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been trying to track down the cause of this mis-fire/pop. as stated earlier the long block was redone and i installed it. bolted up everything and car fired up on first try. had a pop/miss. i checked the coil packs, plugs, injectors, wires, etc...

today i did a compression test, cyl #1 only makes 50psi. imagine that, on a fresh rebuild. looks like the head is coming back off.. i can't think of anything that would cause this besides a stuck/bend or non-seating valve...

When I did my engine swap, I had two plug wires swapped. It would start a little hard but sometimes ok, idle more or less fine, but trying to drive was very hard, popping and missing.

If you've checked the wires and injector harnesses, I'd check the rockers next. Maybe you can pull the plugs and look for one different then the rest. Maybe that can narrow it to one cylinder.

normally i would agree with you j wikoff but his stating only 50PSI on the #1 cylinder tells me compression issue from, like chris mentioned, bent or stuck valve or non seating valve, another thing could possibly be piston rings???

Jeez. Somehow I breezed right over that...

its ok guess we wait to see his results on the pulled head.

tan96ssei wrote:normally i would agree with you j wikoff but his stating only 50PSI on the #1 cylinder tells me compression issue from, like chris mentioned, bent or stuck valve or non seating valve, another thing could possibly be piston rings???

and i got 150psi across the board on 2-6. i don't believe it will be a ring, i took the oil cap off while it was running and plugged it with my hand. it didn't seem like much crankcase pressure was building.

buried at work, will probably pull the valve cover wed. and see if anything looks suspect. after that the head will have to come off. i'm commited to this car now, there is way too much $ in it. i need to daily drive it for several years to get the $ back out...

best of luck to you and good to hear that pressure wasn't building in the crankcase. keep us up to date on this hopefully its something simple.

You can narrow it down with compressed air in the plug hole. Spin the engine over to TDC on #1 and connect shop air to the plug hole, then listen to see if the air is comming out the intake, exhaust or crankcase/oil fill cap. If no large air leaks are found
(less than 20% leakage), suspect a bent connecting rod.

update:

So what exactly is the problem?

J Wikoff wrote:So what exactly is the problem?

the exhaust valve is failing to seat. will update over the weekend, with hopefully a smooth running car...not sure of the valve seat is damaged, valve is bent,etc...

was going to lap the valve but just gave the whole head to my father. will talk with him tomorrow.

had valve cut again, as it was being cut it went, "ert, errrt, errrrt, errrrrrrrrrrrrrrrrrrrrrrrr........"

should be ready to rock! burnouts this weekend if i get head back on...

On a fresh rebuild? What bent the valve? Last I checked, they don't bend themselves.

on stock internals i have never heard of bent valves only logical thing i can think of is valve locks failing and floating the valve (valve floats then piston hits it). only problem is that your not exactly sure why it is not seating. is there to much carbon build-up causing it to not seat? is it bent? best to replace the culprit and get the head and valves serviced professionally to ensure proper angles and seating.

honestly you really raised my curiousity on this one. cause this is a first for me on this site not many break the stock valvetrain it usually requires aftermarket parts to see problems in our heads and valvetrain.

don't believe the valve was bent, just that when the valve/seat were cut it was cut improper. engine never really ran so there was no carbon. this problem occured after a rebuild and i never got the car to run 100% following the install. when i pulled the head the valve and piston looked perfect. must have been the slightest imperfection which prevented a perfect seating valve.

head was at a machine shop earlier this week, head gasket and LIM/charger gaskets come in tomorrow. i'll slap head on this weekend and update...

looks like a compression ring issue. after head work i still have low compression in cyl 1. did a wet compression test and got well over 120...

wonder if the rings will seat in that cyl. the cyl looks fine, no signs of a cracked ring, etc.

it is either put car back together, drive it hard and see if ring seats, pull head again and drop pan to pull #1 piston or yank whole engine again...

arg...

might be time to throw in the towel. this car is taking a lot of my time...

how would a bad compression ring [low compression] cause this pop? i didn't notice any signs of high crankcase pressures which is weird.

Before you take the engine apart again, you should really do a leak down test to find out for sure where the pressure is leaking. I know you got 120 with oil, but that doesn't explain the poping. The poping part sounds like a bad/sticking valve or worn cam lobe? The compression results sound like bad rings? I guess what I am trying to say is, if it were me, I would want to do more testing before tearing.

found the issue... engine has the wrong connecting rod in cyl 1

How'd you determine that?

Mechanical Mike wrote:How'd you determine that?

pulled head/pan. pulled piston, looked fine as did rod. put piston back in and rotated engine over by hand. notice cyl #1 came up short on tdc...