With a laptop it's a walk in the park to troubleshoot issues like that. Due to my shoddy wiring I was having an intermitted break in my air intake temperature sensor readings. It manifested itself as a bucking while driving down the highway, plugged in the laptop and instantly saw my IAT bouncing radically causing a lean condition (on an already pretty lean cruise tune!). I ignored it for the rest of the trip and tracked down the wiring issue when I got home (150 miles later), no real problem. Worse case scenerio I could of unplugged the sensor and made a temporary change to the VE table to account for the default air intake reading. Yes I needed my laptop, but A) I didn't stop and actually do anything about it until I got home so I was never stranded and B) sensors rarely fail, this was an installation failure, aka operator error. I have 35,000 miles on my MegaSquirt and it has yet to leave me stranded anywhere, this instant mentioned actually is the only issue I recall having.
If you change the airflow thru the maf too much it changes it's calibration factor. For instance, they are calibrated with the ECM to see certain resistance at certain airflows. When you change the speed, temp and/or volume of flow thru the maf then you change it's calibration, hence potentially poor running quality. TSB is correct on a lot of stuff., The sensors used in most aftermarket systems are for the most part million mile stuff, original OEM stuff, very dependable. Speed Density for the aftermarket gives a wider range of applications. Otherwise you'd have to have various size Mass Air sensors for different applications based on engine size, level of mods etc. And for the OEM stuff a maf system limits the ability to make big mods without additional tuning, that's what Uncle Sam wants. Most aftermarket systems out now are not a true VE based system. They are Pulse width, period. MS, FAST, Holley, MOTEC etc. Only Accels' in this price range is a true VE based, why? Simple because it takes into account an additional dimension of feedback, manifold surface temp. That along with the intake air temp and coolent temp is calculated to parrallel a MAF system, more accurately measuring the amount of air and consequently fuel entering the engine over and above what a pulse width based system does. Remember cold air is more dense, but hot air moves faster. And we know how fast air moves at certain temps. There are graphs in the Accel software to utilize this info. Hope this helps.
More good info from you guys. That's the stuff we need to help determine how to choose a system for a retrofit. I'm personally looking at using a factory LSx system powered by the eficonnections 24x setup. The tricky part is trying to get the crank and cam sensors installed correctly. I'm figuring on using the cam sensor from the vortec van motors adapted to a stock Buick distributor body. The 24x system provides the cranck sensor, but it's going to be tricky trying to figure out the install since it can't be put in the stock timing cover like in the Chevy motors. It'll probably be done externally the way it was in another one of SilverBuicks posts. The programming trick will be getting the fuel output in the LSx computer rich enough to keep up with a 455. I may have to use the mapping from a Vortec 454 as the base and adjust from there.
I think you're going to be surprised how different those 2 fuel curves will be (LSx vs your 455). I think you'll have to retune the whole thing. Jmo.
Agreed, the BSFC on the LSx engine is probably waaay better than a BBB, and not just at peak power. And you may of noted, mine is a 36-1 wheel. I do things mostly as cheaply as possible to get what I want done (because cheap is the Q-jet and base distributor =P ). I'm thinking of adding a Grand National cam sensor and a set of LS coil backs to go distributorless. Just need to cough up the dough for the coil packs :idea2: I still have no desire to go sequential on my Buick engine as I don't plan on putting in the necessary dyno time and individual AFR monitoring required to take real advantage of it. The coils are for athsetic's and uniqueness on a BBB.
Don't really need the dyno time, you've been mislead there a bit. If when in sequential you can adjust injector timing, then it's not hard to get really close to optimum without a dyno. While at different loads and speeds, watch your O2 feedback. As you change injector timing and get closer to optimum it will need to remove more and more fuel based on your current fuel map. And when it's right you'll notice it will need less transient fuel, you've just made it more efficient. That will be the biggest change. Just like in the old days when you timed cars by ear, the fastest idle etc was the most efficient. Hope this helps.
Oh for sure, you can definitely hear when the engine is happiest, almost like they sing. Datalog wise, like the old days, watch for peaks in vacuum too. And that'll work with the injector timing (relative to the valve events), but I was refering more to balancing the cylinder to cylinder AFR's. The testing one of my friends has been doing on 8 cylinder AFR monitoring (look at the current EMC Hemi article) on a couple different types of engines, they all have about a 1 full point of difference between the leanest and richest cylinder, so you are really tuning the whole engine to the leanest cylinder if you don't want detonation or such damage. That's the part I'm referring too. Both sets of adjustments really only get you that last few percent of HP (about ~30HP on a 1,000+HP n/a engine). *Also, not all sequential EFI systems have the capability to do individual cylinder fuel (and spark) trim. If some one wants to loan me a set of Buick headers with 8 O2 bungs in I'll be glad to borrow them though :laugh:
Obviously balancing cyl to cyl air/fuels is that much harder to do when in batch. Invariably you're firing some of the injectors at exactly the wrong time. Also, some systems do have the ability to do individual cylinder trim. But guess what, even the new latest and greatest XFI 2.0, Holley HP, Holley Dominator, Motec and others can't do what the Accel does. The Accel not only allows you to trim cyl to cyl + or - 25% but also allows you to tailor it to various loads and rpms. I promise you that cyl to cyl balance changes as throttle position, camshaft overlap and other factors change the internal dynamics of the intake manifold.
If you're going for reliability and ease of use then there's not much need to do the per cylinder fuel adjustment. In a perfect world it would happen, but it's not hugely important unless you're trying to squeeze out every drop of power or efficiency. A multipoint system should get your cylinders closer to balanced than a carb just by the design of the fuel path. Also as I noted at the end of my last post, I'm probably going to start with the Vortec 454 tune and work from there. That motor is far more efficient so right from the junkyard it'll probably be running a bit lean. I figure reduced timing and slightly higher fuel pressure should compensate long enough to get the tune right. Seems you're about 2 years ahead of my on this junkyard FI stuff.
I do love a good junkyard build. Got my sensors and pigtails for the harness from there. Same with the fuel pump. I do personally prefer a standalone ECU, but I've never tried using a programmer like HPTuner's to mess with an OE ECU.
I put a Holly projection system on my 55 buick back in 05. I got the system for 300 bucks so i said what the hell. I had to get a 4 barrel intake and used an adapter. had a shop weld in a oxygen sensor bung (20 bucks) and ran a return line to the tank and it actually worked pretty good. i think it was a bit to much fuel for a little 264 though and went back to the 2 barrel before i sold the car, AND sold the projection system for 500 bucks! the throttle response was great....
