Help! My 5.3 Loses Power At Operating Temp
Thread Starter
Joined: Nov 2007
Posts: 413
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From: Albuquerque, New Mexico
Help! My 5.3 Loses Power At Operating Temp Almost completed my 5.3/'98 F150 swap. It starts right up and runs great until it gets to operating temperature. I feel like it's fuel related. It's got a full tank of gas and a brand new performance fuel pump putting out 255 LPH. I'm using a new stock GM fuel pressure regulator. The fuel lines are the stock F150 feed and return line that matches up to the 2000 5.3 fuel lines of the same configuration. It just seems to not be getting enough fuel. It hardly runs at idle and will not pull at all when you give it throttle. Any ideas?
Thread Starter
Joined: Nov 2007
Posts: 413
Likes: 0
From: Albuquerque, New Mexico
Anyone? I have new injectors in fact the entire motor is a new crate which I installed a very mild truck cam. Guess I'll check the fuel pressure while it's running badly to see if fuel delivery is my problem. I was told that with a return fuel system, the 255 LPH should keep the engine from ever seeing vapor lock because the fuel keeps circulating. I'm just wondering now if possibly I'm overloading the return system. Is that possible? One clue is the engine fires right back up after stalling but still runs rough and struggles to idle.
I would not think you would be able to over load the return line since it has not restriction, it would flow the 255 LPH alone with out any issue. I would put a fuel pressure gauge on to make sure there isn't an problem with the fuel system.
I would also put a scanner on and check to make sure all sensor are reading within the operating range. Check for any DTC code and it might lead you to where the problem is.
if it starts up ok.. and runs ok, but once you reach operating temp.. it stalls.. hmmm. .try disconnecting the MAF and see how it runs..
But you're going to have to provide us with more info on what the scanner is reading and anything else.
BC
I would also put a scanner on and check to make sure all sensor are reading within the operating range. Check for any DTC code and it might lead you to where the problem is.
if it starts up ok.. and runs ok, but once you reach operating temp.. it stalls.. hmmm. .try disconnecting the MAF and see how it runs..
But you're going to have to provide us with more info on what the scanner is reading and anything else.
BC
255 LPH pumps are pretty standard stuff for LS swaps. I've never heard of it being too much pump.
I'm guessing that you have a sensor problem. Watch the MAF/MAP readings when cold and compare to when it acts up. Make sure the coolant temp reads correctly. See if the O2s are switching.
I'm guessing that you have a sensor problem. Watch the MAF/MAP readings when cold and compare to when it acts up. Make sure the coolant temp reads correctly. See if the O2s are switching.
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Teching In
Joined: Jan 2006
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From: sd
Check fuel pressure, stock fords have two fuel pump sometimes, a low pressure in the tank and then a high pressure inline inside of the left frame rail by the front cab mount area with a filter ahead of it also
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Thread Starter
Joined: Nov 2007
Posts: 413
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From: Albuquerque, New Mexico
I haven't done a scan yet but I'm leaning more towards a MAF condition. The MAF is brand new but it's a Granatelli cold air unit. Initially, I had it mounted at the stock location next to the throttle body but I have moved it to the end of the CAI next to the filter like most Granatelli MAFs I have seen on Silverados and Tahoes. Even then, lots of people reporting problems with the Granatelli MAFs for 5.3 trucks. All of my sensors are new but of course, that doesn't rule out the sensors. I'll definetly post the update Saturday when I run a scan. Fuel pressure was 60 lbs like it should be with the engine just idling. I will leave it hooked up and report the change, if any, when the problem resurfaces.
I might not be thinking clearly right now but 60 psi at idle seems high for a return style system. Should be close to 60 with engine off or at WOT, but less than that by the amount of vacuum for idle. I want to say 45-50psi but I can't remember.
Should be 58psi, +/- a few psi at most. Bilster, have you monitored your fuel pressure while driving or in gear/ under load? If you have 58 psi under all conditions you can rule fuel delivery out.
