At my wits end with my 98 Explorer Sport not starting when it's warm to hot outside

[Chris_A.]

As Fast Dave mentioned I would focus in on the Crank sensor...super easy and cheap to replace...(Ebay) Do the push start / clutch and drive to local Autozone and borrow their OBD2 tester for free (if you don't own one) and perform a KOER test and see if it picks up bad sensor code.
Do you have the OHV 4.0 ? If so you have to loosen and partially remove serpentine belt near sensor for better access....can do this / entire job from passenger side underneath front of vehicle.... have a large rag handy to wipe all the oil / buildup etc around it.
I replaced mine at night at a do-it-yourself carwash stall

I wouldn't. The push start suggests that is likely to be ok.

An idea for a test would be to run a temporary wire setup (quick attaching), similar to old school, batttery to the starter, solenoid between. If it push starts (indicated) and the old school bypass works; then, his problem is not the battery. It is; then, isolated to the startup circuits. One or more of them has issues.
If this does not work; then, it is likely that he has a bad connection or a weak battery and/or alternator. Might just need new battery and starter cables, if the battery tests good. (The battery is not a known good part until bench tested. A weak battery can show good voltage and not be able to deliver good amperage. Any of the automotive outlets should be able to run a validation test. Suggest doing this reguardless of anything else.) I had a similar issue and it was the battery. Of note, I had to replace the alternator a few months later. And the starter a few months later. Yes, 98 Explorer 4.0L SOHC.

The problem sounds like his start circuit is pulling the ignition voltage below minimum requirements.

Another test, no parts needed, is to attempt the startup with the headlights on. This will quickly indicate a weak start circuit.
Weak = lights fail and no start/ slow crank/or the dreaded clicking.
Good = lights stay on, starter turns over at or near normal speed. Issue is waiting for the failure to run the test and maybe not being able to push start afterwards.

Any other parts or circuits may be a contributing issue; but, are not the fails to start.

 

[EB4X]

I was going under the assumption, although of course could be wrong, that Ford has the PCM setup so that during crank if it detects subpar crank sensor it disables fuel pump / and or spark to not allow engine ignition (all this happening in milliseconds of course).... my 2002 Jeep is set up to do this in scenario.

 

[Chris_A.]

I was going under the assumption, although of course could be wrong, that Ford has the PCM setup so that during crank if it detects subpar crank sensor it disables fuel pump / and or spark to not allow engine ignition.... my Jeep is set up to do this in scenario.

Based upon the senario, the lack of the crank trigger prevents the spark, the computer does not supply fuel (does not supply ground) without supplying spark (emissions control).
On the Ford, this could be similar. But, low voltage will prevent a difference in potential so that none of his sensors are able to provide in-range signals.
Example: computer uses 12VDC to control and sense everything. Low amperage availability drops this to 9 maybe 10VDC. The sensors and other items (fuel pump, HEGO, etc) all want some of what little there is. Until the alternator can start to provide, they get a share of the available wattage. The more complex the circuit, the more sensitive it is to shortages. I think his problem is a bad battery/cables. If it is, he should replace ASAP. He should, also, replace his voltage regulator (weak battery=hard life), battery cables and starter cables (eliminate corrosion), if possible. Also, he should clean all 3 engine compartment grounds + the computer ground wire, replace if needed.
Then, I would reccomend that he have the vehicle OBD2 tested and fix anything indicated by the testing as soon as he is able to. His priority after that should be to fix PATS so that he can enjoy his vehicle instead of whomever decides they want it more.

Personal opinion, Ford ran the cables wrong. The positive terminal has a split that sends 1 wire to the starter and one wire to the battery junction box. This should have been one wire to the battery junction box 4ga, and one wire to the alternator 4ga with splice to the starter 4ga. Understanding the load is why. The starter uses its 4ga wire only at startup. The alternator uses a much smaller wire to run to the battery junction box. This is wrong because the rest of the run time the alternator has a higher resistance wire to go to a terminal on the battery junction box, through a press fit connection to the 4ga wire that then goes to the battery. This results in less voltage to the battery. And the alternator has to work harder to make up the difference. .2V might not sound like much; but, the regulator sees it. And it is a corrosion sensitive connection. As corrosion increases, the battery to alternator voltage drop increases. Corrosion is minimized by running it straight to the terminal. Less drop, less battery for the corrosion cell. Second thought on this is that it increases the voltage stability supplied to the various circuits because the battery is in the circuit first and is better able to 'sink' any variances.
I plan, on the system that I am working on, to do this and to solder the 2 connectors (mine will have 3 for the additional batteries) at the alternator to minimize the losses.

