Slight hesitation while stopped, sometimes dies when starts

The first month I brought this truck home, there was 2-3 times that I would start it and it would immediately bog out and die. It would also do this if I rev'd the engine in park/neutral. I would attempt a restart and it would fire but die unless I gave it some throttle. It hasn't done it since but it always kind of bothered me.

When revving the engine, when the RPM's are coming back to idle, it dips below normal idle RPM's, hesitates, then comes back up almost like it wants to die. Well today I noticed that when restarting it multiple times, black smoke puffed out of the exhaust leading me to believe it is getting more fuel than it is burning. This was during a cold start and I only let it run for about five seconds at a time before shutting it off and restarting it. No checking engine lights are on. I am going to clean the MAF tonight to see if that helps. I have run a few cans of sea foam through the tank and the plugs were done 50K ago. Should I be checking anything else?

 

Check for leaking fuel injectors.

 

That's kinda of what it seems like, like one may be bleeding off. What is the easiest way to test them?

 

Well, some mechanic shops can do fuel injector leak down testing but for doing it home the only method I know is to start the truck to pressurize the fuel system, and the shut it off, wait a few minutes and pull the spark plugs and look for wetness and fuel smell in the cylinders.

When you pull the plugs you can also look at their color. If any are black instead of light brown you know thats the problem cylinder.

 

If it does end up being an injector issue, I would highly recommend upgrading to 12 hole injectors from Dirty Deeds. I wouldn't put anything else in there. And they are reasonably priced IMO.

I don't have them yet but several members have done the swap and like them.

 

I would run either a bottle of Chevron Techron or Seafoam through the fuel system. Both of those are good products and I have had them stop dripping injectors. I run a bottle in the fuel tank yearly as regular maintenance and when I first buy a used vehicle.
I would also clean the throttle body. A dirty throttle body can affect idle quality. These 2 simple procedures might help but won't hurt or be wasted time.

 

May need to do a throttle body cleaning. Use throttle body cleaner only with a tooth brush and micro fiber towel.

50k on the plugs? Depends on their rating. May need changing, as well, but start with throttle body first (cheap).

How do your ignition coils look?

 

I cleaned the MAF tonight so I’ll see if that does it. I may throw some plugs in it because they are cheap. Coils look fine but one was replaced when the plugs were done due to a misfire. I’ll throw a new fuel filter on it as well.

I have access to a Snap-On Solis so I hooked it up after work to check codes and run some tests. It passes with flying colors and had no stored codes of any kind. It may be in my head about the stumble but it has definitely died on me before and I did see some black smoke come out of the exhaust after multiple restarts.

 

Well, cleaned the MAF sensor, replaced the fuel filter and replaced the spark plugs. Seems to have cleared it up. I also found a couple of vacuum lines that were not connected. Not sure what they do but got them reconnected so maybe that helped.

 

Geez...even one vacuum leak will cause havoc. An open vacuum line basically means there is a source of intake air that your ECU doesn't know about...so here it is doing the best it can to keep your engine running right but air is sneaking in the back that it knows nothing about and so can't do anything to fix. 90% those vacuum lines where the problem.

 

Yeah. I’ve had a few various lines over the years slip off and the truck basically let me know right away. I would slip them back on and use electrical tape as a back up.

That area under the hood on the drivers side where 4-5 lines cross over seems to be a culprit. Pays to make sure the OEM clip/stand offs that keeps them organized are still in good shape. Mine were cracked or not holding properly, so zip ties were rigged for extra support.

 

Thank you for posting those pictures @Professional Hand Model, you are pretty handy.

I circled what was disconnected on mine, can anyone tell me what they do?

 

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Well just an update, everything seems to be running 100%. Fires right up in the cold and the hesitation has gone away.

 

Happy endings are the best