Ok, maybe unrelated, about 6 months ago my car began to not start on the first crank of the key, does not matter if it cranks for 2 or 10 seconds. But will start up immediatly on the second crank. Unless restarting within 30 min.
Now, a few times last week it felt like I was running out of gas, running really rough and half throttle just to maintain the speed in traffic only lasted for about 4 or 5 seconds, then BAM starts running normal and takes off due to the throttle being half depressed. It did this around 1-2 times on my drive to and from work the last 2 days. (I've ran out of gas quite a few times and feels exactly like it, never in this car though)
Today it did it about 5 times just on the way to work and almost the whole way home. Actually floored it once just to keep momentum when merging and it stayed at 15mph for like 3 seconds then shit I'm sideways when it kicked in. The SES light flashed for a bit, Then about 2/3 home the SES light quit flashing and it ran normal for about 8 miles.
recent work
-Rebuit T56 and clutch install
-Cooling system flush and fill
Don't think that either would effect this problem but just in case.
I've had sort of the same problem lately too, however mine is unresolved. My 98 T/A doesn't start on the first or sometimes second cranks, but always by the third its fine. I haven't had the sputtering issue like yours though, which is close to the universal sign of "get a new pump."
Other things to check could be a vacuum leak or a clogged fuel filter or injector. Try seafoaming the gas tank and the top end, and check for vacuum leaks. If it doesn't help, it might be time to swap the pump.
From your description, I'm having the exact same problem. When you first turn the key do you notice the fuel pump priming? Mine doesn't. I have to turn it over for a second. Then when it is turned off, and then back on, I hear the pump prime. I only drive the car about once a month(1000 miles in the last year), so I haven't really felt the need to find out what it is, but it has been doing this for over a year.
I had this problem and I figured out it was caused by the power wire that was going to the relay boxs. There is a nut that if not tightened down well will have a bad contact.
This sounds electrical to me, and electrical can effect the fuel pump output.
Have you done anything to your car in the recent that could cause this?
-One O2 sensor bad, just stays at 1107 while the good one varies from 100 to 500. The rear sims working and reading about 450
-Bank 2 FI pulsewidth was around 3
-Bank 1 FI pulsewidth was around 1.7
-Misfires were going crazy on cyl's 2 and 6
-Problem does not occur at WOT
Would the bad o2 sensor cause my issue?
My friend was thinking bad fuel injector, but the 5 I could reach all tested the same impedence.
He also said it could be the driver, as in the PCM itself
-One O2 sensor bad, just stays at 1107 while the good one varies from 100 to 500. The rear sims working and reading about 450
-Bank 2 FI pulsewidth was around 3
-Bank 1 FI pulsewidth was around 1.7
-Misfires were going crazy on cyl's 2 and 6
-Problem does not occur at WOT
Would the bad o2 sensor cause my issue?
My friend was thinking bad fuel injector, but the 5 I could reach all tested the same impedence.
He also said it could be the driver, as in the PCM itself
sounds like you have a injector that has failed mechanically.. The Bosch 3 in your car have coils that never go bad. However they do get clogged and they do leak occasionally. The symptoms you have is classic leaky injector. You can send them to us we will test them on a flow bench for free. Or you can get an exchange set for 120 all reconditioned and ready to go.
__________________ If you order from our website, use the code ls1teck for $5 off shipping!!! info@fuelinjectorconnection.com
sounds like you have a injector that has failed mechanically.. The Bosch 3 in your car have coils that never go bad. However they do get clogged and they do leak occasionally. The symptoms you have is classic leaky injector. You can send them to us we will test them on a flow bench for free. Or you can get an exchange set for 120 all reconditioned and ready to go.
Oh, I forgot to update part... After installing the new fuel pump the car starts instantly on first crank again. But the sputtering not running right continues which I assume could rule out leaky injector.
We ran the snap on injector test, which builds line pressure then sprayes fuel for a specific amount of time and then you record how much the fuel pressure drops. They were all equal.
Does this change anything?
Once again to be clear, sputters at part throttle, runs really rich when having the issue (eyes burning) and probem goes in and out. Might drive 5 miles with no issue, and the mis/problem might kick in and out 5 times the first mile, never know. Its like there is someone with a switch in the pass seat that can switch car from perfect to run like crap and just sits there and flips switch in no rythmic method. NEVER has a problem at WOT, no matter how crappy is running, if I put it to the wood it takes off and runs fine.
did you get the O2s replaced? i know my bad O2 mad my car really rich and made my part throttle fall flat on its face..today i learned running really lean at part throttle makes the car spit and spudder and not want to move!!
__________________ ZL 402 ls6 heads p+p 2.02/1.575 full roller yella terra, 11:9 C.R.,224/228 .535 .538 114 LSA cam, exo-skel clutch,102mm lid, 85mm MAF, bellow, k+n, p+p 82mmTB,ls6 intake, 42# injectors, pacesetter LT's coated headers, 2.5 true dual W/H pipe and dual cut outs, BMR torque arm,SFC/s panhard bar, control arms, and shock tower brace, , HAL drag shocks, ASP pulleys, 4.10 gears, B&M ripper, ls6 slave, mcleod adj. master, Evans t-stat and water pump.150 shot soon! Atap/LS1edit
I have a similar problem on my 98 T/A M6, it's just starting up, I was thinking fuel pump too but after reading what you wrote.... Mine mostly does it right after I start the car (always starts right up) and put it in first and go to pull out, it starts running really rough and sometimes I can't even keep it from stalling, after about 2-4 seconds of pumping the gas it smooths out and runs okay, only 1 or 2 times in the last week have i started to notice a very small hiccup in power loss when accelerating at half throttle. Was the fuel pump hard to change? i'm ordering a fuel pressure gauge today for it to see if it is the pump for me.
Fuel problem,,, maybe?? please help 
