6.0 runs and quits

[4x4k30]

as usual I always run into problems.. just got my 6.0 running in my 79 k20 it started and ran good for about 5 mins. then it got to where it will just shut down and stop running it will fire rite back up but it starts acting like its getting to much fuel flooding out and it quits . I know it has good fuel pressure I can watch the gauge it stays at 70 when running and it still quits running even watching the gauge as it stays at 70 so I don't think its a fuel problem.. it seems like something is making it stop running and I can't figure what is going on .

[BR3W CITY]

Thats too much pressure man. Its a 58psi system, so if its legit being fed 70psi at the rail, your injectors are forcing a significantly greater amount of fuel into the motor on the same injector duty cycle (basically how boost-a-pumps work).

Are you using the truck return system?

[Dustytrix]

Its hard to tell without pulling a code. Since it will run for 5 or so minutes.

[4x4k30]

Originally Posted by BR3W CITY

Thats too much pressure man. Its a 58psi system, so if its legit being fed 70psi at the rail, your injectors are forcing a significantly greater amount of fuel into the motor on the same injector duty cycle (basically how boost-a-pumps work).

Are you using the truck return system?

yes I have the 58 psi fuel regulator and filter its sits at 60 before I go to start it and it jumps to 70 when it starts running its a in line fuel pump I have not runs the codes yet I haven't wired that in yet and the only other thing the 02s are hooked up yet

[mongocanfly]

I agree...way to much....how do you have your filter/reg plumbed?....the outside fitting is the supply and the one in the center is the return on the inlet end

[4x4k30]

Originally Posted by mongocanfly

how do you have your filter/reg plumbed?....the outside fitting is the supply and the one in the middle is the return

I have the return line going back into my dual tanks at the fuel selector switching valve I hooked the return line to the center fitting the one that goes straight thru the filter its 5/16ths and the fuel feed it the 3/8ths from the fuel pump

[4x4k30]

Originally Posted by mongocanfly

how do you have your filter/reg plumbed?....the outside fitting is the supply and the one in the middle is the return

I have the return line going back into my dual tanks at the fuel selector switch I hooked the return line to the center fitting the one that goes straight thru the filter its 5/16ths and the fuel feed it the 3/8ths from the fuel pump I can have them backwards the top one is the feed line from the fuel pump the smaller bottom fitting is where I have the return

[mongocanfly]

although it looks that way the return doesn't go straight thru the filter/reg....
id check the tank switch valve and make sure its letting fuel go back to the tank

correct...the outside [3/8] is from the fuel pump ...the center [5/16] is the bypass return
you could have a bad reg or its deadheaded at the selcto valve

[4x4k30]

Originally Posted by mongocanfly

although it looks that way the return doesn't go straight thru the filter/reg....
id check the tank switch valve and make sure its letting fuel go back to the tank

correct...the outside [3/8] is from the fuel pump ...the center [5/16] is the bypass return

that could be my problem the return line from the filter regulator goes to the fuel selector switching valve and goes to both of the tanks return lines . it may be filling back into both tanks at the same time both tanks were empty when I first went to start it and I put in 2 gallons in one and it quit running so I thought it was running out of gas and I went and got 4 more gallons and put in the same tank so maybe its just going back into one tank

[mongocanfly]

as long as the return going into at least one tank then it shouldnt be a issue....you shouldn't have that much pressure....trying to eliminate whats going on...you might try another gauge to verify the fuel pressure..i think most parts stores have one you can borrow and hook to the Schrader valve on the fuel rails

[4x4k30]

Originally Posted by mongocanfly

as long as the return going into at least one tank then it shouldnt be a issue....you shouldn't have that much pressure....trying to eliminate whats going on...

yea I know I couldnt figure why its running 70psi when running and 60 psi at start up not running .well will keep trying thanks for the help

[davepl]

One time on a C4 Corvette I added a big Aeromotive pump and then wound up with too much fuel pressure because the factory regulator didn't actually flow enough to "bleed" all that excess flow back to the tank...

Point being that insufficient or restricted returns can cause too high of pressure.

[Super73]

Jump the fuel pump relay and run the pump with the engine off. This will give the most possible pressure as the engine is not pulling any fuel as it is not running.

Use this method to make changes to the fuel system isolating the excessive pressure.

