Low BLM at idle only (l98)
#1
Supreme Member
Thread Starter
iTrader: (1)
Join Date: May 2015
Location: Temecula, CA
Posts: 1,149
Received 83 Likes
on
67 Posts
Car: 1989 Pontiac Formula 350
Engine: L98
Transmission: 700R4
Axle/Gears: BorgWarner 3.27 Posi
Low BLM at idle only (l98)
I have a stock 89 L98 w/ stock TPI intake, but Bosch III injectors from SB. Fuel system and ignition system are both new end-to-end. Fuel pressure is 65 w/o vacuum, afpr drops it to 43 1/2 as it should. Timing is bang on 6 btdc. TPS is at .54 w/ car off. IAC cleaned and idle reset.
At idle, my BLMs are at the floor at 108-112. Any other situation they're close to 128. Had a mail-in-tune done and my idle BLMs on that one are the same, even though the rest of the rev range is a bit better.
I can't find any leaks in the manifold nor vacuum system.
I'm trying to figure out if this is simply a difference with these injectors that I can tune around, or if I should ditch them for something else entirely.
Any advise would be greatly appreciated.
At idle, my BLMs are at the floor at 108-112. Any other situation they're close to 128. Had a mail-in-tune done and my idle BLMs on that one are the same, even though the rest of the rev range is a bit better.
I can't find any leaks in the manifold nor vacuum system.
I'm trying to figure out if this is simply a difference with these injectors that I can tune around, or if I should ditch them for something else entirely.
Any advise would be greatly appreciated.
Last edited by thtanner; 09-04-2016 at 12:31 PM.
#2
Senior Member
Join Date: Aug 2002
Location: ARIZONA
Posts: 948
Likes: 0
Received 4 Likes
on
4 Posts
Car: 92 Trans Am Conv
Engine: LB9
Transmission: T5
Axle/Gears: 3.08
Re: Low BLM at idle only (l98)
So you're trying a STOCK tune and the mail tune?
If yes and no vac leaks might be time to check a new o2.
If yes and no vac leaks might be time to check a new o2.
#3
Supreme Member
Thread Starter
iTrader: (1)
Join Date: May 2015
Location: Temecula, CA
Posts: 1,149
Received 83 Likes
on
67 Posts
Car: 1989 Pontiac Formula 350
Engine: L98
Transmission: 700R4
Axle/Gears: BorgWarner 3.27 Posi
Re: Low BLM at idle only (l98)
I did try both stock tune and mail tune, same BLM values at idle.
I had a fogger on vac and couldn't find any leaks.
I have a spare O2 so I'll swap it and re-check. Cheers VI
I had a fogger on vac and couldn't find any leaks.
I have a spare O2 so I'll swap it and re-check. Cheers VI
#6
Senior Member
Join Date: Aug 2002
Location: ARIZONA
Posts: 948
Likes: 0
Received 4 Likes
on
4 Posts
Car: 92 Trans Am Conv
Engine: LB9
Transmission: T5
Axle/Gears: 3.08
Re: Low BLM at idle only (l98)
Try the O2 sensor. Then if that's not it, you can eliminate some problems by correcting the fueling via tune. If it takes it and fixes it then that tells you which path to take for finding the cause.
#7
Supreme Member
Thread Starter
iTrader: (1)
Join Date: May 2015
Location: Temecula, CA
Posts: 1,149
Received 83 Likes
on
67 Posts
Car: 1989 Pontiac Formula 350
Engine: L98
Transmission: 700R4
Axle/Gears: BorgWarner 3.27 Posi
Re: Low BLM at idle only (l98)
I went and did a datalog with the stock tune and BLMs were way better for what-ever reason. The stock tune overall was lean, so I guess I'll be swapping back to the mail tune anyways as that was addressed with it.
I did see the O2 reading jump from 150-200 to over 1000 intermittently. Edit: The more I read the more that looks sort of normal? No idea, I'll probably swap that O2 anyways.
Attached is the xdl from TunerPro RT
Using: $6E-1227265-V1.2.adx
I did see the O2 reading jump from 150-200 to over 1000 intermittently. Edit: The more I read the more that looks sort of normal? No idea, I'll probably swap that O2 anyways.
Attached is the xdl from TunerPro RT
Using: $6E-1227265-V1.2.adx
Last edited by thtanner; 09-05-2016 at 07:48 PM.
Trending Topics
#8
Senior Member
Join Date: Jul 2009
Location: Morgantown, WV
Posts: 524
Received 100 Likes
on
69 Posts
Car: 1990 Trans Am
Engine: 5.7 350 HSR afr195 xfi268
Transmission: T5
Axle/Gears: 3.08 posi
Re: Low BLM at idle only (l98)
Unless I missed something your fp should be at 43 without vacuum.
Last edited by maks10; 09-06-2016 at 01:29 AM.
