My old 87 Dodge d100 with a 318(97,xxx original miles) has been treating me really great for about a year but I was driving on the interstate, which i normally avoid with this truck, and i lost a little power going up a hill and took my exit ramp and at the stop light it was running rough and missing and exhaust was popping about every 5-10 seconds not a consistent pop just every few seconds sparaticly. I got it home changed the plugs(none of the old looked bad) and the rotor and cap which were worn pretty good. wires are about 1.5 years old but nicer wires and look fine has had msd 6a and coil for about 6 mo. I am lost as to what to do next my neihbor said maybe a valve spring was broken or cracked or possibly a burnt/bent valve. how do i test the bent/burnt valve theory? this is my daily driver so I need to figure it out ASAP. thank you so much for your help and input in advance.

 

Do a cyclinder leak down test and a compression test.

 

I did a compression test it looks pretty normal to me i didnt have time to do a leak down test. Im almost positive the problem (miss) is happening on the drivers side cylinders. I have dual exhaust with no H or X pipe and the popping came from that side. But my compression test looks like this 1)139 2)149 3)141 4)140 5)137 6)144 7)151 8)143. if I take the valve cover off on the 'odds' side is there any thing specifically I should look for? I know pieces of metal or obviously damaged parts.

 

with the valve cover off; look it over good for anything obvious then start it and see if any of the rockers are not moving as much as the others...especially number 7.

did you have any "clattering", tapping, type noise from the valve train area?

 

ok i will do that I also did the ol' pull the wire off till there is no difference in how it runs and #5 seemed to make the least amount of impact. I also sprayed carb cleaner all over the intake and main vac lines and got no higher rpm or difference untill i got close to the intake but it was hard to tell if it was getting into the intake at that distance. and thank you sls001 for a direction to head i will update as soon as i get it apart and take a look. - and i wish i could say i had a trained ear to hear for extra valvetrain noise but I cant tell if there is anything stand out

 

Ok I opened up the valve cover and did not see any apparent damage or extra metal I also ran it open and all the rockers seemed to travel the same distance i twisted all the push rods and none seemed bent enough to cause binding as far as i could feel by hand. I triple checked the wires with a known good wire, I also tightened up the exhaust where the header meets the pipes. I ran out of time to tightened the header bolts to the heads but they do not sound like they are leaking.

 

had a similar issue at one time with my 78 318, it ended up being a exhaust valve,had a small chunk missing on the part where it seats in the head,and would pop through the exhaust,every time the valve would close. and also seemed to have a big power loss.

 

I am afraid it is a valve but mine does not pop in any pattern or consistently every few seconds, a couple times if i let off the gas going down a hill or idling it might pop twice quick then another 30 seconds will go by and do another few pops... was the chipped/burnt valve consistently popping every time it would fire in that cyl? but I also forgot that last time I accidently put ethenol(not e85) in and didnt realize it until about 15 gal into it, I am going to run through this tank and see if that helps...

 

Just to rule things out you should consider still doing the cylinder leak-down test

Edit: you should also check the amount of wear on the timing chain\gears by doing a deflection (slack) test

 

i saw that someone said check the timing chain slack. at 97,000 it most likely have slack,along with the weak cam gear that is made from some type of fiber.i would pesonaly change timing chain and gears out.
i put MOPARPERFORMANCE double row roller chain and gears in my 93 318 wich is the magnum engine,made a big differance in power and throttle responce.
i used to have a 87 d100 318,i totally rebuilt the engine,5 angle valve job,bored .030 over,340 cam,bigger valves,the whole works,put about 4,000 in the engine,back in 2004. it was pretty much very powerfull for a truck,would wipe up a few 350 chevelles. 318 has a lot of potential done the right way,not to mention the longevity(how long they last).good luck
let us know how it goes.