they are free of contamination. I am also curious if there are torque specs for the brace that holds down the injector and for the three screws that hold the regulator bowl in place. Other than that once I get the new injector o rings and vacuum lines and install the factory regulator spring I will be testing for pressure again. I should have another update come Saturday.

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Josh...Factory manual refers to the injector brace ("retainer") screws as "tighten retainer screws". Similarly the 3 regulator bowl screws are "tighten screws".  No torque specs, use good judgment, these screws should be securely tightened without stripping threads on the screws or pot-metal TBI parts.  Do not over-tighten and warp parts, either. A good grip on a screwdriver with a good tip, make the screws very "snug"...Make sense? TBI to manifold mounting nuts are 16 ft.-lbs.

 

I'm looking forward to accurate fuel pressure readings. Not sure what you want to do about the regulator adjuster screw. You may need to "make" an adjuster screw. If so, Fastenal and others have high tensile screws with allen heads. (Lowe's has even been known to provide some of these, at least Grade 5 U.S. or Metric 8.)

 

If you can find the right length adjuster screw and access the allen head with a hex allen wrench, that would work. Be very careful removing the sawed off adjuster screw. If you strip the threads of the regulator bowl bottom, you'll be looking for a bowl. Also, make note of any seal here, if the design calls for fuel around the screw, make sure you take that into account and seal it properly. 

 

To save time in the cold weather, here is one more PDF of service procedures. Make certain that all of the parts in the diagrams are present in your TBI unit when you take it apart. Zoom into the illustrations for details. This will help prevent overlooking missing parts:

 

2.5L TBI Service.pdf

 

Moses

 

 

 

 

 

 

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Finally got a fuel reading and almost positive on why my emissions levels were horrible (excessive Fuel pressure). On top of that i got my new vacuum lines installed, new injector and orings (injector no longer drips with key on engine off) . For my PSI readings i had aprox 16-17 psi which is too high. I need to be around 14-15. The weather here is terrible right now so i didnt check for kinked or blocked return lines. Tomorrow it should be decent out just cold so i will check to see if there are any messed up return lines. Worst case scenario would be having to remove the bowl from the TBI and drilling out the old adjuster screw. That wouldn't be too terrible i could take it into work and i have all the tools there to make it an easy job. I did not drive the jeep but i am pretty sure that the jerking/ bucking is gone. It was bucking i believe because my fuel pressure was around 1 psi. Ill do another post hopefully tomorrow to let you know if my fuel return line is messed up.

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oh yeah i forgot to add that i re-installed the factory spring. The spring was in the picture i posted a while back but it was the huge spring. So for future reference for someone that has to do a fuel pressure regulator on this don't use the one that the parts store supplies with the regulator unless you know for sure you can adjust your regulator to the appropriate specs. Again the spring supplied from the store was about 15 psi too low compared to the factory one.

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This sounds promising.  16-17 PSI would likely run okay, though a bit on the high side as you share.  If you can drop it to 14-15 PSI, all the better!  You've worked your way through a lot of "stuff".  The regulator spring findings and return to the heavier spring should be a big help and insight for others.  The use of the pressure gauge tester, in the long run, is a real money saver.  It narrowed down your trouble spots.

 

Good to check the return flow to the tank, just as a precautionary.  Vacuum line renewal can make subtle differences in tune and performance with EFI...

 

You're closing the gap, Josh...Weather permitting, you'll have a reliable Jeep shortly.  This exchange should prove helpful to many other Jeep Wrangler and XJ Cherokee/MJ Comanche owners with pre-1991 2.5L models!

 

Waiting for the good news...

 

Moses

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The jeep does run pretty good at 16-17 psi but I can feel the sputter a little bit at low rpms. I've already done so much work to it in not going to settle until it is running 100%. Tomorrow I am going to use a drill press to make a small hold in the current adjuster screw then use a bolt extracter to remove it. I want to install my own adjuster screw to set the pressure exactly where I want it. The thread pattern looks very course and might be hard to find a bolt with the exact match. Also the return line looks like it is free of restriction but I may go ahead and replace it with a fresh line. Future reference for my next fuel pump I do on it I will probably make it common practice to change that line due to the fact you have to just about drop the tank to get to it. I'm going to check eBay real quick to see if I can find any used or new bowls for sale.

