New 408", 1-2 sec into dyno pull, falls flat, shutsdown till you let off, cause?
11-10-2004, 04:41 PM
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New 408", 1-2 sec into dyno pull, falls flat, shutsdown till you let off, cause? This is a really hard to describe problem...
Have a car that just put a 408" in. Car drives around fine, 1/2 throttle the car pulls really hard and well, and the A/F is fine, LTrims are fine as well.
Sometimes instantly, but usually 1-2 seconds into going WOT the car completely nose dives, not like power is falling off, but its almost like you ran out of fuel or the PCM shuts down completely.
The car doesnt miss or do anything odd until you cross the 50% throttle range and its never at the same rpm. I can take the car up to 5500 rpm, then floor it and it cuts out instantly. Or i can stomp it at 2000 rpm and same thing.
On the dyno the A/F will be nice at the part throttle pull the moment it hits you hit the gas and it shutsdown, A/F doesnt just head lean, it goes immediatly off the scale above 18:1 in a vertical fashion, Meaning the injectors shutoff completely. Duty cycle on the 28.8 injectors is approx 125% on the computer and im going to put 30# SVO's in tonight...but i dont think static injectors could cause this.
Anyone ever had this problem?
Have a car that just put a 408" in. Car drives around fine, 1/2 throttle the car pulls really hard and well, and the A/F is fine, LTrims are fine as well.
Sometimes instantly, but usually 1-2 seconds into going WOT the car completely nose dives, not like power is falling off, but its almost like you ran out of fuel or the PCM shuts down completely.
The car doesnt miss or do anything odd until you cross the 50% throttle range and its never at the same rpm. I can take the car up to 5500 rpm, then floor it and it cuts out instantly. Or i can stomp it at 2000 rpm and same thing.
On the dyno the A/F will be nice at the part throttle pull the moment it hits you hit the gas and it shutsdown, A/F doesnt just head lean, it goes immediatly off the scale above 18:1 in a vertical fashion, Meaning the injectors shutoff completely. Duty cycle on the 28.8 injectors is approx 125% on the computer and im going to put 30# SVO's in tonight...but i dont think static injectors could cause this.
Anyone ever had this problem?
11-10-2004, 04:55 PM
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We checked the fuel pump everythings fine, fuel pressure doesnt drop a bit on the dyno when it cuts out, i think it has to be computer related. Because its pretty random.
11-10-2004, 05:05 PM
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If you mess around a lot with the MAF table in LS1Edit or the like you can get these EXACT symptoms.
SV0 30 lb/hr can support a 408 just fine, a N/A one. My 427 was dynotuned by MTI with the SVO 30s and it had more than enough fuel (coupled with a Racetronix PNP fuel pump).
SV0 30 lb/hr can support a 408 just fine, a N/A one. My 427 was dynotuned by MTI with the SVO 30s and it had more than enough fuel (coupled with a Racetronix PNP fuel pump).
11-10-2004, 05:12 PM
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Hmmm Well the old motor had a SLP MAF on it, and we swapped to the stock one. But it cut out before the swap as well. We didnt make any maf table changes...only PE VS RPM and idle stuff...as the rest worked well from the old tune on the 346"
11-10-2004, 05:27 PM
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I'm going to go with a fueling problem, but it sounds like it might be related to the tuning. Are you running an upgraded pump? If so how much gas was in the tank? A few of us have found that when running a modified upgraded intank pump, with less than a 1/4 tank of gas, the pump will sometimes have a scavenging effect and cause the car to do what you are describing. If you are still on the stock pump then I would look into finding a stock MAF table and loading that into the tune, or just start out with a completely stock tune and start over.
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11-10-2004, 06:04 PM
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Originally Posted by WS6snake-eater
I'm going to go with a fueling problem, but it sounds like it might be related to the tuning. Are you running an upgraded pump? If so how much gas was in the tank? A few of us have found that when running a modified upgraded intank pump, with less than a 1/4 tank of gas, the pump will sometimes have a scavenging effect and cause the car to do what you are describing. If you are still on the stock pump then I would look into finding a stock MAF table and loading that into the tune, or just start out with a completely stock tune and start over.
Ack...ive been all over with the tuning with no luck so far....hmmm
11-10-2004, 06:09 PM
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sorry to go slightly off topic here, but you said your injectors were at 125% duty cycle. how exactly does one tell what duty cycle the injectors are running at?
11-10-2004, 07:24 PM
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I had a problem similar to this that I was convinced
was some kind of abuse mode, it seemed to revolve
around shifts and would hang as described until I
backed out of the throttle and then, pull hard again.
I got rid of it when I went a different way with my
torque management, trying to pull a tapered TM
reduction seemed to be what brought it on and
using a flat reduction and raising the "max KR vs RPM"
value (misnamed somewhat I think in HPTuners but
it sets the minimum spark advance, that any retard
"actor" can pull back to) fixed that mess it seems.
Like there was a spark retard "hole" it fell into and
could not get out.
Check the logs as to whether the advance is falling
back and if so, maybe check out that angle.
Also check your spark advance and fueling maps for
any strange discontinuities, "tiger pits" etc.
was some kind of abuse mode, it seemed to revolve
around shifts and would hang as described until I
backed out of the throttle and then, pull hard again.
