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I have a 1986 foxbody mustang I am building my engine and in the meantime I have swapped in another 5.0 flat tappet lifter block from a 1988 f150 the block has 1987 ho heads on it engine idles good until you go to give it gas and it backfires from the intake side and cyl 1 and 6 are only getting to 150° as others get up to 300° I have ran alot of test and before I go pulling out the lifters and cam I'm curious to see if I'm missing something small. timing has been checked multiple times firing order I'm using is 13786542 has new plugs each cyl is getting spark and also did a leak down test and both dead cyl read out to be just as good as the rest. This engine is using a carb set up
There is your problem, that motor uses the 15426378 firing order.
i have used that firing order as well I tried all 3 that one wouldn't even start w that order cyl 1 and 6 never change position in all 3 firing order and those are the two that are acting weird they fire but not like they should only getting to 150°f others getting to 300°f I just pulled the lifters and they check out fine looked into block at cam and didn't see anything abnormal cells
There are only 2 firing orders, the old 302/5.0 15426378 and the newer 351/ho 13726548, and if you look closely at those two it's only cylinder pairs 54 and 37 that change position.
And just because I don't know if you know this but the ford small block cylinder numbers are as follows..
i have used all of those firing orders and it runs best on what it's at right now but even when I used the other firing orders cyl 1 and cyl 6 were still only reading around 150° and all others are running at around 300° and on all firing orders I've used it backfires from the intake side when you gas it and shuts off idles fine though
Was this a running motor in good condition before the transplant?
Did you remove the distributor at any time? If so did you put cyl #1 at TDC on the compression stroke before reinstalling the dizzy? If you just stabbed it in randomly then ignition timing is going to be all messed up.
Was this a running motor in good condition before the transplant
yes engine ran before just fine it had sat a couple years but ran fine and distributor is in the right position ive checked that multiple times i advanced timing i retarted timing checked timing atleast 6 times everything seems to be working right at idle ive also put a different carb on it as well that wasnt the issue i know timing isnt an issue unless its in the timing chain carb is good did a leak down test cyl checked out perfect and im getting spark to each cyl
Might have two wiped exhaust lobes on the cam. That will cause an intake backfire when the pressure builds up too high when the exhaust valves aren't opening fully.
Thanks for the help y'all used micrometer to check lift on a few of the cam loves had some flat spots got a nice Edelbrock 2122 cam in there now and she's happy