 

[Pete Deering]

Did you rule out the neutral switch. Have try to start it in neutral? There is a ground stud in the engine compartment next to the EEU. On my 95 was very rusty. Take a look at that.

 

[Chris_A.]

Did you rule out the neutral switch. Have try to start it in neutral? There is a ground stud in the engine compartment next to the EEU. On my 95 was very rusty. Take a look at that.

I agree that it will likely need TLC. On his there are 3 major grounds under the hood plus the PCM ground. While this could be the issue, the no start, as described, only indicates the battery system as having an issue. Why? It will push start. If the battery system comes back all good he has issues in his start wiring. I do not think that this is likely as he says that it will turn over by the key. If he does the bypass test, then, a "starts" indicates the start control circuit (bypass creates a different path used to control the start).

The only thing that makes any sense is a excessively low voltage to the ignition system that is only seen during start (by the battery).

This points to battery voltage supply. That it will push start suggests that there is no hard failure in the ignition system (wouldn't start at all) or in the charging system (would start and die). Hense, likely, a weak battery and/or battery cable issues.

 

[C420sailor]

Yeah, rules out PATS too. It wouldn’t allow a bump start but not a crank start.

Your theory makes sense. Could also be causing a weak spark.

I’ve seen this on Megasquirt EFI systems where starter crank on a low-ish battery drops the voltage enough to dump the computer. No start.

You’d think it would be worse cold though...when the battery is being worked the hardest.

What about an ignition coil pack going south? Those often don’t play nice when they get hot...

 

[Chris_A.]

Yeah, rules out PATS too. It wouldn’t allow a bump start but not a crank start.

Your theory makes sense. Could also be causing a weak spark.

I’ve seen this on Megasquirt EFI systems where starter crank on a low-ish battery drops the voltage enough to dump the computer. No start.

You’d think it would be worse cold though...when the battery is being worked the hardest.

What about an ignition coil pack going south? Those often don’t play nice when they get hot...

I think that there are other issues with the OP's vehicle. Just not as pertinent to the request made. I figure that tackling one at a time makes the most sense.

I have been working on a comprehensive schematic and I tend to get overwhelmed as Ford's schematics are disjointed, vary in quality and type (on same page), and are spread over many pages.

The drawing (lousy, arthritis) is a simplified schematic for the Explorer start circuit.

His fuses to check should be
Mega Fuse - Known Good
BJB F5 50A - Known Good
FJP F24 7.5A - Known Good
His start relay
BJB K6 - Known Good
Clutch switch - should be good
Ignition switch - should be good
Wiring - should be good

Symptoms say that these are true. Turns over is the quick test. No start, check PATS symptoms. Light flashes, goes out after being turned to run. Good?? Next stop>

Else, says battery/cables/maybe weak grounds.

Afterwards fix known issues; then, maintenance time/milage.

 

[bullaka]

IMMENSE thanks to everyone for your help! I've obviously got more homework to do.

 

[Chris_A.]

IMMENSE thanks to everyone for your help! I've obviously got more homework to do.

Best wishes!

 

[fast_dave]

The more I read this thread, the more I go back 40 years in my head and I hear my auto shop teacher, for 4 years, say the phrase "Keep It Simple Stupid"

Today I imagine teachers don't dare talk like that, and that's really too bad, because there's a reason why that phrase refuses to die - but I digress....

Approximately $20 spent at Rock Auto could purchase BOTH:

* a Crankshaft Position Sensor (fast_dave & @EB4X)

* Coolant Temperature Sensor (@Mbrooks420 and @donalds )

BOTH are well known parts that have prevented Ex's from intermittently running properly - emphasis on the word intermittently.

There's a reason all four of us went right to those 2 parts after reading the OP's first post

Seriously, good luck and let us know

 

[239]

My 2000 had the same problem when it was warm. It ended up being the fuel pump for me.

 

[fast_dave]

Just sayin - This week it's raining and between 30 and 60 in VA (OP's location) according to weather.com

 

[239]

Just sayin - This week it's raining and between 30 and 60 in VA according to weather.com

It was 40 outside when mine would do that. But the engine was warm haha.

 

[fast_dave]

It was 40 outside when mine would do that. But the engine was warm haha.

OK - I hear you and will give you that
As far as $$$ & Time, I'd look at Crankshaft Position Sensor, Coolant Temp Sensor, and Fuel Pump - in that order, but that's me.

 

[C420sailor]

Do you have a code reader or forscan? Live data will tell you right away if your ECT is out to lunch.

I hate throwing parts at a problem, but that’s just me.