94 won't start when hot outside

[Blizzard]

I've seen threads for some similar issues, but not quite like this.
My Ranger is a 94, 4L, 2wd, manual, 199k miles.

When it's cool outside (mornings or evenings), my truck will start/idle/run/drive as it should. But when temps approach 90+, it will crank stong, but won't start. This happened a few summers ago for the first time, and has progressively been happening more frequently each summer, and now happens all the time.

When it starts, since it runs fine, I'm assuming the main components of my fuel & spark systems are ok, and my problem is some sensor somewhere that doesn't work right when it gets too hot. Is this a good assumption?

I tried getting the local O'Reilly guys to read codes, but they say their code reader will only pull codes if the Check Engine light is on. My CEL is off, but I heard there can be stored codes that don't trip the CEL??? If that's true & it's worth pulling codes, is there a sensor or vacuum hose I could disconnect that would make the CEL come on? Just so their code reader would work?

I'm hoping someone here has seen this before & might have some recommendations. Any advice is appreciated!

 

[RonD]

First thing I would do is clean the MAF sensor, it needs to be done every few years anyway.
http://www.therangerstation.com/tech_library/CleanMAF.html

I think the MAF sensor is also the air temp sensor on the '94, some have separate intake air temp sensors, these help set fuel mix based on cold or warm air.

I would get a can of starting fluid, and the next time it doesn't start(assuming MAF cleaning didn't help), spray some into the intake.
If it fires then dies you will know the fuel system is the problem.
If it doesn't fire, then spark is the issue.

 

[UrbanRedneckKid]

Coolant temp sensor.
The ecu uses this sensor to know the fuel trim when starting.

Just replace it, its cheap enough.

 

[Blizzard]

Cleaned MAF...no start.
Replaced coolant temp sensor...no start.
Sprayed starting fluid into intake while cranking...no fire.
Pulled one of the plugs & cranked...NO SPARK!

Gap looked bigger than it should, but I'm not sure what it should be. I wonder if my plugs are bad (electrode wearing away???), but not sure why that would only cause problems when it's hot.

Thoughts???

 

[RonD]

No spark reads like no power at the coil pack or bad coil pack.

Coil pack will have a 4 wire connector, key off, unplug it.
Key on, one of the end wires will have 12v, test for that, the other 3 are intermittent ground wires used by the computer to fire the 3 coils in the coil pack.

Google: test ford coil pack

There is a video that shows it pretty well, you need an ohm meter.
Heat WILL effect a coil

Have you checked the fuses, EEC fuse for sure, EEC relay sends power to the coil.

 

[Blizzard]

Thanks for the help!
It might be a few days til I can play around with the coil, but I'll post what I find out when I can get to it.

 

[Blizzard]

Worked a little last night when it was cool. As far as I can tell, the EEC fuse & relay are good, but I don't know if they're doing something weird when it gets hot outside.

The vidoes I found testing the coil were just checking the resistance across the pins of the connector, and across the banks of the plug connections. It was cool when I tested it. If I check again when it's hot, should this resistance check show something (assuming the coil is bad)?

For what it's worth, here are the resistances I got:
4-pin Plug (200 ohms):
1 to 2 = 1.7
1 to 3 = 1.7
1 to 4 = 1.2

Spark Plug Connections (200K ohms):
Bank 1 = 13.9
Bank 2 = 13.9
Bank 3 = 14.0

The 1.2 might be a concern, but last night when it was cool, it started right up & ran great.

 

[RonD]

Coil reads as bad but could be the OHM meter, coil would still work just not very well, cooler spark

Primary coils are the
1 to 2 = 1.7
1 to 3 = 1.7
1 to 4 = 1.2
These should all read 0.3 to 1.0 ohms 1.2 is too high as is 1.7, 200ohm setting is OK if that is the meters lowest setting.

Secondary coils
Bank 1 = 13.9
Bank 2 = 13.9
Bank 3 = 14.0
need to be test with ohm meter at it's highest setting they should read between 6,500-11,500 ohms.
On the 200 setting your readings are showing 13,900ohms and 14,000ohms so out of range as well

I would test the ohm meter before buying a new coil
Maybe take meter to auto parts store or wrecking yard and test a new coil with it

 

[Blizzard]

My multimeter is a cheap one from Harbor Freight, but I borrowed a nice one from a buddy, and it gave the same readings.

When I check resistance when the coil is hot, the resistances went up:
1.7 to 2.2
1.7 to 2.3
1.2 to 1.9

13.9 to 15.2
13.9 to 15.2
14.0 to 15.3

I think I'm going to pick up a new coil...

 

[RonD]

Yes, Time for a new coil.

Take your ohm meter with you just to be sure

 

[Blizzard]

RonD...are you sure about the resistance specs for the coil? I ask because I've tested four different brands of coils from O'Reilly & Napa, and they're all 13-something K-ohms. I have not been able to test one from Ford, but I found in my Haynes book that the EDIS coil secondary resistance is supposed to be 13 to 15 K-ohms. This made me wonder if mine is really in question, even though it read 15.2 after sitting in the sun for a few hours.

Anyway, before replacing the coil, I replaced the plugs. The one I pulled to check spark looked questionable, and they were 13 years & >100K miles old. But this did not fix the issue.

So I bought & installed a new coil. Drum roll..........still no spark!!!

Haynes manual talks about an EDIS ignition module. I'm going to work on testing that, but any other thoughts are welcome.

 

[Blizzard]

I've been following the instructions in my Haynes manual (which are less-than-helpful!) for checking the ignition control module. After checking that it's getting power, it says to check the SPOUT signal & that the signal should make my LED test light blink when I crank. I'm not getting any signal at all, but I'm not convinced I'm doing it right...instuctions are pretty shady.

I've searched here, but haven't found any instructions for testing the ignition control module. Can anyone provide any guidance so I know I'm doing this right before I go drop $200 on a new one? Are there any other tests? Or can anyone confirm this SPOUT test is right?

Thanks in advance!

 

[RonD]

I did find a couple of conflicting OHM readings for these coil packs.

1.1-1.8, primary
13-16, secondary


EDIS module should be on radiator support, somewhere, it changed from year to year.

Google: ford edis 6 module image

To see what you are looking for

 

[Blizzard]

Thanks Ron,
I've found the EDIS module, but I'm having a hard time figuring out how to test it. Any advice?

 

[RonD]

Not sure there is a test for it, outside of testing for 12v with key on.

The EDIS 6 module was used from 1990 to 1995 on pretty much all 4.0l engines in any model of Ford having that engine.

The EDIS module, coil pack, and CKP(crank position) sensor(aka VRS) are the big 3 in the spark department.
EDIS doesn't use a CPS(Cam Position Sensor)

From what I have read these 3 will continue to provide spark without the ECU, the ECU only controls the timing of the spark, so if ECU doesn't tell the EDIS otherwise it will spark at 10deg BTDC as long as it is getting input from the CKP sensor.