• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

So it's time for a smaller pulley.

It's very rare that I see anything above -10% the second I start accelerating, WOT or not. Idle has bumped up to -10 through -7% since I tightened that clamp though. I can watch anything with the Torque, I just need to figure out the logging feature. What are all the causes of negative LTFTs (running rich)? I've tried different injectors, a new Denso 02, checked fuel pressure (42 PSI at idle while running, with no bleed down after shut off), no leaking FPR, Fuel pump is rewired, WTF else could it be?

I'm not ruling out the tune, but I've had this problem with my stock tune, the tune"ish" that Scotty did for me, and this Reptile tune.
 


you ever change vac lines? spray everything down, sc to lim, injectors, tb gasket, bbv, and any other vac lines you see?

seems odd its the same bad #'s as it was with the pcm it came with.
 
I've done smoked tests and passed, I don't want to spray everything down cuz it's painted. I have the FPR upside-down, but I don't think that would matter?

Oh yea, all new lines vacuum lines, well, a year ago but newer than 2000.
 
it could be your engine just dont like its own files. like mine didnt. my ltft's used to be a bit wacky too when i had the stock pcm.

i just loaded 05 timing and knock sensor files in my 98 bin, and omg, its like a new car, and my kr is almost gone.
 
Yeah I'm running a beefed up '05 timing table myself since installing the ic, can't quite push the timing I was running before since no xp in this motor, but feels a lot better than it did before. Doesn't have anywhere near the pep off the line like the L36 bottom/GT trans/converter.

Things that could be throwing your trims negative: temperature, fuel (from a different station, maybe different blend, etc), the fp rewire, and maybe the new injectors just flow a little better than your old ones. The tune itself could've been a bit on the rich side to begin with (always the safest route, especially when you're doing the tune via mail), then combined with the stuff above only exacerbated the problem. With a vac leak you'd have positive trims, because the pcm is trying to compensate for air not seen by the maf sensor. Only way you're correcting negative trims that far off is via the tune, imo.
 
Once I can verify that there is nothing wrong with anything else, I'll opt for the tune. I'm hunting for a DHP now, I just a good opportunity, but oh well, lol. I have my alternator off to swap back to the stock pulley so I'mm gonna pull the rear valve cover tomorrow, if I feather the gas with the hood up (via the TB) I hear something that almost sounds like metal clacking in the rear. Very faint sound, but I figure it's worth looking into since it right there. At some point in the neat future I'll be pull my rear header out to move the flex pipe down to the down pipe and I think I'll go ahead and move the 02 to a better location too. Any input on a better location?

Thanks a bunch guys. I know that with a tune I could compensate for this, but I just want to make sure everything is running as good as it can before I do that. Also, how would the FP rewire do anything and if it was, wouldn't my pressure have been to high when I checked it?
 


Depends on what your fuel pressure was before the rewire. It's designed to give you more headroom with stock injectors, but it's not going to make the pressure anything crazy high. But putting more voltage to it is gonna make it pump more. It doesn't take much to throw off trims, honestly. When I save my .bin files, I always put the date so I know what kind of temps it's tuned in, that way I can change the file for winter, summer, etc.

One day you get gas and you might get the full 10% ethanol blend, next tank you might only have 3%, that'll mess with trims, too. That's why you shoot for +-3% ltft, gives you more leeway for all those variables and still have your fueling close enough. At -18, something is off, that's too rich, and making you go way lean under boost. Getting them locked at 0 would take care of most of that kr, I bet.
 
I have noticed that my fuel pump has a very loud whine to it, I must say. You can hear it if I leave the stereo off while the engine is running. Unless I find something tomorrow with the valve cover off, and after I make sure the exhaust and all is sealed up (even if it is leaking I'd be surprised if it fixed the LTFTs), tuning is just gonna have to be my only option. I have a spare MAF laying around, maybe I can just swap it in to see what happens, just for ****s and giggles.
 
The only other way I can think of to get the trims more positive is add airflow, never gone from a 3" fwi to a 4", so I couldn't tell you if that'd be enough, but it's cheap and can't hurt. Even if it does nothing, it costs you $10 and maybe an hour of time, you already have a filter, right?

