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Unread 09-01-2013, 07:58 PM   #1
D0T-C0M
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91 YJ with a 98 cherokee engine, fuel pressure question

My friend bought a YJ with a 4L 98 cherokee engine in it. He has a fuel pump problem and wants to change it but I told him that I believe the YJ 4.0L uses the old injector that run at 39psi. The 98 4.0L should run at 49psi as per the service manual. What does he have to do in order get the proper fuel pressure, adjustable regulator? TJ swap tank?

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Unread 09-01-2013, 08:48 PM   #2
stenyeart
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Is he running a return line fuel rail or a return less?

I would assume it is a return line and he would just buy the yj pump. Up front you just need to find the correct FPR to keep the rail at 49 psi. The yj pump will keep up just fine with the higher pressure. This is how I did my obd2 4.0 swap. If you need the info on the what FPR to buy, let me know and I can look it up.
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Unread 09-01-2013, 09:28 PM   #3
D0T-C0M
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I think he told me that there were 2 pipes coming from his tank. I'll ask him tomorrow to see what he has to make sure?

He did say that there isn't a regulator on top up the tank like my TJ. Where is the fuel regulator located on a YJ?

By all means if you have the info on which proper regulator he needs please post it so I can pass the info along to him.

Thanks a lot
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Unread 09-01-2013, 10:17 PM   #4
stenyeart
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The regulator is on the front of the fuel rail. This is the regulator you need. http://www.naxja.org/forum/showthread.php?t=1043808

Buying one of these will be a lot cheaper than a hesco adjustable regulator and it is a direct bolt in.


Look at the fuel rail. There should be two lines connecting to it at the front of the engine and the FPR located on the same end as the hoses. Of course this is assuming he has the return system. Look at the pic in post #7 here. http://www.jeepforum.com/forum/f12/w...4-0-a-1198259/
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Unread 09-02-2013, 06:34 AM   #5
Que89YJ
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It sounds like he is just doing a block swap and he already had it setup for the fuel injection. What year yj is it and did he change out any electronics?
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Unread 09-02-2013, 06:55 AM   #6
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Quote:
Originally Posted by Que89YJ View Post
It sounds like he is just doing a block swap and he already had it setup for the fuel injection. What year yj is it and did he change out any electronics?
His yj was already fuel injection and he swaped his 91 fuel injection 4.0L for a 98 cherokee engine 4.0L . Everything else is the original wiring.
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Unread 09-02-2013, 08:12 AM   #7
Que89YJ
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So the only thing he did is swap the block, then the fuel system is the original as well as the electronics. Did he use the 91 fuel rail? The regulator is on the fuel rail on the YJ. Did he put in a temp sensor for the ecu? The 98 block only had one and used it for both the gauges and the ecu. The 91 YJ had a sensor for both and it is important for the ecu to have both. What is his exact issue with the fuel pressure?
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Unread 09-02-2013, 02:40 PM   #8
D0T-C0M
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He had told me that the PO had changed the complete engine but I drove over today and it would seem that he only changed the block and is using fuel rail of the 91 so no changes to the regulator is needed. Below is the pics of one of the injectors closeup. Its a
'91-'93
part#33007127
Color:Brown,
Running pressure:39psi,
fuel flow: 21.0lb/hr



Here is his header



The problem he is having is he suspected a bad pump but found that his regulator was faulty because he wasn't getting enough pressure. He wanted to change it but then I asked him if he had the 98 fuel injectors or the 91. He said that they were the 98s. This is where I told him that he would need a different regulator and the stock one wouldn't work. After checking myself, he was wrong.

Sorry for wasting everyone's time.
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Unread 09-02-2013, 04:23 PM   #9
Que89YJ
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No waste of time. The regulator was bad and the pressure was low? Usually the diaphragm rips and the pressure goes high. It's not a waste for the next person searching for a fuel pressure problem. Thanks for posting the fix.
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Unread 09-02-2013, 06:12 PM   #10
D0T-C0M
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Where is the check valve in the fuel system of the 91 YJ? In the pump and/or regulator?
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Unread 09-02-2013, 06:25 PM   #11
Que89YJ
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It's integrated into the fuel pump. I don't know if you checked it bit you should maintain 20 psi for 20 minutes after shutdown.
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