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hi i just bought a mustang and it had a huge miss so what i did was i replaced all wires and the plugs but it seems like the cylinder 5 and 7 isnt firing so i checked compression and it was good on all cylinders and all the same so i tried to swap the firing orders and i put the non ho firing order and it ran little better with that firing order but still has a lagg and seems like its not running on all cylinders someone please help
 

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You need to find the numbers on the ECM and verify you have an HO block (below rear of pass head) if not HO block youll need to verify the cam pattern, youll have top pull the valve covers to find this info.. REport back.
 

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How can I verify it by taking the valve covers off and also why would it run with both firing orders and why would those 2 pistons be down thank you
 

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what about replacing the cap and rotor? Also you can either use an inductive timing light to check for spark, or pull one boot at a time while the engine is running, hold near a metal surface and see if it is sparking/arcing...if not, you know where your problem is
 

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Discussion Starter #6
I've done that all and I'm getting spark but why would the motor run off of 2 diffrent firing orders like the h.o firing order and the non h.o firing order
 

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Discussion Starter #7
When I remove the boot from a cylinder it sounds like 5 and 7 isn't working but I know there is spark going there
 

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Do you have a check engine light on?
If you do which codes do you have?

If you switch the firing orders, cylinders 1,2,6 and 8 will still be firing like normal which is enough for the engine to run.

You SHOULD have a HO which means that it should be the 13726548 firing order.

We need better information of how you are doing your tests and what exactly you are finding. You may know what you are doing, but in order to know that we are giving you accurate help we need to know that you are doing these test correctly.

What I do for a power balance test is put about a 1 inch piece of carbon based vacuum line on all 8 posts of the distributor cap, then put the plug wires on top of the vacuum lines. The vacuum line will conduct electricity so they can still fire the spark plugs and the engine will run fine with them there. Then hook up a test light to ground. One by one touch the test light to each vacuum line. This will give the electricity an easy path to ground and cut spark to that cylinder. Do this to all 8 cylinders and note each ones rpm drop. If a cylinder doesn't drop as many rpms, it's low on power.

This is an easy test that won't shock you and won't damage the coil. Unplugging plug wires while it's running is very hard on the coil since it's still creating voltage without anywhere for it to go.

I would check your timing while your at it too.

If your firing order is correct, and timing is correct, and this test shows cylinders low on power, hook up a spark tester. you can get one for like 5 bucks at autozone. You will then have an adjustable gap that you hook up between the plug wire and spark plug.

If you have spark, then you can move onto an injector balance test which may have to be done by a shop. They can hook up a tester that will open each injector for a set amount of time and compare the fuel pressure drop created by each one. This will find a plugged injector.

Something you could do at home to potentially find a bad injector is to unplug each one, and hook up an ohm meter to the 2 pins. All of the injectors should be comparable to each other. If there is either low or high resistance in the injectors on the cylinders that are down on power, then the injectors are the problem. This won't find a mechanically plugged injector, so if you don't find the issue, a balance test may still be necessary.
 

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Also, I would do a cylinder leakdown test on all 8 cylinders. That is more accurate than a compression test and gives you more helpful information.

What did you get for compression on the cylinders?
 

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Discussion Starter #10
Hi I've done all those tests and I'm getting cylinder 7 and 5 not working but I'm using the non h.o firing order cuz it works better than the other way and a mechanic checked all injectors with a computer and said they are all good and I'm getting spark to all cylinders I checked that too
 

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90 PSI is low... quiet low.

Do a compression leak down test on all 8 cylinders. 10% or under leak down I would consider negligable, but as it climbs from there is a sign of how weak a cylinder is.

If they're higher than that, it doesn't neccesarily mean the engine is done, but if your bad cylinders are worse than the others or if they're all noticeably high it may just be time for a rebuild.

My Escort has 45-85% leak down on all cylinders which it TERRIBLE but they're all bad so it runs smooth... just doesn't make any power.
 

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Also I don't know if your mechanic did it but you could hook noid lights to all your injector plugs to make sure they're getting a signal from the computer.

Also I REALLY lean toward you still having the HO engine. Unless someone swapped in an older engine at some point it has a HO engine. you really need to check that to be sure, which you should find out during your leak down test.

Every 90 degrees of crank rotation 2 cylinders will reach TDC... one on the compression stroke, one on exhaust stroke. As you do the leakdown test starting from cylinder 1 at the top of the compression stroke you'll find out which order they fire in.

Line up the timing mark on the crank, and either cylinder 1 or 6 should hold pressure. The other shouldn't. Then after that cylinder, you'll turn the crank 90 degrees which should line up the next pair at TDC. Then either 3 or 5 should hold pressure. After that either 7 or 4, and either 2 or 8 after that. As you rotate the crank 90 degrees at a time just write down which cylinder is the one holding pressure at that point and you'll get your firing order after 2 revolutions of the crank.
 

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Hi I've done all those tests and I'm getting cylinder 7 and 5 not working but I'm using the non h.o firing order cuz it works better than the other way and a mechanic checked all injectors with a computer and said they are all good and I'm getting spark to all cylinders I checked that too
The cam firing order has to match the firing order of the ecu.
It sounds like this is mismatched from what you are saying.

Verify the cam is of the same firing order as the ecu, regardless of what block you have....
 
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