Tuning Question for the gurus
Tuning Question for the gurus I looked at some logs using a snap-on scanner today on my car. No codes present. I did a WOT blast and had the scantool log. My O2's were in the 970 to 980 range, 0 to 1 degree of knock retard across the rpm range and timing seemed to hover around 22 to 23 degrees. My L-trims never went above or below +/- 3....My questions is why is the car running so rich??? I also logged some cruising runs and the L-trims hover right around 0. The car has a lid, stock screened MAF, Mac headers and custom 2.5" offroad Y with flowmaster collector and 3" hooker catback. It ran rich on the dyno only making 310rwhp and bellowing black smoke. Fuel pressure is 61psi at idle with the large NOS inline pump. Could this be the problem?
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From: Godspeed
Re: Tuning Question for the gurus Pull out the screen from the MAF and see if it leans it out some. If you have an adjustable fuel pressure regulator lower the fuel psi a to about 58 psi.
-Jeremy
[ February 17, 2002: Message edited by: Godspeed ]</p>
-Jeremy
[ February 17, 2002: Message edited by: Godspeed ]</p>
Teching In
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From: Willow Springs, IL
Re: Tuning Question for the gurus DOH, that may not be the best advice, Jeremy. The MAF won't lean it out, just make the idle choppier. There's really no gains measured from removing it.
I think the problem lies in the high fuel pressure. More pressure squirts more fuel into the cylinder per PW of open time. The computer can't overcome that too well without programming in the PW table.
Can you disconnect the NOS fuel pump for everyday driving and reconnect it for racing?
I think the problem lies in the high fuel pressure. More pressure squirts more fuel into the cylinder per PW of open time. The computer can't overcome that too well without programming in the PW table.
Can you disconnect the NOS fuel pump for everyday driving and reconnect it for racing?
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From: College Station, Tx
Re: Tuning Question for the gurus Yep, I'm with brian on the fuel pump issue - 61psi definitely sounds high. If you get LS1 edit you can just scale your injector table to the slightly higher flow level.
If not, try disconnecting the pump to see if that helps - if it does you have found your problem. I wouldn't expect an inline pump like that to overpower the litter return near the tank, but it might be. The hardware option there would be to install a better FPR (just leave it referenced vs. the atmosphere). But if the FP is constant then LS1 Edit may be an easier solution.
Chris
If not, try disconnecting the pump to see if that helps - if it does you have found your problem. I wouldn't expect an inline pump like that to overpower the litter return near the tank, but it might be. The hardware option there would be to install a better FPR (just leave it referenced vs. the atmosphere). But if the FP is constant then LS1 Edit may be an easier solution.
Chris
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Re: Tuning Question for the gurus It is your pump.
Do you have it mounted underneath the car by the fuel filter?
If so you are negating the built in return line.
You need to have the pump mounted right up behind by the tank. Even this isnt the best solution but it is better than down by the filter.
Cheers,
Chris
Do you have it mounted underneath the car by the fuel filter?
If so you are negating the built in return line.
You need to have the pump mounted right up behind by the tank. Even this isnt the best solution but it is better than down by the filter.
Cheers,
Chris
Re: Tuning Question for the gurus [quote]Originally posted by Chris ARE 360:
<strong>It is your pump.
Do you have it mounted underneath the car by the fuel filter?
If so you are negating the built in return line.
You need to have the pump mounted right up behind by the tank. Even this isnt the best solution but it is better than down by the filter.
Cheers,
Chris</strong><hr></blockquote>
The inlet of the fuel pump is connected to the plastic line coming from the intank pump and before the fuel filter. Fuel pressure never drops to below 56 to 57psi at WOT and always runs about 61 at idle. Will a MAFT help???? P.S. Thanks for the help guys. <img src="gr_stretch.gif" border="0">
[ February 18, 2002: Message edited by: cantdrv65 ]</p>
<strong>It is your pump.
Do you have it mounted underneath the car by the fuel filter?
If so you are negating the built in return line.