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Alright so i found a company that sells just about everything you need for the tbi engine on the jeep. They have kits for the regulator, spring, bowl and screws for $30 which is almost half the price of the regulator from napa alone. Anyway the company is called Motor Man Fuel Injection. I am going to give them a call tomorrow to see if their bowl has the adjuster screw or not. Ill post back again tomorrow about this. Here is the ebay link i found

 

http://www.ebay.com/itm/New-Jeep-comanche-wrangler-cherokee-TBI-Fuel-Injector-regulator-rebuild-kit-2-5L-/290612842207?pt=Motors_Car_Truck_Parts_Accessories&hash=item43a9e00edf&vxp=mtr

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Very helpful to 2.5L TBI Jeep owners, Josh!  If you do end up "restoring" the regulator screw, make note of what keeps the screw from backing out.  It may be regulator spring pressure...I have a safeguard idea: Consider placing a lock nut on the screw, outboard of the bowl.  Once you adjust pressure to spec, you can tighten that nut to assure that the screw will not back off. 

 

Also, just another idea:  Consider use a copper sealing washer between the lock nut and bowl if there is fuel in the bowl.  This will provide the "leak proof seal" you need.  There should be a copper washer available with the correct I.D. for your bowl adjuster screw...

 

Moses

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Just made a purchase from Motor Man fuel injection and customer service was excellent. Quick easy and friendly transaction. The gentleman that i spoke with told me that my spring in my regulator bowl was faulty. With his set up, the new fuel bowl and spring will provide the correct PSI needed to run the jeep at factory specs. I told him mine has a broken off adjuster screw and he said it sounds like someone has tampered with it in the past. Maybe maybe not. I will have the parts by thursday so hopefully after work i can install those and get another reading. If my reading does not change i may try another gauge to ensure mine is reading the correct pressure. If both gauges compare then i will go back to looking at my return line. The return line will be the last part of the project that could cause my fuel pressure to be slightly off.

 

Crank Position Sensor- is there anyway way of testing this sensor. I know i can check for ohms but i do not know what the factory specs are.

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A new bowl and spring should do it, Josh! The cut off screw will be visible when you remove the old bowl, this could actually be "California emissions" or some other tamper-proof mandate, maybe a hasty factory method for making sure the adjuster is not cranked up to increase fuel flow or whatever.  Long shot guess.  Curious: Is the Jeep a "California Emissions/EPA" vehicle?

 

The CPS test is across the "A" and "B" terminals (labeled on the sensor connector) with the sensor unplugged.  You're looking for 200 +/- 75 ohms, a fairly wide variance.  The test calls for "engine hot" during the test, so without giving yourself a nice burn, carefully unplug the connector after engine shutdown.  If you have gloves that still offer dexterity, use them.

 

Moses

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I will check when i get home to see if it is california emissions which i do not think it is. Secondly on the Crank position Sensor if i take it out to clean it do you know if it came with a factory spacer to set up the correct positioning of the sensor or is it just plug and play on this model. I know some of the crank position sensors i deal with will have a small spacers on the end of the sensor and once you crank the engine over it removes the spacer. I am pretty sure this one is plug and play just checking before i mess with it. Again thanks for all the help this far! I think i can finally see light at the end of the tunnel

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Should be plug and play, Josh.  At any rate, having been in the housing forever, it should come out and go back into position the same way.  The biggest issue with these durable sensors (which generally either work or they don't) is contamination by oil and grease or grit from the engine and road. 

 

The tin ware needs to be in place at the bellhousing to keep debris out.  What often goes on with sensor trouble is oil contamination caused by a leaking rear main seal on the engine.

 

Light at the end of a tunnel...and it isn't an oncoming train!

 

Moses

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Josh, I'm curious about Motor Man and the regulator parts, as finding these parts is unusual.  Most of the 2.5L TBI pieces are not available from Mopar any longer.  The cohort of Jeep engines that use Renix TBI would be 1986-90 XJ Cherokee 2.5L and '87-'90 Jeep Wrangler YJ 2.5L fours.  I'm wondering what/where Motor Man pieces come from, whether they are NOS Jeep/Mopar or another source?  Let us know. 

