TEST 2: Using Starting Fluid To Confirm Lack Of Fuel
The ‘quick and dirty’ way to check to see if a lack of fuel is causing your 4.0L Jeep to not start is using starting fluid (although it's not the most accurate way of diagnosing a bad fuel pump).
The rule of thumb is that if by spraying starting fluid your Jeep starts, even if momentarily, then this tells you that fuel is missing from the equation (engine start equation: fuel+spark+air=combustion).
NOTE: To get an accurate test result from the starting fluid test, you need to first confirm that the ignition coil pack is creating and delivering spark to all 6 cylinders. You can easily accomplish this by attaching a spark tester to the spark plug wires and having a helper crank the engine (while you observe to see if the spark tester sparks).
IMPORTANT: This is a very fast and easy test but you do have to take one very important safety precaution and this is to reconnect the air intake duct after spraying starting fluid down the throttle bore (although you don't have to fasten it). This will prevent any backfire, that might occur, from scaring the heck out of you when cranking the engine.
This is what you have to do:
Remove the intake air duct from the throttle body. You don't have to completely remove it, since you'll have to reconnect it in one of the next steps.
Open the throttle plate and spray starting fluid down the bore.
As a safety precaution reconnect the air duct after you have sprayed a good squirt of starting fluid (but you don't have to tighten the air duct's hose clamp).
Crank the engine once the air duct is back on and you're clear of the engine compartment.
You'll get one of two results with this test:
1.) The engine will start momentarily and after a few seconds will die or.
2.) The engine will only crank but not start at all.
OK, let's find out what your results mean:
CASE 1: The engine started and ran for a few seconds. This test result tells you that the no-start problem is due to a lack of fuel.
Your next step is to check to see what the fuel pressure is with a fuel pressure test gauge. Go to: TEST 1: Checking Fuel Pressure With A Fuel Pressure Gauge.
CASE 2: The engine did not start, not even momentarily. This usually means that a lack of fuel IS NOT the reason your car is not starting.
Now, remember what I said about this test not being very accurate? Well, I suggest you do one more test and this is to check the fuel pressure with a fuel pressure test gauge. Go to: TEST 1: Checking Fuel Pressure With A Fuel Pressure Gauge.
Where To Buy The Fuel Pump And Save
The fuel pump in your 4.0L Jeep is located inside the fuel tank. The fuel pump can be bought in any auto parts store, but I think you'll find the better price online. The following fuel pumps are pretty good deals:
1997 and Newer 4.0L Jeeps ⇈
1996 and Older 4.0L Jeeps ⇈
Not sure if the above fuel pumps fit your particular 4.0L Jeep? Don't worry, once you get to the site, they'll make sure it fits by asking you the specifics of your vehicle. If it doesn't fit, they'll find you the right one.
More Jeep 4.0L Test Tutorials
If this tutorial was helpful/informative, you can find a complete list of tutorials here: Jeep 4.0L Index Of Articles.
Here's a sample of the tutorials you'll find there:
- Rear O2 Sensor Heater Test -P0141 (1996-1998 4.0L Grand Cherokee).
- How To Test The MAP Sensor (1997-2003 Jeep 4.0L).
- How To Do A Cylinder Balance Test (Jeep 4.0L).
- Jeep PWM Fan Relay Test Troubleshooting An Overheating Condition.
- How To Test The Crankshaft Position Sensor (1994-1996 4.0L Jeep).
If this info saved the day, buy me a beer!