adding 50% fuel at WOT

[Billett]

Truck is at the shop getting tuned and those guys are stumped. Apparently my truck is fine, bit at WOT it adds 50% more fuel than it needs and they have no idea why. O2s are reading fine, and they've triple checked the tune to no avail. They've actually gone so far as to send a copy of the tune out to HPT to see what they thought and they said it looked fine and not corrupted. Anyone have something like this happen? At this point I'm thinking I'll have to find another pcm. The PN on the one in there says its a remanufactured one according to lt1tech

[Angryman117]

Are you running a stock tune? Maybe have them back up your tune and load your PCM with a bone stock tune and see what happens.

[BR3W CITY]

Are the injector table showing an extra 50% fuel, or are the 02's showing that the truck is getting 50% too much?

If its the table, then they should be able to back the table down or just re-scale the whole table again, if for some reason there are a few cells screwing the whole thing up. If they've made changes, but every time they have to come back and do it again, then somethings not taking. There is a reset Trims button in HPT for this. Could be a bad sector in the pcm, but usually you can tell that.

If you are stuck in +Ltrims then the car is going to always ask for more fuel. There is also stupid stuff like cat convertor protection which will make you go rich since your not running one (or rear o2's) its called COT.

[Billett]

Don't think its the tables. I stopped in yesterday to see how it was going. What he told me is that it isn't even WOT. Whenever he gives it more than 75% throttle it adds 50% fuel and falls on its face. Its drivable if I don't race it around, but it still should be doing that. He said he's even gotten it to work a few rimes without it adding the extra fuel, but not consistently and he didn't change anything between those runs so he really has no idea. I think the next step is to toss in a spare pcm and flash it and see if that works.

[BR3W CITY]

Well if its happening before WOT then we can also look at functions related to the 02 sensor function. At WOT the 02s are disregarded.

Your welcome to try a spare pcm but its been rare in my experience that a bad pcm has been the issue often bad sectors or a corrupt pcm will fail in many areas, or may not eveb take a flash

[Billett]

I kind of doubt it's the pcm also, but if HPT actually looked at it and said it looked ok then I'm not sure it's in the tune either. A stock tune wouldn't have that problem anyway so if they didn't change any of those functions why would it change in my tune?

It shouldn't be the o2s either because the mV's are reading correctly, but I'd like them to change those out as well. If the problem doesn't make sense what's the harm in eliminating some variables

[doubeys_nova]

out of box thought... how is the fuel pressure? could hi or low fuel pressure cause this because the O2 sensors do not manage air/fuel at WOT and are you sure you have the correct lb/hr injectors you think your have. a quick run of the p/n will verify that. i had three different lb/hr sets of injectors and they all looked identical just different p/n's. dont beat me up over this, i could imagine these things possibly causing some issues. also agree with a back up pcm verifying the pcm is not the issue.

[Billett]

Injectors was the second thing they checked after o2s. They asked what kind I had and honestly I had no idea. As far as I knew they were stock but you can never be sure. They pulled them to verify and they are the stock lq4 injectors. Fuel pressure could definitely be the culprit, I'll bring it up to them. I put in a brand new inline walbro but you never know.

[Billett]

Just talked with them and they had an idea as well. My cab smells a bit like fuel and I believe the o-ring that goes into the tank is dry rotting and may not be sealed well. Along with that, the lines going into that plate I KNOW are not sealed perfectly. Could the loss of vacuum in the rank be throwing off the readings?

[doubeys_nova]

i dont have the tank gasket on right now so i am pretty sure that isnt the cause. mine leaks if i fill it. i have an inline walbro 255 and 1ft after is the FPR/Filter then about 4ft to the fual rail. it is like the injectors are the culprit to me. injectors dont work at 100% in any application. i cannot remember the recommended % for that but a little research should give you a solid idea. maybe the injectors are being overloaded or not enough load.

maybe the tank is getting air locked. take the gas cap off and check it out. do you have the intake vacuum port hooked up/blocked off on the back of the intake?

[ls1nova71]

Are you sure you have the O2 sensors plugged into the correct sides? I've seen sensors swapped side for side that makes the PCM do some crazy things trying to compensate for the wrong bank. Just a thought.

[BR3W CITY]

From my perspective, I noticed a couple things;

I doubt they are non-stock (or non-truck) injectors, unless the wiring and everything else was changed too ...it would have the fatty MultecII injectors. Unless by some chance they were swapped with 8.1 injectors, there really aren't any other stock looking injectors that would have ended up in there. If its got the fuel rail raised up and the tall skinny injectors, then ya we have something to address right away.

Tank pressure doesn't really do much for the engine, the only time it could set a code is for the emissions (i.e gas cap). You can suck gas out of a dish to bench run a motor.

Doobey is also correct in looking at the FPR. You can unplug the vac source and see what psi its running. Its possible that a bad diaphram or stuck fpr could be causing some problems....its technically vacuum referenced so if there were to be a problem with it (or its vacuum source), you could lose fuel pressure.

Is this shop taking logs of any of this? With HPT looking right into the tune, things should stand out as apparent issue. And how the heck are we not getting any codes?