Keep a charger on the battery to simulate a charge from the alternator (30A charge will be sufficient)

[davepl]

Just throwing out for fun: the later LS engines are not boost or vacuum referenced, the fuel pressure remains a constant 58.

[4x4k30]

I went back today and checked all of my wiring and I don't know how but its rite. and I was going to check to see if they were any codes but when I cut the key on to the code reader its says key not on . but anyways I remember reading somewhere about how to check for a bad maf sensor so I unhooked the wire to the maf sensor and dam if it didn't go to running rite like its supposed too. so I don't know ifs its bad or not I am going to ask the man who tuned my ecm if maybe he has it set to run without the maf system . and as far as the fuel pressure being at 65 to 70 its running ok with it as that I am going later and get another fuel pressure gauge and try it .thanks to everyone who responded to my problem .

[BR3W CITY]

Your tune will not be randomly setup to run without MAF. Speed Density tuning usually uses the custom OS in HP Tuners and isn't usually something a tuner would do without discussing (and charging) for.

[davepl]

Originally Posted by BR3W CITY

Your tune will not be randomly setup to run without MAF. Speed Density tuning usually uses the custom OS in HP Tuners and isn't usually something a tuner would do without discussing (and charging) for.

What years and ECMs are you referring to?

Any halfway modern ECM I've ever seen was already set up to handle no MAF. My 2007 LS7 was. My 2015 LS3 is.

In fact I know authoritatively that as far back as 1994, when they put a MAF on the LT1 for the first time, it supported speed density: I had a centrifugal blower and blew the discharge pipe off and it wouldn't run because the MAF was seeing full flow. So I unplugged the MAF and drove it home to fix the pipe... indicating it had speed density fallback mode as well.

In fact, now that I mention it, every single GM computer I've ever seen has speed density fallback.

I'm running it right now, in fact. The LS3 runs very well in speed density. Until I added the air straightener hex foils I was planning to keep it that way, but with the airflow fixed the MAF setup works well enough for me.

That doesn't mean -every- ECM does, but evey one I've experimented with, does. I also spoke with the guy in charge of GM crate engine calibrations and he confirmed it, and he told me that if it were up to him, all the crate motors would run speed density because it's near impossible for end users to set up a MAF pipe the same as the factory flow rates.

so I unhooked the wire to the maf sensor and dam if it didn't go to running rite like its supposed too.

And there you go, proof of my point. Pretty good guess, huh? :-)

What's happening is one of two things: there's a big enough intake/vacuum/air leak that air is making it into the motor without the MAF seeing it. So it goes way lean because it's not seeing all of the air, so doesn't add enough fuel. But it's gotta be a fairly big leak for that to happen.

The more likely cause is in the intake pipe. The pipe just has no hope of matching the flow characteristics of the stock pipe. So you can either "fix" your airflow, go to a longer tube with less bends, or continue to run without the MAF.

You can try those sections of pipe that have a MAF boss and honeycomb air straightener, which mostly solved my problem. Or you can run in speed density.

Long story short, your intake pipe is different than the stock pipe that was on whatever car that motor came out of, so the MAF location is not calibrated. GM tries to do their best by calibrating it for being in the middle of a straight pipe with 6" on either side of it, that's about the best they can do.

[4x4k30]

the engine I have is a 6.0 out of a 2007 hummer it came with no ecm or tac module or pedal. it has the blue green wiring harness. from what I hear is that this 07 model engine is part of the last ones to run the blue green wiring harness and 24 reluctor crank wheel . they changed in the middle of 2007 to the e38 harness on all gm ls engines and use a 58 tooth reluctor . I had to buy a different ecm and pedal assm.it had no maf either. and the ecm was tuned by a guy in tenn. named erkel55 I asked him about the tune he done but he hasn't got back with me yet he is gona see what tune he did to my ecm.he wasn't sure if he deleted the maf. system.

[BR3W CITY]

Originally Posted by davepl

What years and ECMs are you referring to?

All of them have the capability of running SD when the MAF isn't present, I'm aware of that. You can set the frequency to 0 and be in SD without unplugging anything. But using the fallback SD tables and something like enhanced SD are a bit different. Additional VE multiplier tables, 2+ Bar map capability etc. There's also SD w/ correction. I don't know a reason for anyone to put that work in on a mild setup without at least mentioning it to the customer.

[davepl]

But who cares about the HPT proprietary stuff for a naturally aspirated pickup like this? Are you saying he needs any of that?

