I just pulled the lower intake off my '87 F150 4.9L EFI and found a tremendous amount of carbon build-up at the end of the intake runners and around the injector nozzle. Is that amount of carbon build up typical of these engines? If not, what is likely to be the cause?

 

Too much idling will easily build up carbon. A lot of people like to keep the revs down and baby their engines to take care of them but what they don't know is that this can actually be bad. Obviously, stomping on the pedal at all times will stress things quickly but engines are made to rev and there is nothing wrong with making them do just that. Everyone once in a while I'll goose it just to get the revs up and make the engine work. This is colloquially known as an Italian valve job. Another thing I'll do is before shut down I'll rev the engine up.

Now, unless you've owned this since new you won't know your truck's full history, i.e. you don't fully know how the previous owner treated it. There are a few reasons why carbon would build up but idling is a big one.

 

I've had the truck for almost a year and haven't driven it much because of the idle problem. Previous owner(s) had swapped out the 3.55 gears for 4.10s so it either wasn't driven much or pulled some RPMs on the highway. I really don't know that much more about it other than a whole bunch of new parts had been thrown on it along the way - new radiator, starter, alternator, clutch, and a few other things I can't recall.

 

Ok - cleaned the intake runners out this morning and discovered what appear to be cracks on the bottom of 5 of the 6 injectors. The worst "cracks" correlated with the cylinders that had the most carbon build-up.










Normal wear or time to replace?

 

I think that orange donut is just a protective plastic cap to keep the injector pintle from being damaged should it ever be dropped. I do not think the cracks you show will affect the operation of the injector, assuming everything else about the injector is to spec.

 

Yeah Dave, no worries there. The O-ring seals above that and the nozzle is in the middle of that. Go ahead and run it.

 

Thanks for the feedback guys. I really want it to run better than it did before I tore it down so I'm turning over as many stones as I can looking for problems.