supercharged 05 tahoe fuel pressure issue along with others.
01-29-2013, 05:09 PM
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supercharged 05 tahoe fuel pressure issue along with others.
hey guys. this is my first post on the forum, been lurking a while. kinda gonna be a longer post so i ensure I cover all my basis. i have an 05 tahoe 4.8l with a magnuson 112 kit that is intercooled. i purchased the vehicle jan 2012 in Arizona. I live in Michigan so i drove it home, we went straight thru about 30 hours of drive time. i got home parked the truck for 30 min and unpacked, grabbed my buddy to go for a ride and the trans was all messed up. it was skipping 2nd gear and had no 4th. come to find out the trans had blown the 4th gear. crappy. did some research and ordered a performabuilt stage 2 with a 2500 stall converter.
I put the new trans in got 12 miles on it before it blow. sent it back got new trans in. drove fine for 3000 miles or so. meanwhile i was having hard starts randomly. i believe it happened a few times when i first got it as well but never payed any mind to it. i lost the ability to have tow/ haul mode activate in 4th gear at 55 or higher. called performabuilt about issue and also issue of inability to do a burnout, truck would just fall on its face. i could watch my fuel pressure gauge drop from 56 at idle to about 52. i was told it was not a trans issue. couple days later blow another trans. sent it back replaced it again. still no ability to do burnout or hard starts randomly. called magnuson and told them about issue. was told to replace fuel pressure regulator and pump if i felt froggy about knowing it would be covered. dropped tank, was told to order wrong pump by magnuson so had to reinstall pump and wait for correct part to show up. also realized i did not have the fuel regulator they spoke of so i ordered a new fuel module and correct pump. dropped tank again only to realize magnusons upgrades would not work as gm redesigned the fuel module. wtf. starting to get upset. just installed the new pump and rolled with it. continued to have hard start issues and random shift problems at this point. had trans in for like 2500 miles, transmission blew again.
I called performabuilt and replaced trans and converter this time. told i may have issues with my mass air flow sensor, so i replaced it as insurance. still having same hard start issues cold and randomly warm. called magnuson again and was told to do some data logging. got a a hold of a buddy with efi live and met him and did some checking. was told the short term and long term fuel trims were way off like 13 or 18 percent. was told i would need to upgrade fuel system to a return style and have it re-tuned. got all finished up with them and than realized log was not saved. i called magnuson told them story and the deny fact that the tune was messed up and the need for a return system. still don't know where my fuel pressure regulator is or how it would work with out one. i just want to do whats right. not spend money in places its not needed. if it needs a return system ill do it but don't want to modify if the root cause is still there. magnuson says possible injector but not sure how to go about this. i do plan to cam and header truck at some point in future but till i fix current issue im scared to change anything. i fear im gonna blow something. not sure if i mentioned, current fuel pressure at idle is around 56-58 and drop to 52 under boost. thanks any help would be greatly appreciated.
I put the new trans in got 12 miles on it before it blow. sent it back got new trans in. drove fine for 3000 miles or so. meanwhile i was having hard starts randomly. i believe it happened a few times when i first got it as well but never payed any mind to it. i lost the ability to have tow/ haul mode activate in 4th gear at 55 or higher. called performabuilt about issue and also issue of inability to do a burnout, truck would just fall on its face. i could watch my fuel pressure gauge drop from 56 at idle to about 52. i was told it was not a trans issue. couple days later blow another trans. sent it back replaced it again. still no ability to do burnout or hard starts randomly. called magnuson and told them about issue. was told to replace fuel pressure regulator and pump if i felt froggy about knowing it would be covered. dropped tank, was told to order wrong pump by magnuson so had to reinstall pump and wait for correct part to show up. also realized i did not have the fuel regulator they spoke of so i ordered a new fuel module and correct pump. dropped tank again only to realize magnusons upgrades would not work as gm redesigned the fuel module. wtf. starting to get upset. just installed the new pump and rolled with it. continued to have hard start issues and random shift problems at this point. had trans in for like 2500 miles, transmission blew again.
I called performabuilt and replaced trans and converter this time. told i may have issues with my mass air flow sensor, so i replaced it as insurance. still having same hard start issues cold and randomly warm. called magnuson again and was told to do some data logging. got a a hold of a buddy with efi live and met him and did some checking. was told the short term and long term fuel trims were way off like 13 or 18 percent. was told i would need to upgrade fuel system to a return style and have it re-tuned. got all finished up with them and than realized log was not saved. i called magnuson told them story and the deny fact that the tune was messed up and the need for a return system. still don't know where my fuel pressure regulator is or how it would work with out one. i just want to do whats right. not spend money in places its not needed. if it needs a return system ill do it but don't want to modify if the root cause is still there. magnuson says possible injector but not sure how to go about this. i do plan to cam and header truck at some point in future but till i fix current issue im scared to change anything. i fear im gonna blow something. not sure if i mentioned, current fuel pressure at idle is around 56-58 and drop to 52 under boost. thanks any help would be greatly appreciated.
Last edited by szachtb2; 01-29-2013 at 05:22 PM. Reason: paragraphs?
01-29-2013, 05:54 PM
#3
I would start with the tune. I would pull the ECM, send it to Wheatley, Nelson or Blackbear, and have them send you a good base tune for your current setup.
It sounds like you are running around replacing things and spending money, but aren't narrowing down what is causing the problem. Rule them out one by one, starting with the tune.
If you are concerned you are going to go lean and blow the engine, zip-tie the boost bypass in its current position while the truck is idling, this is the open position (it is located on the driver's side of the s/c, it's a silver rod going into a round black plastic housing). This will prevent you from building boost, making it much less likely you will have a lean condition.
