Subsammich

I have a 98 Cherokee Sport Auto 4.0

I've recently been getting some hard starts, I.e. 4-5 Seconds of cranking, to putter start and then it goes to a 1100-1200 idle rpm, usually settling back down to 600-800 after a few seconds.

I do live in Michigan, and it's cold, but I've had it start right a week or two ago during extreme cold.

I was recently chasing down a problem for no start issues and have changed the tps, cleaned throttle body, plugs, wires, cap, rotor, CPS, and Cam position sensor.

Has been running great the last 1000 miles or so. But now im getting this issue, no CEL. But I still plan to stop and get it ran just to make sure.


I have been reading threads for fuel pressure, and leaky injectors and do plan to diagnose those possibilities, but wondering if anyone has experience similar issues that could save me some time.

I did try leaving the key on for a few seconds and it didn't do anything, and if it fires up and I shut it off and start it again after 5 seconds it does it again, and i'm not certain why it would bleed pressure off THAT fast.

Thanks for any help! and until then ill keep searching around to try to find some more possible solutions.

Thanks!

ehall

Refer to this post for likely cause of long-crank rough start

High idle could be any number of things, usually its vacuum leak so you may have left a hose disconnected in your previous efforts. Could also just be winter weather, or possibly related to the other issue. Hunt for loose vacuum, fix your other problem, then chase it down later if it persists

Subsammich

Thanks I'll take a look at what you've posted. Appreciate it.

cruiser54

There's plenty of guys here familiar with that new-fangled Jeep stuff to help you.

Me, I'm stuck in the 80s and 90s.........

Thanks for posting.

4OHI6

Does it have the original fuel pump assembly ?

Subsammich

I was told it was replaced, but the gauge doesn't work, so idk why you'd pull the tank and not fix all the issues there.

I got a tester kit yesterday, but needed some tape to stop a small drip from the gauge to the house so I'll get a good test today.

Subsammich

I went to HF yesterday and bought a Fuel Injection Pump Tester, and just got a chance to use it.

If I turn the key and let it sit I don't build any pressure, If I crank it over, it starts hard after about 5-8 seconds. Then pressure slowly builds to 43 psi, over like a 10 seconds period. I assumed the fuel rail should pressure up immediately, am I wrong to assume?


I have read I'm unable to add an inline check on my 98', so what's next? Dropping the fuel tank and replacing assembly?

cruiser54

Correct to assume.....

Subsammich

Im going to make sure my hose/connector is depressing the schrader(sp?) valve completely, but i don't have a reason to believe its not.

drhoward1988

If your getting pressure the Schrader is functioning properly. No need to get crazy with it.

ehall

The pump doesn't pressurize the whole line right away, it takes a bit of running for it to catch up. As long as it is able to reach minimal pressure relatively quickly then it is operating okay.

What you are really looking for in terms of hard-start is rapid loss of pressure when the engine is killed. The pump has a one-way check valve that is supposed to keep the line pressurized, and that check valve is very common failure point. You can tell its bad if you turn off the engine and gauge drops to zero immediately, all the fuel in the lines is siphoning back out, and then you have to repeat the long start pressurization again every time. Its not the slow pressurization that's killing you, its having to repressurize every time because of a failed check valve.

You can get an external check valve from ebay, and put it in the soft line right outside the pump, and that will work to hold line pressure. I had to put one in my own POS for the same problem. But they are known to cause problems with 97-up because the FPR is in the tank so the line gets overpressurized as temperature changes. So in your case (assuming profile year is correct) you only have one choice, which is replace the pump.

Subsammich

Ok, welp time to scope best prices for Bosch pumps!

The previous owner said he swapped fuel pump, probably was for a crap brand.

Subsammich

http://www.carid.com/1998-jeep-chero...-23947353.html

Are we in business here?

Subsammich

I'm going to drop the tank and want to do new straps and j bolts while I'm at it.

Spectra straps, are they any good? Seems to have decent reviews at an attractive price point.

Thanks
-sub