I just got done installing new built long block, upon first fire up rpms idled around 1200 then dropped down ,started surging and then died, upon restarting truck would only run above 1500 rpms with my foot on the gas ,revs clean and strong if i let it drop below 1500 rpms it dies out. I am thinking i got a major vacuum leak. IAC is clean and moves freely . I come back to, The builder used tape to cover the intake ports, when i peeled it off it left adhesive stuck to the head I got most of it off but some was still on there. goin to pull intake back off and get every piece of adhesive off and put it back together. Am i on the right track as in a vacuum leak? Thanks for any help.

 

Vacuum leak or ALSO sounds like the problems that have been documented here a BUNCH when the fuel lines disconnect from the fuel filter.

BUT since you just swapped blocks, if it worked right before, it is more likeky something misconnected under the hood

Good Luck

Doug

 

I remember when midsouthbolt put his engine back together he had a similar problem.

Most of the vacuum lines are pretty self explanatory and really can't be messed up or switched except for two. The one on top of the egr and another one I can't remember which. The green line goes to the top of the egr. I would post a pic but I don't have most of those lines anymore.

Good luck.

 

all the vacuum lines are in correct postion and truck did run fine before swap, If it was a fuel ,pump problem it would only idle and when you gave it gas it would want to die out correct? when i rev it to 4000 rpm it smooth and strong boost guage pegs and drops to vacuum when i back off.

 

How long was the engine out of the truck/truck parked??

Reason i am asking is that if the truck sat a while, there is a good chance the rubber hoses in the tank dried out, and then poped off when you put them under pressure again..

Sorry, just re read your post. I doubt that is it.

 

If it runs fine above 1500 but not below, it would not likely be a fuel delivery issue. Other than a vacumn leak.......Is your TPS adjusted correctly? Sensor in airbox?

Good luck.

Steve

 

Don't forget to check the IAC...Idle Air Control Valve....If it is dirty or sticking, the truck will not idle, it will just die when you let off the gas.....

 

AZ, when i installed my built engine My truck did the same thing
What I found was that the base Idle was to low!
Disconnect the IAC and see if it idles. If not your Idle is set to low,
have someone throttle it for you and set the base Idle to about 650rpm's this should take care of your problem! I hope this helps!

Scott

 

Thanks for everybodys help, i pulled the intake and cleaned the sufaces and checked the gaskets, put it all back together with fresh plugs . tried starting almost fired then flooded out , could smell gas so those plugs are wet, read your post scott too late, going to take it to a local shop that works on lightnings and mustangs, i'm done messing with it spent 6 days 5 to 7 hrs a day by myself taking it apart and putting it back together in 105 deg heat, i'm exhausted and frustrated so i just want to drop it off and tell them to call me when it's ready. thanks again for everybodys help i will post when i find out what it was to get it running

 

If you changed the cams and didn't chip it for the cams, it probably won't idle for you.
We just went thru this with a friends truck this week, he put in a very mild set of crower cams and it had a lumpy idle and didn't want to start. I grabbed a PSP 4 way off the shelf that had a little different tune in it and the truck started immediatly and then proceeded to idle like a stocker. His remote start now works perfect. Dale

PS...If you have the option to, try upping the fuel pressure a few pounds and see if that helps.