I have been chasing down a stumble (maybe a misfire) when I first start the truck. This lasts for about 30 to 60 seconds on turning the key, then all is ok.

I have a 4.6 engine (180,000 miles) and have replaced the DPFE, plugs (motorcraft), wires, cleaned the MAF, cleaned the throttle body, changed the fuel filter and the coil packs are only one year old. It seams that the engine is missing, almost like a coil failure, but after 60 seconds, the miss / stumble is gone.

Now I am just throwing parts at it. I was wondering if there is a way to test the injectors for leakage. I am thinking that an injector is leaking after shutdown and causing a flooding condition in that cylinder until it clears itself out. So is there a way to test injectors? Or is tere some other problem I am not seeing.

Thanks for your replies and suggestions.

 

One thing you missed cleaning/replacing - the IAC. Did you clean out the EGR passages when you cleaned the TB?

You can lift the fuel rail with the injectors still attached and test them for leakage - put paper under them and turn on the key, if any of them drip they are leaking. You can try a bottle of Techron in the gas to clean them - that might help.

 

Right, - clean the plenum ports, -specially on bottom for the 4six.

Cold idle is all IAC. Do this correctly by working the mechanicals while cleaning.

 

IAC - Clean or Replace.

 

Thanks

I replaced the IAC, but srtill have the problem. I will take another look at the ports in the throttle body.

Maybe the IAC i bought is hanging up, will look into that also