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Old 07-20-2008, 02:08 PM   #11 (permalink)
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Quote:
Originally Posted by dremd View Post
2 things
1) TBI runs at very low pressure (like 10psi.
2) Injectors do hit a wall on running higher pressures, some more than others.
Okay, good to know. The theory would still hold true. If your stock pressure was 10psi and you wanted to increase your fuel flow 30% (for E85) then you would need your fuel pressure to be 17psi, which the TBI injector should not have a problem with. For flowrate vs. pressure calculations, to increase the flow rate by 30% you need to increase pressure by 70%. So, bottom-line, take your stock fuel pressure, and multiply it by 1.7 to get the fuel pressure needed to run E85. You can definitely get away with less, as the O2 sensor and ECU will pick up the slack, however for cold starting (open loop running) it's better to go with the 30% flow increase. I was running ~17% flowrate increase for a few months with no real problems, however when I bumped it up to ~30% increase cold starts were much smoother.

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Old 07-20-2008, 02:58 PM   #12 (permalink)
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Here's a thread that long and tedious but there is some good info in there.
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Old 07-20-2008, 03:54 PM   #13 (permalink)
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Its a lot easier to change a TBI injector instead of FPR or varibla FPR.
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Old 02-24-2012, 01:32 PM   #14 (permalink)
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Sorry about bringing up this old topic. But with e10 gas price of 1.6e/liter (about 8$/gal) and e85 price of 1e/liter (about 5$/gal) e85 seems to be good option.

I have to be able to use normal gas in winter so I think that injector pulse extender is the best way of using e85? I am not really worried about extending pulse width too much course stock rpm limiter is set to about 7000rpm and I rarely exceed 3500rpm, if stock injector can handle full throttle 7000rpm with pure gas they can achieve 3500rpm with e85.The car in question is 98 toyota corolla with 1.6 liter 4afe engine.

I have good understanding of electronics so I have been thinking about couple of ways to make my own pulse extender. But I would be very interested about what dcb:s circuit is like, and if anyone has any ideas, circuits or even better circuit board designs?

Any other thoughts are welcome also.
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Old 02-24-2012, 02:02 PM   #15 (permalink)
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For most cars with an oxygen sensor, I don't think extending the injector pulse or increasing fuel pressure is the entire solution. The fuel computer is going to try to close the control loop using the O2 sensor, and it won't read correctly using E85 - the computer is going to retract all the trim and you will end up too lean.

Probably depends on the vehicle, but forget about running closed loop for the best economy.
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Old 02-24-2012, 03:23 PM   #16 (permalink)
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Yes, car runs on closed loop. O2 sensor or lambda sensor will work just as good on alcohol as on gasoline. It measures lambda value and lambda value 1 is best for emissions (not necessarily for economy) with gasoline or with alcohol.
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Old 02-24-2012, 04:25 PM   #17 (permalink)
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So engine computer in closed loop will still correct properly using E85, provided you increase the fuel flow? Does it not depend on what cruising/closed loop mixture the computer is driving? Perhaps the differences are minor enough to get an efficient burn...

Interesting.
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Old 02-24-2012, 05:20 PM   #18 (permalink)
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Yes in closed loop computer is always calculating long term and short term correction parameters. If lambda says engine is running rich short term parameter is degreased and when short term correction is below 1 long term correction is also lowered but with slower speed.

Injection time is calculated in closed loop (simplified) original_injection_time*long_term_correction*short _correction
Injection time in open loop is (simplified)
original_injection_time(which is different than in closed loop)*long_term_correction

original_injection_time is the parameter that takes into account all the other parameters that ecu takes into account

But problem with e85 is that the long_term_correction parameter is getting larger than its maximum value and ecu thinks there is a problem in fuel injection system.

Last edited by Speeed3; 02-24-2012 at 05:29 PM.. Reason: trying to make it more understandable
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Old 02-25-2012, 11:53 AM   #19 (permalink)
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Quote:
Originally Posted by Rower4VT View Post
Instead of messing with the injectors or pulse-width, just increase the fuel pressure. My stock pressure was 36 and at 65psi I can run E85 with no issues. Do not go above 65psi however as that is the generally accepted upper limit for injectors.

In terms of tanks and fuel pumps, you shouldn't have to do anything. I converted a '94 Acura Vigor with 200K miles on it. Been running E85 for a year with no problems.
This is the easy way. And the specifics are to put a fuel pressure gauge on the line at the injector, and adjust or replace the regulator.

Often you can unhook the vacuum line signal to the regulator (unplug the vacuum line) which raises the fuel pressure at idle and cruise.

From there, start adding E85. You will find the happy limit pretty easily. If you add too much E85, the check engine light will come on, but the car will continue to run fine (assuming 96 or newer and OBD2). If you have an older car, the car will accept quite a bit more E85, but eventually it will start to cough, have a hesitation, or generally act crabby. At this point you have reached "too much E85" and you will have to add 5 or 10 dollars of E10.


Also, most cars run FINE on E10. To change to E85 is less then 20 percent diffference, not the 30 percent quoted above.
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Old 02-25-2012, 01:19 PM   #20 (permalink)
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I have thought about just increasing the fuel pressure but if I understand correctly increasing the injectors flow 23% would require 50% increase in fuel pressure. Stock fuel pressure is about 40psi over manifold pressure. Would injectors handle 60psi of pressure?

Car is 98 Toyota corolla with 1.6 liter engine. Itís not American model and it doesnít have obd2

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