I got rid of it when I went a different way with my
torque management, trying to pull a tapered TM
reduction seemed to be what brought it on and
using a flat reduction and raising the "max KR vs RPM"
value (misnamed somewhat I think in HPTuners but
it sets the minimum spark advance, that any retard
"actor" can pull back to) fixed that mess it seems.
Like there was a spark retard "hole" it fell into and
could not get out.
Check the logs as to whether the advance is falling
back and if so, maybe check out that angle.
Also check your spark advance and fueling maps for
any strange discontinuities, "tiger pits" etc.
11-10-2004, 09:52 PM
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By what you describe did you car hit a wall that is much more solid than any rev limitor? Wheres its like the car goes dead (loses power fully) to the point where you might as well of have shut the key off to make it do that?
Cause it doesnt pull through it or recover, its fully on its face till you let off the gas
Cause it doesnt pull through it or recover, its fully on its face till you let off the gas
11-10-2004, 11:05 PM
#16
"Duty cycle on the 28.8 injectors is approx 125% on the computer and im going to put 30# SVO's in tonight...but i dont think static injectors could cause this."
I don't want to hijack this thread so hope my question is appropriate and related to the subject.
I'm still a novice and still trying to learn but does engine TM pull timing when the injectors go to 100% static? It would make good sense for the PCM program to do that because the engine would never run lean once the injectors go to 100 % duty cycle. To protect from running lean the motor would just shut down until it can catch up and supply enough fuel again.
Do motors run lean?, Yes but most times it's not because the injectors are running at 100 percent cycle (motors with stock injectors and making less than 450 rwhp). It's timing and tuning issues.
I didnt' think it was possible for an injector duty cycle to be more than 100 percent. At 100 percent the injector is full open and can't be opened to 125% (isn't that correct)?
According to an injector scale whose source is supposed to be accurate, a 28.6 stock injector goes to 100 percent duty cycle at 458 horsepower, a Bosch 30 is 554 and a Bosch 36 is 666. But the pros say you're not supposed to run at 100 percent but at 80 percent instead.
The 408 is going to make some serious rwhp at least 500 or over, so is a 30 enough at 80 percent?
Based on the above information the three injectors above in the same order are good for 366-443-532 hp at 80 %. According to the scale the first two injectors will not supply enough fuel at 80 percent and will go static (100 %) at 458 and 554. But that's on paper and not the real world.
I have been told that I should run 42.5 lbs'ers with an ATI boosted to 8-10 psi and making somewhere between 500 - 550 rwhp. NA the car dynos at 405 rwhp. I ordered 42.5's and will be disappointed if all I really needed were 30's.
I don't want to hijack this thread so hope my question is appropriate and related to the subject.
I'm still a novice and still trying to learn but does engine TM pull timing when the injectors go to 100% static? It would make good sense for the PCM program to do that because the engine would never run lean once the injectors go to 100 % duty cycle. To protect from running lean the motor would just shut down until it can catch up and supply enough fuel again.
Do motors run lean?, Yes but most times it's not because the injectors are running at 100 percent cycle (motors with stock injectors and making less than 450 rwhp). It's timing and tuning issues.
I didnt' think it was possible for an injector duty cycle to be more than 100 percent. At 100 percent the injector is full open and can't be opened to 125% (isn't that correct)?
According to an injector scale whose source is supposed to be accurate, a 28.6 stock injector goes to 100 percent duty cycle at 458 horsepower, a Bosch 30 is 554 and a Bosch 36 is 666. But the pros say you're not supposed to run at 100 percent but at 80 percent instead.
The 408 is going to make some serious rwhp at least 500 or over, so is a 30 enough at 80 percent?
Based on the above information the three injectors above in the same order are good for 366-443-532 hp at 80 %. According to the scale the first two injectors will not supply enough fuel at 80 percent and will go static (100 %) at 458 and 554. But that's on paper and not the real world.
I have been told that I should run 42.5 lbs'ers with an ATI boosted to 8-10 psi and making somewhere between 500 - 550 rwhp. NA the car dynos at 405 rwhp. I ordered 42.5's and will be disappointed if all I really needed were 30's.
Last edited by dlandsvZ28; 11-10-2004 at 11:18 PM.
11-10-2004, 11:29 PM
#19
Ok...so if the EFIlive formula is correct and you're 25 percent short, then a 36 lb will supply 125 % more fuel than a 28.6 which corresponds exactly with the scale I referred to in my earlier post.
But that's still at 100% duty cycle, so the real size should be a 42.5 which will supply the same amount of fuel at 80 percent as a 36 at 100 percent. Again...approximately the same as the injector scale and the size injector suggested for the hp the 408 is making.
Based on this maybe the injector scale I am going by is correct after all and the 42 is correct (for me at least).
But that's still at 100% duty cycle, so the real size should be a 42.5 which will supply the same amount of fuel at 80 percent as a 36 at 100 percent. Again...approximately the same as the injector scale and the size injector suggested for the hp the 408 is making.
Based on this maybe the injector scale I am going by is correct after all and the 42 is correct (for me at least).
Last edited by dlandsvZ28; 11-10-2004 at 11:35 PM.
