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hesitation/bucking/mifiring

Y

yamaha racer 686

Hard-core CEG'er
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Feb 2, 2006
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Location
lancaster PA
so the car is a 1999 ford contour Se V6 about 130,000 miles and a mtx. started last year with some slight hesitation and missing. changed plugs and it went away for a little bit. now its worse. does it sometimes. but becoming more frequent. it goes "bump,bump,bump,bump..." or purrs like a kitten sound, under heavy load until about 3k. at 2.5k the check engine light starts to flash. really misses and hesitates when pulling out. so much that im afraid it might cause an accident. it seems the warmer the car gets the worse it is.

i have no idea what is causing this. so i thought i would ask. i dont want to go around replacing stuff that doesnt need replaced.
 
Alternate experience

Alternate experience

What are your codes?

some optins
FREE: Find out what cylinders are causing the problems. I did a drop test (disconnect a single spark plug wire one at a time with the car running) determine which is not working.

FREE: If you determine which is not working, check the plug, look for evidence of issues (mine were showing blistering white - not enough fuel- accompanied with a lean condition code (0174/0171) and an oxygen sensor not switching P1131 IIRC) (I had cylinders 2,3 and 5 not working).

In my case I had to redo the wiring connections at the fuel injectors (bought them for 6-10$ each at five-0 motorsports)

NOT FREE: do the plugs and wires together...
 
the car isnt throwing any codes. the check engine light just flashes when it misfires then alittle after. after that its gone. the car idles pretty well. except for once and a while the rpms will drop.

gonna change plugs and wires togeather to see if that changes anything
 
if you want to make sure that its the plugs and wires pull them and look for signs of carbon tracking, thats free also. it will look like a pencil mark on the plug and wire boot.

this exact thing happened to my father and I at the same time with out cars. plugs 1 and 3 carbon tracked. car idled great and ran good most of the time. but it would miss fire and cut out between about 2~3 krpm under heavy load. I really noticed it with mine because the exhaust sounds would just about completely cut out also.

always change plugs and wires together. also use alittle dielectric grease on the bottom/bottom inside of the wire boots
 
The MAF sensor can do all the same things. You may have stored codes that happen when the light flashes on.

Also being a 99 you may have low fuel pump pressure if your is a returnless system.

AF
 
Aussie Ford said:
The MAF sensor can do all the same things. You may have stored codes that happen when the light flashes on.

Also being a 99 you may have low fuel pump pressure if your is a returnless system.

AF
Click to expand...

well my dad and i are checking the plugs and wires tomorrow for the carbon tracking. ill pull the and clean it.

the car is a returnstyle fuel system i believe.

ill fill everyone in sometime tmrw.
 
I know it would be a quite obvious... but I had this happen in my 94 SHO ATX car. It turned out that there was a slight leak on the plug well gasket on the back side valve cover. When I pulled the plug (couldn't see down in the well when doing so), but oil was leaking into the well causing the plug wire to arc and misfire under heavy load. Of course when I pulled the plug the oil would all go into the cylinder so I didn't see it. However I did see residue on the plug wire and plug so I put two and two together. Anyway just another thing to check I guess. I would imagine you would have seen it last time you changed the plugs though...
 
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