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97 ETC 89 Coupe Deville
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46 Posts
Discussion Starter #1
I have a 97 Eldorado ETC,It Has A Misfiring.The Plugs Are New And Gap Right,The Wires Are New.I Pull The Codes And I Got U1255,And No PHN Data.Thank You For Any Help To What Misfiring May Be.....:banghead:
 

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90 Eldo -SOLD-, 98 ETC -SOLD-, 86 XR4Ti Track Car, 07 Ranger
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963 Posts
fuel and spark and cylinder leakage, those are usually your 3 culprits.

spark: you have new plugs and wires, good, are all the wires properly seated on the plugs? The boots can 'shift' a bit and prevent good contact on the plugs, make sure they're all locked on and 'click' when they engage the plug. Get a timing light on each wire to make sure it's firing from the coil, i.e. bad coilpack. Also check it in the dark to make sure none of your wires are arcing...

fuel: check for a leaking fuel pressure regulator, put a flat head screwdriver on each injector body while it's running and put your ear to it, are you hearing each one tick? Worst case, get a fuel pressure gauge on your fuel rail while it's running and see what it's doing, bad fuel pressure, if you have a good FPR is most likely a bad fuel pump

compression: do a leakdown test, the procedure is simple but it requires some tools to do it properly as well as some of your time, but it will diagnose intake valve leaks, exhaust valve leaks, ring damage, and headgasket failure, totally worth it IMO...
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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71,110 Posts
These diagrams are important. If the wires are not connected to the proper coil tower, you will have a miss. Google "waste spark ignition" to find out why.
 
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