I have a 2001 s-10 that seems to throw the ses light on when on the highway.Everytime a check with code reader it shows number 4 cylinder misfire.Whats weird is when you drive around city for a while the light will go off.If you get on highway and run for a while as I was going to Northern Mo.fron St. Louis about half way there on the highway naturaly the ses light came on.Any ideas on what this could be as the truck idles and runs fine all the time
thanks for any help

 

it could be your injector or your plug. Have you checked those? Your plug would be the easiest thing to do first.

 

I should have posted this before but I changed the plug and plug wire and new cap and rotor.
Is there a way to check the injector on this cylinder? By the way the truck has only 54,000 miles on it
Thanks

 

if it has poppet nozzles like mine did before I did the fuel injector conversion, I don't think there is. I guess you could try to rip out the injectors and switch them with one another, but you run the risk of ruining the o-ring and you could potentially leak fuel. The way you would want to go is to just buy a new poppet nozzle and replace the number 4 injector. It could also be your meter body.

Since you did the plug, plug wire, and cap and rotor already, the only thing that I could think of after that would be it having a mechanical problem. Like your valves. Rings. You could check your compression. If compression is good, you might have a flat cam lobe.

 

I was kind of leaning toward a possible injector problem but wanted to see what you guys on board thought

 

Do the easiest thing first. Check the compression. Pulling the injector assembly is quite a task.

 

Someone with the right tools can perform an injector balance test to see if you have a leaking or fouled up injector without taking the engine apart.

A compression check would give you good information as well. You could have a leaking valve or broken ring in that cylinder causing the misfire.

 

Thanks for the input guys.Think I will get injectors checked as I checked compression and it was all within about 3 lbs of each other.