Just about out of ideas

[04comporangegt]

I just had the stock 4.6 block in my 04 GT rebuilt with forged pistons, stock crank and rods and comp cams. Now it idles great and is driveable but if you rev it and hold it around 2500 - 3000 rpm it loses a cylinder and starts running rough and something up top starts ticking but if you let it idle back down after about 30 seconds it runs fine again. We replaced the timing chain tensioners because thats what Ken at MD thought it might be and it still does it. We are going to replace lifters next. If anyone has any ideas let me know please. We are stuck. Everything runs fine until that rpm range and there are no check engine lights on. Thanks.

[bobtsgt]

did you have the top end all apart?
did you prime the lifters when you put the heads back on?
are the cams timed properly?
did you degree them?
have you pulled the plugs to see which one is or to see how the motor is running?
Also check out all your sensor plugs to make sure non are loose.
Does it jerk real hard when you hold it around 3K?
does it do better above said RPM?

[04comporangegt]

I am not sure if he primed the lifters or not I will ask him. The top end was all apart and a couple valves were replaced. The cams are timed properly but I don't know if he degreed them. They are the comp cams XE274H so they have a shorter lift on them and Ken at MD said they would not hit with the shorter lift. We have not pulled the plugs but we disconnected the coils to see if we got the ticking noise from when it shuts down and it didn't. I will check the sensors. It doesn't really jerk it just runs rough like it is out of time but it goes right back in when it idles a little bit. It will run still while it makes the noise but I am afraid to go much above 3000 rpm. I can't afford to rebuild it again. LOL.

[bobtsgt]

yeah they won't hit. I have the same cams in my NPI heads and shortblock. I hear ya on not wanting to do it again. Did you do the upgraded valve springs too? It would run like crap if it wasn't timed properly. You may have a fuel problem like mabey a clogged injector. Can you tell which bank the sound is coming out of?

[04comporangegt]

Yeah It runs fine though until 3000 rpm so I don't think it is the timing. We think it is coming from the passenger side but it is hard to tell. I didn't think about the injectors.

[na svt]

Mod motor cams should always be degreed because of all the slop in the hardware that drives the cams. Whether they will hit or not does not determine if they should be degreed.

[bobtsgt]

true. especially going from a stock cam to an aggressive one like the 274H. it is possible to do it in car but its not the funnest thing to do. Pull the plugs and see what its doing. have you gotten it tuned yet with the new cams? also have you cleaned all your sensors like MAF and IAT?

[04comporangegt]

It was on the dyno and it started doing its thing and they did not want to run it so it did not get tuned. We are going to check the plugs and put new lifters in today after I get off work. I will ask the guy about degreeing the cams also.

[bobtsgt]

Do clean your sensors out though just to be safe. Only takes a couple of minutes. Also prime those lifters before you put them in. That way you can eliminate that as an option when you start it back up. When the valves were replaced did they lap them in and check the guides for wear and check the specs?

[04comporangegt]

Yes they checked the guides and specs. I have never built a motor before how do you prime the lifters?

[bobtsgt]

you take a bowl full of oil, put the lifters in the oil and let them soak a little bit, then take a paper clip and you shove it in the hole til you feel the spring inside. Then push on the spring back and forth. You do this while the lifters are submerged. You should be able to see little air bubbles coming out of the lifters. Once primes leave it in the oil til you are ready to put them in and button everything up. That way the lifters aren't waiting for oil to pump them up which sometimes causes the ticking sound due to dryness.

[04comporangegt]

Cool Thanks

[na svt]

It sounds like one of your lash adjusters is pumping up and not allowing a valve to close.