Lope at idle

[V8Astro]

My 08 always had a little lope to the idle when fully warmed up. I recently had the left head off to replace a piston and rod. I added a GM5 turbo at the same time. Replaced the IP and all 8 injectors from Taylor Diesel. The truck runs better than ever but the idle lope it still there. I think it may even be worse than before.

When I turned in my injector cores the rebuilder noted that I had 7-6.2 injectors and 1-6.5 injector. I was sure that was the cause of the lope. I kind of forgot about the issue until I got everything put back together. The truck runs GREAT other wise. Lot more power with just 7psi boost. The engine idles around 550rpm. If I raise the idle to 650-ish the lope is almost gone. It will glide down the highway smooth as a Caddy.

I don't understand why this would only happen at idle. If I had a weak cyl or faulty injector wouldn't it get worse as RPM or load increased? After a few searches I read about return fuel issues. I get fuel on the way home I usually leave the truck running (since it's been so cold). When I twist the fuel cap loose I can hear it relieving a lot of vacuum in the tank. I wonder if this has something to do with it? Is the cap supposed to vent? Or where is the tank vent?

 

[RustyM923]

Isn't the idle supposed to be 625 RPM?

 

[Iceman3005]

The lope is ok, mine does it too! Its is funny because everyone thinks it has tons of horsepower. A diesel that lopes usually has a lot of power, look at youtube in the search box type in loping diesel!

 

[hovenga67]

It is probably sucking air some where. My uncles is doing the same thing. We sprayed a little ether around the injection pump and it idled up. So his is sucking air at the pump.
Brent

 

[nyoffroad]

It is probably sucking air some where. My uncles is doing the same thing. We sprayed a little ether around the injection pump and it idled up. So his is sucking air at the pump.
Brent

The IP will not ''suck air" you may have an air leak at the intake manifold near the pump but not the pump itself. It is also very possible that the engine sucked some ether in thru the air cleaner.

 

[hovenga67]

I disagree. On the low side it can pull air in. I have had it happen on power steering return lines as well. I didn't get it anywhere other than pump. This isn't my first rodeo. Bottom line is it shouldn't lope. It is probably getting air in the system somewhere.
Brent

 

[V8Astro]

I did a few searches and read that I can use clear vinyl hose and put on the pump return fitting. Maybe I'll try that see if I got any bubbles.

 

[Iceman3005]

So if it starts good, runs good, gets good fuel mileage, has a good amount of power with the new pump, injectors, and turbo, then why are you worried about the lope? Besides you said it is almost gone if you set the RPM correctly at 650!?!

 

[donalloy1]

So if it starts good, runs good, gets good fuel mileage, has a good amount of power with the new pump, injectors, and turbo, then why are you worried about the lope? Besides you said it is almost gone if you set the RPM correctly at 650!?!

In gear warm ...what is target rpm? I lope/stumble a little below 500 +/-.

 

[Hasdrubal]

I believe the target is set in park. It states what the idle should be on the air cleaner. In gear, someone with tach said they saw a 100 rpm drop.