98 Trans am Fuel Pressure problem and idle issues?
02-28-2014, 11:45 PM
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98 Trans am Fuel Pressure problem and idle issues? Hey guys I have a 1998 Trans am ls1 with some problems. I have been trying to fix them for a while now so if you could lead me the way to victory in this battle I have been having it would be greatly appreciated. Specs are at end of thread.
Fresh rebuilt motor by 2nd opinion and got new pistons.
Motor has lots of power but has the following problems below.
PROBLEMS:
My car takes about 2 key turns before starting so it wont crank for 7 seconds before starting. Otherwise I have to floor the gas petal while cranking and it will start normally without priming it 2 times. So with that being said I installed a fuel pressure gauge on my fuel rail. It would prime up to 30 psi with first key turn then 60 psi with the second key turn. After each time I prime it I look at the gauge and the fuel psi is dropping at a rate of 10 psi per second. So next I checked for leaky injectors and changed my fuel filter twice. Went to go crank it and still doing the exact same thing dropping 10 psi per second. Then I do some more research and find out it could be the fuel pressure regulator leaking, hose leaking, or check valve in the fuel pump. Next I do the trap door hack on my trans am and pull the pump out and look at it and see no visual defects or cracks. The next ideal step to take would be to replace the fuel pressure regulator in it but instead I just took it off and took the set screw out not thinking then put it back in not knowing how far to go in so I winged it. After putting it back on I took the actual fuel pump motor off and shook it around and played with it for a bit because I was clueless on how to check the check valve so I just put it back on. So now I put the fuel pump back in since I dont have the money right now to replace either right now. I prime the car twice and go look at the gauge and it is now reading 70 psi at the fuel rail and it was holding pressure now?!
So I started the car and it fired right up like it should and I watched the gauge for about 10 minutes and it held all the pressure so I called it fixed and went to bed. So the car sat over night and I checked the gauge to see if it held pressure and it was at 0 psi?! 
Next I primed it twice and it went back up to 70 psi and I watched the gauge and it was slowely losing pressure and then stopped at 35 psi so I left the car there for a few hours and now its at 0 psi again. The fuel pump I am running is stock from gm, not sure if its original or not.
I have a couple questions like
-Is 70 PSI at the fuel rail too much pressure for stock injectors??
-Why is it creating 70 PSI now?
-Why after shaking and taking the set screw out and back in does it hold pressure longer now instead of instantly losing pressure like before?
- Would 70 PSI at the fuel rail cause any damage to the engine?
- Would this cause idle issues?
The other problem I have is my idle is crap but it has gotten better. My car idles at 900 rpms and I read that off of a scanner so its accurate. BUT to even get the car to idle after started and for it to not have a HUGE SURGING idle for about a minute I have to hold the pedal down to where it will stay revved up to about 1100 rpms. After holding it at 1100 rpms for about 8 seconds I can let off the pedal and it idles at 900 rpms like stated before. Once the car is on for about 5 minuets it idles up to around 1300 rpms and stays there the rest of the time. While the car is at 900 rpms and also at 1300 rpms the engine slowly increases the rpms going up and back down to what it was at but the most it increases is about 20 rpms. So you cant even tell unless you get the scanner out or listen very closely to the exhaust. I really want the car to stay at 900 rpms when idling. Because when idled at 1300 rpms my car doesn't loap as much and show off my cam. So I have reset the IAC valve many times doing it the proper way along with resetting the TPS. I dont have any codes being thrown for anything. When I initially put the motor back in after the rebuild my idle was surging terribly and my car would idle at 3200 rpms randomly and stay there even after turning the car off. While this is happening I was blowing the Engine sensor fuse. Obviously the IAC valve was acting up from the fuse blowing or whatever so I cleaned it and reset it and found out the reason I kept blowing the engine sensor fuse. I had two exposed wires in the wire harness behind the passenger head from the cylinder head rubbing the 2 wires in the wire harness raw causing them to ground out. I taped them up with electrical tape very well and BAM I haven't blown the sensor since. And now I am having the problems with the whole 900 rpm idle and 1300 rpm idle after warmed up. I have also tried cleaning the maf with maf cleaner no luck.
