No start-fuel issue

93, 4.0, auto

It has had a slow start since I got it about a year ago. The previous owner had removed the fuel rail and I noticed the #3 injector was leaking onto the manifold and has been for some time. I removed the rail and found no upper o-ring on the #3 and 2 upper o-rings on the #1, so the #'s 1-3 were not properly seating. I removed all injectors, cleaned the carbon with a wire brush, replaced all o-rings with new and put everything back together. It ran smoother but still had a slow start.

The next day after running for a short while then stopped for a while it would crank, but not start. There was little pressure at the valve on the rail, but I pulled the return line and it had pressure when the key energized the fuel pump. I shot some starter fluid in the throttle body and it cranked right up and ran well.

Today, it started slowly and ran well but when it tried to restart it would not. More starter fluid and it cranked right up and ran good. Now it won't start without starter fluid, but once started runs well.

After it would not start the first time, the other day, I replaced the crank position sensor (because I had a spare) and it had no change. The next day I replaced the fuel pump (whole assembly) due to the lack of pressure at the valve. It showed no change. Today I replaced the fuel pressure regulator (from salvage yard) with no change.

Now it will not start without the starting fluid, but once started runs well.

I have checked the plugs and they show normal wear and I can hear each injector firing and everything is wired correctly.

Why is it getting enough fuel to run, but not to start?

Check the ballast resistor on the drivers side fender well.

Try jumping the two connectors and see if it starts up.

Probably not it, but doesn't cost you anything.

Stop dinking around.

By now you could have rented or purchased a fuel pressure gauge to actually test the system.

There are multiple power paths to the fuel pump:

Key ON, power to pump through the ASD relay, bypasses the ballast resistor.

Key START, power to pump through the starter relay, bypasses the ballast resistor.

Key ON, engine running from idle to just short of WOT, power to the pump through the fuel pump relay and through the ballast resistor (eliminated 94+).

Key ON, engine running at WOT, power to the pump through the oxygen heater relay, bypasses the ballast resistor.

Test the different modes above and see when the pump isn't running.

with the key ON the fuel pump energizes
with the key START if the relay was bad the starter would not turn over
with the key ON and running it runs smoothly

I don't think I need a pressure gauge because I know I don't have enough pressure to start.....but the pump is new and after started it runs and idles great.


Tomorrow I am going to check all the lines from the tank to the rail for any crimps or kinks. If I find nothing out of the ordinary, I am going to pull the fuel rail and look for any abnormalities-since the no start issue arose after I changed the o-rings the other day.

If I need a pressure gauge please let me know what I am testing for with it. Am I correct that the start relay also powers the starter and if the starter turns over the relay is good?

Jess said:

with the key ON the fuel pump energizes
with the key START if the relay was bad the starter would not turn over
with the key ON and running it runs smoothly

I don't think I need a pressure gauge because I know I don't have enough pressure to start.....but the pump is new and after started it runs and idles great.


Tomorrow I am going to check all the lines from the tank to the rail for any crimps or kinks. If I find nothing out of the ordinary, I am going to pull the fuel rail and look for any abnormalities-since the no start issue arose after I changed the o-rings the other day.

If I need a pressure gauge please let me know what I am testing for with it. Am I correct that the start relay also powers the starter and if the starter turns over the relay is good?

Click to expand...

Battery main powers the starter, grounded through the engine block. The starter relay provides 12 volts to energize the solenoid.

When was the fuel filter changed last?

IIRC I changed it about 6 months ago, but it might have been one of the other Jeeps. I also thought about the filter, but it seems if the filter is too clogged to start the engine I would see other symptoms such as stumbling, bogging, or stalling while running.

I think the no-start is a further symptom of the slow start it has exhibited since I got it.

Could the cam position sensor have this effect? I know the Renix does not need a valid signal and will eventually start, but is the HO the same?

I am running out of ideas. It seems everything I am thinking of would not only keep the engine from starting, but also from running......but it runs perfect once it is started.

update

Yesterday when I stopped working on it, it would not start at all without the starter fluid. Today when I went out to work on it, it started right up after cranking for a few seconds. I turned it off and restarted it several times and it continued to start on its own.
I then checked all the fuel lines for kinks or leaks and found everything as it should be. I ran a can of Seafoam through the throttle body to clean everything good and then replaced the fuel filter.
Then I removed the fuel rail and checked for leaking injectors and found nothing. I then restarted the enigne and had little pressure at the vlave while running. I swapped the core in the valve with one out of another rail and then had great pressure while running, but immediately lost all pressure when not running.
I pulled the vacuum line off the fuel pressure regulator and examined for leaks, but found none. Out of curiosity, I had a spare 99 rail and swapped the fuel pressure regulator into my rail. It does not have a vacuum fitting, so I plugged the vacuum line and it still showed no change.

Later this evening the wife went out and drove about 3 miles and then stopped for less than 1 hour and when she went to return home it would not start. Once again with starter fluid it started and ran normal.

Then problem appears to be after driving it will not restart. There is not cel on, but with the key on/of it did show a code for the o2 sensor. Could this be a source of the problem? What would cause the rail to lose pressure immediately after shutdown?

Also, I noticed earlier when it did turn over several times before starting it sounded like the starter was grabbing. It almost sounded like the engine was hydrolocking, but then it starts. I assume this is somehow related to my problem, but I'm not sure how.

after some research I think it may be vaporlocking.

What steps should I take to confirm/repair this?

update

Today I got a fuel rail and injectors from a clean jeep in the salvage yard. I installed them and the original fuel pressure regualtor (vacuum operated). I turned the key to ON and pressurized the rail and had good pressure from the valve. The engine cranked up without the slow start and ran well. Upon shutdown the rail maintained good pressure. I started and shutdown several times and everything appeared as it should.

The wife took the Jeep out for a short drive, stopped and returned home without incident. A short time later, she went to leave again and it cranked but did not start. She sprayed with the starting fluid and it make the vapor lock noise but did not start. She the sprayed it again and it once again made the vapor lock noise, but then started. It then ran well.

It seems as though it must still be losing pressure, but I can't track down where the problem is. Any ideas????

Have you done the FSM test procedure for the CPS? I know in that year, mine is a 94, they can overheat and be a general pain when they are old and cause the problem you are describing.