93 Jeep Grand Cherokee Cranks, But No Start

Because the idiot light comes on, I would be suspecting the alarm first.

Second I would be suspecting the body ground is dirty or has failed because of the 'sometimes' factor. The body can steal grounds through things like the gas pedal cable and brake pedal, but it is not consistent.

Some 4.0 engines have a mesh strap from the rear of the head to the firewall and/or from the engine to the frame across an engine mount, but some Jeeps use a negative cable from the battery to the fender for a ground.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

I second that option.

Is there a way to turn off the alarm to test out the alarm system as being suspect? Perhaps a fuse in the panel and/or a possible second one in the factory installed systems? The alarm works fine if you use the original key or electronic key, but 3rd-party made keys can occasionally set of the alarm from the door key hole. The alarm never goes off otherwise.

As a side note, I only have one electronic key, and no Jeep dealer service deparment could get another key attuned to the system simultaneously with the existing one. Only one or the other can be programmed at a time.

As for fuel pump, why? Just based on mileage/years? I don't believe this is the issue, so I'd like to hear your reasoning on why the fuel pump.

Casper did pass the time by typing:

ignition coil is possible, how old is it/the wires/the plugs.

Start by pulling the codes

It could also be the CPS (Crankshaft Position Sensor). That will cause a no-start. By the dipstick (I6) will be a plug that runs around back. Unplug and replug the plug. Then try starting again.

No fuel pressure or a clogged filter can cause your problem. So can crapoline. How long has it been since you replaced the filter?

The overall doodad location page:

Mine died at 9 years, 72,000 miles. It got very intermittant.

Have a CB? You should hear the pump for a second or two when you turn the key. No pump noise, no start. The pump is $100 at PepBoys.

If you get it started, run as much fuel as possible out of it before you attempt to drop the tank.

The last time I got it to start with the old pump, I had to click the key 50 times. When I heard the pump in the CB (with the ANL off), I hit the starter and got to my brother's house with his garage.

I only have third party keys for my 93 ZJ, the keys are just regular keys they are not like the new anti-theft keys. I would be looking at the CPS, fuel filter and engine ground strap.

Snow..

Yes. Everything manufactured has a design life and for OEM Cherokee fuel pumps it seems to be around 100,000 miles. Be happy that yours fails to start, mine gave up the ghost on a section of highway running through a crack neighborhood.

Yossarian, meet Snowden. Snowden, Yossarian. Yossarian here will be dress> Often if you keep turning the ignition on and off until you

There's the clue you should be paying attention to, not being lead away by the red herrings of the battery cables (if it cranks you're already carrying more current than the ignition will ever need) or the blinking security light. If all the electrical accessories are working okay then grounds are low on your list of things to check.

Based on my experience with my own Cherokee I'd suspect:

1. fuel filter 2. fuel pump 3. fuel sender in the tank.

In my case all three gave up, in that order, within a few months of each other.

Snow did pass the time by typing:

Yep. The 93 did not use a chipped key. Just the IR fob.

The only reason the alarm could go off while using the key in the drivers (or tailgate) is that the disarm switch has died. There is a mechanical switch attached to the back end of the key core.

If the horn ain't beeping the alarm/engine kill/ isn't active.

You can also put the alarm in test mode. With the driver door open, Turn the ignition off-acc-off-acc-off-acc

Now every time you open/close a sensor the horn will beep. Test all the doors and the hood Turn the ignition on and it will beep Turn the key in the door (disarm) and it will beep Same thing for the tailgate (the other disarm switch) etc..

To disable test mode just turn the ignition to RUN then use the remote to arm/disarm the system.

(Optima) Battery(s), either old (fully charged) or new, the system cranks. All cables, ground, etc., have been cleaned, checked and appear fine.

You can hear the relays clicking when you turn the ignition to the RUN position, but not the fuel pump, at least not all the time (hearing is not as it used to be). Connected fuel pressure guage and no pressure when key is in the RUN position. This should read at least 20 on the guage. Checked the relays in the engine compartment and they get voltage(click). Checked relay/fuse compartment and it has voltage. Checked rear power feed line to the fuel pump (near tank) and no voltage. My understanding is that 12v should be going to the fuel pump. If there is 12v at the relay box, but not at the rear junction, then where else can I check where the power in not passing through? Since the jeep sometimes starts, then I suspect a short or "open" somewhere between those two points?? (your input here).

One other thought... I'm not very familiar with the security system, so is it possible it is shutting off the voltage to the fuel pump? So far as I can tell, the SS seems to be working fine but now that I have more test info on that, I can test that too if it is tied to the problem. I was told the only way to turn the SS off is a trip to the dealer and $$. I would prefer avoiding turning it off/on and keep it on for the neighborhoods I must frequent. This problem started a few months after I was rear-ended. Since then the rear (door, bumper and associated) has been repaired/replaced. Although the damage did not really look bad, I could not open the rear hatch and there was a small wrinkle in the frame that was straightened. I am not familiar with the wiring to know if the SS is connected to anything in the rear that could cause the voltage to not reach the pump.

Casper did pass the time by typing:

12V is not always sent to the pump.

Long story short.

- turn the key on - pump runs for a few seconds to pressurize the system - pump then shuts off

- engine starts - pump turns on

Swap the AC/or/Fog and fuel pump relays and see what happens.

Here are the schematics.

Already swapped Fuel/ABS and Start/AutoShutdown (All four) relays. Problem perisists. Tested rear junction with OHM meter while turning ignition to RUN position and no voltage.

'Something' is shutting down the fuel pump. Alarms can have that feature....

You should for sure see a voltage spike at the rear junction when the key hits run.

I would next check right at the relay. I would look for the trigger signal when the key hits run. If I have that, then I would be thinking the contact in the relay box might be bad.

Could you have a bad ignition switch?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

Casper did pass the time by typing:

Let's go over the basics then.

From the front of the vehicle, remove the fuel pump relay Looking into the hole:

7 |

6| -8- |10

-9-

With the ignition on, hole 7 should have 12V from the power center fuses 3(20A) and 15(30A) (same location as the relays) Also check fuse2(20A), the ASD power fuse.

Hole 6 should also have 12V, if not check fuse 6(15A)

Hole 9 feeds the pump and the heated O2 sensor (If you found blown fuses take a look at the O2 sensor and follow the wire back along the engine to where a clip holds it to the block, then follow that wire up to another clip up above and forward of the engine mount. sometimes that wire will melt and short out. That short can/will blow fuses.)

If all looks good at this point then Jumping pin 9 to pin 7 will turn the pump on.

You should be able to hear it or watch the fuel rail pressure jump.