• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Why is it still hard starting, new cps and o2 sensor whats next?

tony597fitter

NAXJA Forum User
Location
Plainfield, IL.
My 92 4.0 5 speed has been hard starting lately so I ran the codes and it came up new o2 sensor. So While I was doing that I checked the cps sensor with my ohm meter and it was low (135) cold.So I changed that and it still is hard starting. Whats next? Its spurratic, sometimes it starts fine other times it doesnt want to start or it takes a while 10-15 secs. I gave it a tune up 1000 mile ago when it was running normal. Any help is appreciated.
 
Check the resistance on the plug wires. They go bad after a lot of years/miles
 
Also check to make sure your fuel rail is holding pressure.

After the engine has been off for about 5 minutes, release the pressure on the valve at the front of the fuel rail. Make sure you follow the instructions in the FSM and put rags over everythig that could get sprayed. Then dispose of the rags properly.

The valve looks like a tire valve stem. If there is no pressure, that is your problem. It is very common for the check valve on the fuel pump in the tank to fail and let the pressure bleed off. The valve is not available without buying the pump. I had this problem with my '90 and took about 15 seconds of cranking to start. A new pump would cost about $250 at the stealership.

However, some models of BMW (also use the bosch pump in the tank) had this problem. BMW issued a kit with a check valve so they would not have to buy so many pumps under warrenty. They put the valve between the tank and the fuel filter. That is where I put it on my XJ. Do a search here for the strings "BMW" or "Check valve". The part costs two bucks and change.
MoFo
 
If you don't want to bleed the pressure off to test this let it sit overnite and when you start it in the morning put the key to the 'on' positon, one click before the 'start' position, count to 30 and hit the key to 'start'. If it fires right up it is generally fuel pressure, the pump starts pumping when you turn the key on, that 15 second lag you are experiencing may be the pump bringing the fuel liine up to pressure.
You do realize that the pump runs ALL the time, what fuel is not used is pumped back to the tank, once the fuel pump stops pumping like when you shut it off there is a check valve that is *supposed* to stop the fuel in the lines from draining back to the tank, sometimes they get dirty and sometimes they just go bad. The constant pumping of gas thru the pump also cools it, run it dry a few times and you will for sure toast that pump. It also helps to run a can of carb/FI cleaner thru the system every 8-10K miles, Techron is a good start, seafoam is also good stuff.
 
Back
Top