Upgrading The Fuel System

[ Fuel Injectors | Fuel Rails | Regulators | Pumps ]

Description

This page describes the options available for upgrading the fuel system on 2.2L and 2.5L engines.  You should read the 2.2L/2.5L Turbo Engine Information page and the Turbocharger Concepts page if you are not familiar with Chrysler's turbocharged engines.  Choosing the correct fuel system configuration for your engine is one of the most important decisions you will make.  The right setup depends entirely on your application and on other decisions you have made.  The page is designed to help you go in the right direction.
 

The Scoop On Fuel Injectors

Installing the right injectors is very important.  The "bigger is better" concept does not apply here, directly.  The computer expects the fuel system to perform a certain way and you will get into big trouble very quickly if you are not familiar with it.  Read the 2.2L/2.5L Turbo Engine Information page to learn how it works.  There are other, more precise ways to adjust fuel flow than installing different injectors, such as changing the fuel pressure.

On the other hand, you can extend the life of your fuel pump if you install larger injectors and drop the fuel pressure with an adjustable regulator.  Be sure not to drop it more than about 20psi.  Such low pressures can effect the spray pattern of the injectors during idle and they may fail to atomize the fuel properly.  If you have to bring the pressure that low, then your injectors are too big.  See the Regulating Fuel Pressure section for more info on how to lower your fuel pressure.  To go to a larger set of injectors requires you to know what injectors you currently have.  See the chart below to reference your engine and lookup the flow rate of the injectors you have (big thanks to Garry McKissick for this data):
 

Engine Type		 Flow Rate
(at 55psi)
1985 - 1988 2.2L Turbo I * 27 lbs/hr
1987 - 1988 2.2L Turbo II 32 lbs/hr
1988 - 1993 2.5L Turbo I * 34.85 lbs/hr
1989 - 1990 2.2L Turbo II 34.85 lbs/hr
1991 - 1993 2.2L Turbo III 34.85 lbs/hr
1989 - 1990 2.2L Turbo IV 34.85 lbs/hr
Mopar Performance "803s" (P4452803) 27 lbs/hr **
Mopar Performance "804s" (P4452804) 34.85 lbs/hr ***
Mopar Performance +20% (P4529495) 42 lbs/hr
Mopar Performance +40% "Super 60" (P5249452) 52 lbs/hr
* There was a mid-year change in 1988 from the 27 lbs/hr to the 34.85 lbs/hr injector
** These injectors are supposed to flow 30 lbs/hr, but they don't (see below)
*** These injectors are supposed to flow 37 lbs/hr, but they don't (see below)

The trick is to go to the next size up.  As you can see Mopar Performance supposedly sells oversized injectors for this type of application.  The problem is that these injectors are not what they appear to be.  The "803s" and "804s" turn out to be defective stock early Turbo I and II injectors that flowed too much fuel.  The supply of over-flowing injectors has run out and current 803s and 804s flow the same as a stock injectors (they are actually the same part numbers now).  It's hit or miss with these and you are likely to miss.  Fortunately, the Mopar Performance +20% injectors are what they claim to be.  Here is a chart to help you choose the right oversized injector for your engine:
 

Your Engine Type		 Your Flow Rate
(at 55psi)
Get This Injector		 New Flow Rate
(at 55psi)
1985 - 1988 2.2L Turbo I 27 lbs/hr Mopar Performance "803s" (P4452803) 30 lbs/hr ***
1987 - 1989 2.2L Turbo II 32 lbs/hr Replacement for 1989 Turbo II (5277895) 34.85 lbs/hr
1988 - 1993 2.5L Turbo I 34.85 lbs/hr Mopar Performance +20% (P4529495) 42 lbs/hr
1990 2.2L Turbo II 34.85 lbs/hr Mopar Performance +20% (P4529495) 42 lbs/hr
*** It is unknown if these injectors truly flow this amount.  With the "804" injector scam, you may not want to buy them.

Now that you have an oversized injector, you will need to get an adjustable fuel pressure regulator and set it so that the new injectors will flow the same as your stock injectors did at stock fuel pressures.  See the Regulating Fuel Pressure section for information on how to do this.  You also have the option of fine-tuning your setup to run richer or leaner, if you desire.  If you are installing a Super 60 computer or an ND 3-bar computer, then you MUST use the Super 60 +40% injectors.  DO NOT use these injectors for any other setup unless you really know what you are doing (such as using your own custom computer, a MASC device, or a adjustable FPR with a lot of boost).  Dropping the fuel pressure on these injectors too far may begin to effect the spray pattern of them.  Bigger is not always better!

For information on fuel injector flow rates and part numbers, see Gary Donovan's Fuel Injector Data Page.  It lists the current part numbers for various replacement injectors and as you will see, he hates the "804s" too.  His chart for current part numbers is confusing, but it is useful if you have a set of injectors an want to know what you have.  Basically, it shows how all the old part numbers have been changed to four, basic numbers.  The 1984 Turbo I, the 1985 - 1987 Turbo I, the 1988 2.2L Turbo I, and the 2.5L Turbo I and 2.2L Turbo II, III, and IV injectors.  Here is a simplified chart showing the current part numbers.  Big thanks to Gary for figuring out this big mess.
 

