Hey all,

My current '91 W250 doesn't start nearly as well as my old '90 D250 when its cold outside. The W250 idles rough for a few minutes unless I keep on the accelerator! My old D250 would put out a little diesely smoke for a few seconds, and then be fine - or so my memory reminds me!

Could it be that one of my grids isn't warming up the air? The volt meter drops like it did on my last truck though.

Or could it be that my idle may be different on this truck? OR what does timing advance/retard contribute? I have a rebuilt pump/injectors on the W250 and my D250 was all original.

Thanks a lot,

Brian

 

Is your KSB solenoid working? When it is cold out, there should be at least 10V to the terminal on the KSB unit -- the solenoid looking thing on the side of the pump. You should be able to disconnect and connect that wire, and hear a significant difference in engine sound.

It is also possible that your overall timing is retarded due to faulty rebuild or install of the pump.

 

As far as timing is concerned, the O on the cam gear lines up to the E on the pump gear which as I understand is correct. Plus, I had it 3/16" above the factory mark which gave me turbo boost at higher RPMS. At the factory mark, boost seemed to come much sooner. I take this to mean the timing at 3/16" above was "advanced". The rebuilt injectors pop teested higher than stock for some reason, about 300 psi. Not sure if that is wrong. I will check the KSB. I secured the wire to the solenoid with an "O" connector and nut instead of the spade connector to make a better connection. At that time I knew it to be working, but will double check.

 

Your timing gears are lined up properly. Yes, advancing the pump (toward the cylinder head) will give you more top end/a little less bottom end. Boost will be lower overall with advanced timing. If your reman injectors pop off at a higher psi, you need more timing yet to compensate for the later injector event. 300 seems high, if memory serves...Push your pump toward the head some more and see if it runs better.

 

A point of clarification -- it is possible that the pump was rebuilt to be too retarded, so even if your drive gear is timed correctly, etc., it could be retarded. The only way to tell for sure is with a dial indicator or piezo-electric sender. Anyway, I was not trying to point the finger at you!

 

I tested the voltage at the KSB, its way up at 12-13 volts.

The engine runs smoother if I just barely touch the accelerator pedal. It makes me think the idle is brought down just a hair when its cold out. Maybe the oil is thicker or something??? Or does the idle have to be adjusted up when the pump is rotated towards the head?

Thanks,
Brian

 

They do idle slower when they are cold. Combustion is less efficient and there is more drag from thick oil, both in the engine and the transmission.