1988 Wrangler 2.5L TBI Engine Difficult to Start and Keep Running

[obilankenoby]

Hello, I have a jeep wrangler 2500 from 1988 with a gas system, it started tugging when I made stops and then I started again, the shorter the stop and the more it tugged, this only happens with gasoline gas has no problem, now yes it is aggravated and it is difficult to start it and as soon as it starts it turns off, if I insist I can even go. At the moment I have changed the mono injector and fuel filter, the only test I have done is to turn the key and see if the fuel pump was pushing the fuel, as I turn the key with the engine off the pump squirts the petrol and then stops. I know there are good mechanics here and forgive my writing, I use google translator

[Moses Ludel]

obilankenoby...You will find over 400 posts and replies on 2.5L YJ Wrangler TBI troubleshooting here at the forums.  Search under "Everywhere/All Content" with the words "2.5L", "TBI" or "YJ Wrangler". 

It sounds like you are getting fuel to the TBI unit.  However, you need to check the fuel flow volume and fuel pressure at the TBI pressure port. 

Pressure should read 14.5-15.0 PSI.  You can use a "T" at the TBI port to make this test with a pressure gauge.  Next, check the fuel volume flow at the "T".  Use a safe hose and metal can to test the fuel flow volume away from any engine heat.

Also check the TBI return line to the fuel tank for restrictions.  If all this checks okay, you may have a clogged fuel pickup filter (sock) in the fuel tank.  This could be restricting the flow of fuel to the pump.

Try these things.  If you have any questions, please post them here.  Let us know what you find.

Moses

[obilankenoby]

Thanks Ludel for answering me, do you think I can skip the fuel pressure test by doing the test as I have read in your other conversations that in one minute the fuel pump should fill a 1 liter container

[obilankenoby]

I did the test of the minute and a liter of petrol because I do not have the manometer that measures the pressure of the petrol the result was 1 minute and about 100 cc of petrol as you can see from the images the blue sign is a liter and that little petrol it is the result of 1 minute, I shorted the pump relay as you said or the pump or some block, tomorrow I take off the tank and see what I find and then report here. However, the first symptoms that I did not give importance to were already a month ago, when it restarts from short stops the engine went to fits and starts, then the defect increased more and more, until the day before yesterday it did not start anymore. Your directions were right

[obilankenoby]

I'm sorry, I forgot the pictures

[Moses Ludel]

obilankenoby...The test helps.  You have way too little fuel discharging from the port.  There are four possibilities:

1) Fuel pump is not working properly (defective pump or a bad ground).

2) Sock filter is clogged in the tank.

3) Supply line from the tank to TBI has a restriction.

4) The pressure regulator at TBI unit is stuck open and flowing fuel back to the tank through the return line.

Before dropping the fuel tank, I would check the port pressure at the TBI test port.  Use a fuel pressure gauge for this test.  You are testing the psi (pressure) of fuel at the TBI test port.  You may be more familiar with BAR, and you can convert the 14.5-15.0 psi to BAR if your fuel pressure gauge reads BAR.  15 psi equals 1.034 BAR.

If the test port pressure is normal, consider the #1, #2 and #3 possibilities.  If the pressure at the test port is low, the TBI regulator could be defective or #1, #2 and #3 could be the issue.

I would test the fuel pump volume/pressure in the supply line before dropping the tank.  You can disconnect the supply line from the TBI unit and activate the fuel pump like you did with the jumper.  If you have the gauge at the end of the supply line with no return to the fuel tank, the pressure will be very high.  Make sure the gauge hose and clamp are rated for high pressure EFI use.  Only run the pump for a moment;  pressure could jump as high as 95 psi or 655 kPa without the fuel returning to the tank.  Shut the pump off if pressure rises quickly.  If you check the fuel volume here, it should also be high.  Be careful.  I use EFI hose, EFI clamps and a metal fuel can for this test.

