I have a 1997 ZJ 4.0 liter with 80,000 miles with a cold engine hard starting issue. When the engine is warm (within 20 minutes of turning it off) the engine will start immediately. If the engine is cold, it takes approx. 5 seconds of cranking for the engine to start. However, same cold engine scenario, cranking for 1 second and then releasing the key, let the starter stop spinning, and then key to start again the engine fires immediately.
The fuel pump turns on for 1-2 seconds when the key is in the on position. Fuel pressure is approx. 48 psi idling. After shutting the engine off, the fuel pressure bleeds down to 0 psi within 6 minutes.
Is there a check valve in the fuel pump that is bad not allowing fuel pressure to remain to the fuel rail after shutdown?
Actually, I have this same issue. Had it for years now, to be honest. Just turn key on, let fuel pump do its thing (2 seconds) turn key off, back on, let fuel pump run again THEN crank it. Fires up every time.
It's evident the check valve in the pump assembly is bad in dropping to 0 psi after 6 mins. Drop the tank and replace the whole assembly. Since the fuel filter is on top of the pump assembly on the 97-98 ZJ's you need to drop the tank anyhow to change it out if it hasn't been done in a while. In other words go for the below new Bosch 67649 pump assembly w/filter for $120 w/free shipping for your 97 4.0 and you won't beat that price. Good luck!
Thanks for the info. As I understand on the 97-98 ZJ's, the fuel pressure regulator/fuel filter sits on top of the fuel pump. It appears the regulator is functioning. Do they typically fail? Should I just replace it along with the fuel pump since I have the tank off anyway?
On your 97 4.0 the fuel pressure regulator is built into the pump assembly and it's under the fuel filter on top as well as the check valve being underneath. The check valves are known to fail but don't believe the fuel pressure regulators do. Regardless, replace the whole unit so you'll have a new pump, fuel pressure regulator, check valve, fuel filter, float/fuel gauge sending unit, etc..
BTW, I bought a new Mopar tank/pump rubber seal at the dealer and paid $15 for it. Turns out it came with the assembly so I took it back. You may want to wait and see if it comes with the assembly before buying one. On a side note these Bosch pump assemblies are supposed to be better than OE, the pump runs cooler/quiet, and a Bosch tech rep told me they assembly/supply them for Chrysler. Good luck.