The OEM method is to have the injectors batch fire by bank giving an injector sequence of 1,3,5 and 7, then 2,4,6 and 8. The injector pulse arrives earlier and earlier when measured against intake valve opening reducing the quality of atomizatiom of fuel. It would appear that this quality reduction could be reduced by batch firing injectors 1,8,3 and 4, then 6,5,7 and 2. Smoother running and more power? Has anyone tried it?

 

Interesting concept. I have not heard on anyone doing it but it would not be hard at all to do. Looks like you would have to extend and swap the wiring on the 4 and 5 injectors and the 7 and 8 injectors.

 

hummmmmmmmmm...... good question. in fact, REALLY good question. I guess someone will just have to try it and see how it works... there's probably enough wire length in the factory harness if you scrounge a little. hummm.....

any one have any other thoughts? Traxion/Vader? - you two seem to be pretty good on the ecm stuff...

 

All 8 injectors fire at the same time. There is only 1 driver in the ECM.

RBob.

 

Would swapping to full multiport yield any decent results? Performance and economy wise? Or is it just in the economy.

(Yes, I know its a PITA to do, but very doable)

 

swapping to multi-port would yeild good results. good enough...? probably. - I'm not a factory ecu guy, but I don't understand the single driver thing. I've heard this before, but I've also seen cars running crappy due to swapping the wiring from bank to bank....

 

Like Rbob said, our cars fire all 8 injectors at the same time, least on all the v-8 apps(port injected)

U can run injector wires to any injector and it wont make a difference on our cars.

later
Jeremy

 

You could swap to Sequential Injection, there are guys doing it. The distributor has to be retrofitted with a crank and cam sensor. The economy is better around <2-3000 RPM, after that Sequential becomes batch fire anyways. This would involve swapping in an LT1 ECM or the one from the caddy. I'm not sure on all the details, but you could expect better economy idling and around town. I'm sure its not a huge, huge difference, but you could expect some. Maybe a smoother idle too. My batch fire TPI seems to idle nice and smooth @ 600-650rpm anyways.

 

thats good to know. - hadn't realized that though...hummm makes me see why a good tune could REALLY help a modded car....

 

Wonder how much buying "flow matched" fuel injectors is worth horsepower wise if anything?

 

Heh, kinda reminds me of the old VW CIS-E fuel injection. Basically, constant injection. All the injectors ran full time. Worked good when it did work right. When it broke....oh boy. :\

 

I always thought batch-fire meant each bank of injectors fired at the same time? You know, left-side injectors fire all at once and then the right-side injectors fire all at once. I didn't realize all 8 of them fired at the same time.

TPI batch-fire does have a pretty smooth idle. Sequential is smoother though. The main difference I've notice is at the tailpipe. Sequential MPFI cars have almost zero pressure at the tailpipe when idling. You can barely feel the exhaust pulses at idle. TPI has a more noticeable pulse from the tailpipe at idle. At least from what I can tell.

Forget the sequential injection. I want displacement on demand! I've looked at a few Caddy's with old 368cid V8-6-4 engines at the junkyard and I bet you can devise a system similar to that for SBC heads. A solenoid under the valve cover energizes a cam lever which moves a plate that changes the pivot point of the rocker arms. Pretty simple when you look at it. Using current ECU hardware technology, I bet this could work pretty good on our engines.

In fact, you can make things even easier by getting rid of the "V6" feature because that made for a slightly "unbalanced" condition found on Caddy V8 engine during "V-6" mode. Just program it to run on all 8-cylinders for max power or 4-cylinders when cruising. The Hemi's from Chrysler run the same way. 8-cyl or 4-cyl. Yeah, GM was first with DoD on the '81 Caddy, but the ECU was very slow by today's standards and the TBI system primitive compared to modern port fuel injection.

 

Even if you could cut out the valves you would still have to cut the injectors out somehow. Maybe a switch inline to 4 of them that is activated by a solenoid?

Either way, as soon as the 4cyl kicked in you would have to bury your foot in the floor to keep going, negating most gains. I think a V6 would be most efficient for such heavy cars as ours.

 

The major advantage of sequential injection is the ability of the PCM to control injector pulse widths on an individual cylinder basis, and coincidentally alter individual cylinder ignition timings. I have an LT1 with quite a bit of cam (.540") that idles just as smoothly at 650 RPM as the TPI in the ThirdGen with that wimpy factory .385" lift cam ("LA Cam") on batch fire.



VW Dave,

Gee, thanks for the reminder. I had almost successfully forgotten the Bosch CIS-E systems, then YOU had to remind me. Those whiney-*** pumps barely making enough pressure, feeble control schemes, that moronic little pair micro switches for idle and WOT positions, cloth braided hoses, connectors better suited for kids toys than automotive systems, idle adjustments that never idles, etcetera.

Any wonder why I keep the attitude that Germans shouldn't be allowed to wire anything?