You need to have the pump mounted right up behind by the tank. Even this isnt the best solution but it is better than down by the filter.
Cheers,
Chris</strong><hr></blockquote>
The inlet of the fuel pump is connected to the plastic line coming from the intank pump and before the fuel filter. Fuel pressure never drops to below 56 to 57psi at WOT and always runs about 61 at idle. Will a MAFT help???? P.S. Thanks for the help guys. <img src="gr_stretch.gif" border="0">
[ February 18, 2002: Message edited by: cantdrv65 ]</p>
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Joined: Nov 2001
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From: Godspeed
Re: Tuning Question for the gurus Umm, I thought I suggested he lower the fuel psi as well <img src="images/icons/confused.gif" border="0">
Anyways, many are running descreened MAF's without idle issues including myself. Wether that would make up the difference of the extra fuel psi, I don't know.
[ February 18, 2002: Message edited by: Godspeed ]</p>
Anyways, many are running descreened MAF's without idle issues including myself. Wether that would make up the difference of the extra fuel psi, I don't know.
[ February 18, 2002: Message edited by: Godspeed ]</p>
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Verdad Gallardo Re: Tuning Question for the gurus Can't drive 65? From Texas, I belive it. <G> I went to the Pro Stock Superbowl a few weeks ago, and nobody drove 65. I fell in with a bunch that ran 90 all the way from just south of Dallas to I 10 at Houston.
Anyway, removing the screen will lean it some. Most of the shops I work for always do that. It won't effect the idle either. (Sorry, Brian) The 2002 C5s come with no screen. The MAF tables are scaled up a tad to compensate also. Removing the screen won't lean it as much as you need, however.
Good luck, Ed
Anyway, removing the screen will lean it some. Most of the shops I work for always do that. It won't effect the idle either. (Sorry, Brian) The 2002 C5s come with no screen. The MAF tables are scaled up a tad to compensate also. Removing the screen won't lean it as much as you need, however.
Good luck, Ed
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From: Raleigh, NC
Re: Tuning Question for the gurus Removing the screen did not affect idle before my SC at all.
However, if you get a SC and your stock MAF was screened, if you want a smooth idle, you better leave it in. The increased turbulence at idle will have your motor surging and even cutting off during more sudden stops.
Good luck!
However, if you get a SC and your stock MAF was screened, if you want a smooth idle, you better leave it in. The increased turbulence at idle will have your motor surging and even cutting off during more sudden stops.
Good luck!
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From: Raleigh, NC
Re: Tuning Question for the gurus Ed, it didn't seem it would make that big a difference to me, either. When Jason told me to get a stock/screened MAF from the junkyard and put it in place of my GMAF, I thought I was about to waste $100. But DAM if it didn't work!
Then I broke out my old ported/descreened MAF (would'a tried that first, but Jason said it was the screen, not the MAF itself). Sure enough, it idled rough, too. This was even with Superchips having bumped the idle up 100 RPMs (which did help, it surged badly still, but at least wouldn't quite cut off).
With the screened MAF it idles like stock. <img src="gr_grin.gif" border="0">
Jason thinks the screen helps straigten and regulate the flow of intake air thru the MAF, if I remember his rationale correctly. He based his recommendation to me on real experience though. He said he had plenty instances, mostly with Mustangs I believe he said, where taking the screen out of the MAF made the idle hunt back and forth... exactly what mine was doing.
Seeing is believing. <img src="gr_stretch.gif" border="0">
Then I broke out my old ported/descreened MAF (would'a tried that first, but Jason said it was the screen, not the MAF itself). Sure enough, it idled rough, too. This was even with Superchips having bumped the idle up 100 RPMs (which did help, it surged badly still, but at least wouldn't quite cut off).
With the screened MAF it idles like stock. <img src="gr_grin.gif" border="0">
Jason thinks the screen helps straigten and regulate the flow of intake air thru the MAF, if I remember his rationale correctly. He based his recommendation to me on real experience though. He said he had plenty instances, mostly with Mustangs I believe he said, where taking the screen out of the MAF made the idle hunt back and forth... exactly what mine was doing.
