YJ Fuel Delivery Questions

[jsawduste]

The YJ left me stranded on the road today:ha:. Thought about calling Harold`s but thought the mileage charge might be a bit much.:eek::poke: Only a short walk to home where I got the truck and trailer.

Anyways, it acted like it was running out of gas. Sputter and spit but no backfire.

Once I got home a quick spray of starting fluid in the air cleaner and it would fire right up and run for a few seconds. Which leads me to believe there is a fuel delivery problem.

Can hear the fuel pump turn on but that is not to say it is pumping.

Monday or Tuesday I will spend some time and figure out what is going on.

Anyone know what the voltage should be at the injectors/fuel rail ?

Will check fuel pressure and the other obvious points for a fuel delivery issue.

Of course any thoughts or comments would be welcome.

[Mongo]

Quick check on pressure can be done by the schrader valve. At least to see if there is any pressure. How many miles on the filter?

[Mongo]

I'm looking for voltage, can you get a code?

[Grandman]

YJ is carb not injected correct ? Why is it running a E pump instead of mechaincal ?

Fuel pump most likely either way and change the filter .

[Mongo]

Injected, unless the early ones weren't.


FSM says 12.9 - 15 volts from the pcm to the injectors.

[jsawduste]

I'm looking for voltage, can you get a code?

Thanks Mongo,
filter has about 2,000 miles on it. New tank when the Jeep was built. Never saw the Check Engine light come on. So not sure if a code would have been set.

Have a FP gage connected to the schrader but it Fubared last summer and haven't bothered to fix it. Last time it worked it was about 40 lbs with the vac. line on. Guess now would be a good time `eh ? :hehe:

Also a wide band F/A gage connected to the O2 sensor. Which appears to be working. Even if the O2 would go bad would`nt it have a limp mode ?

[jsawduste]

YJ is carb not injected correct ? Why is it running a E pump instead of mechaincal ?

Fuel pump most likely either way and change the filter .

Pre 91`s had the Renix (Renault and Bendix) system that had the carb. After that they were injected.

Have a fuel filter here at home.

Just getting all my information together so when wifey goes back to work on Monday I can play Jeep tech.

Mothers day and Jeeping don`t go good in this house. :eq::hehe:

[Mongo]

I'm watching the wings and then need to clean the crib. I'll read more tomorrow at work. Hopefully by then the Rover boy will chim in.

[jsawduste]

I'm watching the wings and then need to clean the crib. I'll read more tomorrow at work. Hopefully by then the Rover boy will chim in.

:thumb::thumb::wave:

[Rob the plumber]

A real wideband, or one of those A/F gauges? If the pump was taking a crap it should show way lean. 17ish to 1 to misfire usually. Check pressure at the rail.

[Rover]

Start with checking the fuel pressure, let us know what you got

[Tippy]

This is exactly why I'm having a hard time making my mind up on going to FI, I know it is superior to carbs for what I do with my jeep, but I know with a carb I only need air fuel and fire and I can go.

[Haggar]

Normally, though, its super reliable.


On my truck, something similar happened 2 years ago.

On mine, what happened was that I had some holes rusting into the top of my fuel tank around the pump module. Rainwater would stand there, and leak into the tank (my tank is exposed).

Enough got in, and kind of made a sludge/gel in the bottom of the tank and which got sucked up, and plugged up the lines and filter.

I'd definately do the pressure check. It might be worth it to drain out or get some samples from the bottom of your fuel tank. When I did that (I disconnected the fuel line coming out of the tank, and turned on the pump, to fill a glass jar), it was clearly contaminated looking.

Between bad vents, vented caps, rust, airborne moisture, bad fuel, and just sitting while you rebuilt the Jeep, its pretty easy to get water in the fuel.

[jsawduste]

Start with checking the fuel pressure, let us know what you got

OK, had a few minutes so I checked FP at the schrader valve in the rail.

38 psi was the result.

Did the starting fluid in the air cleaner again and it fired up for a few seconds. Again, no backfire or anything unusual.

Granted I would like to see 40-42 psi but it ought to run on 38.

Next step ?

Jason,
For kicks I tool the gas cap off. No change.

Have run 5 or so tanks of fuel through it since spring and has always run good.

Did get a fill up from on the way home from the last Swamp Stomper meeting......................Other then a quick run to the store the Jeep had sat for about 4-5 days. Time to pump a batch into the jar

[Rover]

Did the pressure hold or leak down real quick?

I think jason may be on to something with the bad gas, contaminents in the gas can also screw up the injectors

[jsawduste]

Did the pressure hold or leak down real quick?

I think jason may be on to something with the bad gas, contaminents in the gas can also screw up the injectors

I

Presure held but found a new symptom.

While atempting to get a fuel sample off the rail.

