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I just read in a post that TPI fires all injectors at the same time. This agrees with what I saw in the wiring diagrams with all the bank injectors hooked in two parallel sets off the ECM.
I initially dismissed it as an oversight.
Is this really true?
How does the engine run well when the other cylinders are not ready for fuel?
This seems very primitive, even for a first gen port injection system.
For most TPI purposes, sequential may be "overrated"...
Any advantage is most likely to show up at low rpm's like idle speed. As RPM increases and valves are opening and closing much faster, the difference between the two diminishes.
Now, I will say this about the Miniram and log style plenum manifolds.... sequential injection will come into play in terms of resolving the "split BLM" problem. You can see this in how GM trimmed the fueling at idle on the LT1's from 94 and up.
Years ago when I was struggling with split BLM, I contemplated swapping over to a sequential injection system out of frustration. But I ended up generating an idle air manifold for my Miniram (basically since I couldn't solve the distribution on the fuel side, I solved it on the air side by ensuring all cylinders got as close to the same amount of air as possible). Search on "split BLM beast" if you're curious.
I confirmed success it by measuring the exhaust header tube temperatures. GM had a similar feature cast into the LT1 manifold (which is where I got my inspiration), but they still trimmed the fueling differently in 94 and up when they swittched to sequential.
But at this point, my idle is already very smooth, so switching to sequential won't buy me anything now. If I changed to a more radical cam, maybe it would, who knows.
But, at the time when these TPIs were new, I can't see sequential injection as making much of a difference.
The injectors are batch fired - Twice per cycle. The result is not much different than TBI in that regard, except that the intake is essentially dry. It seems to work just fine in most cases.
I looked at this quite a bit when I tuned my Holley EFI. I won't claim to fully understand the finer points, but some of the low hangin fruit were that A) You can tune fuel economy to the "N"th degree with sequential, which nowadays is important to the manufacturers. B) Sequential offers better idle for radical combinations. C) More balanced/smoother fuel flow through the fuel rails leading to precise fuel pressure tuning, and D) The ability to tune injector end angle, which was sorta described as setting the timing OF the injectors, lol! -the latter two ultimately leading to higher peak HP and torque, although the difference can often be negligible.
For my basic run of the mill 383, I'm running a batch/paired injection strategy.
As Vader posted TPI is batch fire. And normally fires twice per engine cycle (double fire). In the '86 - '92 TPI ECMs the firmware will go single fire on small PWs. Not sure about the '85 TPI ECM.
Single fire is used with small PWs, the ECM doubles the PW and fires the injectors once per engine cycle. On a 4-stroke an engine cycle is two revolutions.
Down side to using single fire is that due to the way it is implemented, the maximum duty cycle is 50%. Anything over that is truncated. That and being batch fire the engine just doesn't run as well as double fire.
As for sequential injection, it is better but mostly when running large injectors. Say a 80 #/hr or a 120 #/hr. Much easier to control when being single fired along with the injector closing being controllable.
Single fire is used with small PWs, the ECM doubles the PW and fires the injectors once per engine cycle. On a 4-stroke an engine cycle is two revolutions.
Down side to using single fire is that due to the way it is implemented, the maximum duty cycle is 50%. Anything over that is truncated. That and being batch fire the engine just doesn't run as well as double fire.
RBob.
Interesting. Is there a way to disable single fire in 8D? And would there be any benefit to doing so?
I think what's even more amazing here is that the OP has been apart of this website for eight years and is just realizing this now lol...
No, it isn't nor wasn't primitive. The system ran just as good, if not better than the stock LC2 and Fox body systems back then. To place things into perspective, Porsche, Ferrari and Lamborghini... vehicles that out-shined the third gen in every conceivable way, continued to use the K-Jetronic fuel injection system well into the 90's, which was a continuous fuel feeding system, not pulsed. Talk about primitive. But hey... it worked.
Yes. If the injector compensation values are not correct the transition between double and single fire can be abrupt.
RBob.
Hmmm.... seems like it's a non-issue after looking through some TP data. It hits single fire for maybe like 1 second here or there. I'ts not clear what's triggering it, but I guess I'm not really feeling anything abnormal in seat-of-the-pants.
I think what's even more amazing here is that the OP has been apart of this website for eight years and is just realizing this now lol...
No, it isn't nor wasn't primitive. The system ran just as good, if not better than the stock LC2 and Fox body systems back then. To place things into perspective, Porsche, Ferrari and Lamborghini... vehicles that out-shined the third gen in every conceivable way, continued to use the K-Jetronic fuel injection system well into the 90's, which was a continuous fuel feeding system, not pulsed. Talk about primitive. But hey... it worked.
- Rob
Not hard to think that a primative system could make very good power. Look at what the most powerful production gasoline engines which were actually built in the 1930s through the early 1950s used.....A pressurized carburetor, which itself is essentially similar to a TBI unit with a constant flow injector sitting in front of a drawthrough supercharger. A few were also mechanical direct injected. Some of them were also force fed air from a turbocharger and had to operate from sea level to 50,000+ feet while maintaining a decent air/fuel ratio all done mechanically without a computer.
