New LS Install, Back Firing, O2, fuel pressure issues

[peeblesj]

Hey Guys,

I have been searching high and low for information about my O2 readings and back firing. Little background, I just finished installing a 2001 5.3 w/ 4l60e. Got the computer reprogrammed by Brenden at lt1swap. I was initially having trouble getting the motor started and had to raise the idle set screw a bit. Was able to get it running, but not very good. Just finished putting about 6 feet of exhaust pipe on for back pressure.

My motor idles decent (about 1000 rpm) as of now but I will lower the idle. When I crack the throttle, it back fires a few times then is fine. Hooked up the scanner and I found the following graphs of the O2 sensor readings. Bank 1 Sensor 1 seems fine, but Bank 2 Sensor 1 just about flat lines for some reason.... I ended up switching the O2 sensors from bank 1 to bank 2 to see if the sensor may be bad, but the problem stayed in bank 2. Both O2 sensors are brand new...

Also, when I have the truck off and turn the key to run (not start) the fuel pump turns on for 2 seconds and the fuel pressure rises to about 45. Then drops right down to 0. When the truck is running, the fuel pressure stays at about 40. These seem low to me. Not sure if I am not getting enough fuel to Bank 2 or not....

Pics are the following: Top Left was the initial start up of the engine. Top Right was a couple minutes in so it was at close to running temp. Bottom Left shows when I cracked the throttle wide open for a second. Bottom Right shows when the O2 sensors were swapped from bank 1 to bank 2. Last picture shows my running fuel pressure which seems low to me. (Notice above each graph is shows B1 S1 for Bank 1 Sensor 1 etc)

Like I said, I have been searching this site for weeks and I have found a few things to try, but I figured I would post some pics and maybe somebody has had my problem and something sticks out right away. Any help is very much appreciated!! Thanks guys!

[peeblesj]

Sorry, I guess the pictures posted vertically instead of side by side. First pic is of initial start up, second was at running temp, third was cracking the throttle, fourth was swapping O2's, last is the fuel pressure. Thanks again!

[Johns58stepside]

I would check the fuel pressure regulator its mounted on the fuel rail on the drivers side it has a vacuum hose coming from the manifold and it is real common for them to rupture which would dump fuel directly into the manifold. Look for fuel in the vacuum line if there is any the regulator would need to be replaced

[BR3W CITY]

Check your FPR for sure, and double check for vacuum leaks while your in there.

You said it idles at 1000rpm, but I see your commanded idle is only 575.

[peeblesj]

Thanks for the quick replies guys. I will check the fuel pressure regulator right away this morning and come back with any updates. Much appreciated.

[peeblesj]

So I checked the fuel pressure regulator by removing the vacuum hose while it was running. Nothing came out and there was no change in fuel pressure nor in the way the truck was running. Then I replaced the regulator just for safe measure and nothing changed.... I then went to the fuel tank and connected the pressure gauge directly to the supply line from the in tank fuel pump. Same thing, fuel pressure jumped up when I turn the key to run then dropped right down to zero immediately. If I am correct, something is wrong with the fuel pump. I would think that it should hold pressure right at the fuel tank supply hard line..... Thoughts?

[Johns58stepside]

Did you get the little o-ring out when you took the regulator out? For the fuel pressure it should hold I'm assuming your using a return system. Hook the fuel gauge back to the service port on the intake turn the key on to build pressure then try to block the fuel lines one at a time to see if it holds pressure with one blocked off then we will know that's the side with pressure loss.

[peeblesj]

Yes I am using a return system. I was able to get the o-ring out when I changed the fuel pressure regulator. The o ring was replaced. I just went to Autozone and bought a brand new (first one was also new) fuel pump. AC Delco EP381. Got that put in and the fuel pressure problem seems to be fixed. Fuel pressure is up around 50-52 when idling and when I give it gas it jumps up between 55-60. Also, when I turn the truck off, the fuel pressure stays constant at 48.

I am thinking the fuel pressure might be fixed, but my O2 readings are still not correct. Same as before, bank 1 reads good while bank 2 reads very low. It will do one spike on the graph if I give it a decent amount of gas but then goes right back to the low readings.

Is this maybe something to do with it relearning its fuel trim by chance? I have got the idle turned back down to about 725 rpm. It will idle fine but back fire when I give it gas then level back out in a second or two.....

Thanks in advance!

[jweb]

Try swapping your injectors from side to side. See if the problem still stays.

[peeblesj]

jweb, I will try swapping the injectors from side to side.


So I was going to check each plug on bank 2 to see if there was any injector leak, and I didn't find any leak. Which I shouldn't have since the pressure stays constant now.

But I did find the that plugs 6 and 8 look as if they have not even been fired. The look the same as they did when I put them in a couple weeks ago. I would have to think that this has something to do with it. I am going to follow my plug wires back to make sure they are secure. I did relocate my coil packs to between the firewall and the intake and got custom length plug wires.

[dayj1]

Originally Posted by peeblesj

jweb, I will try swapping the injectors from side to side.


So I was going to check each plug on bank 2 to see if there was any injector leak, and I didn't find any leak. Which I shouldn't have since the pressure stays constant now.

But I did find the that plugs 6 and 8 look as if they have not even been fired. The look the same as they did when I put them in a couple weeks ago. I would have to think that this has something to do with it. I am going to follow my plug wires back to make sure they are secure. I did relocate my coil packs to between the firewall and the intake and got custom length plug wires.

Check the injectors on cylinders 6 and 8. It is super common for the injectors to stick closed on these engines when they've been sitting for a while. Just unplug an injector and use a couple of jumper wires with a 9 volt battery to activate the injector. You should hear an audible click. If not, I can get them unstuck 95% of the time just gently tapping the injector with a screwdriver handle or a small hammer while it's still installed in the rail.

