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TSR MAX BOOST FUEL DELIVERY #2
The final part of your T.R. fuel system is the injectors. ½ lb. of fuel per H.P. hr. is a close but not exact rule of thumb guideline. Keep in mind the fuel pump must be adequate to supply any upgrades in injectors. If you have upgraded injectors and now can't maintain 65to 75-psi fuel rail pressure at full throttle, high boost & RPM, reassess your pump situation. T.R.s were near the maximum output of their stock fuel delivery systems when new. That is both the pump and injectors.
Stock injectors will flow 25 to 28 lb. at 3-bar. 43.5-psi is referred to as 3 bar since it is close to 3 units of barometric pressure. 1 unit of barometric pressure is 14.7-psi at sea level. 3 bar is a common reference when dealing with fuel systems.
A base fuel pressure setting of, 40-50-psi will increase to 65-75-psi at WOT depending on the amount of added boost pressure. This is the pressure between the fuel pump output and the fuel pressure regulator. This is the pressure the injectors see at their top/fuel-rail/feed end, in order to maintain Delta pressure at their bottom Delivery end at the intake manifold. Delta pressure simply means the maintaining of the constant differential in pressure between these two points. The fuel pressure is maintained at the constant Delta pressure of the base setting.
As the pressure in the intake manifold changes the fuel pressure changes with it in direct proportion.
Increasing the base fuel pressure setting has little effect on actual total fuel delivery. This is more a function of the capacity of the injectors. Injectors are designed to operate at 3-bar delta pressure. Only small variances can be achieved by adjusting the base fuel pressure setting.
Larger injectors. If your T.R. needs injector servicing, the cost of the labor to change them out is a consideration. You may want to upgrade at this time. There are adequately large injectors now available with high impedance for most upgrade applications. This means that you can run these without modifying your ECM computer with more powerful low impedance drivers. Changing the injector size more than 10% will require a change of chip PROM.
The drive-ability of larger injectors is relatively good. They are surprisingly well behaved. Since this is the case, consideration should be given to the proper sizing of injectors in reference to future upgrades. Doing it once makes more sense than multiple times. Economy is always an issue when it comes to cost effective upgrading.
Injectors are precision machines. They are susceptible to damage from heat as well as fouling from dirt and from "normal use" fuel residue deposits.
Under-hood heat is a concern for all engines. T.R.s are especially vulnerable due to the additional heat the turbo engine produces.
Though they are cooled by fuel flow the injectors build up heat internally themselves from electrical resistance. It is Standard practice that injectors be cleaned or replaced periodically.
The following are some ways to tell if your injectors need attention:
Does your T.R. loose fuel rail pressure after shut down? It shouldn't unless the pump has been modified by removal of the check valve. This valve keeps the pressure up at the pump end of the fuel circuit. Some pumps have been modified by the removal of these check valves to increase flow. You should be able to tell if yours has been modified by removal of check valves because the pressure will drop instantly at shut off if it has been.
The other seals to the fuel loop are the regulator and the injectors. The injectors are so precise that even a particle as small as the width of a hair would cause it to be fouled.
If your injectors are fouled and not closed properly, after engine shutdown, fuel will drip from them causing the fuel pressure to drop slowly.
Other things to look for if you suspect your injectors.
A) Long cranking when starting. This is an indication of the time it takes to build up your fuel rail pressure.
B) Black smoke upon startup from exhaust. This indicates over rich mixture caused by fouled injectors not seating fully closed. When engine is shutdown, the fuel can slowly leak by the fouled injector and drip into a puddle in the intake runner on the intake valve or into the open cylinder. You may also be able to smell raw fuel on startup from this condition.
C) While driving there may by intermittent stumble or misses.
D) Lean condition at full throttle or missing.
Some of these symptoms could be caused by other things. The first two are usually injectors, especially the black smoke and raw fuel smell.
If you have fouled injectors, you may want to try and clean them on the engine first. If this works then you have saved yourself the time and trouble of removing them.
There is a kit available for a simple method cleaning. Just connect a pressurized can of solvent to the Schrader valve at the front of your fuel rail on the driver's side. A line and fitting is provided in the kit with the solvent.
Disconnect the electrical power at the fuel pump just between tank and left rear bumper. Simply unplug connector. Then run engine on contents of can until empty and engine stalls. If you have used the on engine method and still have problems, it might be time for a more complete servicing. This requires removal and back flushing, solvent cleaning and flowing. There are aftermarket suppliers that offer this service. Be prepared to pay insured shipping both ways. Be prepared to wait one to two weeks minimum.
The more expensive method of ultrasonic cleaning might be needed if the injectors have been allowed to sit unused for a long time. The fuel will eventually harden like varnish, and be difficult to clear. Be prepared to replace injectors if they don't flow test out at a close % of each other. If they are close but don't match, the richer ones can be placed in leaner running cylinders to help balance the mixture. Injectors can't be repaired they can only be cleaned and checked. Because of the length of down time involved with sending them out, this would be a good project for when the car is stored for the season.
Another cause of injectors not flowing properly is fatigue. It may be clean and free of obstruction and still not flow right. This can be the result of heat damage to the magnetic coil, which slows opening response time and may limit the travel to less than wide open. This condition would be cause for replacement. This condition is discovered by the flow testing which uses a series of pulsed openings. This method takes the reaction time and the hold open time into consideration in the flow rate.
This is the right way as opposed to just a single wide-open flow. The multi-pulsed method at 43.5 psi is duplicating actual real world operating conditions, and therefore it the most accurate.
Inadequate fuel delivery is worse than total failure of the system. This lean condition will cause engine damage. Try to attain a margin of fuel delivery capacity that is 10 to 25 % greater than the amount actually required to support the estimated horsepower output of your engine.
The stock engine Gross HP figure is 360. Use gross HP figures when estimating fuel delivery requirements.
Use the .5 ratio for ease of ballpark estimates and then allow 10 to 25 % more for a margin of safety.
Stock eng = 360 hp. Fuel required at .5 ratio is, 360 / 2 = 180. 180 lbs of fuel are required per hour to support a stock engines HP output. Fuel weighs approximately 6 lbs per gallon. 180 / 6 = 30 gallons per hour, at 75-psi fuel rail pressure. 30 gallons per hour requires that at a minimum your pump should be able to fill a one-gallon container in less than 2 minutes.
In order to determine if your pump is adequate you must measure the flow against the real world head pressure that it will see at that engine output. The delta pressure comes into play here. You must assume that the pump will be delivering against 75-psi of pressure. Your pump must be capable of delivering the minimum weight of fuel plus the margin of safety that you feel comfortable with.
Follow the procedure in the Max Boost # 2 article for the exact instructions on how to go about this test.
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