Foxbody misfire

Austin5.0

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Mar 2, 2020
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I have a 1990 mustang lx that has a bad misfire. It goes away up above 3,500 rpms but any lower than that it runs horrible. It runs super rich, and it will only run with the distributor all the way advanced. The car will idle for about 5 mins and out of nowhere it will cut off. From what i was told by the previous owner it has
F303 cam
24 lb injectors
BBK mass air
Edelbrock intake
Stock heads
Charcoal canister removed
 
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TOOLOW91

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I have a 1990 mustang lx that has a bad misfire. It goes away up above 3,500 rpms but any lower than that it runs horrible. It runs super rich, and it will only run with the distributor all the way advanced. The car will idle for about 5 mins and out of nowhere it will cut off. From what i was told by the previous owner it has
F303 cam
24 lb injectors
BBK mass air
Edelbrock intake
Stock heads
Charcoal canister removed
For starters being that it does run . How about set the timing correctly . 10-12 deg BTDC spout out . Then once you know the timing is correct pull the plugs and see which are fouled / not firing . Check the plug wires , cap etc . That bbk mass aid isn’t helping your rich condition . Nothing on your car indicates it needs more fuel then stock 19lb injectors .
 

Austin5.0

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Mar 2, 2020
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For starters being that it does run . How about set the timing correctly . 10-12 deg BTDC spout out . Then once you know the timing is correct pull the plugs and see which are fouled / not firing . Check the plug wires , cap etc . That bbk mass aid isn’t helping your rich condition . Nothing on your car indicates it needs more fuel then stock 19lb injectors .
For starters being that it does run . How about set the timing correctly . 10-12 deg BTDC spout out . Then once you know the timing is correct pull the plugs and see which are fouled / not firing . Check the plug wires , cap etc . That bbk mass aid isn’t helping your rich condition . Nothing on your car indicates it needs more fuel then stock 19lb injectors .
 

Austin5.0

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Mar 2, 2020
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Thanks for the help I will check the timing next week. The guy that I bought it from said that the more he drove it the Misfire kinda went away.
 

TOOLOW91

If you're the village idiot what's that make me?
15 Year Member
Nov 29, 1999
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Thanks for the help I will check the timing next week. The guy that I bought it from said that the more he drove it the Misfire kinda went away.
Yeah that’s not exactly a fix lol
 

jrichker

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Dump codes sticky



Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/
 

junkyardwarrior

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Jan 10, 2011
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Doesn't matter at that point. 0 compression means there's a problem. Start digging. It's gotta come apart anyway. Remove rocker cover first and look inside. Ok? Move on to removing the head. Hopefully it's not too bad. Something that one could do in a case like this is a leak down test; and with 0 compression you really don't need a leak down tester. A lot of compression gauges use a standard I-M air hose male fitting on the adapter hose. If yours does, remove the shrader valve from the hose (if it has one), screw the hose into the cylinder with that piston at top dead center compression stroke, and apply air pressure to the hose. If air comes out of the throttle body, you have a leaky or bent intake valve. Out of the exhaust pipe, leaky or bent exhaust valve. If air comes rushing out of the oil filler, may as well plan on pulling the engine.
 
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Austin5.0

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I pulled the heads off and cylinder 4 and 8 and the intake valves are slightly open. All the other valves look like they are fully closed. And there are a few tiny scratches down in the cylinder of #4 that u cant really catch your fingernail on.
 
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