4.0 OHV Persistent Hard Start. Looking for ideas

[Brain75]

+1 to coil pack next
coil pack was on my next list as well - reference back to the 'hard start when hot' troubleshooting .... just about whittled it down to coil/injector/air filter (never once seen one of those that badly clogged)

 

[Kirby N.]

I’ll try the ether idea for sure. So just to clarify- all functional sensors should read about 5v? I did probe the tps and it is reading middle wire .99-4.75 when running. When off .96-4.72. @Shran

 

[Kirby N.]

So the coil. It’s a brand new old stock unit. It’s probably 6 months old. I replaced it trying to see if it was affecting the idle and of course it didn’t. However, I didn’t keep the old coil. I could try a junk yard unit.

 

[Kirby N.]

I'm a stickler for Motorcraft plugs... ate the replacement plugs Motorcraft?

Have you put a spark tester on it?

View attachment 120166

Those coils should be capable of about 60kv. The spark should easily jump that gap with an audible "snap"

Also... the more you crank... the more fuel you add. Try going to clear flood mode if it doesn't fire up on the initial crank. My thought is you could be flooding the engine.

What did the plugs look like when you changed them?

When you do get it started you say it idles poorly. How dies it run up top?

I've heard a lot of complaints on replacement injectors. To bad you didn't retain your old ones. I would certainly be looking for some factory injectors from the bone yard.

Thank you. It seems to run ok on top. I have been questioning that though because of just got my wife a 392 jeep about 6 months ago and everything feels slow after I drive that.

I did do the spark test with a tester like that on a couple of the plugs. I also unplugged the plugs at the coil and each were sparking strong. I will test all when I do the compression test.

I like motorcraft plugs too. I had platinum motorcrafts in it when I put in the rebuilt engine, but the first troubleshooting I did was replace the plugs and I couldn’t get oem ones without ordering them. So it currently has copper autolites. All the plugs looked similar, chocolate brown.

 

[Uncle Gump]

Did you try holding it to the floor during crank to shut down injector pulses?

 

[bobbywalter]

without verifying the continuity of the wires from the sensors and actual signal you do not know what is happening.

the 5 hole injectors certainly are not off the hook, but watching the tps and baro signals on shut down and power up and crank after it sits for an hour will be data worth using.

 

[bobbywalter]

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i dont have facebullshit so i can not read the whole deal to see if it applies here......but i was able to steal the chart....

Understanding Baro Sensors: Key Insights

The barometric pressure (BARO) sensor monitors changes in atmospheric pressure (air density) associated with changes in elevation or ambient weather conditions while driving.

www.innova.com

 

[Brain75]

So the coil. It’s a brand new old stock unit. It’s probably 6 months old. I replaced it trying to see if it was affecting the idle and of course it didn’t. However, I didn’t keep the old coil. I could try a junk yard unit.

If the symptoms were there before the new coil and after, I wouldn't throw money at yet another coil from anywhere....

+1 on this test:

Did you try holding it to the floor during crank to shut down injector pulses?

 

[bobbywalter]

may just be an issue with the central return/46

 

[Kirby N.]

Did you try holding it to the floor during crank to shut down injector pulses?

Ok- I didn’t know that happened when it was wot during crank. Am I looking to see
If it starts, or looking to see if the injectors stop pulsing?

 

[Kirby N.]

may just be an issue with the central return/46

What does that mean? Is that the valve in the middle of the tank?

 

[Brain75]

looking to see if you have a flooding issue or a fuel return issue (it's a loop, fuel goes from tank to rail AND back to tank)

 

[Kirby N.]

Also... the more you crank... the more fuel you add. Try going to clear flood mode if it doesn't fire up on the initial crank. My thought is you could be flooding the engine.

this is what you must mean about holding it wide open to turn off the injectors. I’ll try it

 

[Brain75]

... Am I looking to see
If it starts, or looking to see if the injectors stop pulsing?

looking to see if it starts easier (normal like).

 

[bobbywalter]

i was referring to ground reference.


may be as simple as lazy/sticky injectors.