sik_xj

Alright I know that I am not the first one to come across this problem, I did some research, but I didnt find someone with the exact problem as me (just similar cases).
So here:
I have a 99 Cherokee with the 4.0 and just over 100k.
I have been having an issue with rough starts and it takes a few cranks to get it to start..
I replaced the cap, rotor, wires, plugs, 02s, etc and it didnt help.
I read that I may have a leaky injector so I picked up a set of 784s and threw them in. (They all were working injectors, they all ohmed within spec) First start up it fired right up, I let it sit and idle for about 10 minutes while I cleaned up. I turned it off and then started it back up to take it around the block. It ran fine out of my driveway and down one street, I decided to open it up and see how it ran, it hit 3000 rpm and started to backfire and sputter and slowly the rpms dropped.
I took it back home and checked for leaks, and anything out of the ordinary, there was no leaks or anything. I disconnected the battery and let it sit for a while and then hooked it back up and started it. It had a somewhat hard start and it idled awful it then eventually smoothed out. I put it to the floor and it did the same thing, backfired and sputtered and the rpms drop gradually.
It seems that I can get the rpms to go higher if I go easy on the throttle.

The only thing I touched was the injectors. I am going on day 3 with a bored throttle body though.

My only thing that I can think is the fuel pump is on its way out..
The 4 hole injectors coupled with a bored throttle body = the need for more fuel. Thoughts?

I wanted to get some quick opinions before I dumped a bunch of money into a fuel pump. Any any brands to stay away from on the pumps?

Even though I am pissed, I figure this is a good opportunity to clean up my gas tank skid. (trying to be optimistic)

Any help would be appreciated. Thanks!

sthon

Did you do the injectors one at a time? Any chance you have the plugs wrong?

nowhres

Ballast resistor?

sik_xj

I tried switching any of the plugs I could have gotten mixed up but there was no change.

I didnt know the newer ones had one...where is it located on a 99?

nowhres

I didn't either. Didn't pay attention to the year. The issues you are having sounded the same as when the ballast resistor went bad in my 1989. I can't say for sure whether or not 97+ had them.

sthon

Try resetting the ecu and report back.

https://www.cherokeeforum.com/f2/jee...ocedure-46047/

sik_xj

ill give it a whirl.
I touched the 2 terminal ends together for about a minute. I thought that this did the same thing, but Ill go give this procedure a try since its quick and free

zebvance

Check the fuel pressure regulator yet?

sthon

That probably was good enough. But for ****s and giggles it's worth a shot.

sik_xj

I dont have a gauge, are the regulators adjustable at all?

zebvance

No they are not, it is a very easy job to replace it, I would pick a new one up and pop it in, if it doesn't help the prob you could always return it for your money back or leave it and have the piece of mind that you won't have to replace it in a long time.

sik_xj

How often do those go bad?
They are pretty damn expensive for a little piece like that..it just screws into the rail or how is it held on?

The other thing I could think of is the TPS or one of the other sensors on the throttle body, but I doubt it.

sthon

Did you make sure you didn't pull any vacuum hoses while pulling the fuel rail? Perhaps the map sensor vacuum hose?

sik_xj

I didnt touch any vacuum lines when I did the fuel rail other than the hose from the valve cover to the air box.
I reset the computer and it started rough but seemed to run fine until it got warm then it started with the same symptoms, and anything over half throttle it didnt want to accel. and missed and backfired.

EDIT:
I might just try swapping in another TPS and see if that does anything, the symptoms I had before could be because my TPS was on its last leg and decided to go out on me. Its the next cheapest fix.
I read that a bad TPS, or the TPS putting out the wrong volts can cause similar symptoms, and can cause the MAP to act up as well.

sthon

You may not have but the fuel rail or throttle linkage bracket could have. Never hurts to check. In my experience when you have problems after something simple like this it's usually something is not hooked up or is hooked up wrong. If it ran fine before the swap other than a leaking injector something was likely done wrong. If all else fails you can try swapping your stock injectors back in with fresh o-rings.