Weak start

Whiplash2130

Whiplash2130

YJ Enthusiast
Joined
Jul 16, 2020
Messages
150
Location
Florida
My ‘93 YJ 2.5L 4 banger has been running good since I bought it 2+ months ago. All of a sudden yesterday, she became hard to start. It took about 6 tries to get this little fuel injected 4 cylinder engine to crank to start. She runs like crap for about 1 minute then smoothes right out. What is it?
 
It used to start with one quick pump. Now will only start while pumping. Also this is the first time she has been below a 1/2 tank since I got her. Maybe I should fuel her up and see if it improves.

I ran some quick numbers, it’s been driven 232 miles since last fill up. If I use 15 mpg (figured out on last tank of fuel) it would have used 15.66 gallons of fuel. Fuel gage reads slightly more than 1/4 tank. I think this is all about normal. She was in the shop for a week and there is no way of knowing how long it was run.
 
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Whiplash2130 said:
It used to start with one quick pump. Now will only start while pumping. Also this is the first time she has been below a 1/2 tank since I got her. Maybe I should fuel her up and see if it improves.

I ran some quick numbers, it’s been driven 232 miles since last fill up. If I use 15 mpg (figured out on last tank of fuel) it would have used 15.66 gallons of fuel. Fuel gage reads slightly more than 1/4 tank. I think this is all about normal. She was in the shop for a week and there is no way of knowing how long it was run.
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The reason I ask isn't really related to fuel at all. When our throttles are closed (i.e. gas pedal not touched), the engine gets no air except through idle air control sensor passage way. Sometimes the IAC gets covered in carbon deposits and doesn't work properly, which can block air to the engine when trying to start. Pressing the throttle opens up the ability for the air to bypass the IAC and flow into the engine. What I'm saying in a roundabout way is that your IAC may need to be cleaned or replaced, IF pressing the gas pedal while starting fixes the issue. If it does, that means you are providing the engine air that it can not get through the IAC like it normally does, meaning you may need to pay attention to the IAC and clean or replace it.

If pressing the gas pedal while starting does NOT fix or help the issue, then it's not likely that. At that point there is something else that needs to be figured out. Note: You should never need to press the gas pedal to start it up. If you do, that is indicative of a problem, such as the IAC issues. So, try starting it with gas pedal pressed and without gas pedal pressed, and post back if there is a difference.

As for the fuel stuff dump some fuel in it and see if it helps. Everybody says the YJ fuel gauge is inaccurate, I have no idea how yours is. Mine has always been 100% accurate so mine is trustworthy and I wouldn't consider myself out of gas if it read more than 1/4 tank.
 
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I know it should start without gas pedal but never has. Now no gas pedal - engine cranks but never attempts to start. It does however, make a weak attempt to start with gas pedal depressed and eventually starts.
As you can tell, I was checking accuracy of the fuel gaging system. Right now I believe it has a 20 gallon tank.
 
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If it won't start without gas pedal that tells me you have an IAC (Idle Air Control) issue. Now that it ALSO won't start or does a poor job even with gas depressed, tells me there's more to look into.
 
Your year definitely has a 20 gallon capacity tank, although it may be limited to 15 gallons. The 4 cylinders from 1991 and later pretty much all shipped with their 20 gallon capacity tanks limited to 15 gallons. But, the previous owner may have pulled out the vent tube in the gas tank which allows the tank to fill properly. This is what the dealers would do for people who paid for the "20 gallon" tank option from 1991-1995.
 
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Whiplash2130 said:
I ran some quick numbers, it’s been driven 232 miles since last fill up. If I use 15 mpg (figured out on last tank of fuel) it would have used 15.66 gallons of fuel. Fuel gage reads slightly more than 1/4 tank. I think this is all about normal. She was in the shop for a week and there is no way of knowing how long it was run.
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Wow, 15x15=222 so if you got 232 miles from a 15 gallon tank that's cutting it close. :)

My sending unit is bad so the needle wanders all over depending on which way the wind blows. The gauge itself tested ok.
 
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Flyer58 said:
Wow, 15x15=222 so if you got 232 miles from a 15 gallon tank that's cutting it close. :)

My sending unit is bad so the needle wanders all over depending on which way the wind blows. The gauge itself tested ok.
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It’s got to be a 20 gallon tank.
 
Well she won’t start at all! Maybe it was out of fuel after all. Battery too weak to turn her over after I put 2 gallons of fuel in her. Try again tomorrow.
 
Flyer58 said:
Do you have a fuel pressure tester? You can probably get a free loaner from the local parts store. Check the pressure on the fuel rail by the injectors.
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I do not have a tester. Will check with NAPA or Autozone after I replace the battery.
 
machoheadgames said:
Your year definitely has a 20 gallon capacity tank, although it may be limited to 15 gallons. The 4 cylinders from 1991 and later pretty much all shipped with their 20 gallon capacity tanks limited to 15 gallons. But, the previous owner may have pulled out the vent tube in the gas tank which allows the tank to fill properly. This is what the dealers would do for people who paid for the "20 gallon" tank option from 1991-1995.
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How can anyone tell what they (I) have? It could be that my tank is actually empty and my gas gage reads 1/4 tank or as you say, I don’t have access to 5 gallons of fuel! Very strange!!
 
Whiplash2130 said:
How can anyone tell what they (I) have? It could be that my tank is actually empty and my gas gage reads 1/4 tank or as you say, I don’t have access to 5 gallons of fuel! Very strange!!
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Just to clarify, If the vent tube is shortened or changed the extra 5 gallons will be at the top so your gas gauge will show full as it drains off the first 5 gallons. Empty should be empty unless your sending unit is like mine and not accurate.
 
Ok folks, for those of you who are really interested here is the final result of the weak start problem. Be it known that this happened as a result of a test I was doing to verify fuel milage and quantity. Results are as follows:
1) started to act up (slow start bucking) after running 230+ Miles
2) drove an additional 5 miles - vehicle would not start. Fuel gage read slightly more than 1/4 tank.
3) battery weak. After 2 weak attempts with no start battery went dead.
4) added 2 gallons of fuel.
5) replaced battery with spare used battery and she fired right up.
6) refueled to full. 12.5 gallons. This means this YJ only has a 15 gallon tank.
7) replaced battery with new one and also Installed battery tie downs. Removed bungee cords from previous owner.

Did not check fuel pressure but intend to after I get the fuel filter changed.
 
Well,,, that's one way to test the fuel gauge and tank quantity :) Glad to gear it's running again. I set the trip odometer after every fill up. 16MPG sounds about right.
 
Whiplash2130 said:
How can anyone tell what they (I) have? It could be that my tank is actually empty and my gas gage reads 1/4 tank or as you say, I don’t have access to 5 gallons of fuel! Very strange!!
Click to expand...
Sounds like you have the "15" gallon tank. If you want 20 gallons, then just pull the vent tube out of the tank, cut down to 2-3", and reinsert. Sounds like you also have some inaccuracy in your fuel pump assembly, so I'd watch out and fill up when you get to 200 miles or so to prevent this happening, or drop the tank and fix the fuel sender. The fuel tank capacity mod is easy, just look it up on YouTube.

You may have some sort of blockage or issue with your fuel pickup if you're only able to get 12.5 gallons back in after pretty much running out of fuel. It may not be picking up the bottom few inches of fuel in the tank or something. Been a long time since I was limited to 15 gallons so I'm not really sure. I did run mine to below E a few times and I believe I was able to put in around 13.5-14 gallons with no sputtering or running out of fuel ever. So, who knows.
 
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