Found that I had no flow.

Key on or cranking.

So off to the filter we go.

[Rover]

I

Presure held but found a new symptom.

While atempting to get a fuel sample off the rail.

Found that I had no flow.

Key on or cranking.

So off to the filter we go.

Thatl do it, check that gas though, 2000 miles is damn quick to clog the filter

[Grandman]

Iv seen gas stations sell you a tank full of water before , The shell at the 212 exit use to be a real problem for that . We would tow them in and drain 20 gallons of water out of the tank .

[Rover]

Iv seen gas stations sell you a tank full of water before , The shell at the 212 exit use to be a real problem for that . We would tow them in and drain 20 gallons of water out of the tank .

that or putting desiel in the wrong tank, thats always a fun one

[Beefy]

Iv seen gas stations sell you a tank full of water before , The shell at the 212 exit use to be a real problem for that . We would tow them in and drain 20 gallons of water out of the tank .

Happened to me once at a gas station I worked at, they paid for my repairs :thumb:

[Haggar]

Time for:

http://www.buylowdrugs.com/images/flomax.jpg

[jsawduste]

Time for:

http://www.buylowdrugs.com/images/flomax.jpg

Yep Flomax it is :ha:

Took a before the filter fuel sample. Gas looks good.

But

While the pump turns on it only pisses a small amount (shot glass and a half +/-) before it stops flowing. Cycling the key will dribble out another shotglass full.

Reckon it is time to drop the tank :pissed: and get another pump..........

Poop..........

[Rover]

Is the pump staying on while the flow stops?

when you turn the key to key on engine off the pump should only turn on a few seconds to prime the system.

[Tippy]

Contact Aaron (truckman) he is an expert within this situation from Rausch Creek.:hehe:

Sounds like it is an issue within the tank, hope its an easy fix.

[jsawduste]

Is the pump staying on while the flow stops?

when you turn the key to key on engine off the pump should only turn on a few seconds to prime the system.

Have to check on that. Not sure if it is staying on. But should`nt the pump continue to pump with the engine cranking ?

What would control the pump after keyed up after a few seconds ?

Thanks Tippy !!:thumb:

[Rover]

Yep, should continue when the engine is cranking. I assumed this was when you just had key on engine off.

the pcm energizes the fuel pump relay to prime the system. when the pcm sees rpms the relay will be energized all the time.

[jsawduste]

Yep, should continue when the engine is cranking. I assumed this was when you just had key on engine off.

the pcm energizes the fuel pump relay to prime the system. when the pcm sees rpms the relay will be energized all the time.

Learning a bunch of stuff here.

We get the "prime" flow on ignition 1.

NO flow on cranking Ignition 3

Understand the PCM getting the signal from what I think would be the CAM POS. SENOR. Which is what times the injectors.
While the CRANK POS. SENSOR times (sends the signal to the PCM) the ignition. Since it will run on starting fluid without any hiccups I am going to think the CRANK PS is working OK.

Correct in this application ?

So we now need to look at the Fuel Pump Relay OR the Cam PS.

[Rover]

its tough without the vehicle in front of me to mess with:

so your getting the fuel pump to prime but it wont pump after that. check voltage at the pump connector while cranking, make sure your getting 12volts all the time while cranking.

the pcm will get inputs from the crankshaft position sensor for rpm and fuel pump.

got this from the fsm:
"The PCM monitors the crankshaft position sensor.
If the PCM does not receive a crankshaft position
sensor signal within 3 seconds of cranking the engine,
it will shut down the fuel injection system.
The fuel pump is activated by the PCM through
the fuel pump relay.
Voltage is applied to the fuel injectors with the
PCM. The PCM will then control the injection sequence
and injector pulse width by turning the
ground circuit to each individual injector on and off.
The PCM determines the proper ignition timing according
to input received from the crankshaft position
sensor."

[jsawduste]

Thanks for the leg work.

Indeed, I need to verify voltage at the pump while cranking. Suspecting the FP relay or its fuse F9 in the UH electrical box. My box has a "custom" mount that makes it a royal PITA to get to.

Because the engine never has backfired when it "ran out of gas". Or when starting fluid is sprayed into the AC. I am believing that the CPS is providing the correct timing. But something is messing up the signal to the pump.

The FSM data is very helpful. Time to get the volt-o-meter out.

Thanks !!

[jsawduste]

Been busy for the last couple days. But I did brave the rain and pulled the Fuel Pump and Auto Shut Down relays out. Not impressed with how the contacts look.

Breaking out the Dremel to clean the oxides off. Stole a nail file from Ashley to do the female contacts in the electrical center.

Good cleaning and a hit of electrical spray cleaner.

Maybe I`ll bet lucky. :eq: :dirty::hehe:

Probably not though...........:sadpanda: