Got it running!

[Factory Guy]

Just finishing up my first LS swap into my Squarebody LQ4 and a 4L80e.

I haven't take her on maiden voyage as I cannot keep her idling?

I am using a MAF and a MAP and both O2 sensors, (the fronts I believe), its DBW, stock coil packs. 2003 tahoe ECU had vats removed and was fleshed by BRENDON at LT1swap.com

His side kick Adam did my LS wiring harness.

The dual fuel tanks set up wiring was done by _________. (however I only have one tank hooked up at this time).

The truck starts good however it will rev up to about 2000 rpm's, if I don't keep my foot feathering the throttle it will slowly end up dying.

All of the Drive by wire stuff is stock GM, from a 2003 Tahoe, I got the ECU for the truck and the tach module, the wiring loom from the tach module to the accel pump and I also got the Accelerator pedal. No I do not have a fuel psi gauge in line on the fuel rails.

Picture below is my install.

Suggestions what to look for to keep her idling?

[Joyridin]

Is the MAF sensor located in about the middle of that straight stretch of intake tubing?

[Justin71105]

If you have the odb setup, get a reader and pull codes as well. Mine had 2 issies when I first got it running.

Cant remember code #s but one issues was dbw module, wouldnt rev consistently. Replaced module with one from junkyard and been fine since. So cheap I got two of them and tested both so I have a spare as well now.

Second was cam position sensor, really the wiring on connector, but this just made it spin over several times before actually starting. Had to crinp pin onto wire fully for that one.

Reader picked up codes for both then had to drill it down from there.

[Factory Guy]

MAF SENSOR is located at the air box end of all the tubes, as i understand it, it needs at least 6-12” of tubing in order to “flow” correctly.

[Factory Guy]

Whats really strange is i started this same engine/set up and all the same components outside the truck and let it run for a minute or so, 6 months ago. It idled fine then.

[jessemthompson]

Having your MAF that close to the 90* bend is going to cause issues. The airflow is disrupted in the bend and is going to throw off the reading.

[Joyridin]

That may not work. I had a similar set-up and messed with it for weeks before I realized what I had done. It needs to be about in the middle of that long tube or even closer to the throttle body. The air is coming around that 90 degree bend and missing the MAF sensor.

Try unplugging the MAF sensor. It should run and see if that doesn't fix the problem.

[Factory Guy]

Originally Posted by Joyridin

That may not work. I had a similar set-up and messed with it for weeks before I realized what I had done. It needs to be about in the middle of that long tube or even closer to the throttle body. The air is coming around that 90 degree bend and missing the MAF sensor.

Try unplugging the MAF sensor. It should run and see if that doesn't fix the problem.

Thanks guys I will give it a try!

[Joyridin]

Originally Posted by Factory Guy

Thanks guys I will give it a try!

Maybe I need to clarify my comment Unplugging it will put it in speed density mode and it should run assuming the tune is done correctly. I would not leave it unplugged, but that should give you an indication if that is the problem.

[Factory Guy]

Originally Posted by Joyridin

Maybe I need to clarify my comment Unplugging it will put it in speed density mode and it should run assuming the tune is done correctly. I would not leave it unplugged, but that should give you an indication if that is the problem.

Thanks for the update. I am now out of town for a while and cannot try your suggestions, however as soon as i get home i will try unplugging the MAF. And try it out! I will post my results as soon as i get them!

[Factory Guy]

I unplugged the MAF and now it seems to run a little longer. So I moved the MAF closer to the throttle body (see photo). Runs about the same as unplugged. So I swapped out to another MAF. No change.

To me it seems to be running out of fuel. I can force the fuel pump to run and it seems to continue to idle.

[Custom 68]

When you say force the fuel pump to run what do you mean? It should run a few seconds with key on, then run continuously once it is started. You can also check the fuel pressure at the fuel rail to confirm it is correct.
Once you have that sorted out there is always areas in the tune that affect the idle. that may need to be adjusted, are you doing the tuning or do you have a tuner?
Dave

[Factory Guy]

Originally Posted by Custom 68

When you say force the fuel pump to run what do you mean? It should run a few seconds with key on, then run continuously once it is started. You can also check the fuel pressure at the fuel rail to confirm it is correct.
Once you have that sorted out there is always areas in the tune that affect the idle. that may need to be adjusted, are you doing the tuning or do you have a tuner?
Dave

When I say force it to run-the truck has the 1987 and later square body dual fuel pump selector switch. If i depress the switch in the left tank position and hold it down it acts like a momentary switch and it forces the fuel pump to run? Don’t know why but it does this. Ecu was “tuned” by Brendan at LT1swap.com.

[Rich84]

I would pull codes if any and get a fuel pressure gauge. Mine ran erratically like that when I first started it because the injectors were sticky and leaking. They had been sitting for more then a year. Do you have your exhaust system all together. If not it will screw up the o2 sensor readings.

[Factory Guy]

Originally Posted by Rich84

I would pull codes if any and get a fuel pressure gauge. Mine ran erratically like that when I first started it because the injectors were sticky and leaking. They had been sitting for more then a year. Do you have your exhaust system all together. If not it will screw up the o2 sensor readings.

Yes Exhaust is ALL together O2 sensors are in. I got a fuel pressure gauge today. All injectors were professionally cleaned and inspected prior to starting this engine. The only thing I can't do yet is pull the codes. I will have to get a OB2 reader.

[LeesTruk]

Forget getting a code reader. Get a scan tool! You need to see what your sensors are doing as your engine is running. If you think you're running out of fuel delivery, check your fuel lines. If the engine has a returnless system, it could be that the filter/regulator is hooked up wrong.

[Factory Guy]

Its the fuel pressure. For some reason the fuel pump is intermittently running. When i first start it, it never cycles like Gm originally had them. So if i force it to run, I have about 60 psi. The truck starts right away and apparently it doesn’t run after that the fuel pressure continues to fall. Thus it won’t idle as it has NO fuel.

Really scratching my head now.

[87chevy.com]

MAF in the 1st picture is better than the last picture

When the truck starts and then runs, is the fuel pump actually on?
1987 style selector valve switch is not a momentary switch, it is a toggle switch and it stays in the position you choose, left or right tank...

what did this guy wire up for the fuel system?

[Custom 68]

It just sounds like a wiring issue, I am not familiar with the "1987 and later square body dual fuel pump selector switch" you mentioned.
I am glad you found the issue now to get it corrected. what ever is in that switch needs to be looked at. As you noted the fuel pump needs to run all the time when the engine is running.

[Factory Guy]

Ok, after spending 10-15 hours trying to diagnose the dual fuel tank wiring set up. My ENGINE wiring harness builder Adam Warren (https://lsxharness.com/ who had no responsibility to assist me on the other guys dual tank fuel (he will go unamed for now) harness, Adam assisted me that whole time trying to diagnose the issue.

We never did find the dual Fuel tank wiring issue. In the end we bypassed the dual tank fuel harness and got her running again!

[Rich84]

That's great to hear!
Divide and conquer.