Hey guys, i know im young to be posting a technical problem but my dad did not want to go downstairs and boot up his computer just to get his user name.he looking over my shoulder soo..... One of our trucks is a 93 intercooled CTD 518 auto truck that is COMPLETELY STOCK. When the truck warms up from a 50 degree start (2 minutes warm up about) the engine starts to surge in RPM's pretty severely. It has a factory tach and it seems its at about 600 on idle,not exact but no more than that and by the factory tach its saying its moving down about 25-50? rpm (guess,tach is hard to read) every time the idle surges down.it doesnt sound like it would stall when the rpms go down at all. Maybe its the other way around and is bringin rpm up on every surge?? We dont know but we know it could be the lift pump but it looks shiny so it may have been replaced. Should we turn up the idle screw?? Timing?? water fuel seperator??? Has anyone had this problem before? Thanks for any replies.

crossy and son

 

Fuel filter, first. Also check to see if the jam nut has backed off and let the idle fall a bit. Does the truck die with your foot on the brake and in gear?

 

no truck runs great does not die at all. lots of power for a stock truck. as soon as you tap the pedal and bring the rpm off of the rough spot it runs like brand new. brandon

 

Head scratching..... I dunno, bump the idle a touch maybe.

 

Sounds like the idle spring is broken/mashed.

 

Dave,it figures the day you were in our yard the truck would not start to run rough like that when you were listeining to it purr. now it does it again...dad said he'll probably bump the idle screw and change fuel filter if he feels like it.but the truck is F/S so it will not help to sell if it is running all rough the buyer could thing the IP is goin out which i know its not. thanks for the input guys

 

If it idles at 600 rpm, it needs to be brought up a little. I think the data tag calls for 750-800, depending on which version you get.

Is it a sudden surge, or is it more slow and gradual in its up and down? If it's slow and gradual like a Big Cam III with 900k mi, it may just be the nature of the beast. If it's faster and more erratic, it may be a fuel supply issue.

Daniel

 

my 93 auto did the same thing, 5 bucks says it the return springs on the pump head, mine were broken in three diffrent places, but besides the surging it ran great, mine droped the rpm quite abit, after i put the new springs in all was fine

 

Mine did that and it turned out to be the injector pump

 

What do the return spring do exactly? Mine does this once and a while and I always thought it was the turbo.

 

it is a sudden eratic surge..i dont think its the injector pump because the truck runs really strong for a bone stock intercooled truck. as soon as you tap pedal the surge goes away...the truck does not smoke at all..on startup or WOT. thanks guys

 

We ought to do a 3200 RPM spring and take a look at the idle spring...

 

my dad seems really weery about the truck..he wants it gone bad..he wants to turn the idle up to make the surge go away and dump it quick.then sell the 727 truck and then use money to make the 5 speed a prestine show truck..we picked up a 92 d250 with a 318 with 50000 miles that burns our 727 truck from a dead stop.