My 5.7 is running great, but I've noticed when I'm approaching a stop light and take my foot off the gas, the motor starts surging 200-400rpm. By the time I stop at the light it's idling fine. Any ideas on what could cause this?
HEMI surging on deceleration.
- Thread starter Tincup
- Start date
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lxmodguy
Gen3 Hemi Guru
Fuel trims are off. Is it bouncing up or down rpm wise?
my guess is a TPS sensor ....throttle position sensor .......when you let go off the gas it goes out of range and the computer dosnt know where its at so it compensates and picks up a good reading at idle.....im assuming that you mean a late model computerized 5.7 litre...
It is bouncing up, Idle is 600, it jumps to probably 800-900. Would that also make it run rich?
Yes its a 2005 LX 5.7, everything is brand new, i was a crate motor with only break in miles on it. I suppose it could still be a bad sensor.
After doing a little searching on the TPS, from what I read, the hemi's is built into the throttle body and non-replaceable, is this correct?
lxmodguy
Gen3 Hemi Guru
yes. If it is surging up it is because it is too rich at idle. They trims are probably 15% or more off. You need someone to tune it for you to fix that. The TPS almost never goes bad in those hemi throttle bodies. I have seem like 3 in 8 years and I have done 100's of them
I have a predator, can I use that to take some fuel out?
lxmodguy
Gen3 Hemi Guru
you can, you would be better off to send the tune and a log to a tuner and get it fixed right.
USCG CHARGER
Well-Known Member
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Brian is correct... Fuel trims which can be changed by cmr software.
garyfish340
Well-Known Member
This may not be your answer,but it certainly something to watch for.One thing I found while checking spark plug color was that the coil packs are not always sealed to the valve cover very well,water proof. It causes all kinds of weird surging issues, and can eventually cause misfiring. You say " Oh well the coil failed, and the plug is fouled." and that would be true, sort of. The coil hasn't failed, but if you remove the boot from the coil, most of the time they corrode pretty badly inside that boot, and where it contacts with the coil.( it looks like a spring) This is especially true if you wash your engine often, or have a hood scoop. Dip the boot assembled, ( don't remove the spring ) in a zinc phosphate bath over night. Also with the bootless coil laying on a work bench upright, take an eye dropper and put a few drops of zinc in there too. Zinc is a good conductor so I think it will be safe, and the phosphate should remove the corrosion pretty well.
joeboy
Well-Known Member
Tin,
If it turns out to be TPS related, shoot me a pm... I have the same crate motor and yanked the factory stuff... Don't have a use for the throttle body.
If it turns out to be TPS related, shoot me a pm... I have the same crate motor and yanked the factory stuff... Don't have a use for the throttle body.
MiradaMegaCab
Well-Known Member
X2, I have a SRT hood and scoop on an 07 Hemi Ram truck. I had the same surging issue. The #3 coil packs boots and spark plugs were covered in rust. Water was getting in there. I cleaned the boots and replaced the spark plugs, all 16 of them. I dont have the surging issue anymore.
:dontknow: I never got a missfire code.....
garyfish340
Well-Known Member
Now if we can just fix the serpentine squealing ! How pathetic to be ahead of Chevy for once, and to be plagued by pittance...
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