adding 50% fuel at WOT
 

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

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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

Re: adding 50% fuel at WOT
 

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

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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?

Re: adding 50% fuel at WOT
 

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?

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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 :smoke: 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.

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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...

Re: adding 50% fuel at WOT
 

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)

Re: adding 50% fuel at WOT
 

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?

Re: adding 50% fuel at WOT
 

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...

Re: adding 50% fuel at WOT
 

IS the truck FPR still in the rail?

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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

Re: adding 50% fuel at WOT
 

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?

Re: adding 50% fuel at WOT
 

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.

Re: adding 50% fuel at WOT
 

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

Re: adding 50% fuel at WOT
 

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 :lol: )

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.

Re: adding 50% fuel at WOT
 

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

Re: adding 50% fuel at WOT
 

I called around 4 and the rep I've been talking to said he told the tuner and the tuner was supposed to send it to me, but I haven't gotten it yet. Said he would send it tonight. We'll see.... Also mentioned the fpr thing to him and he's under the impression that since the fuel pressure itself stays constant then the regulator shouldn't be causing any problems. Wonder where he's reading it from though...

Re: adding 50% fuel at WOT
 

The very first thing you need to do is to make sure that the fuel injector data is correct for the injectors that you have (flow rates, pulse corrections, min injector pulse and offsets). If these aren't correct, everything else you do is a waste of time. Once that is done, verify that the fuel pressure at the fuel rail is correct. I believe you have a Gen III which should be 3 bar or approximately 43 psi. The corvette FPR should give you this (assuming it is the from a corvette LS1). To tune the MAF, you've got to adjust the VE table. This is done by logging the data with the engine running and then comparing commanded AFR to actual AFR (you really need a wideband to do this correctly). Based on what the errors to AFR you see, you would then make corrections to the VE table. Now this is way more complicated than I just wrote, but you kinda get the picture. I would like to see the tune also if you don't mine. My email is robhartley@aol.com.

PS. Make sure you have your exhaust connected!!!!!!!!

Re: adding 50% fuel at WOT
 

Damn you got comfortable walking around in HPT didn't ya Rob? haha

Re: adding 50% fuel at WOT
 

:lol:, yeah man, I jumped in deep.....I spent so much time on looking at this stuff when I first started, I was dreaming about it at night......I finally had to take a couple weeks off to clear my head, :D. As soon as I get my cold air box done, I'm jumping back on it.

Re: adding 50% fuel at WOT
 

In theory I don't for see a problem with a vette regulator inline prior the deadheaded factory rail with regulator. Reason being, the vette regulator should be holding the 58psi. Pressure should not creep nor drop through throttle changes. The factory regulator on the rail can't increase pressure beyond what the vette regulator is supplying. Could there be a further pressure drop, I suppose, but with the return blocked, it can't put the fuel anywhere except the injectors. So again, in theory, I don't see it dropping pressure either. You would need a guage on it through throttle transitions to confirm.

Have any of you ever put even an SVO 30lb injector in place of a stock 28lber? The SVO 30's are rated at 43psi (Ford rail pressure) and on an LS rail at 58psi, they act like 36lber's. They will not idle with out injector flow being plaid with or your foot holding throttle and rpm. My point, if the injectors have been changed with out the flow rate being adjusted, it wouldn't even want to run well idle or part throttle. If they are off by 2-3lbs, it might not be that noticable as the Ltrims are doing there job in closed loop, enter PE, go in to open loop and that might change. But simply adjusting PE EQ Ratio should get it in line.

If the truck is running decent part throttle, it is because the vehicle is in closed loop relying on the narrow bands to keep stoich using Ltrims. Enter Power Enrichment and it goes in to open loop. If the VE table does not match the MAF table, or if PE EQ Ratio is way off, guess what, it could be going way rich.

Things like Cat over temp settings will also cause an over rich deal.

Just curious, does this tuner have a track record with GM gen3/4?

Re: adding 50% fuel at WOT
 

The tuner is Race Proven Motorsports over here in DE. They are very well known in the corvette and Camaro community, but I have a feeling they don't do budget swaps like this very often. Fran the owner did go to a pretty respectable school for engine building out in Texas, and they pretty much tune LS's exclusively, but I don't know how high my truck is on the priority list. Biggest problem I'm having right now is communication. Fran, the owner, knows what he's doing but I can't seem to have a good conversation with these guys. Every time I call its just sort of "still doing the same stuff, we have a couple more things to try" but its already been a solid month with no progress.

