why does my tach needle jump around when @WOT

[LX XLR8R]

i have a 5" monstertach that is wired into the the coil right b4 the coil..its been working fine and seems to be very very accurate..i had just replaced my aged accel TFI moduel on the distrubter with a old stock one i had sitting around..the accel finnaly had enuff and quit on me..i used dielectric grease on the metel to metal surfaces...this was doing this even with the aceel TFI...what it basically does is at WOT the car will be at 5k and then the needle will drop to 3k then shoot back up within a split second..you can just barely feel it in the cars pulling..what would casue this??i mean it couldnt be a wire/plug/cap/rotor cuz they are after the coil..should i try swapping the coil with a stock one??the coil is accel also..im stumped..and BTW the my plugs are white??could this be because i have one of the bad pr0-m77 mass air meters(rich down low, lean up top, cuts out uptop)..does the mass air have any say with spark??i mean even if i was running really lean that wuold not casue the coil to skip a beet like that??im stumped..thanks in advanced

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1987 black notch(ex 4 banger)
DSS 306 w/ main support...Elderbrock 6028 heads..gt-40 intake..24# injectors...70 mm tb..77 pro-m...accel 300+..mac full legnth..tremec w/ pro5oh...full MAC exhaust,off road h-pipe,long tubes, catback...ron davis radiator..subframes, control arms...CFDF II..o yea holley FPR sucks..dont buy one..
AIM=onesillynotch

[LX XLR8R]

TTT

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1987 black notch(ex 4 banger)
DSS 306 w/ main support...Elderbrock 6028 heads..gt-40 intake..24# injectors...70 mm tb..77 pro-m...accel 300+..mac full legnth..tremec w/ pro5oh...full MAC exhaust,off road h-pipe,long tubes, catback...ron davis radiator..subframes, control arms...CFDF II..o yea holley FPR sucks..dont buy one..
AIM=onesillynotch

[PKRWUD]

if it started after you swapped the TFI module, go buy a new one. Since you can feel it as well as see it on the tach, it's not the tach. I doubt it's the coil, either. The tach registers competed ignition circuits, which is why you will see a dip in the needle if you have a fouled plug. Just because it's wired before the coil, doesn't mean everything after the coil is good.

Sounds like a TFI module to me.

Take care,
-Chris

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Retired Moderator
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[Fostang]

Are you sure the distriburator isn't a tooth off? I remember once a friend of mine brought me his car confused as to why his rpms were jumping around and the car sputtered and sure enough when I went to check the distriburator it was off. He had taken it out for a cam change. After a the timing was set it worked correctly.

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67' Fastback-Mean Temper
67' Coupe Under Construction
70' Torino Cruiser
84' Svo Original

[LX XLR8R]

Originally posted by PKRWUD:
if it started after you swapped the TFI module, go buy a new one. Since you can feel it as well as see it on the tach, it's not the tach. I doubt it's the coil, either. The tach registers competed ignition circuits, which is why you will see a dip in the needle if you have a fouled plug. Just because it's wired before the coil, doesn't mean everything after the coil is good.

Sounds like a TFI module to me.

Take care,
-Chris

hmmm...my car does seem to run a lil better after i change my plugs but my plugs are the complete opposite of rich...i am running crazy lean up top..plugs are as clean as they came out the box..lack of fuel wouldn have anything to do with the needle jumping around would it though?could i been burning plugs up???and it doesnt do this all the time..it varies but when its doing it bad its real bad


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1987 black notch(ex 4 banger)
DSS 306 w/ main support...Elderbrock 6028 heads..gt-40 intake..24# injectors...70 mm tb..77 pro-m...accel 300+..mac full legnth..tremec w/ pro5oh...full MAC exhaust,off road h-pipe,long tubes, catback...ron davis radiator..subframes, control arms...CFDF II..o yea holley FPR sucks..dont buy one..
AIM=onesillynotch