Misfire/Hesitation that's baffling me
07-21-2012, 11:09 PM
#1
Thread Starter
Join Date: Oct 2011
Location: United States
Posts: 21
Misfire/Hesitation that's baffling me
94 GT 5.0
getting an intermittent misfire that comes and goes, seems to happen under low load 15-1800 rpm, started first about 6 months ago then disappeared, thought I had it behind me, and then bummer, it returned this week.
it will misfire/skip for a split second and engine light comes on then right back off, then repeats whenever it feels like it...
Did a tuneup, cleaned all injectors, checked grounds, replaced battery terminals, replaced rotor, all plugs and plug wires but didn't help.
where should I start next ? it doesn't feel like a tranny issue (had it checked at the tranny place twice and they can't find anything) but more like an electronic issue but not sure where I should start digging next.
suggestions ? coil ? egr? computer ? i don't want to just throw money at it blindly looking for a gremlin, hoping somebody is aware of a common issue and can point me in the right direction..
getting an intermittent misfire that comes and goes, seems to happen under low load 15-1800 rpm, started first about 6 months ago then disappeared, thought I had it behind me, and then bummer, it returned this week.
it will misfire/skip for a split second and engine light comes on then right back off, then repeats whenever it feels like it...
Did a tuneup, cleaned all injectors, checked grounds, replaced battery terminals, replaced rotor, all plugs and plug wires but didn't help.
where should I start next ? it doesn't feel like a tranny issue (had it checked at the tranny place twice and they can't find anything) but more like an electronic issue but not sure where I should start digging next.
suggestions ? coil ? egr? computer ? i don't want to just throw money at it blindly looking for a gremlin, hoping somebody is aware of a common issue and can point me in the right direction..
07-21-2012, 11:55 PM
#2
6th Gear Member
Join Date: Nov 2006
Location: Spfld, MA
Posts: 9,240
Coil, EGR, and TPS are really the only possibilities here.
Coil would likely have a much wider range of failure.
EGR would likely pop the CEL until the EGR wasn't being commanded anymore(idle, decel, WOT, 4k+ RPM)
TPS would only need a very small problem in the voltage sweep to spike a little stumble. It's likely the cheapest of the 3 if you're without the means to do any testing.
Coil would likely have a much wider range of failure.
EGR would likely pop the CEL until the EGR wasn't being commanded anymore(idle, decel, WOT, 4k+ RPM)
TPS would only need a very small problem in the voltage sweep to spike a little stumble. It's likely the cheapest of the 3 if you're without the means to do any testing.
07-22-2012, 12:12 AM
#3
Thread Starter
Join Date: Oct 2011
Location: United States
Posts: 21
Coil, EGR, and TPS are really the only possibilities here.
Coil would likely have a much wider range of failure.
EGR would likely pop the CEL until the EGR wasn't being commanded anymore(idle, decel, WOT, 4k+ RPM)
TPS would only need a very small problem in the voltage sweep to spike a little stumble. It's likely the cheapest of the 3 if you're without the means to do any testing.
Coil would likely have a much wider range of failure.
EGR would likely pop the CEL until the EGR wasn't being commanded anymore(idle, decel, WOT, 4k+ RPM)
TPS would only need a very small problem in the voltage sweep to spike a little stumble. It's likely the cheapest of the 3 if you're without the means to do any testing.
07-22-2012, 07:12 AM
#4
1st Gear Member
Join Date: Jul 2009
Location: PA
Posts: 64
There's a chance it could be a vacuum leak somewhere. Vacuum leaks can cause some strange problems that come and go. I always check all the connections 1st by wiggling and such, then try the old stand-by with starter fluid and wiggling lines while its running. The whole thing will only cost you an hour or so of time and a can of starter fluid.
07-22-2012, 06:31 PM
#6
Thread Starter
Join Date: Oct 2011
Location: United States
Posts: 21
i'm not familiar with continuous memory test care to explain for informational purposes ?
07-22-2012, 09:55 PM
#7
6th Gear Member
Join Date: Nov 2006
Location: Spfld, MA
Posts: 9,240
DIY KOEO/KOER/Cylinder balance test
Acronym explanation: DIY = do it yourself
KOEO = Key on, Engine OFF
KOER = Key on, Engine running
Basically a vehicle self test, including failure code retrieval
07-26-2012, 06:15 PM
#10
Thread Starter
Join Date: Oct 2011
Location: United States
Posts: 21
ok... well, car is back, and so far its running fine with no issues but i'm a little confused,
was told it was a dirty Idle Air Control Sensor, cleaned it up and running fine, besides some diagnostic time and a couple of vacuum lines replaced, that's it. So.. it was a cheap visit to the Car Doc, but not what I expected.
Does it make sense that the IAC would cause a misfire/bucking like that ?
was told it was a dirty Idle Air Control Sensor, cleaned it up and running fine, besides some diagnostic time and a couple of vacuum lines replaced, that's it. So.. it was a cheap visit to the Car Doc, but not what I expected.
Does it make sense that the IAC would cause a misfire/bucking like that ?