Tuning issue forces cam change (w/Radix)
09-19-2005, 12:15 AM
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Tuning issue forces cam change (w/Radix)
This weekend we swapped the Thunder Racing CheaTR (215/232) out of my truck. We decided to go with the LPE GT2/3.
What prompted the change was a untunable cold idle issue. The problem lies in the following combination:
1. A larger cam with high airflow demand at idle (the CheaTR took about 13-15 g/s at idle to run with the AC off and on) and lower vacuum (CheaTR gave about 14 inches)
2. A Radix or most likely any other belt driven supercharger.
3. E-fans.
The first two can cause the problem, the e-fans certainly contribute in a major way and make it a lot more frustrating.
The problem is that all these place load on the engine at idle. It's all good when the engine is warmed up to full operationg temperature, but when the truck is cold, it is prone to having idle oscillations. For instance when giving the truck a little throttle, like to get out of a low driveway up a small rise and stopping at the top, when you let off the throttle it would dip low and then rise above the set idle and then dip low again. Sometimes it would just die. That is not acceptable.
Taking off the e-fans helped some. Didn't cure the issue by any means. If anything it would die 10% less often. In my opinion any dying is unacceptable.
I dialed in my STIT and LTIT's (short term and long term idle trims). Even when they were perfect this would still happen. Don't try to second guess because you would be wrong. They were right on.
I even dialed in many, many combinations of Throttle follower decay and delay. This was ineffective as well. HP Tuners even told me to go back to stock settings which were also ineffective. A few different combinations seemed promising, but when the truck was fully cold again it was still just as likely to die. In my opinion having to wait up to 10 minutes for the truck to fully reach operating temp to not have to worry about it dying is not a good situation.
Enabling learn mode at a colder temp didn't help either.
The real solution was to take the cam out and go with something that idles closer to stock because I still had the Radix drag at idle. The radix and the LPE GT2/3 cam require about 9.5-10 g/s at idle. Stock setting for the H2 was about 6 g/s. As you can see the LPE cam and Radix is a half step between the full stock setting and CheaTR with the Radix.
Best of all is that the truck doesn't try to die when I do the same things that caused problems with the other combo. It would probably be okay with e-fans but I already sold them so I can't even try it.
IF YOU DON"T READ ANYTHING ELSE READ THIS...
The message here is that some combinations of high load accessories like superchargers, electric fans (the turn on spike makes the alternator drag increase), cranking the steering wheel in parking lots (more power steering pump drag), and having the A/C on can cause problems with rolling idle when the engine has lower vacuum from a cam. Sometimes the warm engine and the various program features can help control these. In general, though, cold idle is all about the STIT and LTIT's and they can't fix everything. When you have enough drag on the engine it will overshoot when trying to correct idle speed errors (oscillations). The more it overshoots the target speed the worse the error gets until it finally stalls.
Choose your supercharger cam wisely. The CheaTR is a good cam and it does give good gains. Works great on NA engines. Might work on Turbo's. Doesn't work on HD trucks with a Radix!
What prompted the change was a untunable cold idle issue. The problem lies in the following combination:
1. A larger cam with high airflow demand at idle (the CheaTR took about 13-15 g/s at idle to run with the AC off and on) and lower vacuum (CheaTR gave about 14 inches)
2. A Radix or most likely any other belt driven supercharger.
3. E-fans.
The first two can cause the problem, the e-fans certainly contribute in a major way and make it a lot more frustrating.
The problem is that all these place load on the engine at idle. It's all good when the engine is warmed up to full operationg temperature, but when the truck is cold, it is prone to having idle oscillations. For instance when giving the truck a little throttle, like to get out of a low driveway up a small rise and stopping at the top, when you let off the throttle it would dip low and then rise above the set idle and then dip low again. Sometimes it would just die. That is not acceptable.
Taking off the e-fans helped some. Didn't cure the issue by any means. If anything it would die 10% less often. In my opinion any dying is unacceptable.
I dialed in my STIT and LTIT's (short term and long term idle trims). Even when they were perfect this would still happen. Don't try to second guess because you would be wrong. They were right on.
I even dialed in many, many combinations of Throttle follower decay and delay. This was ineffective as well. HP Tuners even told me to go back to stock settings which were also ineffective. A few different combinations seemed promising, but when the truck was fully cold again it was still just as likely to die. In my opinion having to wait up to 10 minutes for the truck to fully reach operating temp to not have to worry about it dying is not a good situation.
Enabling learn mode at a colder temp didn't help either.
The real solution was to take the cam out and go with something that idles closer to stock because I still had the Radix drag at idle. The radix and the LPE GT2/3 cam require about 9.5-10 g/s at idle. Stock setting for the H2 was about 6 g/s. As you can see the LPE cam and Radix is a half step between the full stock setting and CheaTR with the Radix.
Best of all is that the truck doesn't try to die when I do the same things that caused problems with the other combo. It would probably be okay with e-fans but I already sold them so I can't even try it.
IF YOU DON"T READ ANYTHING ELSE READ THIS...
The message here is that some combinations of high load accessories like superchargers, electric fans (the turn on spike makes the alternator drag increase), cranking the steering wheel in parking lots (more power steering pump drag), and having the A/C on can cause problems with rolling idle when the engine has lower vacuum from a cam. Sometimes the warm engine and the various program features can help control these. In general, though, cold idle is all about the STIT and LTIT's and they can't fix everything. When you have enough drag on the engine it will overshoot when trying to correct idle speed errors (oscillations). The more it overshoots the target speed the worse the error gets until it finally stalls.
