'88 Cherokee won't start half the time......

[rkymtnhy]

1041603

I have an 1988 cherokee LTD, v6, 4.0, FI. 162k miles. Half of the time when I try to start it, it won't start. New battery & cranks fine. I can hear the fuel pump hum when I turn on the ignition but seems like it's not getting fuel. There is no pressure in the fuel rail after I hear the hum of the pump - should there be? After about 20 minutes of trying to start it finally starts. When it's running, it has a very weak idle. I have heard about crank sensors, pump relays and regulators - I just dont know were to start. Can anyone help? Thanks.

[addsig]

 

[RookieJeeper]

1041604

in your "I6" what does it do when you try to start it? does it crank over at all? is it a slow crank? does it just keep turning over? [addsig]

 

[rkymtnhy]

1041607

When I try to start it, it's a good strong, continuous crank. I haven't checked if it's getting a good spark yet. [addsig]

 

[MudderChuck]

1041609

I´m not getting exactly what motor you have. On the multi port injection model there is a pressure test point on the fuel rail. With the key on, there is a good bit of pressure in there usually around 15 PSI. On the throttle body type, if you remove the inlet, hook up a rubber hose and run it to a container, it will usually fill up a guart bottle in about a minute. There are some test procedures in the Haynes manual. Don´t forget to check/replace the fuel filter, on the inside frame rail near the left rear tire on my 87.

If you have a multi point type, a refrigeration hose and gauge will screw right up. Works great for a pressure test. For the throttle body you have to buy a special fitting.

If you have a throttle body, take a look down the throat (saftey glasses) while somebody is trying to crank her. If there is no or very little gas, fuel system is probably your problem. If there is a good bit of fuel it´s probably ignition.

For multi point I usually listen to the injectors, they will click when they are passing fuel (or air).

If you dump a good bottle caps worth of fuel down the throttle body or down the plenum (air intake after the rubber elbow) and she pops right over, you ´ll know it´s a fuel problem. Stand back or you might get a free hair styling.[addsig]

 

[rkymtnhy]

1041612

I have an injected I6. There is a threaded presta valve on the fuel rail. Thanks for the help.[addsig]