Engine surge
02-03-2018, 10:16 AM
#1
Engine surge Engine surges at part throttle while cruising, WOT is good with plenyt of power,
what can I check on my own to see what might be causing it.I don't see any surging at the fuel pressure gauge but don't know if that means anything.
Forged 5.7
243 ported heads
Fast 90/90 intake with TPIS throttle body with stock IAC and TPS
1 7/8 headers
Cam 242/248 .608/.612 110 lsa
ANy suggestions would be appreciated.
what can I check on my own to see what might be causing it.I don't see any surging at the fuel pressure gauge but don't know if that means anything.
Forged 5.7
243 ported heads
Fast 90/90 intake with TPIS throttle body with stock IAC and TPS
1 7/8 headers
Cam 242/248 .608/.612 110 lsa
ANy suggestions would be appreciated.
02-04-2018, 05:39 PM
#7
TECH Fanatic
Yes, starting fluid aka "Explosion In A Can" is a good way to find a vacuum leak. Using an unlit propane torch with the valve open and flowing is also good - wave it over and near the potential leaky areas.
Rick
Rick
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02-05-2018, 11:13 PM
#8
TECH Fanatic
Sounds pretty normal for a cam that size. Try pulling a few degrees of timing while it's surging (with the scanner) and see if that helps out. That and lean it out, slightly. I'm guessing this happens around 1500-2000 rpm range, right?
02-06-2018, 08:19 AM
#9
Correct, it's that RPM exactly, I'll try your suggestions, thanks for the advise.
03-12-2018, 09:00 PM
#11
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03-12-2018, 10:28 PM
#12
TECH Fanatic
Glad to hear that you got it figured out. Fuel and timing can and will cause surging on a big cam, especially with the MAF enabled. I know you had yours in SD, but if not tuned right it will surge too, and worse if the STFT's are enabled in OL. I've been through a few rowdy cams in my cars, and pulling timing and fuel is the only way to calm them down sometimes.
In fact, with a lot of overlap, the O2's will read a false lean condition at low RPM, specifically idle, because unburned air and fuel enter the exhaust during overlap. O2 sensors don't care about fuel in the pipe, only air. So that small amount of unburned air skews them into thinking it's running lean. So if STFT's are being used, the PCM will add fuel, which then overshoots, goes rich, and then switches back, etc... Which is what we call "surging".
On my wideband, I shoot for about 15.5-16.5 AFR at idle tapering off to 14.6 up to 1600 RPM, or somewhere between those depending on overlap. The car won't surge that way, and will idle and drive great. Because those readings are again, false lean. You can rest assured that the actual AFR is much lower.
In fact, with a lot of overlap, the O2's will read a false lean condition at low RPM, specifically idle, because unburned air and fuel enter the exhaust during overlap. O2 sensors don't care about fuel in the pipe, only air. So that small amount of unburned air skews them into thinking it's running lean. So if STFT's are being used, the PCM will add fuel, which then overshoots, goes rich, and then switches back, etc... Which is what we call "surging".
On my wideband, I shoot for about 15.5-16.5 AFR at idle tapering off to 14.6 up to 1600 RPM, or somewhere between those depending on overlap. The car won't surge that way, and will idle and drive great. Because those readings are again, false lean. You can rest assured that the actual AFR is much lower.