Again im not throwing any codes for anything. I have also used a multi meter on the TPS while running at both 900 rpms and 1300 rpms and it shows the throttle at 2% then 3, 5, 4, 1 and its constantly changing extremely fast so its not ever showing a constant throttle %. With the car off I run the same test moving the Throttle body and it shows precise throttle percentage so the sensor is good I assume. Also I dont have any vacuum leaks I already checked. My car does smell rich when driving but Im sure that's from the cat delete.
Question
-Why does it idle at 900 rpms when cold then 1300 rpms when warmed up?
-Why do I have to hold the petal down to about 1100 rpms for 8 seconds when first started to get it to even idle.
-Is my TPS supposed to be constantly changing throttle % at idle?
MODS:
LS6 Intake, double valve springs, ported polished stock heads, ms3 cam, double roller chain, clevite bearings, Forged Mahle Pistons LS6 Crank, Mid length headers, slp maf EGR delete, 1000cc injectors swiched back to stock after 1 minute of run time, spec stage 4 clutch, aluminum flywheel, pro 5.0 shifter, polly tranny and engine mounts, frame connectors, 4.11 gears, Cat delete, 3" straight pipes to back of car.
I don't have a tune on this car as far as I know. Although I DON'T throw any o2 sensor codes even though its straight pipe and I am NOT throwing any codes from the egr delete. So what do you think? Do I have some sort of delete on the pcm for those? Also if I unplug my o2 sensors it will throw the code saying its not plugged in. So im not sure if I have a tune or not.
Engine: LS1
Engine Miles: 35 miles
Body miles: 120,000 miles
Color: red.. lol
Thanks guys I know its alot of information but I tried to put the most detail in it all so I dont get any questions about if I tried this or that and asking if I have this done to it lol.
Fresh rebuilt motor by 2nd opinion and got new pistons.
Motor has lots of power but has the following problems below.
PROBLEMS:
My car takes about 2 key turns before starting so it wont crank for 7 seconds before starting. Otherwise I have to floor the gas petal while cranking and it will start normally without priming it 2 times. So with that being said I installed a fuel pressure gauge on my fuel rail. It would prime up to 30 psi with first key turn then 60 psi with the second key turn. After each time I prime it I look at the gauge and the fuel psi is dropping at a rate of 10 psi per second. So next I checked for leaky injectors and changed my fuel filter twice. Went to go crank it and still doing the exact same thing dropping 10 psi per second. Then I do some more research and find out it could be the fuel pressure regulator leaking, hose leaking, or check valve in the fuel pump. Next I do the trap door hack on my trans am and pull the pump out and look at it and see no visual defects or cracks. The next ideal step to take would be to replace the fuel pressure regulator in it but instead I just took it off and took the set screw out not thinking then put it back in not knowing how far to go in so I winged it. After putting it back on I took the actual fuel pump motor off and shook it around and played with it for a bit because I was clueless on how to check the check valve so I just put it back on. So now I put the fuel pump back in since I dont have the money right now to replace either right now. I prime the car twice and go look at the gauge and it is now reading 70 psi at the fuel rail and it was holding pressure now?!
So I started the car and it fired right up like it should and I watched the gauge for about 10 minutes and it held all the pressure so I called it fixed and went to bed. So the car sat over night and I checked the gauge to see if it held pressure and it was at 0 psi?! Next I primed it twice and it went back up to 70 psi and I watched the gauge and it was slowely losing pressure and then stopped at 35 psi so I left the car there for a few hours and now its at 0 psi again. The fuel pump I am running is stock from gm, not sure if its original or not.I have a couple questions like
-Is 70 PSI at the fuel rail too much pressure for stock injectors??
-Why is it creating 70 PSI now?
-Why after shaking and taking the set screw out and back in does it hold pressure longer now instead of instantly losing pressure like before?
- Would 70 PSI at the fuel rail cause any damage to the engine?
- Would this cause idle issues?
