4.0 OHV Long Crank in morning

[Bunger317]

Got a weird problem I haven't been able to pin down. Had this truck about a year (1994 4.0 4x4). Morning and basically after sitting or cooling down it'll crank about 5 seconds or more before it fires up and runs great. When running it runs like new. Another intermittent issue is if I run to the store, come back out and start it 1/10 times it'll run rough like a misfire for a minute or until I blip the throttle.

Fuel pressure is within spec. Cycling the key/pump a few times in the morning doesn't help. I had it at a shop they ruled out headgasket/ and fuel related issues(fpr/injectors/ect. I replaced the ECT sensor and both o2's. Thinking crank position sensor possibly?
Open to any ideas or things to test/try.

Thanks!

 

[Shran]

If you know someone with an oscilloscope you can check the crank sensor that way - should be making AC voltage as the engine turns over.

My buddy who is a long time Ford mechanic told me that the misfire on warm starts on 4.0's is usually a tiny crack in the head somewhere that allows a little bit of coolant into one or more cylinders and temporarily fowls the spark plug. It won't happen when the engine is cold because the coolant has some time to evaporate and the crack closes as the head cools and shrinks so it won't leak more. Just what I was told, take it for what it's worth. In my experience hard warm starts are usually caused by a bad fuel pressure regulator or leaking injectors that flood the engine to some degree.

My 92 Explorer does the misfire thing, has for years and it never gets better or worse. I have a brand new set of heads on the shelf in case I ever need them but so far it's just annoying.

 

[Bunger317]

Got a weird problem I haven't been able to pin down. Had this truck about a year (1994 4.0 4x4). Morning and basically after sitting or cooling down it'll crank about 5 seconds or more before it fires up and runs great. When running it runs like new. Another intermittent issue is if I run to the store, come back out and start it 1/10 times it'll run rough like a misfire for a minute or until I blip the throttle.

Fuel pressure is within spec. Cycling the key/pump a few times in the morning doesn't help. I had it at a shop they ruled out headgasket/ and fuel related issues(fpr/injectors/ect. I replaced the ECT sensor and both o2's. Thinking crank position sensor possibly?
Open to any ideas or things to test/try.

Thanks!

If you know someone with an oscilloscope you can check the crank sensor that way - should be making AC voltage as the engine turns over.

My buddy who is a long time Ford mechanic told me that the misfire on warm starts on 4.0's is usually a tiny crack in the head somewhere that allows a little bit of coolant into one or more cylinders and temporarily fowls the spark plug. It won't happen when the engine is cold because the coolant has some time to evaporate and the crack closes as the head cools and shrinks so it won't leak more. Just what I was told, take it for what it's worth. In my experience hard warm starts are usually caused by a bad fuel pressure regulator or leaking injectors that flood the engine to some degree.

My 92 Explorer does the misfire thing, has for years and it never gets better or worse. I have a brand new set of heads on the shelf in case I ever need them but so far it's just annoying.

The crack makes sense and that's what I originally assumed knowing these heads are prone to cracking. The shop pressure tested the cooling system so I know it's not a large leak. I've got a o scope at work I'll try to "borrow" it and do some testing. The misfire like you said hasn't gotten worse or better and doesn't bother me all that much.

the long crank does seem to be getting worse and that's the one that concerns me since I use this truck for hunting in some remote places and am dreading the day it won't start at all

 

[RonD]

Watch the CEL(check engine light)

Key on, CEL comes on, that means computer has booted up correctly
When you turn the key to START and engine starts to spin, CEL should go OFF, that means computer is getting a good timing signal from Crank Sensor

If there is a delay before CEL goes off while cranking then check crank sensor tone ring for mud build up, also unplug crank sensor and check connector for water intrusion, plug it back in, unplug and plug back in cleans contacts

Crank sensors rarely fail, and generally if they do, there is a no start, ever, not intermittent or slow to start
Replacement of crank sensor is not expensive or hard to do

 

[Bunger317]

Watch the CEL(check engine light)

Key on, CEL comes on, that means computer has booted up correctly
When you turn the key to START and engine starts to spin, CEL should go OFF, that means computer is getting a good timing signal from Crank Sensor

If there is a delay before CEL goes off while cranking then check crank sensor tone ring for mud build up, also unplug crank sensor and check connector for water intrusion, plug it back in, unplug and plug back in cleans contacts

Crank sensors rarely fail, and generally if they do, there is a no start, ever, not intermittent or slow to start
Replacement of crank sensor is not expensive or hard to do

Good to know. I'll check that when I leave work today. Thanks for the info.

 

[Manscout]

Make sure both the temp sensors are plugged in. I had this exact issue in my truck for over a year. I went to replace the ECU temp sensor when I saw -40 being read off OBD. That's when I saw it was unplugged. remember there are two sensors across from each other. That immediately fixed my problem.

