94 warm start problem

[BoydK]

Greetings my 4L 94 sxt runs great except for 2 issues
1- If engine's at normal temp when I park and I turn it off for anywhere round 10 minutes it won't restart for me. I end up sitting in it for 15 minutes before it will start again (and, it seems to work better if I don't crank it between it failing and the retry). Engine turns over fine, it occaisionally give a half hearted stumble as if it might "catch" but doesn't. Restarting before 10 minutes passes, it'll start probably 80% of the time but between 10 and engine cool down I'm stuck on this weird "sit and facebook" thing for 15 minutes or possibly a cycle or two of 15 minute waits. It's my daily driver, need to figure out what's up asap any pointers -greatly- appreciated.
2- (which might be #1 or related, I dunno) when I'm at normal temperature on the freeway, if I press the pedal enough to load the engine a little but not enough to downshift (auto trans) it "misses" meaning it feels like the brakes are punched just quickly. I don't hear a backfire, just... the thing stutters. So I guess "runs great" could be greater at the moment.

Any diagnostic tips are greatly appreciated. Plugs and wires are just over a year old. Engine light stays off (tho last year had a code about some volt level issue and found a loose starter cable).

 

[Eddo Rogue]

I noticed you have no replies, and figured I would throw in a cent or 2...

These are both sorta those "could be anything" deal, and could even be related, here's where I'd start:

Both sound like fuel delivery issue. I think your fuel pump and /or pressure regulator is on its way out, or clogged fuel filter.

If you haven't replaced the fuel filter recently, start there....swap in a new fuel filter (preferably motorcraft).

its in driver side frame rail near engine, I unhook the lines and unbolt the whole bracket, then do the hose clamp part.

Otherwise start snooping around your fuel pump....

click the key on (but no crank, ignition only), can you hear it prime? It should run for a sec, nice steady tone, no up and down squeal

When its doing the warm no start, crank it for a 5 seconds and listen if the fuel pump primes again when you stop cranking.

if none of thats happening, maybe test it for voltage, check fuses etc...

Check you your fuel pressure regulator, does it look crappy? maybe do a pressure test or at least hit that schrader valve to see if it shoots fuel w/ some good pressure (watch yer eyes tho)

if you got high mileage (100k+) I'd just throw parts at it anyways, new fuel pump and filter to start.

Besides that it could be MAF and/or throttle body is dirty....you can grab a can of mass air flow sensor cleaner and throttle body cleaner sprays (dont use brake cleaner). Theyre both super easy access and it might help anyways, but be careful if you clean the throttle body, spray only, go very easy on it (there's a factory coating on the butterfly)

Hope that helps...

 

[RonD]

Replace ECT sensor, just on speculation, they are cheap
There are two temp readers on your 4.0l engine, a sensor and a sender, both located above thermostat housing on lower intake
You want to change the SENSOR which will have a grey/red wire and a light green/red wire, two wires, this is used only by the computer, runs on 5volts

SENDER is single wire, black/light blue wire, this is for the dash temp gauge only, runs on 12volts

Thinking that the ECT sensor is telling computer engine is COLD when you first turn on the key, computer will then run CHOKE mode, RICH fuel mix and advanced spark, which would cause a No Start on a warm engine


Second thing, a failing coil pack, its getting heat soaked when engine is off
When you shut off a warmed up engine the fan is off and all the parts under the hood get real hot real fast, heat soaked
Pop the hood to let things cool off, then try restart to see if "heat" might be the issue

Third, Leaking injector or FPR
You would have a drop in MPG for this to be the problem, have you noticed this?

 

[Eddo Rogue]

Replace ECT sensor, just on speculation, they are cheap
There are two temp readers on your 4.0l engine, a sensor and a sender, both located above thermostat housing on lower intake
You want to change the SENSOR which will have a grey/red wire and a light green/red wire, two wires, this is used only by the computer, runs on 5volts

SENDER is single wire, black/light blue wire, this is for the dash temp gauge only, runs on 12volts

Thinking that the ECT sensor is telling computer engine is COLD when you first turn on the key, computer will then run CHOKE mode, RICH fuel mix and advanced spark, which would cause a No Start on a warm engine


Second thing, a failing coil pack, its getting heat soaked when engine is off
When you shut off a warmed up engine the fan is off and all the parts under the hood get real hot real fast, heat soaked
Pop the hood to let things cool off, then try restart to see if "heat" might be the issue

Third, Leaking injector or FPR
You would have a drop in MPG for this to be the problem, have you noticed this?

I forgot to mention the coil pack and injectors possibilities too....And Ect senor is a cheap easy try. I would change the sender too if looks ugly. Check the wires while in there. So, +1 to what Ron said

 

[franklin2]

A quick and dirty way to run a test is to keep a can of brake cleaner with you. When it doesn't start, spray some of that in the intake and see if it starts. If it does, you know you have a fuel delivery problem. If not, then you can move on to something else. Do you have a factory tach in the dash? If so, watch it when it's cold and cranks up. Then watch it again when it's cranking but not starting. If the tach is dead when it doesn't start, that can be a indicator of a ignition problem, like some sort of ignition module. I am not too familiar with the coil pack type of ignition.

 

[RonD]

Just to add to the above, even without a tach, watch the CEL(check engine light)
It comes on with key on, that means computer is booting up
And it should go OFF when trying to start engine, cranking, that means computer is getting a Crank signal from crank sensor, thats the Tach signal franklin2 mentioned

 

[ranger_gord]

Sorry to interject but could your Fuel pump relay be going south (intermittent)?

 

[Eddo Rogue]

Just to add to the above, even without a tach, watch the CEL(check engine light)
It comes on with key on, that means computer is booting up
And it should go OFF when trying to start engine, cranking, that means computer is getting a Crank signal from crank sensor, thats the Tach signal franklin2 mentioned

Dang Ron way to catch the details! +1.