high rpm, delayed shift, very little power, knocking sound

[muldoon]

1974 gmc, 454. 

I have done quite a few things with the truck, edelbrock 750cfm, holley fuel pump, regulated to 4psi.  All vacuum lines connected and in good shape. 

Electrical is MSD6, HEI redtop distributor, msd plug wires and now new ac delco good quality copper plugs. 

A few weeks ago I bough new headers to replace the old cast headers because the flange was warped on the passenger side and an exhaust leak was present.  I took the truck to have the headers installed because I was worried about the old bolts and not wanting to get in over my head.  This was probably a mistake. 

Truck was running ok before the shop, carb was rich, but I was planning to adjust after exhaust was done.  Would squeal tires on command, drove ok on street and highway.  sucks gas, but what are you gonna do? 

I get the truck back and notice it is not running right.  It does run, but has a rough sound, a bit of a knock every few seconds.  Driving it gives a high rpm, and seemingly delayed shifting.  Very little power.  Exhaust sounds quieter than I remember or expected from new vortec long tube headers.  At the time this happened, I was in the process of moving and didn't get it back in the shop right away.  I assumed they dropped a spark plug or something and that once I replaced the plugs it would be fine.  For some reason I got it in my head that one cylinder was probably not firing correctly and that I could fix it easily.  I replaced the plugs this past weekend and reseated all plug wires.  Verified the firing order, but the truck still sounds and drives the exact same. 

Now I am second guessing myself and not sure where to go with it now.  Any thoughts? 

[ehjorten]

This wouldn't explain the lack of power, but is your vacuum kick-down connected?  That would produce full-throttle like upshifts.

[muldoon]

The truck does not have one.  I can provide a picture of anything anyone wishes to see. 

[timthescarrd]

what transmission?

[muldoon]

I crawled under the truck and using this guide, the pan is definitely a TH400

http://www.hotrod.com/techarticles/identifying_gm_automatic_transmissions/photo_02.html

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It makes a knocking thudding sound every few seconds in park, which was why I did not think transmission. 

[FlatBlack77]

unrelated to the lack of power i know but the knocking thudding sound could be the new headers/exhaust hitting against something like the frame

[rich weyand]

Which side of the Edelbrock is the vacuum advance connected to, driver's side or passenger's side?

[muldoon]

Rich, the distributor vacuum line goes to manifold vacuum, it is on the right; drivers side. 
I do not have any emissions control on this truck. 

The ported vacuum (left/passenger side) is capped. 

The vacuum on the back of the edelbrock goes to brakes. 

[muldoon]

Also, I crawled under the truck to investigate if pipes of anything is hitting the frame.  I do see some minor vibration, but everything appears to clear any metal contact.  I pulled down on the muffler tips to provide more clearance but was able to pass a leather glove between muffler and above metal.  The sound never changed. 

I did take a video with my phone, it might clear up any description about the sound I am hearing.  knocking, occasional thumps.  All of this is in park. 

http://youtu.be/WkVP_c3qgPU

[bd]

Check for a cracked spark plug.

[muldoon]

bd, I thought the same thing and just replaced all 8 with new ac delco plugs last saturday.  No difference. 

[bd]

Flip the distributor cap over and look for carbon tracking and cracks.  Inspect the carbon button for wear and the center of the cap around the button for discoloration from heat stress.  Remove and inspect the rotor for pinhole perforations.  Difficult to be certain from the video, but the sound clip suggests electrical misfire and seems louder closer to the engine.  Another possibility from the symptoms is exhaust restriction - perhaps something was accidentally dropped into the exhaust during the exchange(?). 

[bd]

Here's an idea:  procure a ~1.25" thick-wall rubber hose about three feet long.  Use the hose as a listening tube to try and locate the source of the noise.  The 'tube' generally works better for automotive noises than a stethoscope or long screwdriver, because it is flexible and it suppresses extraneous noises that enter from the sides while "channeling" sound from the specific item you're investigating.

[muldoon]

I'll do the hose listen tomorrow. 

The distributor on the truck is from the previous owner, I do not know when it was installed or the history.  I just ordered a new cfr performance hei online for $55 and it should be here in a few days.  I'll check the old one once I have it off, but really, I am just going to swap it either way. 

Also, while I was on amazon I picked up a cheap IR thermometer to look at those cylinders.  If I have a plug not firing, I should see a pretty obvious temperature difference...  I will update the thread once I have some more information. 

other ideas welcome.. 

[muldoon]

I did two things to try to locate a bad plug.  I started the engine up and let it warm up.  Then at the distributor I unplugged each spark wire one at a time.  As I unplugged each one, I listened for a noticeable change in the idle.  When I got to number 8, I did not hear a difference.  I made sure everything was reseated well. 

Then I used the IR thermometer, that was cool to play with.  Sure enough, number 8 cylinder was consistently lower in temp than every other one.  I took measurements by putting the red dot on the spark plug boot, and at the port in the header for each cylinder.  It was cool to see the operating temps in real time.  All 7 cylinders were fairly consistently the same temp, with the exception of number 8.  When everything else was in the 210 range, 8 was 150. 

I let it cool down, and replace it with a new plug.  Made sure to be very careful with it.  Plugged the spark plug wire back in, same thing.  Runs rough.  IR temps after ten minutes of idle shows number 8 to STILL be consistently lower.  This is the plug closest the back on the passenger side. 

I put an ohm meter on the #8 plug wire, checking for continuity, and then resistance.  I read somewhere between 1.9 and 2.1 ohms.  The wire does not appear to be damaged. 

Then I disconnected the #8 from the alternator and started the truck.  She fired up, I was about to test for arc using a plastic handled screwdriver hovering above the #8 on the distributor but before I got there she just died.  I reconnected the plug wire and she will not start at all now. 

Going to let it sit a while.. going to drink a beer instead now. 

Thoughts?