EFIDynoTuning Forum

Im working with a 2003 Mach 1 that has a rebuilt 97 mark viii short block, 04 aviator heads, 01 cobra intake cams and long tube headers. Everything else is stock. I reused the mark viii timing chains, guides, metal ratchet style tensioners and sprockets because they had less than 19000 miles on them. Ive put a little over a hundred miles on the car so far. Last night when i started it i noticed that it had a very slight shutter or miss. I thought that maybe it was the plugs since ive been doing some tuning on the car that maybe they were slightly fouled. So against my better judgement I drove my kid to practice and it ran good other than the stalling issue ive been dealing with. Driving home in 4th gear between 2-2700rpm the wideband would go from rich to lean and the engine would rev up and down following the afr. And then i heard a weird "whooshing?" noise come from the engine and it lost power and started misfiring extremely bad. I managed to limp it home and pulled the coils and the checked the plugs to make sure it didnt blow a spark plug out. All the plugs were tight. It struggled to start back up but finally did, and then I noticed a weird metallic rubbing/clanking sound coming from the front side of the driver head. The sound was not very loud and kinda faint. It almost sounded like it was coming from the chain that ties the two cams together. Its gonna be a few days before i can work on it again. Anybody have any ideas of what i should look for or what it might be?

I would definitely check under the valve/timing cover. I'm not super familiar with where the cam sensor sits on 4v engines, but you might be able to snake a borescope down there if you've got one and see if you've got some broken chain guides without pulling the valve and timing covers.

sounds like the secondary chain came loose

Decipha can this do lot a damage to the valve train or engine? when you say came loose are you referring to the bolt that holds the sprocket on the cam? And I also want to note that the oil pressure was perfect and coolant temp was perfect the entire time and the engine never made any rattling noises other than the noise i noted above.

Im afraid that one of the cams locked up and broke the secondary chain. I hope thats not the case.

Update: It looks like the secondary chain tensioner had a bolt back out and it came loose. The secondary chain broke. Good news is the cams are not seized. Now i need to pull the valve cover all the way off and get final assessment.

its an interference engine so unless the intake cam was just barely opening a valve whwn the chain came off then you most likely bent or tweaked a valve. I'd think about a 1 in 5 chance you didnt hurt anything. Its possible but not usually my luck.

The plan is to put it back together and do a compression test on it and go from there. Fingers crossed! But I'm definitely not holding my breath.

either way its really not that big of a deal

those engines are simple after you do one you can do the next blind folded

Finally got the mach back together and the compression on cyl 5-8 is 145#. I think i got lucky and didnt bend any valves.