ViciousZ

iTrader: (1)

Aw jeez, I meant to say the BLM is too high. whoops.

Ok, I'll try to make a long story short: rebuilt 355, lots of performance goodies, including #24 injectors and a custom prom from Fastchip. Anyway, my scanner is showing a block learn of 148, way too lean, but it's been corrected (the integrator is back around 128) Anyway, I turned up the fuel pressure some and it didn't really change things. Right now it's at 54 psi (yes, with the vacuum line off) and the BLM is still too high. I figure this is a problem with the PROM programming, but for now there's nothing I can do about that. So should I keep bumping up the fuel pressure? And if so, how high is too high? Or should I just drive it (breaking it in now) since the INT is OK?

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91 Z28
Come see The Vicious...

[This message has been edited by ViciousZ (edited November 21, 2001).]

86TpiTransAm

From what I've heard if you run the fuel pressure too far over 50psi, it's hard on the fuel pump... even a good aftermarket pump but especially a stock pump. If the engine wants more fuel, install bigger injectors and then you'll have more fuel at a lower psi. Either that or have your chip reprogrammed.

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1986 Trans AM
355 TPI
4 Wheel Disc Brakes
9 bolt Borg Warner Rear (2.77's....oh joy) :P
6" rods, approx. 9.7:1 Compression, Stock TPI (soon to be ported), 24#/hr LTI injectors (cleaned and flowmatched by Cruizin Performance), Hedman Shorty Headers, 3" exhaust with 80 series flowmaster, SBC 993 heads completely redone and modified for 1.6 RR, 1.52 RR (for now), Comp Cams XE262-14 TPI Cam, Holley AFPR, TPIS airfoil, MSD wires, MSD 6-AL Ignition, Hypertech 53,000 volt coil.

Track times to come.

Matt87GTA

This definately could be adjusted in the PROM, as I was saying before. But if you can't have it changed at this time, you will likely be OK to drive it with a BLM like that. It is showing a lean condition, but not so lean as to ruin anything, IMO.

As for cranking up on the AFPR goes, I really don't use it as anything but a fine adjustment on the WOT fuel stuff. As you are stating, I haven't found that the higher fuel pressure settings will have much of an effect on part throttle BLMs. That is because of the regulator backing off the pressure with vacuum present. Raising the pressure a bunch with no vacuum present just doesn't do much to the rail pressure when vacuum is applied to the regulator. The AFPR has it's limitations. The answer to the problem is in the PROM.......

As for how high is too high with the rail pressure.... I feel that anything above 50 psi is seriously stressing out that fuel pump, unless it is a larger capacity, heavier duty, replacement one.

I am not really sure how good of an idea this is, but it might be possible for you to set the fuel pressure to a slightly lower pressure (say, around 48 psi or so, so as not to stress the pump out too much), and leave the vacuum line off the regulator to get a larger increase in fuel volume at part throttle. Now this may create some driveability issues and other odd conditions, but it might get your BLMs to a reasonable level while you are breaking it in. Again, I am suggesting this for a quick fix for break-in only, and it is probably going to stress the fuel pump out plenty, as well. But the break in time is a crucial one to have the mixture correct, so it might be useful for you.....

Laterzzzzzzzzz
Happy Thanksgiving!!

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

Grim Reaper

Vicious, when you are hittin the high BLM values are you idling or driving? What RPM and MAP readings do you have when you get these readings?

As Matt said, higher fuel pressure has it's greatest effect at high load (low MAP) values like WOT and least effect at low load (high MAP) such as idle or light part throttle.

If the high BLMs are occurring only at around idle, what is your voltage? If your volts are a little lower (say under 13/5), which often happens at idle if you have a lot of accessories on, too low of an idle speed or underdrive pullies; adjusting the Injector PW vs Battery Voltage inside the eprom is the normal "fix".

What you should do is get a range of BLM values for various RPM vs MAP readings. Find a good hill (a "dyno hill" in eprom circles) that will allow you to get a high MAP value without going into PE. I have a feeling that you are going to find at lower RPM & MAP values that your BLM is too high and the reverse at higher RPM/MAP values.

ViciousZ

iTrader: (1)

Thanks for the quick responses guys. Anyway I finally got someone to help me put the hood back on so I took it for a spin. The BLM goes down to around 132-134 while cruising. Much better. But now I noticed that the IAC is wide open while I'm cruising. Like at about 115. It's not supposed to do this, is it? I thought it would open when I took my foot off the gas, like when coming to a stop, but not while I'm cruising. Suggestions? I hate to jump to conclusions and blame the PROM tuning.
Oh yeah, I might mention that the IAC is already to high at an idle, about 60 in park and 95 in drive.

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91 Z28
Come see The Vicious...

Matt87GTA

Have you set the minimum idle in the TB yet? If not, do that and make sure it is OK. It is common to have to redo this adjustment when a largish cam is installed.... Am I to assume that the high IAC readings also are present with an idle speed that is pretty high? If that is the case, then the PROM is likely the culprit. They may have just set your idle A LOT higher than it used to be.... or maybe higher than it needs to be. Those figures seem a bit high for idle for a stock engine, but aren't really all that high for a modded one. An IAC count of around 60 should yield an idle of around 700 rpm.... But the rpm versus IAC counts relationship is dependant on the minimum idle settings.

As for what the IAC should be doing during driving, it shouldn't go to zero when driving. They don't have it close so that it can give you a nicer transition from open throttle to idle. If it stayed closed when driving, it would have all kinds of trouble finding an idle when you slam the throttle plates shut. It is supposed to open up to around 100 to 170 when you get going (depending on pretty much everything ) and step down to give you an idle when you let off of the throttle.

But it is completely possible that your IAC is toast, as they are known to not last forever. Keep in mind that the readings on your scantool are commanded figures and not actual figures....

Hope that helps some...
Happy Thanksgiving!!

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
My GTA

The Minnesota F-body Club

Grim Reaper

Vicious, your IAC positions that you are quoting are not too far off from mine. At idle (fully warmed) with the engine in drive, my IAC is around 65ish. I can't remember what the IAC is at idle in park.

While driving, my IAC can vary all over the place depending on the load. I run around 100-110ish, sometimes higher, sometimes lower.

At WOT, it is somewhere around 110-120ish. Again, I would have to review some Diacom runs to tell you, but that is the range that I recall.

When you start getting IAC readings below 30 (while idling in drive) or near 160, then you have a problem and SHOULD adjust your IAC. From your description, you appear to be okay.

ony

sounds like the bpw constanace needs to be raised or the second fuel table needs a slight increse