 

Below is a 1987 YJ Wrangler engine block (side view) for those unfamiliar with this engine.  For detailed information on tuning and troubleshooting a 2.5L TBI four, see my 2.5L four 'how-to' article coverage at the magazine with a full set of photo illustrations:

 

post-1-0-77777700-1387443242_thumb.jpg

 

Moses

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I just received my parts and they look exactly like the factory ones. I am not sure where they get them from but they look legit. The spring is large like the original one and even the regulator looks the same too. The other regulators had minor discrepancies when compared to the original but this one is spot on. I'll have more time Saturday to do everything to it and get back to you.

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Good news!  Sounds like parts that will work and replicate the OEM pieces...You now have an adjustable regulator—and the pressure tester to verify spot-on 14-15 PSI fuel regulation at the TBI unit!

 

Did you take your tester to work and check the accuracy of the Harbor Freight fuel pressure gauge?  Probably a good safeguard as you set the new regulator bowl's adjuster screw.  I doubt whether they can "pre-set" these adjusters to exact pressure.  Let us know how close the adjuster is "out of the box".  I would guess that you'll be setting the pressure adjustment...

 

Moses

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Today i installed the new spring, new regulator and new fuel bowl. The parts that i got actually looked like the original (bad) parts that i first took out. Definitely go with Motor Man parts over auto zone, rock auto, Napa etc. These guys have quality parts that work excellent.

 

I hooked my TBI up and used the fuel pressure tester and fired up the jeep. The jeep instantly turned over and idled perfectly and quiet. The psi reading was exactly 15psi and did not bounce at all just a steady and solid 15. I noticed that i still had a minor sputter so i checked my tps voltage and everything was still with in specs. The second thing i did was to see if i still had a sputter if i disconnect the hose from the EGR valve and my sputter instantly cleared up. As of right now i have the EGR disconnected because it runs great without it.

 

I then took it for a ride and it is running perfect i have zero complaints about it. I had good power through all gears feels about what a 4 cylinder should have. I believe i shouldn't have any more issues with the fuel system/engine for a good while. I am going to run it all weekend and week to see if everything holds up and i will get back to you for hopefully a final post in this thread. 

 

post-93-0-20456100-1387654609_thumb.jpg Here is my gauge hooked up after i re installed the new spring and new regulator and also the new bowl.

 

post-93-0-17306400-1387654663_thumb.jpg Here you can see the difference in the regulators. The one on the left is from Motor Man which looks exactly like the original. The one on the right is the same ones that rock auto, Napa etc will supply. I feel if the regulator on the left was good enough for Jeep to use then its good enough for me and that's the one that i used.

 

post-93-0-03202000-1387654757_thumb.jpg Here i have my two springs, the one on the left is the original i believe from 1989 and the one on the right is from Motor Man. It's a small difference but you can clearly see the original is slightly worn out. The one or the right is about 1/8" taller then the original. With that small of a difference it changed my fuel pressure from 16-17 to 15 psi and now my jeep runs perfect. Also, like Moses said, this proves how important the correct fuel pressure is. 

 

I had a lot wrong with my jeep and now i feel i can finally close this chapter and finally enjoy driving my jeep around and now have some money for other add-ons for it!

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Josh, this is great news.  You rode it out, learned a bunch and solved your Jeep's problems!  Motor Man looks like quality, OE type parts. 

 

As for the EGR, check your vacuum hoses. The EGR should not open at an idle, as it uses a "ported" vacuum source.  Ported, like with a carburetor, means vacuum sourced from above the throttle valve.  Ported vacuum will be near zero at a closed throttle, then pick up immediately as the throttle opens, then drop to nearly nothing at wider throttle openings.

 

The EGR actually has a positive function in addition to lowering NOx for tailpipe emissions requirements.  The EGR cools the upper cylinders from as high as 4800-degrees F to below 2500-degrees F for NOx reduction.  This dramatically reduces risk of detonation/ping and upper cylinder fatigue.

 

If your EGR does not seat completely, that could be a defective or clogged valve.  From what you describe, though, the EGR does work fine with vacuum removed.  When your vacuum hoses are correctly hooked up, you will have close to zero vacuum applied to the EGR when the throttle is closed (idle) and ported vacuum is very low.  Identify a ported vacuum source for the EGR.

 

Congratulations, Josh!

 

Moses

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