Where are you located?
It sounds like you are running around replacing things and spending money, but aren't narrowing down what is causing the problem. Rule them out one by one, starting with the tune.
If you are concerned you are going to go lean and blow the engine, zip-tie the boost bypass in its current position while the truck is idling, this is the open position (it is located on the driver's side of the s/c, it's a silver rod going into a round black plastic housing). This will prevent you from building boost, making it much less likely you will have a lean condition.
Where are you located?
01-29-2013, 06:26 PM
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I live in michigan. I agree putting parts without an answer s worthless. Im a 7 year chevy tech so im fimiliar with tgese vehicles. I felt safe throwing the pump in at 100 and the mass air is hard to diag so I just replaced it as well and tgats where it ends with throwing parts around. Im considering that but was not sure where or what to do.
01-29-2013, 07:16 PM
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BTW magnuson technical support sucks. After wasting like a week of my time on the phone with these clowns, they now tell me they are unable to help me after telling me that my truck has a fuel pressure module on the rail which it does not have. WTF. Now im really upset. dont want to just keep wasting money on guesses. any solid tests i can perform to get some real answer and not just assumptions. im way past the wanting to guess stage at this point. thanks guys. whats a pcm tune cost? how long of a turn around time. this truck is my daily driver, not my cruiser hobby rider. thanks guys
01-29-2013, 07:32 PM
#6
PM Wheatley or Farmtruc (Nelson) on here, but they are around $300 I believe. Even if you weren't having problems, I would definitely recommend a tune from them, you will get more power and better driveability over a canned Magnacharger tune.
No offense, but just to better understand, you are a 7 year GM tech and aren't sure where to find your fuel pressure regulator or don't know where to find the proper literature?
My fuel pressure regulator for my return style system is on the driver's side fuel rail.
No offense, but just to better understand, you are a 7 year GM tech and aren't sure where to find your fuel pressure regulator or don't know where to find the proper literature?
My fuel pressure regulator for my return style system is on the driver's side fuel rail.
01-29-2013, 07:54 PM
#7
The fuel pressure regulator is part of the fuel module in the tank on returnless systems. Seems like Magnuson is referring to the return systems where it is mounted on the rail.
I agree get a decent tune. The canned tune that came with my MP112 kit was for a return style system instead of the required returnless = lean under boost.
Hard start/slow to build fuel pressure.. check for fuel leaking back into the tank i.e. a hole in the hose to the pump inside the fuel module, bad or missing check valve in fuel pump outlet, bad regulator in pump module. These could also cause your fuel pressure to drop off under boost if it still doing so with a high flow pump. Also check that the pump has the same features as the stock pump did to operate the venturi system that keeps the fuel bucket filled even when the tank level is low.
Does the fuel pressure hold after key off or drop right away?
I agree get a decent tune. The canned tune that came with my MP112 kit was for a return style system instead of the required returnless = lean under boost.
Hard start/slow to build fuel pressure.. check for fuel leaking back into the tank i.e. a hole in the hose to the pump inside the fuel module, bad or missing check valve in fuel pump outlet, bad regulator in pump module. These could also cause your fuel pressure to drop off under boost if it still doing so with a high flow pump. Also check that the pump has the same features as the stock pump did to operate the venturi system that keeps the fuel bucket filled even when the tank level is low.
Does the fuel pressure hold after key off or drop right away?
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01-29-2013, 08:26 PM
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drops to like 40 after a few seconds or less. but holds there for the most part. my issue is there is no pressure regulator or a fuel pressure module which changes duty cycle of the pump. the pump is new and is same one magnuson put in it. is there any check other than a visual for a hole in line gm changed the fuel module design so cant just get a new module. sort of an issue.
01-29-2013, 10:05 PM
#9
The FPR is built into the pump module. There are a few different designs. Excess fuel dumps back into the bucket. The system is just designed to maintain a constant pressure, so the change in injector flow rate with vacuum/boost is compensated in the tune. With an external vacuum/boost referenced regulator on a return style system the injector flow rate in the tune is constant as the pressure adjustment maintains a constant flow rate.
If everything was working properly I would expect a high flow pump to be able to hold pressure on a 4.8 on moderate boost. Might be a small drop but it should hold steady after that. Could be a weak spring in the regulator.
The replacement pump that came with the MP112 kit for my 04 Av did not have the extra outlet to drive the venturi system that siphons fuel into the bucket that the GM pump had. On top of that the Av fuel module only had a single flapper valve to allow fuel to flow into the bucket. So under high demand, with low fuel levels in the tank it was possiible for the bucket to drain faster than it refilled. On other trucks it is actually the fuel dumped from the regulator that drives the venturi system and there are dual flapper valves.
In the Av module the regulator is just a ball and spring attached to the top of the filter as shown in the pic below.
If everything was working properly I would expect a high flow pump to be able to hold pressure on a 4.8 on moderate boost. Might be a small drop but it should hold steady after that. Could be a weak spring in the regulator.
The replacement pump that came with the MP112 kit for my 04 Av did not have the extra outlet to drive the venturi system that siphons fuel into the bucket that the GM pump had. On top of that the Av fuel module only had a single flapper valve to allow fuel to flow into the bucket. So under high demand, with low fuel levels in the tank it was possiible for the bucket to drain faster than it refilled. On other trucks it is actually the fuel dumped from the regulator that drives the venturi system and there are dual flapper valves.
In the Av module the regulator is just a ball and spring attached to the top of the filter as shown in the pic below.
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