 

While individual cylinder control is a big advantage, the main reason that the OEM's use SEFI is for emissions reasons. Emissions are much less in SEFI systems in the low and mid RPM ranges while overall performance (throttle response mainly) is only a little better as compared to PFI setups. Once the mid RPM range has been exceeded, the emissions and performance are nearly identical. HTH

 

That whole system was a big mistake. Ironically alot of cars used it. Ferrari, Porsche, VW, Audi, I think Mercedes did too. BMW might have...

Whats worse? The Digifant that came out after that. Oh my ***. The car would get into a limp home mode, that you can change every sensor, every wire, AND the computer and it will STILL be locked in that mode. Most technicians hear that car and run away screaming.

The new stuff is pretty good though. At my performance shop, we got a 500hp GTI on stock based computer with different programming. Hits 36psi on race fuel. I drove my turbo to Daytona at 85-90mph over 250 miles, got a few surges over 120mph, and was in stop and go for a few miles and still somehow managed 30mpg. *Shrug* Mine is far from stock.

Its gotten alot better as everything else has.

 

Germans??? Have you looked at any Jaguars lately? Now there is some quality wiring, I tell ya!

 

Kinda weird to say that when Ford bought them out, their reliability went up.

 

I believe the early Jaguars used Lucas electronics and wiring. That was the biggest problem with those cars right there. I would bet that a Lucas setup is just as bad as the Bosch CIS-E system Vader was referring too.

Fortunately, the newer Jaguars (after Ford took control) are very reliable. A friend of mine has a '00 XK8 and it's a reliable car I must say. It has a better build quality than even the new Corvette. However, for nearly 80K MSRP back in 2000, the XK8 should be a very well made car.

This discussion of sequential fuel-injection reminds me that the Grand National was the first GM production car to have SFI. Back in '84 when Chevrolet was still playing around with 4bbl carburators on the Camaro Z28, Buick had the 3.8L SFI turbo which had state-of-the-art sequential fuel-injection and distributorless ignition.

 

My pre ford 89 xjs with a 5.7TPI/700R4 is a nightmare if you need to work with any of the origional garbage. Damn limey's didn't know the meaning of "colour codeing". Everything is the same frickin colour!

 

Nonsense. The Pinouts show clearly there are two injector drivers... the ecm sneds out one pluse width signal for both, but there are two seperate drivers:

 

But they both fire at the same time. I think maybe its incase one burns out? Or maybe they were just on crack.

 

Hmmn,
Where did you get that pinout? It's not the same one that is in my '89 Helms.

Incidentaly, I did hook my Oscope up on my '89 to the left and right banks, it's a tough to trigger signal, but cleary shows both banks firing at the same time.

 

There is one driver that is routed to both pins. Grab an ohm meter and measure the resistance between the pins. They are connected together.

RBob.

 

Now if we had a schematic of the printed circuit board there "might" be a spare driver. Then the circuit board would have to be modified and then the source code changed. If the base information was available for the both the circuit board and software it would be easy enough to do.

 

I'm not so sure there are even two drivers, my ECM pinout in my Helms only shows one driver, going out to two pins on the ECM, if memory serves.

Besides, from what I've read, even the sequential systems go batch at WOT.

And who really cares about gas milage with a V8 anyways?

The juice is getting cheap, I just payed 2.06 for regular!

 

There really is only ONE driver in the 7730. If you don't believe it, open up the ECM and look for yourself. The 7749 ECM is almost identical to the 7730 (TPI ECM) but has two drivers.

 

The original question still remains unanswered in one respect, "Is there any improvement in non WOT performance if the injector sequence is altered?" We seem to have established that a 7730 sends only one signal to the two injector circuts, therefore no simple improvement is possible. But, if the 7749 sends seperate signals that are 180 ignition degrees of rotation apart , then the original question can be answered. If more torque can be created from a given amout of fuel, I for one would be glad to have the side benifit of better milage as the time spent at WOT is miniscule in the grand sceme of driving.

As for VW's CIS, it was a stroke of German injunity that eliminated all the functions of a carb with a simple fuel metering block controlled by engine air flow mechanically connected to it by a fulcrum and lever. And yes the fuel pump was its weak point, it was the only part of the system I replaced in 100,000 miles. Another neat point was the A/F ratio could be adjusted with an Allen wrench.

Now if someone has the necessary test equipment and a 7749 we will be able to learn the answer to the original question. Thank you to all who have contributed to this discussion and advavced our knowledge of TBI.

 

Firing one side 180 apart from the other side is not going to give you much if any advantage. The only way to improve batch firing is to go to SFI, 8 injector drivers, every injector firing independently. The 7749 will not help in this respect at all.

A SFI ECM will deliver smoother idle, lower emissions at low RPM's and slightly better throttle response at part throttle. It will not help in WOT.

If you want to read about people working on switching to a LT1 SFI ECM read this thread: https://www.thirdgen.org/techbb2/sho...hreadid=331767