View Full Version : starting issues

05-30-2007, 06:00 AM
Anyone else had a problem with their 4.0L starting? When I try to start my truck the first time, no matter how long I crank it for it doesn't start. As soon as I try starting it the second time, it fires up instantly....???

Any idea's? I'm thinkin maybe a clogged fuel filter?

05-30-2007, 12:46 PM
there's a fuel pressure check valve (in the fuel pump i think) that is pretty common for them to screw up and start to not hold pressure in the fuel line making the fuel pump have to re-pressurize the line every time you start it back up.

could b fuel filter too.

05-30-2007, 08:53 PM
Sounds like a crank sensor going. Common on the 4.0litres. To make sure it's not fuel, prime the circuit before cranking. Turn the key on for 5 seconds, you should hear the pump run then turn off. Turn key off for 5 seconds then back on for 5. Do this a few times to build up pressure. If it's a fuel drain back problem, this should prime it enough to start up.

Crank sensors on the other hand can cause an intermittent no start. Usually they just up and die, but can cause both.

06-10-2007, 10:49 AM
damnit! Well there's no harm in replacing the fuel filter, their cheap.

I'm starting to think its the crank sensor, because it starts the first time I try cranking it only once every 20 times, the rest I've got to crank it, stop, then crank it again and she fires within the first crank of the engine the second time?!

06-10-2007, 10:58 AM
crazy jeeps....

06-10-2007, 11:29 AM
crazy jeeps....

who woulda thunk it eh

06-10-2007, 12:01 PM
Most long crank starting issues are related to the fuel pump in the 4.0s like smurf said the check valve in the fuel pump is bad for going and you have to replace the pump to fix it. I have never had a TDC sensor (crank position sensor) cause this issue, it usually causes no start/no spark period or intermitent no start/no spark that just stopping cranking and immediately recranking won't cure. Depending on the year of the 4.0 the other common sensor to long crank issues in the 87-90(Renix) 4.0 is the Hall Effect sensor in the distributor, this sensor has nothing to do with ignition timing, the TDC sensor alone bases the ignition timing(only Jeep/Renault could put a sensor in the distributor that does not deal with ignition) the hall effect switch does time the fuel injectors if this hall effect switch fails the computer can default/limp mode and time the injectors based off the TDC sensor but when in this mode it takes a long time for the computer to find #1 cylinder, so the engine cranks for a long time before it starts.

06-10-2007, 08:00 PM
Well the jeep is a 1998, so I'm assuming that its going to be the fuel pump.... shat.

06-14-2007, 10:22 PM
So is there any way that I can run any tests to narrow it down to the check valve? What does the check valve do?

06-16-2007, 10:41 AM
Stops the fuel from bleeding back into the tank while the vehicle isn't running.