But it starts. '99 F250 PS. Had code P1670, cleared it. No other codes. Started truck back up and ran KOER test with AE(which I'm not very good with). The code did not come back. It is hard to start plugged in cold or warmed up. I have WTS light and it goes out(glow plugs are original). RPMs are slow to come up (almost starts before it kicks in). Doesn't matter if fuel tank is full or not. Oil level is fine. Batteries are charged and check good. Starter checks out ok. Buzz test was ok. Now when I run KOER do I need to do anything other than hitting the initiate button?

 

KOER isn't going to tell you anything.

Do you get smoke out the tailpipe while cranking, or is it just cranking like the batteries are almost dead?

Put a volt meter on one battery and watch to see the voltage drop when the key is turned on, and again when the engine is cranked. Repeat for the other battery. If RPM's are slow, then batteries, cables, connections or the starter is suspect.

 

When you say hard to start...do you mean it cranks fine but wont catch or is it slow to crank?

 

volts on each battery would drop to over 9 plus. That was with key off. pretty much the same with key on. the thing I am seeing is the rpms do not come up until the truck just about fires off and run.

 

If I am reading this right... you have just over 9v on the batteries with KO? That isn't enough for it to fire. These engines need a minimum of 10.5 to even fire.

 

10 plus with the key / glow plugs on is the lower end of where the truck will still start up without struggling.

If both batteries read that voltage, and the grounds are good and not corroded, then I'd say it's time for new batteries. To confirm, try jump starting with another diesel truck and see if it starts easier. Or if allowed, swap batteries for a minute and try it.

 

I know 10.5v is the ideal, but I have seen these trucks fire off with less than that.

The 9v plus is with the engine cranking over. Voltage is 12.8 plus KOff

The problem I see is the rpms do not come up until just before the engine fires off.

 

]That was with key off.]

That was with key off, just cranking the engine over, but not starting.

 

Don't focus too much on that. Just monitor the RPM's to see if they move while cranking. The rpm signal isn't mechanical, so there can be a delay before you see movement. If the engine starts to crank and the tach or scanner is still at zero, it's obviously wrong.

Welcome to the wonderful world of electronics that's supposed to make our lives easier.

 

Replaced the starter. Starts good now.

 

Always was amazed at how replacing an old tired starter.... would make a truck crank like it was brand new again