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Topic: funky backfiring problem (Read 1092 times) previous topic - next topic

funky backfiring problem

my 5.0 so tends to backfire on the idle down if revved at a stop and let to idle down on its own and not lowered slowly, not sure if its to do with my ignition timing or that maybe an emissions system is malfunctioning (smog equipped cfi motor), would appreciate the help as it bugs the  out of me that i cant ever use WOT without sounding like firing a shotgun while driving

funky backfiring problem

Reply #1 –
check to see that your idle control motor plunger is automatically extending out when you manually add gas.
if not, and the plunger is staying put, then whats happening is your demanding instantanious Idle fuel / air delivery within a nano second of letting off the gas pedal.
thats a pretty traumatic experience for an engine in general.

what happens is that the isc motor will extend out a little bit and when you let off the gas, a little tab will land on the ISC plunger, then the plunger "feels" the spring loaded pressure, then the plunger backs off within approx 2 seconds slowly reducing rpm from approx 1000rpm to idle ,, it happens electronically pretty quick but its not an instantanious event.

id check this first, its been my experince that when the isc is not working, the motor feels like it almost dies then recovers if you let off the gas from a high rpm situation... cant remember if it back fired but thats likely tied to a different symptom imho.

remove your serpentine belt, start car, see if it does it with the belt off.. if not then possibly the smog pump is wearing out. you can short belt the system if you want.

lots of CFI goodies in my diy link below... above should get you started though.

funky backfiring problem

Reply #2 –
this is for all the later style 5.0s correct? my motor runs vbelts, im also not sure how the idle is controlled but will look into it, but it seems as though the timing doesnt retard immediately upon being off throttle, ive heard that a malfunctioning smog pump might cause this too

funky backfiring problem

Reply #3 –
SMOG PUMP!!!!  Check the valves and related components!!!
I spend money I don't have, To build  cars I don't need, To impress people I don't know

HAVE YOU DRIVEN A FORD LATELY!!

funky backfiring problem

Reply #4 –
is there a way i can just bypass it? dont need it anyways

funky backfiring problem

Reply #5 –
http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_air-pump-idler-bracket-proform_22740041-p?searchTerm=68110&zoneAssigned=1

Proform 68110, Done. V belt? Swap the pulley.
 

funky backfiring problem

Reply #6 –
pulled the outlet hose off today and it fixed the problem, and what are you you referring to by swapping the pulley? ive got a ribbed belt for the smog pump and alternator and a v belt for p/s, a/c has been deleted