Need help 98 sport with 99 4.0

[nj350z]

first of all i am new to the forum and hoping i can get some info on getting my 98 explorer sport in running shape. here is my deal. i live in Nj and jus bought a 98 explorer sport for the winter months. the explorer has had the engine replaced with a 99 4.0 SOHC. it runs like crap. it barely idles. i am fairly knowledgable and experienced with working on different types of vehicles. i just dont even know where to start on this thing to get it in somewhat reliable running condition. my first question is i see the fuel return is capped off. seems like a good place to start. is there any differences in the fuel systems between the 98 and 99 4.0? the thing takes forever to start, idles like crap, but runs well about 2k rpm. any help would be appreciated

 

[2000StreetRod]

returnless fuel system

In 1998 Explorer switched from a return to a returnless fuel system. The return system has a fuel pressure regulator (FPR) mounted on the fuel rail. The returnless system has an FPR mounted in the fuel tank and a fuel pressure damper mounted on the fuel rail. You may have an early 1998 with the return system. I suggest that you perform the Fuel pressure test procedure to find out what your fuel pressure is.

I also suggest that you replace your fuel filter if it is due to be changed. See Why change fuel filter?

Then I would add a bottle of fuel injector cleaner to your tank.

I would also clean the MAF sensor with MAF sensor cleaner and clean the IAC valve.

Then I would read the OBD diagnostic trouble codes and post them on the forum.

 

[ranger7ltr]

Your system has a few issues...

The fuel pressure is probably very low for the requirements of the 99 engine... In 1999 the fuel pressure requirements went up to 65-72 psi...Since your return line is plugged, the fuel rail has no regulator mounted on it, and the fuel pressure regulator is not mounted in the tank as it should be for the 1999 engine fuel system, I wouldn't even begin to guess what the fuel pressure is running...When the engine does run, is the vacuum line to the fuel pressure regulator that is not there plugged as well?

So you have a couple of options; replace the in-tank sender and pump[although the pump is the same between the 98 and 99 model years] to place the regulator in the tank...

Or replace the fuel rail on the 1999 engine with a fuel rail from a pre-99 engine...This will place the fuel pressure regulator back on the fuel rail. as it should be for the 98 model year, and allow the fuel return line to be used as it should be for this truck...

BTW, the fuel pressure should be 30-45 psi depending on the amount of vacuum on the fuel pressure regulator...Honestly I would find a fuel rail and replace it and the fuel filter and call it good...

 

[2000StreetRod]

ranger7ltr is correct

The fuel pressure is probably very low for the requirements of the 99 engine... In 1999 the fuel pressure requirements went up to 65-72 psi...Since your return line is plugged, the fuel rail has no regulator mounted on it, and the fuel pressure regulator is not mounted in the tank as it should be for the 1999 engine fuel system, I wouldn't even begin to guess what the fuel pressure is running...When the engine does run, is the vacuum line to the fuel pressure regulator that is not there plugged as well?

So you have a couple of options; replace the in-tank sender and pump[although the pump is the same between the 98 and 99 model years] to place the regulator in the tank...

Or replace the fuel rail on the 1999 engine with a fuel rail from a pre-99 engine...This will place the fuel pressure regulator back on the fuel rail. as it should be for the 98 model year, and allow the fuel return line to be used as it should be for this truck...

BTW, the fuel pressure should be 30-45 psi depending on the amount of vacuum on the fuel pressure regulator...Honestly I would find a fuel rail and replace it and the fuel filter and call it good...

Unless your PCM has been reprogrammed it assumes that you have the stock system and the injector pulse widths are set accordingly. There was probably a PCM or injector change from 98 to 99 to adjust for the fuel pressure change. Your mixture could be off. In closed loop the PCM may be able to compensate by adjusting the short term fuel trims but it will always be lagging because its from the O2 sensors. In open loop the PCM would not compensate for the fuel pressure change.

 

[nj350z]

thanks for all the replies. im gunna go to autozone this weekend and pull the codes from the ecu. i was also planning on going to the junkyard and getting the fuel pressure reg and the fuel rails from a pre 98 and put all that on. im gunna test the fuel pressure saturday also and i'll post that up. thanks for all the help

 

[nj350z]

also i know this is a longshot. but does anyone have a underhood picture of a pre 98?. so i can kinda get an idea wat the heck im missing so i kno where to get started. whoever did this swap really screwed it up. thanks for all the help. its much appreciated.