I'd unplug the MAF and drive it. The speed density tune is excellent, at least in the LS3. And to be honest I'd trust GM's SD tune a lot more than I would HPT, all else being equal.

[BR3W CITY]

Originally Posted by davepl

But who cares about the HPT proprietary stuff for a naturally aspirated pickup like this? Are you saying he needs any of that?

I'd unplug the MAF and drive it. The speed density tune is excellent, at least in the LS3. And to be honest I'd trust GM's SD tune a lot more than I would HPT, all else being equal.

Nope, what I'm saying is that most tuners for stock-ish flashes won't force fail the MAF into SD and solely use the VE tables. I'm assuming it was tuned with HPT simply because its got the largest market share.

And the Enhanced SD is actually great for N/A motors, specifically those with significant cam. GM's SD and HPT's SD aren't the same, so all things are not equal.

My intent isn't to debate SD efficacy, we can do that in another thread if you want. I'm simply saying its unlikely to be the OP's problem on his tune being SD-only, since that in and of itself, is less likely to start. If I'm wrong and his tuner did that, then so be it, at least his problem gets solved.

[4x4k30]

I have not heard back from the tune guy yet . I did try another maf sensor that I had laying around and as soon as I pluged it up the engine stublemed and just cut off again . so that tells me something is not wired rite or tuned . I have another truck with a 2006 6.0 and it has the maf and runs fine. and I am gona try to unplug it and see how it runs with it unhooked I will try it tomorrow and post how it does with the maf unplugged its been a long cold and windy day in ga.

[Super73]

Originally Posted by davepl

But who cares about the HPT proprietary stuff for a naturally aspirated pickup like this? Are you saying he needs any of that?

I'd unplug the MAF and drive it. The speed density tune is excellent, at least in the LS3. And to be honest I'd trust GM's SD tune a lot more than I would HPT, all else being equal.

Take this in to consideration. GM's fall back SD mode puts you in a low timing table with most ECU's. Commanded timing in this "low" timing table has anywhere from 10-15* of advance pulled.

In addition every one I have forced in to SD by either unplugging the MAF or failing it through the tune has required VE table clean up. They are no where near stoich at idle/light throttle and are heavily relying on the factory narrow band O2 sensors to compensate which are not tied in to WOT fueling which should absolutely be addressed.

[davepl]

I'm simply saying its unlikely to be the OP's problem on his tune being SD-only, since that in and of itself, is less likely to start. If I'm wrong and his tuner did that, then so be it, at least his problem gets solved.

I might agree with you, not sure. I think he has a mechanical/physical problem with what the MAF sees due to location in the tube or an air leak. I don't blame the tune, MAF, or ECM, I bet they're all fine.

Originally Posted by Super73

Take this in to consideration. GM's fall back SD mode puts you in a low timing table with most ECU's. Commanded timing in this "low" timing table has anywhere from 10-15* of advance pulled.

In addition every one I have forced in to SD by either unplugging the MAF or failing it through the tune has required VE table clean up. They are no where near stoich at idle/light throttle and are heavily relying on the factory narrow band O2 sensors to compensate which are not tied in to WOT fueling which should absolutely be addressed.

I've never seen this. What ECMs do you believe cause this, as it would be important to avoid, but there's no info here. So far as I can tell the LS3 doesn't do that.

You'd want to fix the fallback timing table and clean up the VE if that's true, though I haven't actually encountered either, I'm by no means familiar with every GM ECM.

You guys are sorta funny - I've been daily driving the car you guys are afraid won't even run this whole thread! What doom and gloom! Of course I can only claim this for the LS3 but it works great.

I did try another maf sensor that I had laying around and as soon as I pluged it up the engine stublemed and just cut off again . so that tells me something

Doesn't tell you what you think it does. Your tune is likely fine and both MAFs are fine, you either have a air leak like an unrestricted PCV or the MAF is sampling from a bad spot in your tube. It's one or the other. You'll need to fix it or run without the MAF.

Stop cleaning and replacing your MAF, there's nothing wrong with it!

[BR3W CITY]

Should be that way on most GM ECM's. People will copy the High Octane table into the Low Octane table so when they fail the MAF, it'll still be seeing the High Octane table values. All genIII stuff will work that way. The GenIV Ecm's use GMVE/VVE, but afaik the SD defaults to the low octane set of values in either case.