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?
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.
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/
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?
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
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.
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.