Redzee Posted February 6, 2014 Share Posted February 6, 2014 I was wondering if anyone has had any issues with their cars losing power when shifting into 4th gear at the drag strip? the car pulls hard through the first 3 gears and goes flat after the 3rd to 4th gear shift, if you pedal it a few times it recovers. I thought it might be a fuel supply issue so I increased the size of the pickup from the fuel tank, still no change (1/2" pickup) then I thought it might a be fuel sloshing issue so I added a surge tank, changed the fuel pump, still no improvement. fuel pressure is rock solid at 60 psi through out. but the car still loses power when shifting into four gear. it is a 2002 ls1 dynoed at 380 RWH...no issues on the dyno carter super pump feeding surge tank with #10 lines walbro 255 with a #8 suction and # 6 supply lines aeromotive regulator, stock rails and injectors Quote Link to comment Share on other sites More sharing options...
WarlordZ Posted February 6, 2014 Share Posted February 6, 2014 misfire with computer temporarily going into safe mode or low fuel pressure. It's calling on that fuel pump in 4th. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted February 6, 2014 Share Posted February 6, 2014 (edited) Could it just be from the big rpm drop going from 1.43 to 1.0 gear ratio? What rpm are you shifting, and what does it drop to on the shift? What size rear tires? What kind of rear tires at what air pressure? Dirty fuel from using 40-year old tank; check your filter? You racing 1/8-mile or 1/4-mile? Is the car missing, sputtering, or just losing power while running smoothly? I wonder if the computer is programmed to pull timing in 4th? Was this motor ever on nitrous? Edited February 6, 2014 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted February 6, 2014 Share Posted February 6, 2014 Does this only happen after you eat a big, greasy hamburger? Quote Link to comment Share on other sites More sharing options...
Redzee Posted February 7, 2014 Author Share Posted February 7, 2014 fuel pressure is consistant at 60 psi, fuel tank and filters are clean, running 1/4 mile, no sputtering or missing just no power, like you shut the key off Tires are 225- 50 16's at 22 psi, never been on Nitrous. seems to pull 4th gear fine on the dyno, tuner said the MAF and IAT reading seem to be a little irratic Quote Link to comment Share on other sites More sharing options...
Redzee Posted February 7, 2014 Author Share Posted February 7, 2014 I rarely eat big greasy hamburgers Quote Link to comment Share on other sites More sharing options...
Redzee Posted February 7, 2014 Author Share Posted February 7, 2014 I shift a 6000 to 6200rpm Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted February 7, 2014 Share Posted February 7, 2014 Are you Canadians actually drag racing this time of year??? You should try a hamburger, ay, it makes everything seem better, mostly just hurts your 60' time. Kidding aside, I'm just brainstorming: what could be different on the track compared to the sterile environment of the dyno room.... Is the problem intermittent or constant (every time)? In Canada-fuel freezing? Did you have this problem in the summertime? Super high (cold air) or low (altitude) air density? Bad IAT (inlet air temp) sensor? Brake drag? Clutch slippage? Do you lose power in 4th on the street? Can you post a typical time slip so we can see your 60', mid-track, 1/8-mile and 1/4-mile times and mph? What gearing in the diff? Are you by chance spinning thru 1st, 2nd, and 3rd, the suddenly getting traction in 4th? Is your fuel pressure gauge in the cockpit where you can see it? Do you have a cold-air intake outside the engine compartment? Got a gopro video that shows the problem? I think Sunny Z uses some kind of IAT trick to pull timing for his NOS. Try PM-ing him. I bet the problem is there. What else would cause power loss, while preserving smooth operation (no stuttering or missing)? If you are racing this time of year, maybe the IAT sensor can't handle the cold air that it sees when you are flying down the track with a 100mph wind blowing on the IAT sensor. Quote Link to comment Share on other sites More sharing options...
Redzee Posted February 7, 2014 Author Share Posted February 7, 2014 haha, no not drag racing this time of year, little too slippery, cold pavement or ice LOL, yes even on the street if you go hard from third to fourth, no clutch slippage, tires hook good in second, 3.55 rear end ratio, fuel pressure is cockpit visiible, maybe a short when the load on the engine increases with the higher gear?? Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted February 7, 2014 Share Posted February 7, 2014 Don't know what you mean by a "short." Still thinking IAT or maybe that MAF, especially if the tuner says they are sketchy. It only does it when you shift hard, not if you shift smoothly? Will the car continue to accelerate and gain speed and rpm? What happens when you go to 5th and 6th? When I go 1/4-mile, due to the drop in rpm, when I shift into 4th, the car doesn't accelerate as fast as it was before the shift, but there is quickly an rpm where the car really pushes you back and the car starts to boogie right up to 6200. I don't know what rpm that is where the cam seems to "come alive," but it is almost orgasmic. But there is definitely less power available just after the 3-4 shift. Watch my videos on the RebekahsZ chanel of youtube and you can see how my car behaves from cockpit views and from tire level views. Look for the videos from Alabama International Dragway. Quote Link to comment Share on other sites More sharing options...
Redzee Posted February 7, 2014 Author Share Posted February 7, 2014 Electrical short in the MAF and IAT to ECU Quote Link to comment Share on other sites More sharing options...
Redzee Posted February 7, 2014 Author Share Posted February 7, 2014 even smooth shift, Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted February 7, 2014 Share Posted February 7, 2014 I guess before looking for a short (can be hard to find) I would check the components. See if any of the local guys will let you borrow their IAT first, then their MAF for a treat drive. Maybe you will get lucky. Quote Link to comment Share on other sites More sharing options...
Redzee Posted February 8, 2014 Author Share Posted February 8, 2014 I found a guy willing to go for a test drive with his tech II program to see if we can capture what the computer is seeing when the thing falls on its face, got my fingures crossed Quote Link to comment Share on other sites More sharing options...
ktm Posted February 8, 2014 Share Posted February 8, 2014 It's odd that it manifests itself at only the 3rd-4th shift. My car had an issue where if I accelerated brisky or turned left hard, it would lose all power and then get it back. Long story short, the battery cable on the back of the alternator had come loose and would contact the engine mount and create a short. Quote Link to comment Share on other sites More sharing options...
Redzee Posted February 10, 2014 Author Share Posted February 10, 2014 hmm interesting, yes it is a strange hiccup Quote Link to comment Share on other sites More sharing options...
Phantom Posted February 20, 2014 Share Posted February 20, 2014 Redzee - Not sure if RebekahsZ might be onto something. One difference between my car and yours is that I'm running a 3.70 LSD R200 rather than a 3.545. I have always been pleased with the performance I've gotten from the car. I have never seen an acceleration drop-off in 4th. It just keeps pulling like a freight train. I'm running 225/50-16 street radials so the differential sounds like the only big difference in our drive-trains. I'm thinking the slight RPM difference might be keeping the LS1 in a sweeter spot on the torque/HP curves? There might be a reason other than just weight that GM usually equipped LS1 cars with 3.73:1 differentials. Quote Link to comment Share on other sites More sharing options...
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