Fuel Injected motor...miss from 1-3K

Rich Biebel · 06-11-2012, 08:39 PM

I was constantly trying to tune my LT-1 myself and really needed to get it tuned on a dyno......I was using an Innovate LM-1 to get as gar as I did....on my own....

One raceday I was making Fuel Map changes across the board.....Just put in a percentage change richer......I thought it was a relatively small change.....

Well on the next run....It idled fine....drove up to the lanes fine....went to do a burnout and when I stepped on the gas.....nothing....motor basically did not even have enough power to spin the tires in the water at part throttle..... I staged it anyway and made the run and was not really off by much from an earlier run....

Took the enrichment back out and it was fine after that.....

It was just too rich to begin with and the added fuel really killed it.......

Eric Merryfield · 06-11-2012, 09:18 PM

Thanks for all the replies......I will be pulling data riding around the pits and doing a "fake" staging to simulate the issue....I will try it cold and warm, will also pull a data run with MAP sensor disconnected(did that in the trailer this morning, and it seemed to rev up smoother, not totally smooth, but better than it did with it in....Will be sending off logs to tuner...didn't find any loose sensors, will get a nice smooth low rpm tweak and that should fix the drama.....but staging it bumping it it at idle then on with 1400lb of brake pressure to hold it while it stumbles up through 3 to two step at 4K is a bit of a challenge.....driving it up the trailer is another one!

Thanks

Eric

Ed Wright · 06-11-2012, 09:46 PM

Eric, it is a pain, but you won't get acurate O2 log data at low RPM & lower throttle angles with open headers. Make up a header extention about 3' long, preferably with like a 45 deg bend in the middle, for logging your idle, driving down the return road or pits, and bringing it up against the brake (no 2 step!) to see where you are. A little time spent there wil make it all a lot easier for you or whoever is trying to tune it for you. Big cams pull clean air in open headers (The exhaust actually pulses in & out) during the overlap cycle. That causes bogus lean indications from your wide band. That compunds the issue if your trying to run it in closed loop! A muffler or long enough extention will keep the clean air from reaching the O2 during those pulses.

Good luck.

Tommy Gaynor · 06-11-2012, 11:59 PM

I had a similar problem a few years ago and when we got it on the dyne with an ignition scope it showed a very weak coil. replaced the coil and picked up about .20 and miss down low was gone. Just my two cents.

Tommy

buzzinhalfdozen · 06-12-2012, 08:09 AM

As mentioned, a weak coil could cause this as 3000 is around where the multiple spark ceases to operate. trying to "pulse" a weak coil multiple times would really show up, where 1 strike may be more bearable for it, just a thought. Joe

Ed Wright · 06-12-2012, 08:17 AM

Makes perfect sense. I hadn't thought about that one. You ain't just real dumb, are ya? LOL

Eric Merryfield · 06-12-2012, 11:40 AM

Quote:

Originally Posted by Ed Wright

Makes perfect sense. I hadn't thought about that one. You ain't just real dumb, are ya? LOL

MSD Coil on order....along with another Accell cap and rotor ..no downside to having the spares..if they aren't the issue....it does fit with Toms scenario.....as it just up and lost some

Thanks

Eric

buzzinhalfdozen · 06-19-2012, 12:31 PM

Eric, any updates on your problem? Fixed, not yet, still working on it? Joe

06-11-2012, 08:39 PM	#1
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,315 Likes: 25 Liked 544 Times in 213 Posts	Re: Fuel Injected motor...miss from 1-3K I was constantly trying to tune my LT-1 myself and really needed to get it tuned on a dyno......I was using an Innovate LM-1 to get as gar as I did....on my own.... One raceday I was making Fuel Map changes across the board.....Just put in a percentage change richer......I thought it was a relatively small change..... Well on the next run....It idled fine....drove up to the lanes fine....went to do a burnout and when I stepped on the gas.....nothing....motor basically did not even have enough power to spin the tires in the water at part throttle..... I staged it anyway and made the run and was not really off by much from an earlier run.... Took the enrichment back out and it was fine after that..... It was just too rich to begin with and the added fuel really killed it....... __________________ Rich Biebel S/C 1479 Stock 147R

06-11-2012, 09:18 PM	#2
Eric Merryfield Senior Member Join Date: Apr 2008 Posts: 872 Likes: 1 Liked 502 Times in 130 Posts	Re: Fuel Injected motor...miss from 1-3K Thanks for all the replies......I will be pulling data riding around the pits and doing a "fake" staging to simulate the issue....I will try it cold and warm, will also pull a data run with MAP sensor disconnected(did that in the trailer this morning, and it seemed to rev up smoother, not totally smooth, but better than it did with it in....Will be sending off logs to tuner...didn't find any loose sensors, will get a nice smooth low rpm tweak and that should fix the drama.....but staging it bumping it it at idle then on with 1400lb of brake pressure to hold it while it stumbles up through 3 to two step at 4K is a bit of a challenge.....driving it up the trailer is another one! Thanks Eric __________________ Eric Merryfield 1883 STK

06-11-2012, 09:46 PM	#3
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: Fuel Injected motor...miss from 1-3K Eric, it is a pain, but you won't get acurate O2 log data at low RPM & lower throttle angles with open headers. Make up a header extention about 3' long, preferably with like a 45 deg bend in the middle, for logging your idle, driving down the return road or pits, and bringing it up against the brake (no 2 step!) to see where you are. A little time spent there wil make it all a lot easier for you or whoever is trying to tune it for you. Big cams pull clean air in open headers (The exhaust actually pulses in & out) during the overlap cycle. That causes bogus lean indications from your wide band. That compunds the issue if your trying to run it in closed loop! A muffler or long enough extention will keep the clean air from reaching the O2 during those pulses. Good luck. __________________ Ed Wright 4156 SS/JA

06-11-2012, 11:59 PM	#4
Tommy Gaynor Member Join Date: Aug 2002 Location: Vancouver WA Posts: 253 Likes: 2 Liked 5 Times in 3 Posts	Re: Fuel Injected motor...miss from 1-3K I had a similar problem a few years ago and when we got it on the dyne with an ignition scope it showed a very weak coil. replaced the coil and picked up about .20 and miss down low was gone. Just my two cents. Tommy __________________ "Go With Confidence"

06-12-2012, 08:09 AM	#5
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: Fuel Injected motor...miss from 1-3K As mentioned, a weak coil could cause this as 3000 is around where the multiple spark ceases to operate. trying to "pulse" a weak coil multiple times would really show up, where 1 strike may be more bearable for it, just a thought. Joe __________________ Joe Buchanan SS/BX 3117

06-12-2012, 08:17 AM	#6
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: Fuel Injected motor...miss from 1-3K Makes perfect sense. I hadn't thought about that one. You ain't just real dumb, are ya? LOL __________________ Ed Wright 4156 SS/JA

06-19-2012, 12:31 PM	#8
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: Fuel Injected motor...miss from 1-3K Eric, any updates on your problem? Fixed, not yet, still working on it? Joe __________________ Joe Buchanan SS/BX 3117