+1 .. .You need a regulated 58psi... you may be able to start up and idle ok. .might be able to get some RPM.. but anything under load might crap out..
I've read some have tried to run TPI or LT1 pump.. and had somewhat of the same ...
BC
I've read some have tried to run TPI or LT1 pump.. and had somewhat of the same ...
BC
I disagree. The fuel pressure with no vacuum in the intake should be 58-60, but at idle, the regulator will reduce the fuel pressure in the line by the same amount of vacuum that is in the intake. So at running idle, the fuel pressure should be 58-60 minus manifold vacuum.
To me it sounds like bad regulator or it is not connected to vacuum.
To me it sounds like bad regulator or it is not connected to vacuum.
Unless you have a vacuum referenced Regulator.. the fuel pressure should be regulated to 58-60psi.. and would not be any higher.. But you should see the pressure drop under load (injectors having a higher duty cycle) as commanded by the ECM.
Do you have a Vacuum Referenced Regulator ?.. if not, vacuum should not come into play ???
If your seeing constant 58-60 psi. I would be looking at other areas..
I have also recall in the past that those Granatelli MAF can be a problem.
BC
Do you have a Vacuum Referenced Regulator ?.. if not, vacuum should not come into play ???
If your seeing constant 58-60 psi. I would be looking at other areas..
I have also recall in the past that those Granatelli MAF can be a problem.
BC
2000 5.3 has vacuum regulated fuel system. He said new stock gm fuel pressure regulator in the first post, and that he hooked up to the stock f150 feed and return lines.
58-60 key on engine off. Less than that idling.
58-60 key on engine off. Less than that idling.
The OP hasn't been back on in a couple of weeks. he might have fixed it by now.
Since this was his first start up it could be something simple. Like Old Geezer said, probably having issues when it tries to go into closed loop mode. So air leaking by the MAF, MAP sensor bad, something not plugged in, it is also pretty common for people get the left and right side 02's corss wired. Need to check the basics and rule out the stupid mistakes before the trouble shooting can get too theoretical.
Since this was his first start up it could be something simple. Like Old Geezer said, probably having issues when it tries to go into closed loop mode. So air leaking by the MAF, MAP sensor bad, something not plugged in, it is also pretty common for people get the left and right side 02's corss wired. Need to check the basics and rule out the stupid mistakes before the trouble shooting can get too theoretical.
new guy with a question Thread Starter
Joined: Nov 2007
Posts: 413
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From: Albuquerque, New Mexico
Sorry for not getting back sooner but my work schedule got crazy. I'm not sure if I isolated the problem completely because I cleared the codes after fixing things and I haven't had them return yet. So my problems were two fold. First one was just newbie ignorance. I didn't have my Vehicle Speed Sensor (VSS) hooked up at all. I stupidly thought this sensor was for speedometer reading only.
The second problem was my placement of the Granetelli MAF sensor. It's critical to mount the sensor right after the air cleaner element...not in the stock location which is right before the throttle body. Luckily I'm using a CAI designed for a 2000 Silverado and was lucky enough to package it. In the latest Hot Rod Magazine, there is an article on custom fitting the new Coyote 5.0 Ford motor. MAF placement is super critical in that application and it hit home that a good tune may not be critical when hybrid building an LSx powered vehicle but it's a great idea.
I've only driven the truck around the area near my house. I need to take this thing out for an extended drive which includes some freeway driving before I can honestly say the problem is solved.
The second problem was my placement of the Granetelli MAF sensor. It's critical to mount the sensor right after the air cleaner element...not in the stock location which is right before the throttle body. Luckily I'm using a CAI designed for a 2000 Silverado and was lucky enough to package it. In the latest Hot Rod Magazine, there is an article on custom fitting the new Coyote 5.0 Ford motor. MAF placement is super critical in that application and it hit home that a good tune may not be critical when hybrid building an LSx powered vehicle but it's a great idea.
I've only driven the truck around the area near my house. I need to take this thing out for an extended drive which includes some freeway driving before I can honestly say the problem is solved.