4.0 cranks but wont start unless starter fluid used - JeepForum.com
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Unread 08-14-2009, 02:25 PM   #1
romo1000
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4.0 cranks but wont start unless starter fluid used

ok so i have a 91 yj with 4.0. this is an intermiten problem. the engine will crank but will not start unless you play with it for awhile. the check engine light does come on. there is spark. it looks to me like their is fuel I can get it to spray out of the check valve. sometimes is starts right up, cold, hot, just shut off, been sitting all day anytime. other times it just cranks. when it just cranks I can spray some starter fluid in the throttle body and get it to start and pump the gas a bit and it will run fine after that. can there be an intermitten problem with the fuel pump?. this one is stumping me. I've looked at the thread on the ecm but my check engine light comes on. I've searched a number of different ways but am not finding a similar thread. it's like it doesn't get gas until it's running when the problem happens. thanks for any help.

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Unread 08-14-2009, 03:36 PM   #2
Alfons
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I would attach a fuel pressure gauge and see what's happening in that area.
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Unread 08-14-2009, 05:15 PM   #3
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Do you have any codes showing ?
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Unread 08-14-2009, 05:34 PM   #4
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Does it sputter for a bit and then die? Or just won't start randomly after shutdown? Any time I have a fuel pump fail, I get the death sputter as the fuel pressure starts to drop, then dead until you whack the tank. Easy way to tell if pump is even spinning as get under the back end and have a friend turn the key to the run position (not crank the motor) and listen for the fuel pump in the tank. About three seconds of Whrrrrr and a click is normal.
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Unread 08-15-2009, 07:58 AM   #5
romo1000
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it is throwing some codes but nothing that seems to relate. but like I said sometimes it starts fine sometimes it doesn't and when it doesn't all I have to do is spray some starter fluid in the throttle body and it starts. then it will run fine. Can a fuel pump go out intermittenly. I've only seen where they work or don't work. And if it was a fuel pump why would the jeep run after I got it started. When the problem is happening I'm getting power to the fuel pump with the key on and power to the third pin when your cranking the engine.
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Unread 08-15-2009, 10:55 AM   #6
romo1000
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it just started dieing again after starting fine all morning weird. when I started it this time it idled at like 500 rmps kinda puttering and then died this went on for a couple of minutes each time I tried to start it would do that so I sprayed some starter fluid in and after about 30 seconds and more spray i got it to run. when it's sputtering if you try and give it gas it just dies. once you can get it passed the initial sputtering it runs fine. it's almost like it gets totally flooded and has to clear out then goes but I could be completely wrong on that one.
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Unread 08-15-2009, 05:41 PM   #7
Alfons
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A pump can be intermittent but you won't know if that's it without some testing.
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Unread 08-15-2009, 05:55 PM   #8
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Quote:
Originally Posted by romo1000 View Post
ok so i have a 91 yj with 4.0. this is an intermiten problem. the engine will crank but will not start unless you play with it for awhile. the check engine light does come on. there is spark. it looks to me like their is fuel I can get it to spray out of the check valve. sometimes is starts right up, cold, hot, just shut off, been sitting all day anytime. other times it just cranks. when it just cranks I can spray some starter fluid in the throttle body and get it to start and pump the gas a bit and it will run fine after that. can there be an intermitten problem with the fuel pump?. this one is stumping me. I've looked at the thread on the ecm but my check engine light comes on. I've searched a number of different ways but am not finding a similar thread. it's like it doesn't get gas until it's running when the problem happens. thanks for any help.
Try starting it witout the air filter element in it. If it does start and run well....you know you just found your problem.

When was the last time the in-line fuel filter was changed? If it is clogged up you lose fuel pressure and get these symptom also. You can cehck it by replacing the filter with a bit of fuel line hose and two clamps. If it starts and runs fine then you know the filter was clogged and was causing your grief.

The '91 is the first year for MPFI if I remember right. There is an Idle Air Control (IAC) sensor in the back of the TB. I have removed them (2 torx screws IIRC) cleaned the IAC sensor itself and the core it sits in with carb cleaner and some fine steel wool. That may solve the start/idle problem. DON"T pull the probe in the IAC out at all or you ruin it.

Make sure the MAP sensor which is mounted in the middle of the firewall is getting good vacuum also.
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Unread 08-16-2009, 03:03 PM   #9
romo1000
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we'll symptoms changed a bit. It just died while I was driving it this time. tried starting immediately and nothing. So I sprayed some starter fluid in and it idled at 500 or so then I hit the gas and it ran. Got me home. I changed the fuel filter last year probably has 10k on it since. With the air filter disconnected it doesn't fix the problem. I will clean the IAC and make sure the MAP is getting good vacuum. This is such a weird problem. The intermitten ones stink.
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Unread 08-16-2009, 03:37 PM   #10
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I would still check the fuel filter,even though it only has 10k on it it can be clogged up easily in an old tank from rust and dirt..etc..do like was said,by-pass the filter and see if that makes a difference.

I would do what laybackman suggested as a process of elimination to target your problem,too many people just geuss and replace things spending alot of money,but if they would of diagnosed in simple ways could of saved a bunch
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Unread 08-16-2009, 04:43 PM   #11
laybackman
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Another possibility is the imfamous Crank Position Sensor. Some times do this when they go bad. They don't just die they torment you for a while and then they die.
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Unread 08-16-2009, 08:51 PM   #12
romo1000
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Ok so the last 2 times that it happened I wacked on the bottom of my gas tank skid and it started. Now this could just be coincidence so I'm going to try that a little more when it happens and if 2-3 more times it works I'm gonna drop the tank make sure everything is cool (wires and the filter sock) and if it is try a new pump.
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Unread 08-16-2009, 10:01 PM   #13
Socaljeep1
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my brother-in-laws YJ had a very, very similar problem. it turned out that the YJ has two fuel relays and both were bad.
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Unread 08-17-2009, 03:42 AM   #14
Alvy
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Romo I would take Alfons' advice and put a fuel pressure guage on at the fuel rail and measure it while the failure happens. You may indeed have a bad pump but thats a lot of work and $$$$ if its not a bad pump. Measure twice, cut once.
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Unread 08-17-2009, 06:24 AM   #15
romo1000
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alvy I did do that when it happened a couple of times ago and I wasn't getting any reading out of the gauge when cranking the engine. I figured I had a bad gauge or it wasn't hooking up correctly. so I tried the squirt test and fuel did squirt out but that don't mean alot. I'm gonna get a different fuel pressure gauge today and try that again the next time it shuts down or doesn't start. thats the really hard part is it's not all the time. so I have to wait till it doesn't start to test stuff.
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