Carguy26

Hello guys. New to this so im goin to make it short in case this is not the place to post my concern....i have a 99 jeep grand cherokee laredo and want to know why my jeep just cranks but does not start. I have more info about that whole situation

dave1123

Welcome to CF! This is the place!

If you don't have fuel or spark, it's usually the crankshaft position sensor. This is a magnetic switch that tells the PCM (computer) that the crankshaft is turning. When the PCM gets this signal, it turns on the ASD (auto shutdown) relay and fuel pump relay. The ASD relay controls the ignition and fuel injector circuits. Without the ASD engaged, you can crank it forever or until the battery goes flat and it won't fire.

Now feed me the rest of your info!

JSJJ388

You always seem so eager to help everyone!

Ill just add that if you have an alarm system, that can also cause a crank no start if it is tripped. My 94 (I know its a zj not a wj) sat for two weeks while I figured out how to disarm it. Could also be as simple as the ASD relay gone bad...

Carguy26

Ok thanks for the replies! Here it goes. Brought the car home from work. On the way here it stalled on me. I get it home. Changed igintion coil (guy i brought it from said it needed it) check engine light was on. When I changed it cel went away and the jeep started! Next day went out and to my dissapointment it just cranked but no start! I wiggled around the pcm unplugged n plugged. And it would start then die. Start then die. Before this there was no fuel pressure then after wiggling around the pcm there was. Ok. Brought a pcm flashed n plugged in n now nothing again. Just crank no start. I have spark. So figured the crankshaft sensor is fine. New fuel preassure on fuel rail. I can here fuel pump turning on. N have fuel from fuel line into filter. And out the filter. So no what?? Lol

Carguy26

Meant to say no fuel pressure not new fuel pressure lol.

JSJJ388

What is the fuel pressure at the rail?

Carguy26

It started at zero. Then the truck started and was fine. Then barely registered 5 psi. Now back to square 1 with zero psi. Fuel comes out when i disconnect the fuel line from the fuel filter.

JSJJ388

That sounds to me like your fuel pump. Or possibly fuel pressure regulator.

dave1123

It sounds like an intermittent fuel pump or bad fuel regulator. Clue me in, guys! Is the 96 an internal or external filter? If it's internal, the pressure regulator is on top of the tank near the electrical plug. If external, it's part of the filter. Start by checking for power at the pump, wiring plug, and chaffed wires. You should hear the pump run a prime sequence every time you turn on the key - for a couple of seconds. Then it should run continuously while cranking. If it runs and you have no pressure, the regulator is bad with either the pressure relief valve stuck open or spring broken. OH....make sure there is fuel in the tank! Never forget the obvious. If it's sucking the bottom of the tank, there could be debris in the valve. The filter in the tank is just a fine mesh sock and can pass tiny junk easily. It could also be plugging, then clearing itself when it is allowed to rest. My wife's Dodge Caravan did that. The filler neck was rusted out and road crap got into the tank.

About being eager to help, I'm retired with not much else to do anyway! LOL! I wish I had this kind of help in MY younger years. There was no internet then! I learned a lot working as a part time gas station mechanic and drag racing.

Carguy26

Yes runs continuiously when cranking. And i hear it when i turn the key to on. So the fuel regulator is located on the pump itself?

dave1123

If the fuel filter is inside the tank, the regulator is on top of the tank where the hose comes out. If the filter is on the frame rail, it's inside the filter or right next to it.

Carguy26

Fuel filter is not inside the tank. But didnt notice anything that poppped out that would tell its the fuel regulator. I would have to go on under the truck again tommorow and keep u guys updated! Thanks ive always read car forums for help but never actually been part of one lol

dave1123

Okay, if there are 3 hoses on the filter, one is supply from the pump, one is supply to the fuel rail, and one is overpressure return to tank, meaning the pressure regulator is inside the filter housing. I good pump without a pressure regulator puts out around 100 psi. The pressure regulator drops that to 35 to 50 and sends the rest of the fuel back into the tank. If that valve hangs open, all the fuel returns to tank except a tiny bit from backpressure. That's where you're getting your 5 psi.

JSJJ388

Maybe things are different on the 99s but on my ZJ the fuel pressure regulator is on the front of the fuel rail I think. Has a vacuum line from the manifold going to it.

dave1123

Yes, and on the V8s, it's on the throttle body. I'm just going by my own experiences with 2 jeeps, a 97 ZJ and my current 2000 WJ, 2 Dodge Caravans, PLUS info I've retained from this forum. I don't consider myself an expert in any way. Just passing on what I DO know.

That thing on your fuel rail, unless it has a fuel return line to the tank, it isn't a pressure control. Besides that, we're talking about a 96, not a 99. My 2000 has a small mushroom shaped thing on the fuel rail known as a pressure compensator. It's designed to smooth out the pulses of the injectors drawing fuel.

This is, after all, an opinion site. Nothing is to be taken as gospel!