I have an 1977 454 engine in a 1980 short bed stepside truck. the engine was rebuilt, the truck has been driven about 5 mikes since the install, just can't get it right. The timing is good, oil pressure is good, and it does not overheat. It also idles great, sounds great, but misses and pops with it has warmed up and loses power under load. it has dual exhaust, the problem is on the right side, any idea's?
The engine was rebuilt but what kind of parts were used? Does it have flat top pistons or pistons with domes on them? What kind of camshaft did you use? What type of heads were used, a good set of large oval port heads like the 781's or the 049's or a set of peanut port heads? Did the block have all 4 corners checked for being square. What compression ratio do you have? I know when I rebuilt my 454 engine I checked my piston to deck height and was shocked. I had .017 on #1 cyl., .016 on #3 & .015 on #5 cyl. and .019 on #7 cyl. and the right bank was just as bad. I had to disassemble the short block and take it to the machine shop to have it milled. Have you done a compression test yet? If that checks out do a leak-down test too. I would hope maybe it is something simple like the advance curve. Have you pulled the valve covers and used a remote starter switch to turn the engine over to watch the rocker arms to see if the valves are opening and closing the same? Have you readjusted the valve lash since the breakin? There are so many things to check so get some of this done to see what you find out.
please print and perform this test first.. http://i.imgur.com/Mo57rdb.jpg there will be a power distribution stud on the firewall to perform test 5 to..
lack of grounds can make some engines go haywire.. its only about 5 minutes to perform
next i would like to look at the HEI distributor.. and this is just because i have run into issues before..
i am taking that the spark plug wires are in holders.. not bundled up together.. please verify the spark plug wires at the spark plugs are not burned thru on the headers and are not loose on the spark plugs.
mark the wires with some masking tape and numbers at the cap ends.. making it easier to reinstall. sometimes you can if the wire retaining ring is not installed on the cap. one can remove the 2 screws and lift off the coil cover.. examine the area where the coil wires are.. there should be a folded metal strap that was installed prior to the installation of the coil in the cap.
without the strap the coil will not be grounded.. it may be destroyed in a violent fashion.
please remove the coil from the top of the cap. lift the silicone seal.. the carbon contact should be in the cap UNDER the silicone seal.. contact first.. seal.. coil... in that order..
inspect the sides of the coil for discolorations like these.
with the cap off.. please examine the RFI capacitor harness.. i included some part numbers in the lower left corner to make replacements easier to find. do you see the cap mounting screw.. that also connects the coil ground connection to the distributor housing.. the screw must not be loose..
with the cap off.. please examine both sides of the ignition rotor for signs of burn thru .. look up inside the cap.. there are Four flat spots where the coil mounting screws are located. if there is a bump in the middle of the flat area.. the coil screws are too long and are busting thru. since the coil frame is grounded. . if the screws come thru the plastic. it will steal the spark as the rotor passes and cause the weirdest misfires you have ever scratched you head trying to find.
next with the cap off.. and a bright flash light.. examine the sides of the pickup coil.
warning.. some aftermarket imported distributors have a slightly offsize diameter pole piece.. they hit the stock GM distributor reluctor tips.
these are just things to check in HEI distributors.
if you can describe when it backfires or misfires.. it might help with a diagnosis.
Can you give us some information about your engine. Post the casting numbers of the heads. They are located under the valve covers. Type of distributor you are using. Anything you have check out so far.
If the problem is only on one side i would look for a tight valve or a vacuum leak to start. Also triple check the firing order. it is real easy to mess up 5 and 7
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