Seeing is believing. <img src="gr_stretch.gif" border="0">
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From: Raleigh, NC
Re: Tuning Question for the gurus Here is some text I saved from my experience with this previously:
Thanks for clearing that up, Jason. <img src="gr_stretch.gif" border="0">
On a MAF note, I have three MAF's:
1. Stock with screen
2. Stock without screen and (basically) ported
3. Granetelli MAF
I've tried the Granetelli MAF and the Stock De-screened MAF AND the GMAF Ends with the stock MAF sensor. Conclusion:
The screen in the MAF levels out the velocity of the air flowing thru the MAF at idle, thereby smoothing the surging at idle. It's probably not an issue with an N/A car, but the blower is pushing quite a stiff flow of air thru the MAF and throttle-body at idle. Everytime there was a slight surge (I guess from the load of the compressor), the surge was excacerbated by a pendulum-like effect of the MAF trying to chase the fluctuating air velocity at idle.
With the GMAF or stock de-screened MAF at idle, it would actually cut off at some dips in idle. The problem was barely noticeable with the screened MAF.
The GMAF is an added, unnecessary inconvenience with the FI. I remember Dave recommending the Twin Turbo guys go back to the stock screened MAF when a discussion of compatibility came up... I don't remember all his reasons.
The GMAF gave me about 1 to 2 tenths in the 8th mile, so it is a good unit... I'll just sell it to someone who is N/A, if they want it. I also have a Direct-Flo lid, a cool-air induction and a Hypertech Programmer sitting around with no one to love.
Thanks for clearing that up, Jason. <img src="gr_stretch.gif" border="0">
On a MAF note, I have three MAF's:
1. Stock with screen
2. Stock without screen and (basically) ported
3. Granetelli MAF
I've tried the Granetelli MAF and the Stock De-screened MAF AND the GMAF Ends with the stock MAF sensor. Conclusion:
The screen in the MAF levels out the velocity of the air flowing thru the MAF at idle, thereby smoothing the surging at idle. It's probably not an issue with an N/A car, but the blower is pushing quite a stiff flow of air thru the MAF and throttle-body at idle. Everytime there was a slight surge (I guess from the load of the compressor), the surge was excacerbated by a pendulum-like effect of the MAF trying to chase the fluctuating air velocity at idle.
With the GMAF or stock de-screened MAF at idle, it would actually cut off at some dips in idle. The problem was barely noticeable with the screened MAF.
The GMAF is an added, unnecessary inconvenience with the FI. I remember Dave recommending the Twin Turbo guys go back to the stock screened MAF when a discussion of compatibility came up... I don't remember all his reasons.
The GMAF gave me about 1 to 2 tenths in the 8th mile, so it is a good unit... I'll just sell it to someone who is N/A, if they want it. I also have a Direct-Flo lid, a cool-air induction and a Hypertech Programmer sitting around with no one to love.
Re: Tuning Question for the gurus Just putting the screen back in fixed the idle? That is strange, I have tuned a train load of blown LS1s with no screen, and no idle problems. Heck, old as I am I have not seen it all yet. I still see something new every day.
Take care, Ed
[ February 23, 2002: Message edited by: Ed Wright ]</p>
Take care, Ed
[ February 23, 2002: Message edited by: Ed Wright ]</p>
Re: Tuning Question for the gurus Well I removed the inline fuse I installed to the NOS pump and fuel pressure dropped to about 57psi at idle. This definitely leaned the car some an it also performs better. The car STILL runs rich even with just the stock pump. On the TNT 150 shot, I will require the extra flow the pump provides. So heres the question, can I use the MAFT to tune the car with the inline pump on? Will it allow enough adjustment to get the proper mixture? Could i just disconect the MAFT and inline pump when I want to run NA????
[ February 26, 2002: Message edited by: cantdrv65 ]</p>
[ February 26, 2002: Message edited by: cantdrv65 ]</p>