My first step would be to run a fuel pressure check at the TBI test port.  If pressure is normal (14.5-15 psi) and the fuel volume is still only 100cc in a minute, move to #1, #2 and #3.  If you narrow this down to a weak fuel pump, drop the tank to replace the fuel pump and install a new sock/pickup filter at the same time.  Clean the fuel tank before installing the pump module.  Make sure the new fuel pump is for the 2.5L TBI engine.  The MPI (4.0L) pumps look the same but put out too much pressure.  TBI is a lower pressure system.

Moses

  

 

[obilankenoby]

Okay Ludel, I'll let you know

[obilankenoby]

Good morning I solved, it was the petrol pump as you said Ludel in your three options, I bought the petrol pressure gauge and while I was waiting for the package I heard the pump make a noise like continuous telegraphy, so I decided to disassemble the tank and change it. I replaced the pump with the Airtex pressure 1.20 and the machine went immediately well. There was still a problem I was hoping it would disappear by replacing the fuel pump, at departures I sometimes lack the power at 1500 rpm it could be connected because the jeep when I turned it off was on LPG and the start is on petrol. I hope google gives me a good translation

[Moses Ludel]

obilankenoby...Glad the new fuel pump solved the problem.  Does the engine start on petrol then switch to LPG?  Or does the engine run on gasoline (petrol) all of the time? 

To troubleshoot the hesitation at 1500 rpm, can you run the engine on petrol (only) without using LPG?  Try that to see if the 1500 rpm hesitation goes away.  If the hesitation goes away, the problem could be related to the LPG system.

Moses

[obilankenoby]

Hello, sorry for my absence but I had many things to do, the car always starts on petrol then accelerating after a certain number of engine revolutions it switches to gas. The problem is that he doesn't always do it, but after a short stop at the restart with petrol around 1500 rpm there is a weakness. The problem occurs only with petrol also because it always starts on petrol

[Moses Ludel]

Hi, obilankenoby...The symptoms could be related to spark timing advance.  Have you checked the spark timing advance in both the petrol and LPG operating modes?

I am curious how the petrol-to-LP gas (LPG) system works.  Some conversions retain the carburetor or TBI and flow the LPG through the air intake stream.  The engine can then be run on either LPG or gasoline when desired.  Other systems use an LPG "injector" into the intake manifold.

Please explain how your system works and the "weakness".  Some questions:

1)  Is this a "factory" LPG conversion or aftermarket?  Are you running LPG, or is this CNG? 

2)  Can the engine be switched to run just on petrol? 

3)  If you can run on petrol alone, do you get the "weakness" at 1,500 rpm?  Or is this weakness when the engine converts to LPG? 

4)  Most LP (propane) engines usually start and run on propane.  How is your system different?

5)  Where is the source of the LPG?  How and where does LPG enter the engine? 

6)  Is there a "mixer" or LPG/propane injector in your system?  Where does the LPG enter the intake?

7)  What do the spark plugs look like after running the engine:  rich, lean or correct color?

8)  Does the ignition produce good spark?

9) Does the ECU/ECM continue to operate after the switch to LPG?  Does the spark timing advance when engine speed increases?  Have you checked the spark timing advance with a timing light?

10)  Are the oxygen sensor, MAP sensor and knock sensor still functioning and adjusting spark timing in the LPG mode?  Have you checked the ignition spark timing advance with the engine running in LPG mode?

11)  Is the EGR valve supposed to operate in the LPG mode?  What does the LPG service manual say about EGR operation?  Is the EGR valve still operating?  Does it work properly in petrol mode?

If the system can be run on just petrol, the engine tune can be tested in petrol mode only.  That way, you can diagnose the petrol fuel-and-spark management system by itself.  You will know whether the problem occurs only during propane/LPG operation.  Make sure the petrol TBI fuel-and-spark management system works properly before diagnosing an LPG problem.

Photographs of the LPG system would be helpful.  Any service information, like details from a manual for the LPG system, would be helpful.  It is important to know whether the spark timing advance depends on the oxygen sensor.

Moses