8.1L Timing - How low is low?
04-20-2013, 07:11 PM
#1
Teching In
Thread Starter
Join Date: Oct 2010
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
8.1L Timing - How low is low?
I have seen several posts where folks say the 8.1's like low timing?
How low is low? How far should I go? Motor breaks up in the 2500 to 2800 rpm range. HPTuner scanner shows I am still getting some knock retard in this range. I started with the stock curve from a 2003 suburban and have been adding fuel and taking out timing. AFR's are pretty good, so I am assuming it must be timing.
I have been taking out 1 to 2 degrees at a time. Should I be pulling timing in 5 and 10's instead?
For HPTuner guys, tune file and log file attached. (Also any other bonehead mistakes you find in the tune file let me know)
How low is low? How far should I go? Motor breaks up in the 2500 to 2800 rpm range. HPTuner scanner shows I am still getting some knock retard in this range. I started with the stock curve from a 2003 suburban and have been adding fuel and taking out timing. AFR's are pretty good, so I am assuming it must be timing.
I have been taking out 1 to 2 degrees at a time. Should I be pulling timing in 5 and 10's instead?
For HPTuner guys, tune file and log file attached. (Also any other bonehead mistakes you find in the tune file let me know)
04-30-2013, 06:35 AM
#3
Teching In
Thread Starter
Join Date: Oct 2010
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
I think I am narrowing down my problems. I may have several small issues rolling up into a larger one. Bank 2 is running leaner that Bank 1. I have dual widebands on it as well as the factory sensors both are showing Bank 2 as lean. Possible bad injector or bad plug wire and/or coil
I starting with the cheapest fix first. I replaced the plug wires. That helped some, the difference between Bank 1 and Bank 2 is slightly less. I was finally able to make a WOT run, and maxed out the injectors to 100% duty cycle.
New 42# injectors will be here today. I will swap them out and see what happens next.
Just to be sure I understand you correctly, your base timing curve had a peak of 28 degrees and peak of 10 degrees of MAP advance.
Thanks
I starting with the cheapest fix first. I replaced the plug wires. That helped some, the difference between Bank 1 and Bank 2 is slightly less. I was finally able to make a WOT run, and maxed out the injectors to 100% duty cycle.
New 42# injectors will be here today. I will swap them out and see what happens next.
Just to be sure I understand you correctly, your base timing curve had a peak of 28 degrees and peak of 10 degrees of MAP advance.
Thanks
04-30-2013, 09:25 AM
#5
Teching In
Thread Starter
Join Date: Oct 2010
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
Fuel pump was my first guess. I added a fuel pressure sensor to the data logger and it is holding 50 to 51 psi at WOT. Fuel pump is a walbro 255. If pump becomes my next weak link I will probably go to dual pumps.
Trending Topics
04-30-2013, 12:16 PM
#8
Teching In
Thread Starter
Join Date: Oct 2010
Posts: 24
Likes: 0
Received 0 Likes
on
0 Posts
The paperwork says BP202, but I think that is the 102.
I had a red/yellow CJ3b with a 406 in it years ago. But you are probably thinking about another CJ with 8.1L from Alabama. I have seen photos and videos of it.
This is the current project
I had a red/yellow CJ3b with a 406 in it years ago. But you are probably thinking about another CJ with 8.1L from Alabama. I have seen photos and videos of it.
This is the current project