[peeblesj]

dayj1 thanks for the suggestion. All four injectors on that side were firing (clicking) when I ran power directly to each one individually. I then used a noid light to verify signal from the computer and all four on that side flashed. Used a spark plug testing light to verify spark at each plug and all four again flashed when they were supposed to. So I have signal from the coils to the injectors, injectors are "clicking", wires show spark at each plug. This is baffling.....Thank you for everybody's input. This problem will be solved yet

[dayj1]

Originally Posted by peeblesj

dayj1 thanks for the suggestion. All four injectors on that side were firing (clicking) when I ran power directly to each one individually. I then used a noid light to verify signal from the computer and all four on that side flashed. Used a spark plug testing light to verify spark at each plug and all four again flashed when they were supposed to. So I have signal from the coils to the injectors, injectors are "clicking", wires show spark at each plug. This is baffling.....Thank you for everybody's input. This problem will be solved yet

Since your coils were relocated, was the wiring harness modified pertaining to how the coils are connected? It's worth verifying that the correct control wire is going to each coil and that the secondary (high voltage) lead is going from the correct coil to the correct plug. A real quick and dirty test would be to swap the #6 and #8 plug wires and see if it runs better.

[peeblesj]

All I did to relocate the coils was move the coil packs to the firewall. I drilled a couple holes and bolted them on. The harness was able to stay the same. Nothing was added nor removed. The plug wires had to be lengthened to reach from behind the intake to each of the plugs. I will try to switch 6 and 8 around, but when I follow my plug wires back, they go back to the supposed correct coil/coil wires at the harness. I am also going to check to make sure the O2 sensor wiring has not been mistakenly switched side to side.

[peeblesj]

I think that I am going to call it a day today.

Just let it run for about 4 minutes and get to temp. Unplugged MAF and that didn't change anything. Created a vacuum leak and that didn't change anything either. As for the O2 sensor wiring, I have purple with the white line going to the driver side (B1S1) and solid purple wire going to passenger side (B2S1).

Check to make sure all 8 injectors fire and they do. Still have one loud back fire when I start the truck then it seems to run and idle fine.

The exhaust from drivers side (bank 1) is hot while exhaust from passenger side (bank 2) has a whitish tint and is much cooler.

The scanner allowed me to fire each injector individually and record the fuel pressure drop. All 8 injectors started at 51-52 psi with key in run but truck not running. After each injector fired the fuel pressure would drop to 34 psi (each injector fired for a predetermined amount of time, about 2 seconds). This was consistent on all 8 injectors.

This picture shows the relearn of the fuel trim in process. Seems like Bank 2 is significantly higher than Bank 1 in both short term and long term.

Not sure if any of this is helpful in figuring out these low O2 readings on Bank 2.

[Johns58stepside]

Bank 2 being positive 25 % on fuel trim would lean toward a lean condition possibly a vacuum leak try spraying around the intake gaskets on the passenger side and watch fuel trims so if anything changes

[solidaxel]

What is the compression reading on that bank, does 6 and 8 read about the same as 2 and 4?

[peeblesj]

Hey Guys,

I will try to get the compression readings sometime today or tomorrow. I sprayed some brake cleaner near all the intake gaskets and didn't notice any difference in the fuel trims. I may try it again later today. I did take the truck for the first drive and it would backfire when under anything more than minimal load. I mainly just coasted in drive and let the truck go its own speed. I threw some cheap thrush mufflers on to maybe help with back pressure and that wasn't the best idea, I can barely hear at the moment. Anyways, I am about out of ideas other than to check the compression at 2,4,6,8 cylinders.

I was wondering what would happen if I would move the harness and the O2 sensor from bank 2 to bank one and visa versa? Also, could there be a bad ground to that O2 sensor that is showing lean? I believe it is the "body grounded" sensor from what I can tell on lt1swap.com. Maybe I need an extra ground going to my coil relocation bracket or something?

[truckdude239]

if you poped a muffler like that its dumping raw fuel into the muffler and it blew up

[peeblesj]

Yeah I figured something along those lines to cause that kind of backfire. It's just weird that it is reading that it is running lean but then backfires that bad on that bank (dumping fuel into exhaust). Would a valve not working right cause this?

[BR3W CITY]

You can read lean but be rich if there is a leak before the 02 (like in the collector or a primary). Exhaust gasses are under pressure but because of the pulse width, they come under a temporary low pressure (vac) area and can draw in clean air.

This will tell the 02 your lean, PCM will try and correct, dumping fuel.

Is there a wideband in this thing too that we can log separately?

[peeblesj]

BR3W CITY, I do not think they are wideband. They are both just new stock replacements for a 2001 Silverado. They are the case grounded type. I will check all connections in the exhaust before the o2 which is only the collector and the header to the cylinder head. I will test the compression in all 8 cylinders tomorrow as well.

Thank you guys for all your input, I really appreciate it! Cant wait to get this thing running correctly

[peeblesj]

GOT IT FIXED!!! That's the good news. Bad news is that it was my own fault that it wasn't correct in the first place. When I did the coil relocation, I thought that I had the correct coil plugs in the correct locations. I was wrong. I had the coil plug from cylinder 8 on cylinder 2 and cylinder 6 on cylinder 4. It was off my 180 degrees so the timing was completely off. Weird enough though the truck was able to run and idle.

I did a compression test and that was all goo between 155 and 165 on all 8 cylinders. So i figured I would double check all my grounds and other wiring just to make sure. I printed off the schematics from lt1swap.com and noticed the coil plugs were in the wrong location. Once I put them in the correct coils, it started right up and ran like a champ!

Just want to say thanks to everybody that chimed in with ideas! This site is awesome! Can't wait to get all the finishing touches done on the LS swap!