I'm only on like page 19 of your build thread so far, so I don't know if you've done any dremel work on your TB and SC inlet, but that would get some more air in as well, and be cheap/free. Otherwise, just get a photosynthesis set up for your mods and hope its closer than your curret tune, lol. You could also give it a couple tankfuls of gas and see if you just got an odd mix on your last fill up, I try my best to use the same station, even same pump if possible every time I I've fill up. Never fill up if you see the truck there filling the tanks, either, wait til the next day or go somewhere else.
 
OMG I died laughing at the photosynthesis, lolol. I live in a small town, and no one caries 4 inch stuff since it's not up to code. The nearest Home Depot is 60 miles away, so it's a trip to get the stuff. I make a list of things to get in Springfield of stuff to get, then when the list is big enough I make a trip. That list is getting pretty close to requiring a trip up there, lol. Being a small town, I typically use the same station, there is one station that has no ethanol I run them from time to time, depending on the price (they charge $.20 more because there's no ethanol). I haven't done anything to the TB as of yet, but once I get the tuning stuff I'll probably just upgrade to a N*. I keep kicking myself in the ass for not buying that DHP while I had the chance. Oh well.

On a plus note, I swapped back to my stock pulley on the alternator and had it tested. While the car was running and had the stereo on(not loud) and everything else on their tester still maxed out at 100A, it couldn't test any higher...at idle. SO that's nice to actually have some good news, lol. My battery tested bad though, and it's under warranty so I get to go out and pull in 5* weather...yay.
 
When you say DHP, are you talking about tuner or PCM? 5* holy crap, glad to be out of that kind of weather, rather deal with the heat any day. Cold hurts, hot is just uncomfortable.
 


DHP tuner, not PCM. I just put the new battery in and took it for a test drive after getting to temp. Still way negative. I drove about 5 miles then did 1 WOT run and it was ~-15% the whole time.
 
Ah, in that case, continue kicking yourself, lol. Maybe I missed it, but why did you swap injectors from what you had in there before? At what point did you start noticing the high - trims?
 
I've noticed them for awhile, but I had no KR and I've slowly been trying to repair it. I swapped out the injectors because I thought that one of them may have been leaking causing the negative LTFTs. It was a stock for stock switch, no upgrades or anything. No change from that, lol.
 
Since I'm half drunk right now, and only read through the last couple of pages, one thing comes to mind.
A leak in the upper side of the engine will cause a POSITIVE fuel trim. An exhaust leak before the front 02 can cause the trims to go whacky either way.
 
I've ruled out vacuum leaks, and the trims show negative anyways. I'm still going to make sure the exhaust is all sealed up and everything to be safe, but other than that, it has to be my tune. All three PCMs I've had have had negative LTFTs so it's not really the tune's fault it's my car needing a different tune that most others lol. I'm not sure what else to do but wait for a deal on a DHP or HPT. I'll just keep my foot out of it until I track it down. I figure it'll make it to AZ since I'll just be cruising the whole time, right?
 


Yeah not gonna affect anything for normal driving. Pcm's are for those that will do a few basic mods, a pulley, and leave it at that. For those of us that have the need to constantly tinker with the car, and an insatiable desire to mod more, a tuner (or someone close by with one) is a must, imo.

After doing the basics on my '99 GT back in '02, I knew I would be working with this platform for a long time, so once I got started with top swapping a '97 GT I picked up for cheap (this was before top swapping was a thing, Lynoise was the only one to have done it on his Impy at the time) I dropped the $500 for a powrtuner. There were very knowledgeable people on the dhp forums at the time that were more than happy to help if you were having trouble. Then the excel worksheets they came up with made things 1000 times easier, sucked so much manually doing percentages to update your maf table one cell at a time.

Anyways I'm rambling, so yeah, invest in the tuner, you have it total ezmode nowadays, lol.
 
I'm constantly playing with my tune. I had a 3.5mps on my gen V with only headers on an L67 bottom end and I dropped timing down to 10* to be safe had zero kr with timing at 15* I saw 3-5* so I put a 3.8 MPs on and bumped timing now I'm editing MAF again. Come spring if it ever comes I'll be switching back to E85 eventually. But in my opinion I like timing over boost. However with the 3.5 I'll try to get timing to 20* with the E85 I have stage 3 p&p heads to install but I refuse to until I get the cam so I can actually enjoy the heads more then just running a stock cam. But timing over boost is my point.
 
You must log in or register to reply here.
Back
Top