Engine Type		 Current
Part Number		 Flow Rate
(at 55psi)
1984 2.2L Turbo I 4275312 27 lbs/hr
1985 - 1987 2.2L Turbo I 4418474 27 lbs/hr
1988 2.2L Turbo I (early) * 4418475 27 lbs/hr
1988 2.2L Turbo I (late) * 5277895 34.85 lbs/hr
1989 - 1993 2.5L Turbo I 5277895 34.85 lbs/hr
1987 - 1990 2.2L Turbo II 5277895 34.85 lbs/hr
1991 - 1993 2.2L Turbo III 5277895 34.86 lbs/hr
1989 - 1990 2.2L Turbo IV 5277895 34.86 lbs/hr
* There was a mid-year change in Turbo I fuel injectors in 1988.

There are three different Turbo I part numbers because the style of the fuel injector and fuel rail changed in 1985 and again in 1988.  They actually increased the fuel flow to the early Turbo II engines from 32 lbs/hr to 34.85 lbs/hr.  This is equivalent to adding 10psi of fuel pressure!  If you have to replace your early Turbo II injectors, you'll probably want an adjustable fuel pressure regulator to lean your mixture back out.  While the computer can compensate for the richer mixture during normal throttle operations, the 1987 Turbo II logic module cannot compensate for the richer mixture during cold start and WOT.  Later computers could, to some degree.
 

Fuel Rail Options

Though fuel rail design differs on some engines, the stock fuel rail on your engine should be sufficient to at least 250-300 hp.  In general the early Turbo I fuel rails are more restrictive than the later Turbo I and Turbo II rails.

For applications were the stock fuel rail does not flow enough, custom fuel rails are available through LRE.
 

Regulating Fuel Pressure

Stock Regulator

The stock fuel pressure regulator is designed to maintain 55psi of fuel pressure, relative to the manifold pressure.  So at 0psi of boost, there will be 55psi of fuel pressure at the rail, while at 10psi of boost, there will be 65psi of fuel pressure.
 

Adjustable Regulators

Fuel pressure regulation is an area where fine tuning can be made through the use of an adjustable fuel pressure regulator.  If you have to make modifications to your fuel system, I highly recommend one because it will make the fine tuning of your fuel system a snap.  Even if you have a custom programmed computer from ND Performance, you will likely still have to make some fine adjustments.  Adjustable fuel pressure regulators are available through LRE.  You want to be careful not to adjust the pressure too low.  Since 20inHG of vacuum drops the fuel pressure by about 10psi, then lowering your fuel pressure by 20psi will give you only 35psi at idle (55 - 10 - 20 = 35).  Such low pressures can effect the spray pattern of the injectors and they may fail to atomize the fuel properly.  If you have to bring the pressure that low, then your injectors are too big.

If you used the oversized injector guide in the Fuel Injectors section, then you need to know what fuel pressure to set them to with your new adjustable fuel pressure regulator.  To do this, you will need a fuel pressure gauge.  This can be purchased at some auto supply stores.  You can either get a guage with a schrader valve fitting that can screw right on the fuel service valve on the fuel rail, or you can hook it up with a cheaper make-it-yourself pressure guage.  See my Make A Fuel Pressure Gauge page for more information.  Install the fuel pressure guage as described on that page.

To take a fuel pressure reading, you have to remember that during idle, the vacuum causes the fuel pressure regulator to lower the fuel pressure to maintain 55psi between the fuel pressure and the manifold pressure.  For every 1inHg of vacuum, there is a 0.49psi drop in pressure at the rail.  So, 15inHg of vacuum will make about 47.6psi of fuel pressure on a stock regulator.  To accurately set the fuel pressure, you either have to calculate the proper fuel pressure by measuring the manifold vacuum, or you need to unplug the vacuum line from the regulator.  This will make the regulator think the manifold is at 0psi of pressure and the fuel pressure will rise to 55psi.  Do not leave the regulator unplugged when you are done!  If you drive your car with the regulator unplugged, the engine will lean-out and severe engine damage could result!  While at idle, the engine will run rich because of the rise in fuel pressure, so don't do it for too long.  With your fuel pressure now at a constant, atmospheric pressure, you can reliably adjust it.  To lower the fuel pressure, turn the adjusting screw on the adjustable regulator counter-clockwise.  To raise it, turn it clockwise.  With the engine idling, you will see the pressure change on your guage.  To set the pressure of an oversized injector to flow as the stock injector did (using the chart provided in the Fuel Injector section), use this chart:
 

Your Engine Type
Your Oversized Injector		 New Fuel
Pressure
1984 - 1988 2.2L Turbo I Mopar Performance "803s" (P4452803) 44.55psi
1987 - 1989 2.2L Turbo II Replacement for 1990 Turbo II (5277895) 46.37psi
1989 - 1993 2.5L Turbo I Mopar Performance +20% (P4529495) 37.87psi
1990 2.2L Turbo II Mopar Performance +20% (P4529495) 37.87psi

To make this calculation by yourself, use this equation:  the new pressure equals 55psi times the desired flow rate squared, divided by the base flow rate (at 55psi) squared.  Here is the equation put more simply:

p = 55 * (Rdesired^2 / Rbase^2) where "p" is the required fuel pressure, "Rdesired^2" is the desired flow rate squared, and "Rbase^2" is the flow rate at 55psi squared.

