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Hello, this sounds like you may have a vacuum leak or a failing coolant temperature sensor, the engine must run a little rich when cold so if there is excess air the engine will not run as crisp, also if the coolant temp sensor is stuck more to the hot side then it will make the ecm run more to the lean side which will give you the same effect. there is a very slight chance it can be because of the mass air flow sensor and the tubes you , so if all else checks out fine you may want to see if a different angle of the tubes helps direct flow across the air flow sensor properly. i had a personal experience where the air flow at low speeds was not passing directly through the mass air flow sensor so it made the ecm run lean causing misfires for no reason. hope this helps, Lou P.
ok you will have to ohm the sensor at different temperatures to see if it matches the chart. ill try and get you the chart .
as for the engine swap it should not matter that much. if it did the engine would run like that no matter the temp i would assume. so lets rule out the other items first.
dont forget about the vacuum leak.
here is the chart
also a sticking idle air control valve would also cause a vacuum leak fyi, just an internal leak.
My apologies I will have to opt out to let another expert assist. I will not be able to respond until Sunday and I do not want you waiting on me. Lou
do you have the gt40 or gt40p heads?
are you using the mustang ho cam firing order?
did you have problems with the spark plug angle?
what firing order are you using, the 137 or the 154
what did you set the base timing to on the distributor?
did you use a timing light?
I just got done rebuilding a 1995 302 ford it was for a boat tho, but same thing.
are the plugs hitting the manifold?
20 at idle seems like alot of advance at idle. I set mine to 10 at idle.
nice. I heard alot of people having problems with the location of the plugs on the gt40p heads
I have a 351w cam and 351w heads on mine, it makes a ton of torque, but its a marine engine.
does your heads have the egr holes in them?
I think i'm thinking about the gt40 heads not p. I dont think the p heads have the holes that need to be plugged.
you should put a vacuum gauge on it and see what it does when its running rough.
do you think you have a misfire when cold?
have you tried cleaning the throttle body and mas air sensor
did you check compression?
its alot of work.
were you able to get any codes?
what it you have a stuck piston ring, then when the piston warms it expands then seals.
while its running rough, pull a plug wire off the dist cap one at a time and listen for an rpm to change. use a pliers with rubber handles and wear gloves.
that way you can narrow down which cylinder is missing. then focus on that cylinder.
I am here to help, you got the best ford 302 tech on here lol
Let me know what you come up with.
Hello again Dan here,
I am contacting you because the post has not been closed or rated. We have 7 days to get a post rated before it times out. When a post times out, that means its no longer on my active list (if you reply I never know it.) You have already paid the fees to get this question answered, but it appears you’re not pleased, or need more help.
Let me help some more. Is there anything else you feel I could offer so you would be pleased with my help.
Dan again, hoping you are satisfied with my service.