02 Explorer 4.0 xlt Starting issues

[taxman9]

A few days ago my wifes 02 Explorer 4.0 (115K) 4x4 wouldn't start. There is plenty of battery and it kicked over very strong just wouldn't engage and run. Next day I went down and it started right up and drove fine. I drove it to a friends garage to have a look at it and he couldn't replicate the issue. Started it a couple dozen times on Saturday and Sunday and it started each tmie. I picked it up Sunday afternoon and it started up fine and drive home, my wife did say there was a little heavier exhaust coming out as she followed me home. Her tank was pretty low so I added some premium gas just thinking she may have got some crappy gas in the tank. Yesterday morning it wouldn't start again. Let is sit for a while and the it started fine later in the day (temperatures aren't an issue as it's parked in a heated garage). It started fine this morning then wouldn't engage again in the afternoon on the first try but then did on the second. I'm trying to figure out what the issue could be that would occur intermittently on starting only, no issues once it's running. I'm not sure a fuel pump, fuel filter, vacuum lines, spark plugs, or plug wires could cause the issue sometimes and not others. The filter, plugs, and wires definitely need a change. Any thoughts on this sometimes there sometimes not issue...I'd concerned about the wife and kids getting stranded somewhere this winter.

Thanks for the help!!

[shorod]

You're really going to need to determine if, when it won't start, you're not getting sufficient fuel pressure or spark. Since it will start and run sometimes, we won't consider a compression issue.

Two things come to mind, a weak fuel pump or a failing Crankshaft Position Sensor (CKP). If you have insufficient fuel pressure when it won't start, or maybe even low fuel pressure when it does start, suspect the fuel pump. If you don't have spark when it won't start, suspect the CKP. Both are relatively common on Explorers (as well as several other vehicles) and would cause a no-start condition with a strong battery. Often a weak fuel pump would start with symptoms of failing to start after short drives. For example it may start fine in the afternoon, you'd drive a few miles to the grocery store, spend 15 minutes in the store, come back out and the truck won't start. Come back 2 hours later and the truck starts just fine.

-Rod

[taxman9]

Thank you Rod - I think I will start with the CKP and see if that fixes it up. Where is it located and what is the easiest way to get to it, I read around and it seems it's located by the distributor shaft? Is it a simple unplug, unbolt, remove, replace, rebolt, replug?

[shorod]

The Camshaft Position Sensor (CMP) is the sensor located near the distributor (which is driven off the camshaft). The Crankshaft Position Sensor (CKP) is located, well, near the crankshaft. It will be bolted to the block just behind the crankshaft pulley. If you provide this forum with information as to if your 4.0L engine is the SOHC or OHV engine, we'll get you even better location information.

For the most part it is as simple as disconnecting the small electrical connector, removing a bolt or two, remove the part, install new part with bolts, reconnect. Some CKP sensors have an elongated bolt hole and require using a cardboard spacer to properly space the CKP away from the tone ring on the crankshaft.

-Rod

[taxman9]

Hello again - just back into town and it's not starting at all now. It is the SOHC engine. Should I start with replacing both the CMP and CKP? Any help on the location would be helpful!

[shorod]

Maybe there was only one 4.0L engine choice for 2002. The factory service manual shows the CMP for the 4.0L engine as being located in the forward top of the driver's side valve cover.

The CKP is located on the passenger side of the crankshaft pulley. It appears to be held in place with a single bolt, and the wiring harness loops around underneath the A/C compressor.

A faulty CMP should not prevent the engine from starting, a faulty CKP would. If you want to shotgun parts, I'd start with the CKP. Have you confirmed that you do not have spark but have fuel? If you do not have a spark tester or a fuel pressure tester, you can pick up a spark tester for little money at the local parts store or at Harbor Freight or probably Sears. You could also spray some throttle body cleaner down the throttle body and see if the engine starts or acts like it wants to start. If so, you probably have spark in which case the CKP is probably not the issue.

-Rod

[taxman9]

I found the sensor and seemed pretty easy to get to from underneath (seems to be two bolts). I went to the parts store and picked up the CKP sensor as well as a spark tester. I hooked up the spark tester first and cranked the engine over and there is spark when the ignition is trying to start. I think I'll try laying underneath the tank and listening to see if the fuel pump engages when the ignition is turned on. A friend said if you don't hear it engage then give it a couple whacks with a hammer to see if the sending unit might be off a little....

[taxman9]

caved in and called the tow truck - brought it to the shop at the prognosis is fuel pump to the tune of $900. Happy Thanksgiving.