304 running on 808 in ski boat - idle surge
Posted: Tue Nov 14, 2017 6:53 pm
Hi all,
Been reading through this forum with great interest for a while, really great information!
Been working on the tune for my ski boat recently and have an issue that I can't quite figure out... The surge/stumble at idle when out of gear.
Few details about the setup:
- Running an 808 with 12P (eeprom - so no live tuning)
- Modified the 808 for high speed logging
- 4 wire narrow band O2 sensor
- Running a knock sensor with V8 knock board
- Engine is raw water cooled with a thermostat (means operating coolant temp is about 65-75 degrees)
...Lake water is pumped through the engine, exhaust manifold jackets and then dumped into the exhausts about 150mm downwind of the O2 sensor.
- Cam - DUR@50 209/209, V/LIFT 448/448 (nothing crazy)
- Dog clutch
It runs well cruising and it's pretty good at idle with the dog clutch engaged (idling forward). It's not very happy at idle without a load on it.
The revs fluctuate increasingly until it reaches limit where revs drop greatly, at that point the IAC catches it, it revs up and the cycle starts again. This is about a 5 second loop.
I've tinkered with a few different iac settings and idle spark control without much success...
I'm now starting to think that its running lean at idle... the O2 signal looks way too lean to be corresponding with the AFR demanded.
I can only experiment during certain weekend with the boat on the water, so I'm trying to get a rounded idea of the different factors that I should be looking at.
The fact that it idles better in gear than without any load on it makes me think that the issue only starts up at MAP values lower than 40 kPa... but unsure
If anyone has any thoughts, hints or tips on the matter it would be VERY MUCH appreciated.
As you can imagine, having a rock solid idle is a HUGE benefit for a boat, I'd also LOVE to get the idle RPM as low as possible to slow the forward motion at idle right down.
Apologies for the long winded message, just wanted to try and give the best description I could.
I've attached the BIN and log file; below is a timeline of what was going on during the logging time:
0-0:50- Idle out of gear
0:50-1:50- Idle in gear
1:50-6:20- Light cruise in gear (lean cruise engages at 4:20) -- still pondering whether I should disable LC
6:20-6:52- Idle in gear
6:52-8:15- Idle out of gear (best section to get an idea of the surging)
Been reading through this forum with great interest for a while, really great information!
Been working on the tune for my ski boat recently and have an issue that I can't quite figure out... The surge/stumble at idle when out of gear.
Few details about the setup:
- Running an 808 with 12P (eeprom - so no live tuning)
- Modified the 808 for high speed logging
- 4 wire narrow band O2 sensor
- Running a knock sensor with V8 knock board
- Engine is raw water cooled with a thermostat (means operating coolant temp is about 65-75 degrees)
...Lake water is pumped through the engine, exhaust manifold jackets and then dumped into the exhausts about 150mm downwind of the O2 sensor.
- Cam - DUR@50 209/209, V/LIFT 448/448 (nothing crazy)
- Dog clutch
It runs well cruising and it's pretty good at idle with the dog clutch engaged (idling forward). It's not very happy at idle without a load on it.
The revs fluctuate increasingly until it reaches limit where revs drop greatly, at that point the IAC catches it, it revs up and the cycle starts again. This is about a 5 second loop.
I've tinkered with a few different iac settings and idle spark control without much success...
I'm now starting to think that its running lean at idle... the O2 signal looks way too lean to be corresponding with the AFR demanded.
I can only experiment during certain weekend with the boat on the water, so I'm trying to get a rounded idea of the different factors that I should be looking at.
The fact that it idles better in gear than without any load on it makes me think that the issue only starts up at MAP values lower than 40 kPa... but unsure
If anyone has any thoughts, hints or tips on the matter it would be VERY MUCH appreciated.
As you can imagine, having a rock solid idle is a HUGE benefit for a boat, I'd also LOVE to get the idle RPM as low as possible to slow the forward motion at idle right down.
Apologies for the long winded message, just wanted to try and give the best description I could.
I've attached the BIN and log file; below is a timeline of what was going on during the logging time:
0-0:50- Idle out of gear
0:50-1:50- Idle in gear
1:50-6:20- Light cruise in gear (lean cruise engages at 4:20) -- still pondering whether I should disable LC
6:20-6:52- Idle in gear
6:52-8:15- Idle out of gear (best section to get an idea of the surging)