Misfire, can't find problem and have tried everything. Please Help

Is the plug wire isolated away from any others?

 

Valve springs look fine. I have watched the rockers move at least 5 times and see nothing wrong. I have changed the plug wire twice and ran it away from all the others.

 

Maybe go over the order and maybe even try the other order..

 

Broken valve springs are tough to see sometimes. So, quadruple check it.

Hydraulic cam?

If so?.. then the lifters may be pumping up during running rpm and not showing issue on the compression test since oil pressure doesn't top out during cranking speed. Back off the rockers and readjust both(I/E) valves. A RUNNING compression test like Darren mentioned a long while back would show these types of issues. Be sure to release pressure on the tester a few times after the car has started for improved accuracy.

If no broken springs.. or that running test/valve adjustment doesn't do it?.. then you need t start over from square one and separate each individual system during troubleshooting because you're obviously missing something along the way. All things mechanical related don't cause mysteries unless something is missed. Which then makes them more like.. missed-eries.

 

Thanks for the help. I am going to take some time off from working on it. I am going to reinstall intake and check rockers, then my mechanic is going to come over and give me a hand. I will let everyone know how it turns out. I just need to let it go for a week or so b/f I lose it.

 

Vacuum gauge helps me figure if it is mechanical. Gives a good hint where to start. No point chasing ignition and electrical if its a mechanical issue. And yes you can have a good static comp test a fail a running test. A good static test doesnt take much of a valve opening to get good numbers. A running test will pick that up instantly.
Agree bigtime he needs to start over. Was just trying to give him a starting point. I spend a lot of my time chasing misfires here . Shoulda been a plumber!!!!

 

Just because the valves are moving doesn't mean they are functioning properly.

A proper compression check will show variances in cylinder pressures. Once you have that baseline, if the cylinder in question appears to be lower in comparison then you do a leak down test to ascertain whether it's a ring or a valve issue.

If you are running adjustable rockers and one of them is to tight, it can cause the problems you are having.

Without the numbers from the compression test and further investigation after you know the results, we're sorta shootin' in the dark here.

 

I understand that! One more thing I can think of, is there a vacuum line port on that cylinders intake runner? If there is and you have a vacuum leak, that will cause a misfire on that cylinder! I had that issue once on a car with vacuum power brakes. The booster leaked somewhat and caused a miss. This was noticeable mostly at idle and slow speed, though.

 

Hi fellas,
I know it's been over a year but still haven't figured it out. Took it to mechanic, he couldn't figure it out. He Caught carb on fire and gave up, said it was internal. I dissasembled and reassembled entire engine this past winter, everything except dropping the crank. Measured and checked everything. Motor looks brand new and all measurements were spot on. Found 5 slightly bent intake valves and one bent exhaust valve. Had fixed and reassembled engine. Fired it up and still has misfire, popping through carb again, fire and all. Tried all new ignition components and no difference. Tried brothers carb, no difference. I think it is timing but we can't fix it. I know it is tdc. We even tried 180 off. I know it is Ho firing order because I looked up the cam card. What am I missing.? I am so frustrated the mechanics don't even want to look at it, all they do is tell me I've done everything they would do. HELP!!!

 

I just read through this whole thread and suggest you do the same. Some really good advice was given and more than one suggested running a compression test and posting the results. One step at a time........

 

You pulled the engine apart and found bent valves...You needed to determine what bent em before putting it back together. You may have way too much valve lift causing the pistons to hit the valves...This usually bends intake valves as you noted, you have em. Other main cause of bent valves...Incorrect mechanicle timing/Push rods are way too long causing valves to hit pistons let alone not close properly...Did you notice if you had any bent push rods...Either way...Tear it down again, I bet you have more bent valves...My guess...too much valve lift/incorrect mechanicle timing/wrong length push rods...Good luck man.

 

You said this was an 89 5.0. Which 5.0 is it ? What pistons are in it ? For what application ? Do they have valve reliefs ? What cam do you have in it ?

 

Engine is 89 5.0 ho out of mustang. Stock bore and stroke, Ford racing pistons with valve reliefs, Ford racing rods (not bent), Aluminum Ford SVO heads with ford racing valves and seals. Machine shop fixed bent valves, replaced all seals and flow benched heads also checked pushrods and none were bent. Lunati street strip cam with HO firing order (looked up cam card to be sure). Proform 1.6 roller rockers, adjusted 3 times and all at 1/4 turn preload. Compression reads 170 to 175 for every cylinder. Cannot do running test because it is backfiring through carb so bad, feel as if It will break something. I think it is timing but don't know how it could be off. I have even unwrapped every wire that is ignition related to make sure nothing is crossed or broken. I believe I bent the valves by over-revving engine, I don't baby this thing.
My brother in law is helping me through all this and he has built several high performance engines, mopar not ford, and he is stumped as well.

 

I have tried different plugs, wires, distributor, msd box and coil all to no avail. I think it is timing because of the carb backfire, doesn't that mean it is igniting opposite of when it should. I have also timed it to TDC and then 180 off.

 

Check cam clock/timing with index wheel?