These values assume that the injectors are flowing to spec, which they don't always do.  You must have a air/fuel guage installed to fine tune this setup (see the Choosing Your Gauges page).  Once you have set this base pressure, disconnect the fuel pressure guage and reconnect the vacuum line to the fuel pressure regulator.  Go for a careful test drive and watch your A/F guage.  You want to see at least 8 lights at WOT.  If you get less than 8 lights, then you are too lean and you need to raise your fuel pressure a couple of psi.  If you are seeing 10 lights, then you need to lower your fuel pressure a few psi.
 

Variable Rate Regulators

If you are running boost levels that are above what the computer can measure (bleed on the MAP sensor, etc), then you can compensate by adding more fuel  with an adjustable variable rate fuel pressure regulator.  These regulators don't maintain a fixed amount of pressure difference between the fuel rail and manifold.  For example, a rising rate gain fuel pressure regulator that has a gain of 2 and is set to 55psi of fuel pressure at 0psi of boost will provide 75psi of fuel pressure at 10psi of boost (instead of 65psi).  You just have to multiply the change in manifold pressure by the gain of the regulator.  So it can be said that a stock fuel pressure regulator actually has a gain of 1.  These types of regulators are available from LRE.  Choosing the right one is difficult.  Generally a gain of about 2.5 is needed.  Gus Mahon uses a rising rate gain adjustable fuel pressure regulator with a gain of 3.  He then bleeds the vacuum hose to the regulator with a tiny bleed to reduce the gain.  This procedure should be done at your own risk.

The appeal of these regulators is that they can properly compensate for rises in boost pressure.  Matching each psi of manifold pressure with 1psi of fuel pressure is not enough.  The computer normally adds even more fuel by increasing the duty cycle of the fuel injectors.  If you are "fooling" the computer with a MAP sensor modification and don't want to use extra injectors, you can try this method.  It requires a lot of tuning and fiddling around, but it works.  An extra injector is usually more appealing.
 

Fuel Pumps

The stock fuel pumps on most cars will provide sufficient fuel for up to about 250 hp, assuming it is in good condition.  The Super 60 fuel pump, available from Mopar Performance provides more than enough fuel for greater than 300 hp.  Other fuel pumps are also available from Walbro.  They are less expensive and can provide even more fuel than the Super 60 pump.  The Walbro pumps are available through V.E.Peterson (1-800-537-6212).  Here are the part numbers for the Mopar and Walbro fuel pumps, which include adapters for all Chrysler models:

Typical Stock - 34 gal/hr (129 L/hr) Mopar Standard Turbo fuel pump (typical)
P5249511 - 60 gal/hr (227 L/hr) Mopar Performance Super 60 fuel pump
GCA 724-2 - 50.2 gal/hr (190 L/hr) Walbro fuel pump
GCA 723-2 - 67.4 gal/hr (255 L/hr) Walbro fuel pump

Other pumps are available, but most require some modifications to your setup for it to work.  All of these, except the Super 60 pump, mount right into the fuel tank the way it was meant to.  For more information on the fuel delivery characteristics of the Walbro fuel pumps, try this page.

Another consideration for fuel pumps is the power feed.  The power to the fuel pump is drawn through a long chain of wire and connectors, which creates a significant voltage drop.  It goes from the ASD Relay, through a 14 gauge wire, to a 20 amp fuse, through a 16 gauge wire to the left body connector, and then through a long 14 gauge wire to the pump.  Voltages of 8V to 12V at the pump are not uncommon (when the system is at 14V),  You can get rid of a lot of this loss by running a 10 or 12 gauge wire right from the ASD relay to the fuel pump.  Be sure to install your own 20A inline fuse.  Also check the ground for the pump, which often is fed by a ground lug in the trunk.

Keep in mind that in-tank fuel pumps depend on the gasoline inside the tank to keep the pump cool.  Frequently running on a dry tank of gas can cause the pump to run hotter and shorten its life.

Lastly, if you are installing a large pump, then you may want to consider upgrading the fuel lines.  The stock fuel lines are 5/16" OD steel lines.  Upgrading to at least 3/8" OD will be sufficient.  For most engines, the stock fuel lines are sufficient, as long as they are in good shape.
 
 
 
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This page is maintained by Russell W. Knize and was last updated 06/03/99. Comments? Questions? Email minimopar@myrealbox.com.

Copyright © 1996-2003 Russ W. Knize