-   ZJ Grand Cherokee Forum (
-   -   Hard starting before and after new fuel pump (

ghost98 11-14-2013 10:19 PM

Hard starting before and after new fuel pump
I have a 98 5.9 that I'm having trouble with hard starting after it sits for a while. If it doesn't sit too long it fires right up. I read the threads that suggested priming the fuel pump 2-3 times before starting and that did work so I figured I needed a new fuel pump. I bought a brand new Bosch fuel pump (it also had a new fuel pressure regulator) and had it professionally installed. It seemed to help a little bit but it still has hard starting. I also cleaned the IAC with no change. Does anyone know what would be the next thing to check or replace?

August88 11-15-2013 04:26 AM

This sounds like a similar problem that rhall128 asked about in this thread:

I have a '97 ZJ 5.2L V8 and I have had the same starting issue for two years. When it has been sitting for two hours or more it won't start when the starting motor is engaged. A mechanic told me that there was a check valve in the fuel line and as long as the line was full, it should start right up. His explanation was that while the vehicle was off and standing, the fuel would slowly leak down past the check valve. According to him, all I needed to do was to turn the ignition switch to on and wait a few seconds (15 - 30) while the pump filled the line. At first that worked about half the time. Now I know what to expect so I engage the starter for 10 to 15 seconds, turn the switch to off, wait 3 - 5 sec and engage the starter. It then starts with no hesitation. This work-around works independent of the ambient temperature, the humidity, and any other variable, i.e., it hasn't failed in two years.

The mechanic stated that the check valve was not readily accessible and his estimate to replace it was $400 - $500 and he suggested that I just live with the work-around until/unless I needed other work 'in that area' in which case the additional labor wouldn't be a substantial cost. I am not a mechanic and I don't know whether he fabricated the check valve and its behavior, but the solution works. The only downside is I have to inform anyone who may be using or moving the vehicle of the issue, otherwise they will sit there and let it crank on and on.

On the positive side, I now have solutions for my tailgate not opening, my ABS light and what to do if I decide to replace my rear wiper! There is a lot of great information posted in this forum. Thanks for openly sharing the forum!

ghost98 11-15-2013 09:49 PM

I don't think there is a check valve in the fuel system. Anyone have any other ideas?

JS97ZJ 11-16-2013 08:31 AM

The check valve is part of the regulator which is in the pump module.
Some of these aftermarket pumps are junk right out of the box. Do you know which brand was used?
Bosch pumps are the original pumps that came with your Jeep when it was new. They cost a little more, but won't leave you situation when you least expect it.

ghost98 11-16-2013 09:30 AM

Yes it was a brand new bosch fuel pump

JS97ZJ 11-16-2013 10:21 AM

Do you smell raw fuel in the exhaust when you have a hard time starting it?
Fuel injectors leaking? (run a couple of bottles of fuel injector cleaner through the tank)

xcaliber81 11-16-2013 11:36 AM

my buddies 5.9 does this also if you prime the pump it will start fine, no prime takes longer.

ghost98 12-06-2013 03:08 PM


Originally Posted by JS97ZJ (Post 17751977)
Do you smell raw fuel in the exhaust when you have a hard time starting it?
Fuel injectors leaking? (run a couple of bottles of fuel injector cleaner through the tank)

No not really there isn't a strong fuel smell or anything. My negative battery cable is not in very good shape could that possibly cause it? If i prime it it starts just fine but thats just annoying

Kingr98 12-06-2013 04:04 PM

Have you checked your fuel pressure on the rail? When you shut off your Jeep for a few hours, the pressure in the rail should drop but liquid gas will remain in the line. When you turn the key on, the pump should be able the pressurize the fuel rail almost immediately. If you are having to prime the fuel pump to get the pressure to 49psi, it isn't working correctly. The fuel is either draining out of an injector or back through the regulator into the tank. Checking your fuel pressure through the entire cycle is the key.

newfieZJ 12-06-2013 04:15 PM

how many K , and how long since a tune up ?

You should repair the ground wire for sure .

The time now is 07:09 AM.

Powered by vBulletin Version 3.8.8
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.