More on the fuel pump for the 1995 Grand cherokee jeep?

Question

Well the mechanic put a 2nd pump in Tuesday after me telling him I tapped it and it started for me. so after doing this he wanted to keep it over last night and try fto start it again this morning guess what it DID NOT START just as it DID NOT START for me for many days except when I banged the gas tank
hE SAID IT IS NOT THE FUEL PUMP AND NOW THINKS IT IS THE IGNITION SWITCH
I also noted that the colder it is the mmore difficult it is to start too which brought me to the pump but dosen't seem to be the problem\ One other note is when I personally went to the mechanic and tried to start it with no start right with the mechanic he lifted the hood and un done a bolt and connected a guage --and asked me to start it and then it started so he took the guage off and told me the pressure was fine.
ANY MORE IDEAS FROM ANYONE

Answer 1

I have a problem with the diagnosis of the igniotion switch.

If in fact it is the ignition switch, banging or tapping the fuel tank would in no way make a difference.

Check the wiring at the fuel pump itself, make sure that the wires are clean with no corrosion, not loose etc. The wires I am referring to is the clip that connects to the fuel pump. It's a pain, and the tank may need to be dropped yet again, unless you have an access panel to get to it.

The pressure he was checking was the fuel pressure, to make sure the pump was working correctly and maintaining pressure when running.

Answer 2

My two cents again, You either have no fuel or no spark.
Connect the fuel pressure gauge BEFORE you crank it. Watch it while cranking. No pressure, no start. Tap the tank as you are doing?????!!!!!! If THEN the pressure comes up and immediately starts, I go back to a bad ground at the tank.
If you have pressure during cranking and NO START..STOP! The pump is not the problem. Either you have no spark or the injectors are not working. There is a test light to install in series for the injector circuit. They cannot all be out unless a computer problem. You said that you have replaced the crank sensor.
OK..ONE more...Long shot, but your ignition coil is mounted on the block and due to the heat they do fail, but can do so intermitantly. LONG SHOT!!
Still need to know, if, during no start, do you have fuel pressure, spark, and power to the injectors. It will run if all three are working, so one of them must not be.
Good Luck...keep us posted!!! NO MATTER WHAT?

Answer 3

Their is a security box under the dash that has been known to shut down the Fuel Injectors when it gets cold outside. It is a bit larger than a pack of smokes and bright orange in color.

I ran into two of these and luckily I had a patient custumer for the first one(I never changed the fuel pump out on them though!).

Get the scanner on to the vehicle for monitoring the injector pulse width when trying to start. If no pulse width is read- Look for that box.

ASE Cert Auto tech, since 1978

Answer 4

if you are beating on the fuel tank to get it started it is not the ignition switch. there was a tsb about a check valve but a whole fuel pump module should have fixed that, how much are these pumps costing?? i still say you need to take to the dealer and have them check it. you don't have to get it fixed there, just pay the diagnostic fee. should be $100.00 or less for a true trained tech to check. you are just wasting your money, don't let this guy throw more parts at it. i bet they are putting the wrong pump in it or junk used parts(or new junk parts lol) i think this guy is in over his head. the proper way to check fuel pressure is to hook it to the car and drive it cause it is electronic and they don't have to loose pressure constantly,it can drop in an instant . i feel bad for you, i know how irritating it can be. hope this helps