shizn

Hey guys,

So I have an old 2000 3.8L mustang approaching 200k miles. I had an issue with the engine shaking at certain RPMs that I resolved by replacing the harmonic balancer. Upon completing that replacement, I revved the engine pretty hard in neatral to ensure it was working fine, car let out a bit of smoke (I never get on it so that might be why, probably hit 5k rpm during this time but it was only for a second).

I thought everything was fine then when I started driving it I got a Service Engine Soon flashing light at 45mph in 4th. I took it on the highway and it was almost constantly flashing that light (misfiring, could feel it each time). If I keep the RPMs around 1800 and lower it runs smooth and doesn't flash a misfire.

I pulled the codes and got Misfiring in cylinders 1 and 5. I happened to have some spare plugs so I changed those out and made sure my spark wires were routed nicely (I once had an arcing issue once which caused misfiring in cylinder 1). Changing the plugs didn't help and I still throw misfires any time my RPM is 2k or above. I can drive all day under that RPM and it seems fine.

The engine seems smooth as butter at idle or very low RPM. Any time I get to 2k or put any load on the engine it now knocks horribly loud. I was able to replicate the knock on low RPM by going up a steep incline (was horribly loud) but typically no knock/misfire on a flat surface with low RPM.

The only things I can think of would be a coincidence of the coil pack/wires going bad while the car sat for 2 weeks while replacing the harmonic balancer, I blew something revving it afterwards or the new HB's timing sprocket is bad (the new one had had some cheap stamped metal compared to my stock HB, but it was supposedly OEM)

Anyone have any suggestions on where to go next? I could throw parts at it (a new coil pack/wires) but I don't know jack about engine internals so I'm thinking of just taking it to a mechanic or just buying a new car but I'm down to try anything feasible. I can usually follow guides online if I know the right direction to head.

Any suggestions/help would be much appreciated.

Derf00

When was the last time you replaced the plug wires? If you have a miss on Cylinders 1 and 5 inspect the boots on them. If you don't remember the last time the wires were changed, it wouldn't hurt to do so now. The knock is probably caused by the misfire. Fix that first then see if the knock persists.

Also, any areas where the boots contact the exhaust manifold will damage the boot and cause arcing prematurely.

shizn

Probably 4 or so years, same with the coil pack I believe. I rechecked the codes after replacing plugs 1/5 and both cylinders are misfiring again. Ordered some new motorcraft wires and a coil to rule that out but I doubt it's arcing because I checked when replacing the plugs that the boots were clear and the wires are pretty nicely routed + cable tied.

I still wonder if maybe the camshaft position sensor might be having a hard time reading the 'teeth' on the new harmonic balancer (I did confirm that even though it looks different (cheap metal), they are aligned/timed the exact same). I have the old one so if it's possible that is the reason I could remove it again, swap out that base part with the old harmonic balancer and try that if anyone could confirm that might be the issue.

If only I could find an 04 cobra < 15k right now I'd be done with this

Daehawk

He said that in his post so since he didn't replace the wires then it wouldn't hurt to do it now.

Sixer4Life

Mine started doing that right before I shattered a rod... mine had 244k miles on it. Hell I've been inactive on this forum since then but I picked me up a new engine for $700 that only has 34k miles so now I'm back

shizn

Well I replaced the coil pack and wires (motorcraft) and cleared the codes but unfortunately it didn't help and it's still misfiring (same cylinders).

Not sure where to go from here, thinking about putting the old HB back on and seeing if it clears the misfire - if so then can perhaps change the timing part of the HB onto the new HB counterweight (assuming the crank position sensor isn't reading the new timing part of the HB)

PNYXPRESS

You may have gotten the wrong balancer. The 2000 model cars came with two different balances depending on which half the model year they were built.


Also it should have never revved past 3K while in neutral. There is a rev limiter to prevent that.

shizn

It's the right balancer (external), everything matches except the cheap cast metal on the new one

shizn

Just to add closure to this incase someone finds themselves in a similar situation via searching - replacing the timing sprocket on the new balancer resolved this issue. Very odd issue as the timing distances were exactly the same and the part was the OEM replacement. The only difference is the metal was a very thin painted black cast metal whereas the original part was thick aluminum