The other problem I have is my idle is crap but it has gotten better. My car idles at 900 rpms and I read that off of a scanner so its accurate. BUT to even get the car to idle after started and for it to not have a HUGE SURGING idle for about a minute I have to hold the pedal down to where it will stay revved up to about 1100 rpms. After holding it at 1100 rpms for about 8 seconds I can let off the pedal and it idles at 900 rpms like stated before. Once the car is on for about 5 minuets it idles up to around 1300 rpms and stays there the rest of the time. While the car is at 900 rpms and also at 1300 rpms the engine slowly increases the rpms going up and back down to what it was at but the most it increases is about 20 rpms. So you cant even tell unless you get the scanner out or listen very closely to the exhaust. I really want the car to stay at 900 rpms when idling. Because when idled at 1300 rpms my car doesn't loap as much and show off my cam. So I have reset the IAC valve many times doing it the proper way along with resetting the TPS. I dont have any codes being thrown for anything. When I initially put the motor back in after the rebuild my idle was surging terribly and my car would idle at 3200 rpms randomly and stay there even after turning the car off. While this is happening I was blowing the Engine sensor fuse. Obviously the IAC valve was acting up from the fuse blowing or whatever so I cleaned it and reset it and found out the reason I kept blowing the engine sensor fuse. I had two exposed wires in the wire harness behind the passenger head from the cylinder head rubbing the 2 wires in the wire harness raw causing them to ground out. I taped them up with electrical tape very well and BAM I haven't blown the sensor since. And now I am having the problems with the whole 900 rpm idle and 1300 rpm idle after warmed up. I have also tried cleaning the maf with maf cleaner no luck.
Again im not throwing any codes for anything. I have also used a multi meter on the TPS while running at both 900 rpms and 1300 rpms and it shows the throttle at 2% then 3, 5, 4, 1 and its constantly changing extremely fast so its not ever showing a constant throttle %. With the car off I run the same test moving the Throttle body and it shows precise throttle percentage so the sensor is good I assume. Also I dont have any vacuum leaks I already checked. My car does smell rich when driving but Im sure that's from the cat delete.
Question
-Why does it idle at 900 rpms when cold then 1300 rpms when warmed up?
-Why do I have to hold the petal down to about 1100 rpms for 8 seconds when first started to get it to even idle.
-Is my TPS supposed to be constantly changing throttle % at idle?
MODS:
LS6 Intake, double valve springs, ported polished stock heads, ms3 cam, double roller chain, clevite bearings, Forged Mahle Pistons LS6 Crank, Mid length headers, slp maf EGR delete, 1000cc injectors swiched back to stock after 1 minute of run time, spec stage 4 clutch, aluminum flywheel, pro 5.0 shifter, polly tranny and engine mounts, frame connectors, 4.11 gears, Cat delete, 3" straight pipes to back of car.
I don't have a tune on this car as far as I know. Although I DON'T throw any o2 sensor codes even though its straight pipe and I am NOT throwing any codes from the egr delete. So what do you think? Do I have some sort of delete on the pcm for those? Also if I unplug my o2 sensors it will throw the code saying its not plugged in. So im not sure if I have a tune or not.
Engine: LS1
Engine Miles: 35 miles
Body miles: 120,000 miles
Color: red.. lol
Thanks guys I know its alot of information but I tried to put the most detail in it all so I dont get any questions about if I tried this or that and asking if I have this done to it lol.
03-01-2014, 12:16 AM
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thanks for the reply but wouldnt it throw a code for the TPS sensor? I agree with you on the regulator and tune.
When hooked up to a multi meter and the engine not on it shows the TPS is working just fine?
When hooked up to a multi meter and the engine not on it shows the TPS is working just fine?
03-01-2014, 12:32 AM
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yeah im really lost in this whole deal...
well when I pulled the harness off to fix the two wires that got rubbed raw I pulled off all the plastic shielding and checked everything and made sure the pigtails were fine. but yeah the tps wiring is fine.
well when I pulled the harness off to fix the two wires that got rubbed raw I pulled off all the plastic shielding and checked everything and made sure the pigtails were fine. but yeah the tps wiring is fine.
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03-01-2014, 01:27 AM
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It has been like this even before I messed with the FPR. Whenever I took out my IAC valve a while back and hooked it up outside of the TB I watched it go in and out everytime I turned my ignition on but even then I was having idle isues. But now for some reason it doesnt move at all when I take it out and turn the ignition on...? the only thing it will occasionally do is go all the way out to where the spring inside doesnt even touch it.
