Hi

After some months fixing the blown head gasket, grinding valves, finding out messes prior fixes caused, etc. The 2004 Discovery is back on the road but my iCarsoft analyzer is reporting issues that are revealed by uneven running...

Besides the oxygen sensors that I knew needed replacing after this head job, it reports misfires on cylinders 2, 4 and 7.

I am using new Champion Platinum plugs and a Magnacor "competition" spark plug set. I'm reasonably confident that I have the cables plugged into the correct holes in the coil assembles.... so what would cause misfires?

 

Bad coils could, but with those being on opposite sides I find that unlikely (but still possible). Injectors are also an idea (had to replace some of mine today), or a vac leak. Get a cigar and do a leak test. Double check your plug wiring too. I know you're pretty sure, but double check just to be safe.

 

LRguy, I had lost track of your thread. I'm glad to see that you've finished your top end rebuild.

Since you have problems on both sides and on different coils, and if you are sure that you have the coils wired correctly, I agree with Alex that you probably have a vacuum leak. But I have had more than a few misfires and have some ideas for things to check. I assume you have a scanner...

Check all of the harness connectors on driver side of upper intake.

Check scanner for any codes or pending codes on 02 sensors. I swapped an old o2 sensor in a couple of weeks ago and my engine started misfiring. I didn't even know that was possible. I swapped it back out and the misfire went away immediately.

Spray starter fluid from MAF to intake, then on all vacuum lines and connections. I remove my fan when I do this just so it doesn't go everywhere and so I can hear. Listen for change in engine. Listen for a hiss anywhere indicating air being sucked in.

Did you remove the fuel rail? Did you replace the injector o rings? Did you lubricate the new or old o rings when you pressed the fuel rail back in? They are easy to damage and it is hard to find a vac leak there with a smoke test die to the location.

Did you reattach the grounding strap on the driver side head (to the firewall)? This has to have good contact.

 

Hi

I have handed the car over to greater Rover minds than mine....

I did not remove the fuel rail so O rings are original. I replaced the rear ground strap with a slightly longer starter cable between the same two points.

At the time, I saw that the gasket blow to outside had only burnt away the gasket and there were no marks on the head and block of any significance so I gambled (20:20 hindsight shows the bad choice) that the head did not need machining. But new studs, new gasket, and tightening just as instructed, it blows between cylinders this time. That needs fixing again....

Current thoughts, to be confirmed, are that the valve gear is fine, sparks get to all plugs (but intermittently), but the flex plate may be the issue. There is also a vacuum leak and oxygen sensor issues to be looked at.

 

Wow. You are the first person I've ever known who demonstrably needed to plane the heads. I have read that exhaust can cause a groove in the head surface or the surface of the deck, but never seen in even in three sets of abused heads (on separate engines). Very sorry to hear of your troubles after such an effort.

 

Hi

Here's the original photo I posted... not exactly a groove where the gasket blew....

 

Its pretty common practice to plane the heads. Not because of a groove but because of warping, especially near the rear water jacket where they warp the most.

Also, my friend uses a honing stone on the block(fine side) to make sure its flat, you can see sections that are high and low when you pass the stone over the mating surface.

 

you take an expensive gamble when not decking the heads.

not only are you gambling with the $200 in gaskets and bolts,
but your gambling with 8 hours of labor, be it yours or someone else.

two pieces of metal bolt them together under torque and run them thru several thousand heat & cool cycles,
do you think they will warp?

 

I agree. I meant I've never known of anyone who said they weren't going to plane the heads, risked it, and then immediately had a problem. I've done both ways (planed and not planed, on different engines) and not had a problem either way. But I planed the heads on the one engine that mattered, which immediately ruined itself on other grounds.