How is your fuel pump wired? Are you getting full voltage to the pump at all times? A bad ground, small gauge wire, or badly wired relay can all result in voltage drops as the pump, especially under load. Where is your fuel pump (in tank or inline), and what kind of filters are you running? W

Whatever the cause, I'm guessing the engine is either detecting, or getting a false positive for a lean condition. This causes the demand for more fuel, which the ECM tries to deliver, but just dumps 50% on top and neuters itself. While its possible there is still a problem in the tune, none of the "normal" problems do what you describe.

[doubeys_nova]

lb/hr differences was all i was saying not style of injector. My 4.8L injectors were bigger than my 6.0L injectors and the 6.0L were bigger than my 5.3L injectors. they all looked identical even in color but had different p/n's. i can't remember the lb/hr of each so i wont even guess but it was about 5-10 lb/hr difference between all three.

[Billett]

Fuel pump is external, grounded to the frame and wired into the harness from CPP. They tell me fuel pressure stays fine through the whole band, so I think that's fine. Haven't heard from them in a few days so no updates... I may have to get it back soon even with those problems...

[BR3W CITY]

Originally Posted by doubeys_nova

lb/hr differences was all i was saying not style of injector. My 4.8L injectors were bigger than my 6.0L injectors and the 6.0L were bigger than my 5.3L injectors. they all looked identical even in color but had different p/n's. i can't remember the lb/hr of each so i wont even guess but it was about 5-10 lb/hr difference between all three.

99's and some early 2000 4.8/5.3's had 19lb injectors, after that EVERY ls truck had the same 24# injectors...with the exception of the flex fuel trucks (~32ln/hr)

[Super73]

I know you said they e-mailed the tune to HPtuners, would they mind e-mailing it to me? I would be happy to look it over for you and see if I catch anything. shaunliddy@hotmail.com

Are they tuning with or with out the MAF?
If with MAF, have they tried disconnecting it and forcing it in to speed density mode and tuning just the VE table to see if proper fueling is achieved?

They say fuel pressure stays flat, but what is the pressure? 58psi?

What do the power enrichment tables look like?

[Billett]

I'll ask them for a copy of the tune tomorrow.

They are trying to run with the MAF. I did ask about an S/D tune and he said that would work but he would prefer to get it figured out with the MAF and o2s. It's been a month for a tune though and I'd prefer to have a running truck haha. Couldn't tell you if it developed the same fueling problem on S/D though. Not sure they even tried it.

50psi is what they tell me. I'm running an external walbro 255 GSL392 from the stock tank behind the seat to a corvette filter and regulator then to the rail. The rail is stock and is a return-style, but I ground down a bolt and blocked off the return with it and an o-ring.

Hopefully you'll see them tomorrow. I'm actually in the middle of tuning, (read as: trying to pass inspection), my brother's 240sx at the moment. Been learning a lot while working on that so I'm kind of curious myself. I would have liked to tune my own truck but HPT is a bit pricey and PowerFC was free so...

[BR3W CITY]

IS the truck FPR still in the rail?

[Super73]

Corvette reg should have fuel pressure at or very near 58psi.

It would take them 5 minutes to force the truck in to sd to see if there is something besides ve and pe causing the problem.

[truckdude239]

is the stock truck fpr still hooked up?? just blocking the return and running a vet filter and reg is going to cause problemsto run the vet filter you need a returnless style fuel rail. if the truck fpr is still on the rail its trying to regualtor the pressure as is the vet filter

[Billett]

Yes the truck regulator is still on the rail. I got the idea from someone over on the ls1tech boards. I messaged him and he told me how he did it and said he had no problems running it that way. Now I'm curious as to whether he did have problems and just didn't know it... Unfortunately I can't test it now because he has an ls3 style intake and rails.

That's my plan eventually, l92 intake and rails, which is why I didn't want to plumb the return style only to get rid of it in a few years. I was hoping that the corvette regulator would pull it down to the appropriate 58(ish) psi and then the regulator on the rail would have no need to reduce it any further so there would be no extra fuel. Along the same line of thinking why would the regulator on the rail be able to put in MORE fuel than needed especially when more fuel is being burned up?

[Super73]

Will,

Have they turned off cat over temp? I have ween it do similar things. It dumps a ton of fuel to keep the cats from burning up.

[Billett]

Just emailed them a few minutes ago so hopefully I can get you the file soon.

[BR3W CITY]

Originally Posted by Billett

Along the same line of thinking why would the regulator on the rail be able to put in MORE fuel than needed especially when more fuel is being burned up?

LS1tech is like highschool. You can learn a ton, but mostly from whats NOT being said. (oh, and you end up hating everyone after 4 years )

So the FPR isn't adding MORE fuel, its likely supplying less (or erratically). Something also tells me that dead-heading the return style rail is going to cause the rail pressure to rise, possibly causing the on-rail FPR to try run LESS.

When the ecm see's the "need" for fuel that should be freely flowing to the injectors, it tries to use MORE injector to compensate for the fuel. In this case, it sounds like it can't, or it does but its actually NOT needed.

Buy a returnless rail, slap a couple of spacers on the mounting studs and see what happens.

[Super73]

Any update on the shops willingness to send over their tune?