Part throttle misfire/tach jumping
06-29-2011, 07:17 PM
#1
Staging Lane
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Part throttle misfire/tach jumping Been doing a lot of searching and googling and cant find any straight answer.
one idea i found was to check the grounds on the cylinder heads, which i will be doing tonight once the engine cools off...
anyway, heres a discription of everything i have noticed:
the problem generally rears its head when cruising at 10-15% throttle (if that...) under light load between 2 to 3000 rpm.
the engine will sputter and it sounds like it is missing on one or multiple cylinders..
it drives on normally, but sounds wrong, and has less power
if you tip into the gas pedal even just a little, the missing goes away and all power is returned and the engine sounds fine.
often times right before this happens i will notice one or a combination of the following:
-tach blips/jumps from current RPM up to about +1000 RPM (from say.. 2500 to 3500) with no change in engine speed.
-my raptor shift light will flash one time for only an instant
-more rarely, i have also seen the speedo jump
i have even spotted my tach jump from idle at 1000 rpm to 2000, again, without the engine rpm doing anything.
not getting any codes that make me immediately suspicious of anything.
ONE time, i saw the engine light flash, but then go out, but usually it never flashes, and no misfire codes or anything are stored.
only codes i have are due to
clutch sensor switch (improperly adjusted clutch pedal switch with tick master)
no MAF sensor in the car (SD tuned)
and nothing giving me any leads.
---
car details:
1999 C5 FRC
SD tuned
LS2 402
249/255 @ 110
AFR TEA Stage 3 Ported Heads
and all other supporting bolt ons
3.91 rear gears
MN12 trans
this problem was pestering me about 2 or 3 months ago, so i pulled all the plugs, saw no problems.
put her back together, and after that it never happened again.
out of the blue it just started doing it again.
hopefully someone with more wisdom than i can help point me in the direction of a solution.
thank you all kindly, and let me know if you need any other info
one idea i found was to check the grounds on the cylinder heads, which i will be doing tonight once the engine cools off...
anyway, heres a discription of everything i have noticed:
the problem generally rears its head when cruising at 10-15% throttle (if that...) under light load between 2 to 3000 rpm.
the engine will sputter and it sounds like it is missing on one or multiple cylinders..
it drives on normally, but sounds wrong, and has less power
if you tip into the gas pedal even just a little, the missing goes away and all power is returned and the engine sounds fine.
often times right before this happens i will notice one or a combination of the following:
-tach blips/jumps from current RPM up to about +1000 RPM (from say.. 2500 to 3500) with no change in engine speed.
-my raptor shift light will flash one time for only an instant
-more rarely, i have also seen the speedo jump
i have even spotted my tach jump from idle at 1000 rpm to 2000, again, without the engine rpm doing anything.
not getting any codes that make me immediately suspicious of anything.
ONE time, i saw the engine light flash, but then go out, but usually it never flashes, and no misfire codes or anything are stored.
only codes i have are due to
clutch sensor switch (improperly adjusted clutch pedal switch with tick master)
no MAF sensor in the car (SD tuned)
and nothing giving me any leads.
---
car details:
1999 C5 FRC
SD tuned
LS2 402
249/255 @ 110
AFR TEA Stage 3 Ported Heads
and all other supporting bolt ons
3.91 rear gears
MN12 trans
this problem was pestering me about 2 or 3 months ago, so i pulled all the plugs, saw no problems.
put her back together, and after that it never happened again.
out of the blue it just started doing it again.
hopefully someone with more wisdom than i can help point me in the direction of a solution.
thank you all kindly, and let me know if you need any other info
06-30-2011, 10:15 AM
#3
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What about your plug wires? Could one be melted through and making contact somewhere with the headers/block/heads? That would give you your random ground problem and possibly be why it sounds like your missing (while its making contant and you not getting spark to the plug)
06-30-2011, 11:07 AM
#4
TECH Senior Member
Possible causes (based on erratic RPM):
- CKP sensor wiring has melted and on occasion they short,
- CKP reluctor is walking on the crank,
- cam sprocket coming loose (where CMP signal is read from).
- CKP sensor wiring has melted and on occasion they short,
- CKP reluctor is walking on the crank,
- cam sprocket coming loose (where CMP signal is read from).
06-30-2011, 04:20 PM
#5
Staging Lane
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i just put a new battery in (optima yellow), mine was toast (ac delco) a week ago.
but this didnt creep up til a few days after that.
originally i thought the problem was with battery volts, because i knew my delco batt was getting weak, but the problem went away before i changed it.
i have MSD wires, and theyre awfully well insulated, i didnt see any issues on them when i pulled them.
HOWEVER.
upon inspection last night, i found 2 loose grounds on the passenger side of the block.
the bolt holding the 2 lugs to the block was beyond finger tight, i couldnt turn it by hand, but the 2 ground lugs would rotate under the bolt head.
tightened it down with a 15mm.
no issues on the drive to work this morning. i think this was my problem. i will be doing some driving this evening and if it doesnt come back, im almost certain that was my issue.
ill be ecstatic if that was it. i can turn wrenches all day, but electrical gremlins are my worst nightmere.
i thank you guys for all of your input, i will keep you posted if the issue creeps back because i only have 15 clean miles since finding the loose grounds. if it comes back, ill be checking crank/cam sensors next i think.
thanks again
but this didnt creep up til a few days after that.
originally i thought the problem was with battery volts, because i knew my delco batt was getting weak, but the problem went away before i changed it.
i have MSD wires, and theyre awfully well insulated, i didnt see any issues on them when i pulled them.
HOWEVER.
upon inspection last night, i found 2 loose grounds on the passenger side of the block.
the bolt holding the 2 lugs to the block was beyond finger tight, i couldnt turn it by hand, but the 2 ground lugs would rotate under the bolt head.
tightened it down with a 15mm.
no issues on the drive to work this morning. i think this was my problem. i will be doing some driving this evening and if it doesnt come back, im almost certain that was my issue.
ill be ecstatic if that was it. i can turn wrenches all day, but electrical gremlins are my worst nightmere.
i thank you guys for all of your input, i will keep you posted if the issue creeps back because i only have 15 clean miles since finding the loose grounds. if it comes back, ill be checking crank/cam sensors next i think.
thanks again