#11
Senior Member
Join Date: Aug 2002
Location: ARIZONA
Posts: 948
Likes: 0
Received 4 Likes
on
4 Posts
Car: 92 Trans Am Conv
Engine: LB9
Transmission: T5
Axle/Gears: 3.08
Re: Low BLM at idle only (l98)
I haven't looked at the log but changing injector constant is not how you fix this issue unless you changed flow rate. and that also wouldn't make sense that the oem tune is better.
#12
Re: Low BLM at idle only (l98)
You know what they say about opinions. His blm averages in the log were about 133 so my method would absolutely work in bringing his averages down. Or, he could turn fuel pressure up until his blm average came in closer to 128. Mass air cars don't have VE tables to tune like your 92.
#14
#15
Supreme Member
Thread Starter
iTrader: (1)
Join Date: May 2015
Location: Temecula, CA
Posts: 1,149
Received 83 Likes
on
67 Posts
Car: 1989 Pontiac Formula 350
Engine: L98
Transmission: 700R4
Axle/Gears: BorgWarner 3.27 Posi
Re: Low BLM at idle only (l98)
The low BLMs were present in both tunes, that is what prompted me to post. Of course when I checked/logged yesterday, they were way better. I dug out my new O2 from my parts pile, so I'll put that in before moving forward.
I'll run both tunes again after that to see if I can replicate my original issue. If not, could have just been an intermittent O2 sensor. I can't exactly modify my tune until I get a chip burner though.
I'll run both tunes again after that to see if I can replicate my original issue. If not, could have just been an intermittent O2 sensor. I can't exactly modify my tune until I get a chip burner though.
#16
Senior Member
Join Date: Aug 2002
Location: ARIZONA
Posts: 948
Likes: 0
Received 4 Likes
on
4 Posts
Car: 92 Trans Am Conv
Engine: LB9
Transmission: T5
Axle/Gears: 3.08
Re: Low BLM at idle only (l98)
Mr ****** I already proposed something. And asked more questions along the way that still need answering.
Until the answers and o2 are checked I will not suggest anything further as that is incompetent.
OP you've said that the stock tune has an idle BLM issue and that it doesn't. So which is it?
You need to narrow it down to using one tune or the other. Don't flip flop.
Until the answers and o2 are checked I will not suggest anything further as that is incompetent.
OP you've said that the stock tune has an idle BLM issue and that it doesn't. So which is it?
You need to narrow it down to using one tune or the other. Don't flip flop.
#17
Senior Member
Join Date: Aug 2002
Location: ARIZONA
Posts: 948
Likes: 0
Received 4 Likes
on
4 Posts
Car: 92 Trans Am Conv
Engine: LB9
Transmission: T5
Axle/Gears: 3.08
Re: Low BLM at idle only (l98)
And no it won't really with your solution. This is a bandaid solution to a single minded BLM view. You don't tune BLMs with injector constant. There's a MAF calibration table you use. What you propose is not an EFI solution to an EFI problem. It's a carb solution to an EFI problem. It doesn't work that way if you want something done right.
You don't flood a sink to fill a cup.
You don't flood a sink to fill a cup.
#18
Supreme Member
Thread Starter
iTrader: (1)
Join Date: May 2015
Location: Temecula, CA
Posts: 1,149
Received 83 Likes
on
67 Posts
Car: 1989 Pontiac Formula 350
Engine: L98
Transmission: 700R4
Axle/Gears: BorgWarner 3.27 Posi
Re: Low BLM at idle only (l98)
Mr ****** I already proposed something. And asked more questions along the way that still need answering.
Until the answers and o2 are checked I will not suggest anything further as that is incompetent.
OP you've said that the stock tune has an idle BLM issue and that it doesn't. So which is it?
You need to narrow it down to using one tune or the other. Don't flip flop.
Until the answers and o2 are checked I will not suggest anything further as that is incompetent.
OP you've said that the stock tune has an idle BLM issue and that it doesn't. So which is it?
You need to narrow it down to using one tune or the other. Don't flip flop.
It was initially suggested to swap the O2 sensor (by you, Vanilla Ice). I said that I have one, and will be doing so. After that, if the low BLM issue does not surface again, then it was most likely down to an intermittently bad O2 sensor, correctly diagnosed by you.
If it does surface again, then it's something else screwing up, and probably not a tuning issue.
#19
Senior Member
Join Date: Aug 2002
Location: ARIZONA
Posts: 948
Likes: 0
Received 4 Likes
on
4 Posts
Car: 92 Trans Am Conv
Engine: LB9
Transmission: T5
Axle/Gears: 3.08
Re: Low BLM at idle only (l98)
No worries, I was under the impression from the log post that the stock tune did in fact correct the BLM idle issue but you were going to swap the O2 anyway.
#21
Re: Low BLM at idle only (l98)
And no it won't really with your solution. This is a bandaid solution to a single minded BLM view. You don't tune BLMs with injector constant. There's a MAF calibration table you use. What you propose is not an EFI solution to an EFI problem. It's a carb solution to an EFI problem. It doesn't work that way if you want something done right.
You don't flood a sink to fill a cup.
You don't flood a sink to fill a cup.
Thread
Thread Starter
Forum
Replies
Last Post