Misfiring under heavy load

95gt444

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Car misfires only when engine is warm. If rpms are under 2000 in higher gears if you give part throttle is misfires badly. So far new coil, new pip, new wires, and new iac. No change. Mods as follows, codes stored 552 553 565

trickflow street heat iintake
msd pro billet ddistributor
bbk cold air iintake
accel super coil
ford 9mm wires
mac equal shorty headers
Mac offload h pipe
no a/c no smog no p/s
adjustable fpr set at 45
walbro 190
timing at 16 tdc
 

toyman

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I suggest you back off on the timing. Also, confirm that the balancer hasn't spun and the timing is correct. 16* (spout out) is a lot of advance.
 

kb1982

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http://www.scribd.com/doc/13500016/EEC-IV-Codes Your codes are indicitive of the smog garbage that has been removed. Could be part of the problem if you have that stuff removed and not turned of with a tune. When an engine is cold, or a full throttle, systems such as the smog stuff and the o2 sensors arent used because the computer is in open loop. A bad/ dirty maf can cause a misfire at part throttle, that will clear up when at full throttle. To see if this may be your problem, unplug the maf and see if the problem still resides.
 
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95gt444

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Tried unplugging maf no change. Balancer is brand new. All mods are a few years old, just started happening few weeks ago. Did notice that at idle my fuel pressure fluctuates from 40-45 not a constant number.
 

kb1982

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Try unplugging the o2 sensors to force the car in open loop and see if it still occurs when warmed up.
 

toyman

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The O2s are located in the mid pipe before the cats. Just follow the wiring back to the connectors then disconnect.
 
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95gt444

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Plugs look good. Unplugged o2s car would not stay running. Replaced o2s and car seems to be fixed. Had the original ford sensors in it with 108k on them. Another thing that I did notice is as the car warms up my fuel pressure drops. When cold it is 45ish, when hot 34ish. Is this normal? I am running a Mallory fpr, and a walbro 190.
 

kb1982

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Are you pulling the vac line off when checking the fuel pressure?
 
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95gt444

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The msd dist. Has a new pip. I put the oem dist. Which also has a new pip back in last night, set timing at 14 with spout out, runs so much better but pings. Set it at 12 still pings in 3rd gear wot. Car is low on fuel and has some 87 in it. Going to get some fresh 93 try that, and see. With the msd dist. Was running 16 with no ping at all. Balancer is a pioneer Sfi new last year.
 

87hurricane

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My car runs on 87 fine without pinging, even when it's super hot, my timing is set to 12. If you still have stock compression, you really should be able to get away with 14 or so without any issues. Either your markings or timing pointer is wrong, or you've got other issues causing pinging, like excessive carbon buildup.
 

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