If you already replaced the sensors already, look at the reading when hooked up to the OBDII.

 

[Bunger317]

Make sure both the temp sensors are plugged in. I had this exact issue in my truck for over a year. I went to replace the ECU temp sensor when I saw -40 being read off OBD. That's when I saw it was unplugged. remember there are two sensors across from each other. That immediately fixed my problem.

If you already replaced the sensors already, look at the reading when hooked up to the OBDII.

i'm certain they are both plugged in. I just replaced the temp sensor for the ECU. Unfortunately, this truck is an OBD one since it's a 94 so I don't have the luxury of reading the temperature input.

 

[Bunger317]

Just left work and it's cranked and cranked with cel illuminated indicating a issue. Turned ignition off and back on and it fired up immediately. Is there a relay that could be having an issue?

 

[Bunger317]

Like a relay for the ignition or ECM?

 

[Bunger317]

I also have read some thing about the 1994 ECM's having bad capacitor's or something like that?

 

[RonD]

1994 4.0l has a separate spark system, EDIS-6

Consists of these 3 parts:

https://imgur.com/4cuB7HX

EDIS-6 Module(ICM)
Crank sensor with tone wheel
Coil Pack

This system runs independent of the engine computer for start up
Engine computer does suggest spark advance after start up
The EDIS-6 does pass on the Crank Sensor timing signal to the computer, so you are correct, if EDIS-6 was bad or off-line then CEL would stay on while cranking

Just one relay involved, the EEC(PCM) relay, but.........................
This relay powers up the computer with key on, which causes the CEL to come on
Same relay also powers the Spark(EDIS-6) system
So if CEL comes on have to assume EDIS-6 is also powered up, might not be but long odds in that

CEL not going off while cranking means no crank sensor signal, check the connections

Yes, 1994 and older Ford EEC-IV computers can get leaking capacitors after 20+ years
The 3 Blue ones in this picture: http://www.auto-diagnostics.inf/ford_eec_iv

But.......these caused issues with fuel system, because thats all these model computers dealt with, not spark/timing issues

Not much to the 1994 4.0l wiring but here it is

 

[Bunger317]

1994 4.0l has a separate spark system, EDIS-6

Consists of these 3 parts:

https://imgur.com/4cuB7HX

EDIS-6 Module(ICM)
Crank sensor with tone wheel
Coil Pack

This system runs independent of the engine computer for start up
Engine computer does suggest spark advance after start up
The EDIS-6 does pass on the Crank Sensor timing signal to the computer, so you are correct, if EDIS-6 was bad or off-line then CEL would stay on while cranking

Just one relay involved, the EEC(PCM) relay, but.........................
This relay powers up the computer with key on, which causes the CEL to come on
Same relay also powers the Spark(EDIS-6) system
So if CEL comes on have to assume EDIS-6 is also powered up, might not be but long odds in that

CEL not going off while cranking means no crank sensor signal, check the connections

Yes, 1994 and older Ford EEC-IV computers can get leaking capacitors after 20+ years
The 3 Blue ones in this picture: http://www.auto-diagnostics.inf/ford_eec_iv

But.......these caused issues with fuel system, because thats all these model computers dealt with, not spark/timing issues

Not much to the 1994 4.0l wiring but here it is

Appreciate the reply and info. Last night I pulled the connector off the crank sensor. Everything looked good but cleaned everything anyways and added a few dabs of dielectric grease and that didn't fix it. Bad sensor perhaps?

 

[RonD]

Maybe but crank sensors rarely fail, its a VR sensor so not much to fail in it, but possible

Its wires run up and around the water pump to top of lower intake and then into a wiring harness, just follow it up as best you can to see if its been damaged any where

Its 2 wires run to the EDIS-6 module
On my 1994 the EDIS-6 is on the drivers side of rad support, on the FRONT side
You have to look up from under the bumper to see it, it runs hot, like all ICMs, so needs air cooling

 

[Bunger317]

Maybe but crank sensors rarely fail, its a VR sensor so not much to fail in it, but possible

Its wires run up and around the water pump to top of lower intake and then into a wiring harness, just follow it up as best you can to see if its been damaged any where

Its 2 wires run to the EDIS-6 module
On my 1994 the EDIS-6 is on the drivers side of rad support, on the FRONT side
You have to look up from under the bumper to see it, it runs hot, like all ICMs, so needs air cooling

Found two sections where the plastic sleeve was gone expanding the shielding but without tearing the front end apart I couldn't check the whole run. The icm has moist dirt all around the edges like it's been leaking some sort of oil or something?

 

[Bunger317]

Icm