I know the problem is odd but I'm frustrated to say the least. The majority of the cars they seem to get in are toys shipped in from Cali and Florida, but I use mine every day and really need it back... just stuck between a rock and a hard place because I don't want to piss them off while they still have my truck and even if I go get it from them I still won't have a tuned truck and there aren't any other shops near here that do work like this.

Re: adding 50% fuel at WOT
 

My truck runs the SVO blue injectors which I think are the ones you refer to . They are close to 40lbs at rail presssure, and do a nice job fueling my cam only lq4. Iirc the tuner said duty cycle didn't breach 75% to do so.

Re: adding 50% fuel at WOT
 

I imagine that means the 26 #ers are about tapped out with a stock engine then.

Re: adding 50% fuel at WOT
 

YES

My guy often laughs because he gets that question a lot. The stock injectors can BARELY support the engine as it is.

*and now just for kicks, I'll take a stab at anyone running a boost-a-pump. People think jamming an enriched FPR, a boost-a-pump, or jamming a massive pump behind stock injectors somehow helps. It doesn't so stop. You can throw 15v and 100% duty cycle at the stock fuel system but it still won't want to support anything past a hot cam. You see this in homemade tunes when using the PE and VE to get it to run, they wind up using almost full duty cycle to barely maintain fuel thru the range. *

Re: adding 50% fuel at WOT
 

SVO 30's are red top. Going from fords rail pressure of 43 to the ls rail pressure of 58 they become 36lb. When I first had the 347ci motor in the truck, at 449rwhp through an 80e and 11.4x @ 117mph these injectors were in the low-mid 90% duty cycle.

Stock 01 camaro fuel system (28lb) injectors, I made 405rwhp with bolt ons and a cam through a 6speed) injector duty was high 90%.

Same car before the cam swap but with bolt ons (335rwhp) plus a 125 dry n20 hit, I was > 100%.

I agree that I don't like the bandaid boost a pump deal. Can they get you out of a punch, sometimes. Build the fuel system right instead.

I now have 60lbers I put in the 347 almost 5 years ago. Now being 418" and on e85, I am in the low 90's again. Time for an upgrade which I will do when I hang the twin 67's on it.

Re: adding 50% fuel at WOT
 

Mine are like the navy blue.... is that 36lb Cobra injector? The ford guys can't keep it straight on their own forums.

Re: adding 50% fuel at WOT
 

A lot of these replies are good but, there is no way to trouble shoot this without seeing the tune and a log of when this vehicle starts to go "50% rich". We could tell you to try this and try that all day and would honestly be a shot in the dark. Part number of the injectors would be good to have as well. Way to many moving parts to the equation to pin it to one thing.

Re: adding 50% fuel at WOT
 

Sounds like they are tuning only the primary ve table with maf disabled. The secondary must be tuned first. When the maf is disabled the secondary table provides all fueling calculations.

Re: adding 50% fuel at WOT
 

So, I'm finally back on. Got the truck back Friday. From what he tells me the tune in the pcm was originally a bone stock van tune, and he hasn't worked with one before. The way it was explained to me is that the problem wasn't that it added extra fuel at the top end, but for some reason had been cutting it out at the bottom end. The o2's can't read that large of a range so they were going by the low end readings as normal. Whenever they would tune in the proper amount of fuel the o2s would go crazy. Once he adjusted the bottom end a little and things started getting better he realized what was going on, and now it runs great. I meant to get the tune on a USB when I picked it up but forgot to ask. I'll still try to get a copy anyway.

Not quite as high as I was hoping, but to be fair its not bad for a bone stock engine with just headers and a tune.
http://i1130.photobucket.com/albums/...ps2bb946c8.jpg

If someone else ends up having a similar problem feel free to PM me and I'll get you in touch with the tuner. I'm happy with their work, just wish it didn't take so long. Definitely missed my truck with all this snow.

Re: adding 50% fuel at WOT
 

Glad they got it fixed for you.

Did they ever pull it past 5,100? Looks like it was still making power.

Also, did they try leaning it out more? Looks like it is still a bit on the fat side in the high 11's for AFR. Kind of doubt that the motor made best power that that AFR. I bet there is a good 15-20rwhp right there.

Makes me wonder where they set timing, if they ever did.

IMO a 6.0 with headers and tune should make a solid 325rwhp+