yj sputters while driving... idles fine... only happens when at operating temp - Page 2 - JeepForum.com
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Unread 07-25-2013, 06:39 AM   #16
vadslram
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1990 YJ Wrangler 
 
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Not saying it can't be the pump cutting out but here is my reasoning against it.
An electric fuel pump runs at one speed no matter what the engine speed. It is either on or off. If the engine isn't using all the fuel being put out by the pump the regulator bypass opens up and runs the fuel back into the tank. Actually the load on an electric pump can be higher when idling than when WOT is using every drop it can put out. If the pump is failing due to overheat it would do it at every engine speed. As for overheating almost all fuel pumps but aftermarket like the FASS on my truck are inline and the fuel flowing THROUGH the actual pump motor cools it, Since the flow never stops or slows the pump motor can't get more than x degrees hotter than the fuel you have. This can be a problem when you run the tank to empty when there is only a gallon or two (if any) flowing through the pump, through the hot engine bay, back into the tank ,and pretty much right back into the circuit immediately. Usually you will see issues with fuel boiling and vapor locks when this happens but that sputtering is not pump related.

The pump could be failing by not putting out enough fuel, or the flow is restricted because of blockages somewhere or your pressure regulator could be bad(open) and at open throttle conditions you can't keep enough pressure to run the injectors/fill the carb.

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Unread 07-25-2013, 07:26 AM   #17
clush
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1994 YJ Wrangler 
 
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Just sayin I had the exact same symptoms. Chased it for a couple of years (not my daily driver anymore just a toy) , and fixed it with a new fuel pump 4 months ago. Been driving it all summer now w no more issues. Dropping the tank is a pita by the way.
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Unread 07-30-2013, 08:17 PM   #18
mdoddroe
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New...

Had a friend come out and switched out MAP and TPS sensors. No luck. Tested the fuel pressure lines at the rail, results: turn Jeep to"on" pressure went to 38 psi. started engine and pressure went to 80 psi.

Next, checked vacuum lines. Elbow on fuel pressure regulator was cracked, replaced, no luck. going to replace fuel pressure regulator tomorrow...

Any other suggestions of why fuel pressure would be that high????
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Unread 07-30-2013, 09:03 PM   #19
TSEJEEPERS
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Blocked or kinked return line.
Check in the rear where the lines go through the rear crossmember.
(Before the tank)
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Unread 07-30-2013, 09:50 PM   #20
mdoddroe
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Is there a way I can check for pressure in return line or if there is any fuel in the return line???
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Unread 07-31-2013, 06:28 AM   #21
vadslram
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disconnect the hose. If gas drips out you had fuel in it.
Then blow into it. If you can't or it takes a lot of pressure you have a blockage.
Sometimes the simplest ways are the best.
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Unread 07-31-2013, 07:22 AM   #22
mdoddroe
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Where would I disconnect it at? The rail? Or is there rubber hose by the gas tank on the return line?
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Unread 07-31-2013, 08:41 AM   #23
mdoddroe
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Changed out fpr, no luck. However new discovery: turn Jeep to "on" position, pressure goes to 40-45psi, but loses all pressure within 10-15 seconds. Before changing out the fpr it maintained all the pressure. When I turn the Jeep over it still goes to 80-90psi.
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Unread 07-31-2013, 11:04 AM   #24
vadslram
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When you first turn the key the pump should cycle for a couple of seconds then, if it doesn't detect a signal from the engine that it is running, shut off.
If it wasn't bleeding down before then you definitely had a clog somewhere.
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Unread 07-31-2013, 05:46 PM   #25
mdoddroe
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So question, would there be a kink in the supply line or return line to make the pressure that high? I don't see any kinks in either line and see where both go through the cross member in the back of the Jeep before the tank. Jeep has that inch body lift and its rubber line... Still, question being, I can't wiggle either and they are pretty snug inbetween the cross member and Jeep body. Don't believe either are kinked though. Vacuum hoses have pressure, could it be the guy who owned it before me put in a high pressure pump??? Or do all have the same amount of pressure???
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Unread 08-01-2013, 06:02 AM   #26
vadslram
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Quote:
Originally Posted by mdoddroe View Post
So question, would there be a kink in the supply line or return line to make the pressure that high? I don't see any kinks in either line and see where both go through the cross member in the back of the Jeep before the tank. Jeep has that inch body lift and its rubber line... Still, question being, I can't wiggle either and they are pretty snug inbetween the cross member and Jeep body. Don't believe either are kinked though. Vacuum hoses have pressure, could it be the guy who owned it before me put in a high pressure pump??? Or do all have the same amount of pressure???
To be overpressure the blockage (doesn't have to be kink, can be chunk of something inside)would have to be in the return, if it were on the intake side you would be getting low pressure. There are both high pressure and high volume pumps out there, What you have

I don't know that 80 psi is too much though. I'll look through the shop manual and see what they say.

Looking back through the thread I thought of a few things.
Why would it get worse after running for some time? What changes?...Emission controls kick in after engine comes to operating temp.
Is your engine more or less stock? any emissions bypasses done in the past?
Do you have a condition where the timing changes wrong after the system goes into closed loop? Is your coil overheating after it is on for a while and shorting out intermittently?
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Unread 08-01-2013, 02:03 PM   #27
mdoddroe
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I have no idea. What coil are you talking about? I have a mechanic thinking it's the distributor. The symptoms did come about after keep was at operating temp... But now it's whenever the Jeep is running. doesn't lose any fuel pressure when it happens. If I could post a video on here I can show you what i'm talking about
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Unread 08-01-2013, 05:23 PM   #28
bigbossd1030
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Quote:
Originally Posted by mdoddroe
I have no idea. What coil are you talking about? I have a mechanic thinking it's the distributor. The symptoms did come about after keep was at operating temp... But now it's whenever the Jeep is running. doesn't lose any fuel pressure when it happens. If I could post a video on here I can show you what i'm talking about
YouTube, then post link.

Sent from my iPhone, probably because I am bored at work.
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Unread 08-01-2013, 05:25 PM   #29
vadslram
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The primary ignition coil. That which takes ~12 volts and makes it 20,000 then sends it to the spark plugs.
I'm ignorant on the 2.5 but on the 4.2 stock it is a soda can in size and shape, on an HEI/DUI it is the bundle of wrapped wires in the top, middle of the distributor cap.
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