Choose your supercharger cam wisely. The CheaTR is a good cam and it does give good gains. Works great on NA engines. Might work on Turbo's. Doesn't work on HD trucks with a Radix!
09-19-2005, 12:37 AM
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Why are your e-fans coming when the truck is cold??? I can see when Op temp has been reached, but cold?? Thought if they were not running, should not be pulling a load??? Did you have a dc control for the fans, to control fan speed according to coolants temps??
How about raising the idle rpm??
I have notice that SD mode idles rougher than with MAF on.
Specs on the cams???
How about raising the idle rpm??
I have notice that SD mode idles rougher than with MAF on.
Specs on the cams???
09-19-2005, 01:34 AM
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e-fans come on when air comes on...Nelson harness...
No biggie though, It was the combination of all things....I know after tuning engines for the last 10 years that this was not an exceptable cold start and idle for such a small cam. Plenty of LS1 supercharged cars running alot more stouter cams than this...In fact I'm building one now with a procharger that I know will idle better with a bigger cam. Just the combo....
We even sent many files back and forth with a WELL KNOWN truck tuner, with our logs (we only have HP tuners for this year vehicle) hoping his other tuning programs would open more tables and parimeters (like the RAF table). After two months of tuning we finally had to go with a cam that kept the vacuum to an exceptable level in order to run these heavy accesseries. I think we are at 200 flashes now for programming and now we see the light again...sucks though.....
Two other things that may have played a roll in this was the fly-by-wire throttle body (no IAC) and the use of 60 lb injectors (don't seem to act as fast to transitions as the 42's that came with the Radix kit, but seems to run fine). The lack of a real IAC does pose some real issues with tuning when the throttle body open transitional percentages roll up and down faster (by logging software) then a more traditional slower IAC...Hopefully there will be more tuning tables in the updates to come for this area...
Jimbob
No biggie though, It was the combination of all things....I know after tuning engines for the last 10 years that this was not an exceptable cold start and idle for such a small cam. Plenty of LS1 supercharged cars running alot more stouter cams than this...In fact I'm building one now with a procharger that I know will idle better with a bigger cam. Just the combo....
We even sent many files back and forth with a WELL KNOWN truck tuner, with our logs (we only have HP tuners for this year vehicle) hoping his other tuning programs would open more tables and parimeters (like the RAF table). After two months of tuning we finally had to go with a cam that kept the vacuum to an exceptable level in order to run these heavy accesseries. I think we are at 200 flashes now for programming and now we see the light again...sucks though.....Two other things that may have played a roll in this was the fly-by-wire throttle body (no IAC) and the use of 60 lb injectors (don't seem to act as fast to transitions as the 42's that came with the Radix kit, but seems to run fine). The lack of a real IAC does pose some real issues with tuning when the throttle body open transitional percentages roll up and down faster (by logging software) then a more traditional slower IAC...Hopefully there will be more tuning tables in the updates to come for this area...
Jimbob
09-19-2005, 01:43 AM
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Curious...what size alternator do you have on the H2?
On the plus side, I bet you learned a lot about tuning, eh?
Jimbob (defeated tuner syndrome setting in
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09-19-2005, 01:47 AM
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Originally Posted by 8100hammer
Why are your e-fans coming when the truck is cold??? I can see when Op temp has been reached, but cold?? Thought if they were not running, should not be pulling a load??? Did you have a dc control for the fans, to control fan speed according to coolants temps??
How about raising the idle rpm??
I have notice that SD mode idles rougher than with MAF on.
Specs on the cams???
How about raising the idle rpm??
I have notice that SD mode idles rougher than with MAF on.
Specs on the cams???
Or course I tried raising idle. Didn't work. 850 rpms was no better than 700, or 750.
If it was that easy it wouldn't have been a problem. It's not like I wanted to change the cam... it takes about 9 hours in the H2. I tried everything.
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09-19-2005, 01:49 AM
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Harris post up some numbers on the cams.
Jimbob
Last edited by jimbob; 09-19-2005 at 02:01 AM.
09-19-2005, 01:51 AM
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Originally Posted by Naked AV
Curious...what size alternator do you have on the H2?
Also, will you be putting the e-fans back on?
On the plus side, I bet you learned a lot about tuning, eh?
Also, will you be putting the e-fans back on?
On the plus side, I bet you learned a lot about tuning, eh?
As for the e-fans.. I guess you didn't read the post.
As for the learning a lot about tuning... I know more than you ever will and more than I wanted to.
For the record a pro couldn't fix it either. Only covered ground that I had already been over with the same unsatisfactory results. Not his fault, it was a combination issue.
09-19-2005, 01:58 AM
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Originally Posted by CHarris
Like Jim said.. 145 amp.
As for the e-fans.. I guess you didn't read the post.
As for the learning a lot about tuning... I know more than you ever will and more than I wanted to.
For the record a pro couldn't fix it either. Only covered ground that I had already been over with the same unsatisfactory results. Not his fault, it was a combination issue.
As for the e-fans.. I guess you didn't read the post.
As for the learning a lot about tuning... I know more than you ever will and more than I wanted to.
For the record a pro couldn't fix it either. Only covered ground that I had already been over with the same unsatisfactory results. Not his fault, it was a combination issue.
However, I do know what it's like to have to find things out the hard way, especially when supposed 'experts' had their turn and couldn't figure it out.
Thanks for sharing your experience with us, it's greatly appreciated.
