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I'm pretty new to tuning, so bear with me. I have an LM7 that I swapped into a GMT400 truck. The issue I have is that it will usually not allow me to use more than around 30% of the throttle without bogging down. Eventually after driving it enough the amount of throttle required to bog down will decrease until it just stalls out. What's even weirder is that once it stalls itself out, after I start it back up it won't bog down anymore and will allow me to use up to like 50% throttle but continue to slowly decrease in how much throttle I can use and the cycle repeats.
Another thing is that this only happens in gear until it bogs down to the point where I can hardly drive, then putting it into park or neutral it will do the same thing, but usually, it revs up perfectly fine in park or neutral. I've also noticed that the throttle response is really delayed.
How is the fuel pressure?
Using O2 sensors? If so it sounds like you have exhaust leak(s) that would affect their function.
Was this a cold or hot start?
Fuel pressure is good, brand new EP381 fuel pump. I have one heated o2 sensor installed in the y pipe, and it's an open y pipe currently. This was a hot start, usually at cold start it starts out good and bogs down over time.
AT the Y? Or right after one side of the engine?
Tell us what is in the engine.
Size, heads, compression, cam (full specs) carb or injection?
Stock tune or ??
AT the Y? Or right after one side of the engine?
Tell us what is in the engine.
Size, heads, compression, cam (full specs) carb or injection?
Stock tune or ??
It's a bone stock 5.3 efi. I tuned it for open loop and the o2 sensor is on the left side of the y
You mentioned open . O2 sensors tuned out also?
For best results put it all back to closed loop and MAF, THEN see where it goes.
If it gets worse as it warms the tune likely needs looking at
You mentioned open . O2 sensors tuned out also?
For best results put it all back to closed loop and MAF, THEN see where it goes.
If it gets worse as it warms the tune likely needs looking at
What is the best way to go about tuning out the front o2s
How have you done what was done so far? Usually you need HPtuners.
Closed loop INCLUDES O2 sensors. You really should leave them in. They tell the ECM whether you're running lean or rich.
How have you done what was done so far? Usually you need HPtuners.
Closed loop INCLUDES O2 sensors. You really should leave them in. They tell the ECM whether you're running lean or rich.
I've tuned it with HP Tuners so far, just not really sure where I went wrong and why it's doing this
Load the stock tune back in and start over. Put an O2 sensor in the side that needs it, and if possible put the MAF back in.
Try not to reinvent the wheel.
Load the stock tune back in and start over. Put an O2 sensor in the side that needs it, and if possible put the MAF back in.
Try not to reinvent the wheel.
It did it with the stock tune, which is why I tried to tune it for SD, which did not help
It did it with the stock tune, which is why I tried to tune it for SD, which did not help
You need O2 sensors on both sides.
Make sure you have at least 58psi at the rail.
Check any fuel filter in the line. Pressure will show good until there is ANY demand if a filter is clogged.
Check all grounds. The system relies HEAVILY on good ground connections.
So I installed a fuel pressure gauge on the rail where the 1/8 NPT connector is with a schrader valve. The fuel pressure while idling is around 45 if I leave the vacuum line to the regulator in, and 58 with the vacuum line pulled. Fuel pressure is constant when revving the engine cold. The problem arises when the engine warms up, after driving it around for 10 minutes or so. I put it in park and went under the hood and revved it. The fuel pressure was dropping down below 20 when revving the engine. So I'm really lost now, and advice would be greatly appreciated.
Make sure you have 12 -14 volts on the fuse going to the fuel pump.
It seems like your pump or regulator is failing, it should maintain 58.
Check your fuel filter it may be clogged. ether way you did find your problem. Motor not getting enough fuel.
Make sure you have 12 -14 volts on the fuse going to the fuel pump.
It seems like your pump or regulator is failing, it should maintain 58.
Check your fuel filter it may be clogged. ether way you did find your problem. Motor not getting enough fuel.
I did check the voltage and was getting 12-13 volts, and the fuel filter is brand new along with the fuel pump. It just doesn't make sense for it to be the regulator because it was fine when I pulled it out of the truck it was originally in.
I had a similar problem when i first did my swap back in 2011. I had a fuel pressure problem and it ended up being the hose on the pump in the tank came loose. Could also be your regulator.
I had a similar problem when i first did my swap back in 2011. I had a fuel pressure problem and it ended up being the hose on the pump in the tank came loose. Could also be your regulator.
Did you notice fuel leaking everywhere or was it not enough to be noticible?
When you turn the key to activate the pump (without starting the motor) than turn the key off, does it still show 58, if it drops than you may have a bad check valve on the pump or the regulator is gone.
Show us a the video of the gauge under pressure "turning the key, wait 5 seconds than off" it should hold a long time.
Last edited by Tramminc; Nov 18, 2020 at 04:46 PM.
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LS Swap stalling under load 
