Engine loses power around 5000RPM

[Jacksboys]

I'd bet it's either dist drive and bushing, or the preload on the lifters. Who assembled the engine? Was the oil pump dirve and bushing new when it was fired? I would pull the distribuotr out, and take a screwdriver to the slot on the drive. Wiggle it. If it moves in any direction except straight up and out, you need to replace them both. If the bushing isnt sized properly when it's pressed in, the drive and bushing can wear out in a verys short amount of time. Seen it twice on rebuilt engines assembled by guys who didnt know about the dist drive broaching tool, or who figured the tight fit would loosen up when it ran. He was right. But at 3K miles, the drive and bushing were worn bad/shot. The fac that another dsitribuor did the same at a different rpm is the hint.

I personally assembled the engine and I checked the preload on the lifters and they were in spec.  The dist. bushing looked and felt good when I assembled it.  The oil pump had about 3000 miles on it from the previous build and did not show any signs of wear.

   If it was the bushing, why would it only cause this problem at a certain RPM?

   A question was asked further back about springs? did you check how much preload is on the lifters?? Are they adjustable rockers??

Also the springs are the Edelbrock versions that come on the RPM heads.  They are suppose to be good upto .575" lift and my cam is only .477" and .480"
As I said above, I checked the preload on the lifter while installing and they were within spec.  I have the non-adjustable rockers.

[ntstlgl1970]

*disclaimer* - this is just my experience.

I would still start with the simple stuff - it's the most common - 97% of the time it will be this stuff

in order:

1. Ignition - plugs, wires, coil output, primary ignition stuff like the pickup coil or + coil voltage low.
2. Fuel - pressure, volume

then *after* you verify
- as in measure/check etc., not just say "well it's new so it must be good"  -
all this stuff, start looking for what I would call "uncommon" stuff which makes up the other 3%

I've had a fuel pump eccentric tab shear off and leave me on the side of the road with no fuel pressure, but I would never suggest that someone pull their timing cover off to check that just because their car runs bad.

[matt63]

I agree that the easy/cheap things should be checked out first.  Don't rule anything out without verifying it first. 

Although it is unlikely that this is your issue, the stock Edelbrock valve springs won't suit all cams.  I would look at Comp Cams spring recommendations/specs and compare them against the Eddy spring specs.  The XE cams are fast rate of lift so they may need higher spring rates. 

[moper]

   If it was the bushing, why would it only cause this problem at a certain RPM?

So was it and the drive new? Or re-used? I cant tell you exactly why to be honest. Just that what you have for symptoms match what I had (except mine was higher rpm). Try wiggling the dist. Another thought occured to me... You can alsotry disconnecting the vaccum advance can and plugging the line. I have seen where a moderate built engine will pull enough vaccum to cause the advance to come in, even tho technically, it shouldnt. If you unplug it and it doesnt miss, then take an allen wrench and add two turns counterclockwise to the screw inside the vaccum can's nipple. Then plug the hose back on, and re-test. I also had that once or twice..

[Stacked440]

Does it almost sputter at high RPM's or is there just nothing there at all.

[Jacksboys]

So was it and the drive new? Or re-used? I cant tell you exactly why to be honest. Just that what you have for symptoms match what I had (except mine was higher rpm). Try wiggling the dist. Another thought occured to me... You can alsotry disconnecting the vaccum advance can and plugging the line. I have seen where a moderate built engine will pull enough vaccum to cause the advance to come in, even tho technically, it shouldnt. If you unplug it and it doesnt miss, then take an allen wrench and add two turns counterclockwise to the screw inside the vaccum can's nipple. Then plug the hose back on, and re-test. I also had that once or twice..

I reused the drive from the previous build (3000 miles), but it appeared in like-new condition and fit like new.

I currently do not have the vaccum line connected because I thought I heard it ping under 2/3 throttle and just disconnected it.  The full advance starts at a low RPM anyway, so it is not a big deal.

Does it almost sputter at high RPM's or is there just nothing there at all.

It is hard to tell, but I do not think so.     It is pulling very strong until it reaches that RPM and feels almost like it hit a wall.   

[Jacksboys]

I did a little testing to day while I had the car out.  I found out that my fuel is not the problem because under full throttle at 5000 rpm, my O2 sensor is still reading rich, so it is not a lean issue.

So I guess I can try a new cap and rotor first and go from there.

[Moparal]

You sure your tach is accurate?

[Jacksboys]

You sure your tach is accurate?

It is a new Autogage tach, so I hope it is.

Is there way to check that?

[Moparal]

Maybe by installing 2 side by side. Your cam is only good to around 5500 and if the tach is off, then you may be getting everything it has already.

[nivvy]

I have the 5" Monster tach in the car and I run a mini tach under the hood... so i can tell if ones ever off..

[Grancoupe]

I would really consider the Coil. If the symptom came back with two different distributors I would rule that out. Not a fan of Mopar distributors but they should work weel enough to get the motor past 5G's. Do you have a spare coil you can borrow from someone?

[Jacksboys]

Maybe by installing 2 side by side. Your cam is only good to around 5500 and if the tach is off, then you may be getting everything it has already.

True, but even if it is a little off, that still would not explain why it would shutter back and forth at a certain RPM, right?

[Jacksboys]

I would really consider the Coil. If the symptom came back with two different distributors I would rule that out. Not a fan of Mopar distributors but they should work weel enough to get the motor past 5G's. Do you have a spare coil you can borrow from someone?

Yes, I can try my father's coil one of these days.

 

It might be a week or two before I can find the time to do more testing.  I have a few family problems that just started, so I will be a little busy the next few days.

[Jacksboys]

Well, I know it has been a while since I posted about this problem, but I have been very busy so it was put aside for a while. 

Update:  I was able to put my father's coil in my car and.....  ..... you guessed it, I still had a problem.  So I have at least ruled out the coil, saving me a few dollars.

I guess I will order some new plug wires one of these days and see if that helps.