Slight RPM Fluctuation (Normal ?) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

PHOENIX · 02-17-2003, 04:16 PM

OK this is not related to the new msd module I installed.
It has done this with both the stock module and this msd.

I dont think its a big deal or anything, but just wanted to see what you guys have to say.

When at idle my rpm (on AutoMeter tach) will slightly fluctuate up and down. The lines on the tach represent 100rpm. It will move about 50 rpm. It doesnt move alot and it doesnt move fast. Just a little "floating" type of movement. Im just curious is this normal, if not what could casue this? If it is normal, when is the fluctuation not normal, how much fluctuation is normal?

Thanks!

Prerunner1982 · 02-17-2003, 04:22 PM

not sure if its normal but mine does it as well

Tom · 02-17-2003, 06:04 PM

Pretty sure its normal. My 350 does it also, anywhere between 50-100rpm. I used to get pissed, but dont worry about it anymore.

PHOENIX · 02-17-2003, 06:23 PM

Yeah its done it forever and I though maybe its just the stock module, but then I installed this msd module and its pretty much the same as far as the fluctuation goes.

The msd module is much smoother at high rpm's then the stock module. Engine feels like it runs smoother above 3k.

79BIG10 · 02-17-2003, 08:41 PM

It has done it ever since I had the tach hooked up. I've checked for vacuum leaks with a gauge and steady reading even with RPM "bouncy".

PHOENIX · 02-18-2003, 03:16 PM

OK I thought it was normal, just freaks me out sometimes, because I have had the stock module leave me stranded a few times.
But Im hoping this msd
will leave me trouble free
Cause you know me
I dont want to pay that tow truck fee

**swervin ervin** · 02-18-2003, 04:15 PM

Mine does it too. I think all engines do this to some degree. I've never seen a tach sit still totally.

Prerunner1982 · 02-18-2003, 04:21 PM

i noticed today mine stays pretty constant in park, but in drive it fluctuates a bit..

Capitol68 · 02-18-2003, 06:03 PM

does the lopiness of the engine have anything to do with it ?

PHOENIX · 02-18-2003, 06:07 PM

I thought about that, but it shouldnt, the engine should still be rotating at a consistant speed.
Either way mine is stock w/ manual trans. and does it. Runs smooth at idle too.

02-17-2003, 04:16 PM	#1
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	Slight RPM Fluctuation (Normal ?) OK this is not related to the new msd module I installed. It has done this with both the stock module and this msd. I dont think its a big deal or anything, but just wanted to see what you guys have to say. When at idle my rpm (on AutoMeter tach) will slightly fluctuate up and down. The lines on the tach represent 100rpm. It will move about 50 rpm. It doesnt move alot and it doesnt move fast. Just a little "floating" type of movement. Im just curious is this normal, if not what could casue this? If it is normal, when is the fluctuation not normal, how much fluctuation is normal? Thanks! __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *

02-17-2003, 04:22 PM	#2
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,906	not sure if its normal but mine does it as well __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call

02-17-2003, 06:04 PM	#3
Tom driving is in my blood Join Date: Dec 1999 Location: Mesa AZ Posts: 5,714	Pretty sure its normal. My 350 does it also, anywhere between 50-100rpm. I used to get pissed, but dont worry about it anymore. __________________ -78 c10 short/step: 388cid, M20, 5/5 drop, lots more. Playtoy and first vehicle. -98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes. -02 Suburban 4x4: leveled front -CBR600F4i, CBR600RR, CBR1000RR, and standup skis DISCLAIMER: I cant spell for the life of me.

02-17-2003, 06:23 PM	#4
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	Yeah its done it forever and I though maybe its just the stock module, but then I installed this msd module and its pretty much the same as far as the fluctuation goes. The msd module is much smoother at high rpm's then the stock module. Engine feels like it runs smoother above 3k. __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *

02-17-2003, 08:41 PM	#5
79BIG10 I'm back with 2nd truck! Join Date: Feb 2002 Location: Texas Posts: 3,775	It has done it ever since I had the tach hooked up. I've checked for vacuum leaks with a gauge and steady reading even with RPM "bouncy". __________________ 1979 Chevrolet Bonanza Big10 "Tootsie Roll" 1985 Chevrolet Silverado (wife's) Member of the Southern Bowties Club "Don't underestimate how sexy a fat man who drinks to excess can be." Homer Simpson

02-18-2003, 03:16 PM	#6
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	OK I thought it was normal, just freaks me out sometimes, because I have had the stock module leave me stranded a few times. But Im hoping this msd will leave me trouble free Cause you know me I dont want to pay that tow truck fee __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *

02-18-2003, 04:15 PM	#7
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Mine does it too. I think all engines do this to some degree. I've never seen a tach sit still totally. __________________ Mike 1985 Chevy C-10

02-18-2003, 04:21 PM	#8
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,906	i noticed today mine stays pretty constant in park, but in drive it fluctuates a bit.. __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call

02-18-2003, 06:03 PM	#9
Capitol68 Registered User Join Date: Sep 2002 Location: Austin,Tx Posts: 327	does the lopiness of the engine have anything to do with it ? __________________ '68 Fleet LWB orig 307 .030 over GM Hei/w Accel Super coil orig. stock TH 400. _______________________ “What we do for ourselves dies with us. What we do for others and the world remains and is immortal.” Albert Pine English author d.1851

02-18-2003, 06:07 PM	#10
PHOENIX Registered User Join Date: Oct 2002 Location: Phoenix, Arizona Posts: 4,703	I thought about that, but it shouldnt, the engine should still be rotating at a consistant speed. Either way mine is stock w/ manual trans. and does it. Runs smooth at idle too. __________________ * AVOID: LOPER'S PERMORANCE / LOPERSPEED.COM OF PHOENIX, AZ & COTTMAN TRANSMISSION *

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