STFT LTFT way in the negatives even with dsmchip?

Killa_dsm · 09-14-2007, 02:50 AM

I have a vr4 pump, PTE 780cc and a dsmchip that is programmed for 780's that I have. When I am cruising my STFT, and LTFT seem to be way in the negative. The car does a lot of popping through the exhaust and I can't seem to figure out the problem? Could it be that my stock fpr is going bad or being overrun? But I have heard the stock fpr is fine with the vr4 pump?

Any help would be great. Thanks

Apeximprt2nr · 09-16-2007, 05:47 AM

Do you have an SAFC to compensate for the injectors? Usually with those chips you can get the car to run decently well with bigger injectors, but you still may have to adjust with an SAFC.
I'm not sure about the VR4 pump though, but it is possible, it's a decent size pump.
What #'s are you getting on the logger for STFT and LTFT?

zippyshoe · 09-16-2007, 11:42 AM

The only way to determine with any certainty whether or not you are experiencing fpr overrun would be to connect a fuel pressure gauge to your fuel system - you could use a gauge that installs on top of your fuel filter, for example. With the vacuum line disconnected from your fpr, you should see about 43.5psi (2G base fuel pressure.) When you re-connect the vacuum line to the fpr, you should see your fuel pressure fall by about 1psi for every 2inHg of vacuum you see at idle. For example, if you are seeing 18 inHg of vacuum at idle, then your fuel pressure should read around 43.5psi - 9psi = 34.5psi with the vacuum line connected. If you are reading a significantly higher fuel pressure than these expected values, than that would indicate fpr overrun. Hope this helps.

Killa_dsm · 09-17-2007, 01:15 AM

Quote:

Originally Posted by Apeximprt2nr

Do you have an SAFC to compensate for the injectors? Usually with those chips you can get the car to run decently well with bigger injectors, but you still may have to adjust with an SAFC.
I'm not sure about the VR4 pump though, but it is possible, it's a decent size pump.
What #'s are you getting on the logger for STFT and LTFT?

Most of the time my LTFT is in the -12's and my STFT is at -11. The only time my LTFT turns to -3 and my STFT to 0 is when I am in gear and let off the gas.

I tried leaning it out with the S-AFC but to do so I have to take quite a bit out of it. So I decided to zero it out. The Vr4 pump is rated similar to Walbro 190.

Back when I had just my Evo 560cc's and S-AFC, I didn't have this type of problem. And I don't think the Chip would be that off to be that rich?

I might go to a local junkyard and see if I can get another fpr just to see if that makes a difference.

Any idea's?

Jst4Cyl · 09-17-2007, 03:37 AM

Is it popping like a miss ? (running lean) <<<<<< Sounds like this to me

Is it popping like a back-fire/loading up type(running rich)

How does your mafs reading look?

FTW, I would get a adj FPR no matter what...

That way it is one more thing that you can control and monitor

Killa_dsm · 09-17-2007, 02:31 PM

Quote:

Originally Posted by Jst4Cyl

Is it popping like a miss ? (running lean) <<<<<< Sounds like this to me

Is it popping like a back-fire/loading up type(running rich)

How does your mafs reading look?

FTW, I would get a adj FPR no matter what...

That way it is one more thing that you can control and monitor

It sounds more like a popping like a back-fire. Yeah, I'm in the process of shopping for a AFPR. And if I'm still gettting the problem I will probably get my injectors flow tested to see if they are actually 750cc's. I know they are PTE since they have the sticker on them, so it might have a chance of being 880cc's. Not sure I have to look into that since I bought them used.

Apeximprt2nr · 09-18-2007, 08:47 PM

I would go get those injectors flow tested. It seems like you had your chip set to 750's though it's acting as if youre running larger injectors since its still running rich, and leaning out the SAFC is getting to the point where it's getting dangerous.

Killa_dsm · 09-18-2007, 11:42 PM

Quote:

Originally Posted by Apeximprt2nr

I would go get those injectors flow tested. It seems like you had your chip set to 750's though it's acting as if youre running larger injectors since its still running rich, and leaning out the SAFC is getting to the point where it's getting dangerous.

Yeah I am going to contact pte about them so I can identity if they are really 750's. I also contacted Jeff at dsmchips and he is sending me a leaner tuned chip. Lets just say he provides great service!

GoldÐiamond · 08-07-2008, 09:09 AM

Quote:

Originally Posted by Killa_dsm

It sounds more like a popping like a back-fire. Yeah, I'm in the process of shopping for a AFPR. And if I'm still gettting the problem I will probably get my injectors flow tested to see if they are actually 750cc's. I know they are PTE since they have the sticker on them, so it might have a chance of being 880cc's. Not sure I have to look into that since I bought them used.

I have a very similar problem. I currently run:

190 Rewired Walbro
650cc Injectors
Stock FPR
2g MAS
KeyDiver Stage 3 Chip

And it backfires/pops/sounds flat on decel or light cruising, like its running rich. And all 3 of my fuel trims read around 81%. I took a few points off on the SAFC and it increased the fuel trims a little. Should I keep taking points off on the SAFC or is that dangerous?

Do you think the stock FPR is being overrun?

tsitalon03 · 08-07-2008, 09:34 PM

I think you have to use your afc and add fuel....your prob running lean. My mods are in my profile...i had the same prob....it would pop when i'm driving in a parkinglot at low speed....99% chance you have to add fuel.

Killa_dsm · 08-07-2008, 10:05 PM

Quote:

Originally Posted by tsitalon03

I think you have to use your afc and add fuel....your prob running lean. My mods are in my profile...i had the same prob....it would pop when i'm driving in a parkinglot at low speed....99% chance you have to add fuel.

No I think it would be the opposite. For 1g's anything over 100% is lean and anything under is rich. 1g person could you correct me if I'm wrong.

To GoldÐiamond question. Yes its fine to take away fuel. Try to get your fuel trims as close at 100% as possible. Thats what I had to do. The problem could be the fact that the fpr is being over run since I'm running the stock one as well. But adjusting the S-AFC worked for me.

GoldÐiamond · 08-08-2008, 08:27 AM

So you just kept taking away fuel until you got to 100%, and the popping/backfiring stopped?

How much fuel did you take out, and what is your setup?

Killa_dsm · 08-08-2008, 12:04 PM

Well I contacted Jeff at dsmchips.com and he sent out a leaner tuned chip for me. That helped the problem a lot, but I still had to take out some fuel.

As of right now I have a different chip from before and havent been able to play with it much. Since I'm out of the county. I still needed to take out fuel tho. Once I save up enough money I think I'm just going to upgrade to link. That way I can get a perfect tune.