Tuning Jeep Inline Six Stroker
Motors with EFI or MPI Fuel Injection
Converting a Jeep 4.2L/258 inline six from carburetion to
multi-point fuel injection (MPI) gains an immediate 50 horsepower. For those building a stroker motor hybrid
from 258 and 4.0L parts, the use of MPI or TBI is always a practical choice.
Mopar's mid-'90s prototype MPI/EFI Conversion for the 4.2L six has provided a sensible alternative for CJ
and early YJ Wrangler owners. When building a stroker 4.6L six, it is practical to convert these models to EFI
The Mopar EFI
Conversion Kit (above) prototype was originally the 1995 Wrangler 4.0L fuel-and-spark management system.
Later, 1997-99 single-rail 4.0L OEM components provided the kit's platform.
all 4.0L inline six models (the XJ Cherokee, Grand Cherokee and Wrangler), MPI is original equipment.
1987-90 XJ Cherokees use the AMC/Renix system. All 1991-up Jeep 4.0L engines have Chrysler designed MPI. The 4.0L
cylinder heads are high and low port designs. Improved, high-port heads are available from
Note: HESCO offers an aluminum, 50-State approved cylinder head that fits
both 4.0L and 4.2L blocks, using 4.0L style intake and exhaust manifolds. Some prefer OEM cast iron; an all-out
performance or racing engine will benefit from the HESCO head.
are two distinctions in the Jeep/Chrysler (1991-up) 4.0L MPI fuel-and-spark management
applications have a dual-rail fuel system with a return line from the engine to the tank. They
have a pressure regulator at the MPI fuel rail.
2) 1996-2006 4.0L engines
have the pressure regulator atop the fuel tank pump module and a single fuel rail system without a return line
from the engine.
systems operate at high pressure. The 1991-95 systems (two-rail) regulate at 39-41 psi
during cranking and 31 psi once vacuum applies at the pressure regulator. At an idle warm, this system will
read 31 psi at the test port. Disconnecting the vacuum line at the pressure regulator raises an idling
engine to 39 psi at the fuel rail test point.
The 1996-up (OBDII era) single rail systems, with the pressure regulator at the fuel pump module of the
fuel tank, operate at a higher 49.2 psi +/- 5 psi. (Lowest pressure with engine idling would be 44.2
psi.) Pressure can regulate to as high as 54.2 psi. The fuel pump on either single rail or two-rail
systems produces more than the peak operating pressure for the system.
EFI/MPI: Stroker Motor
stroker motor run with a stock Jeep 4.0L MPI system (or a Mopar Performance EFI Conversion package) has
specific needs. For years, an aftermarket, adjustable pressure regulator from HESCO has enabled the 4.0L
two-rail systems to get a pressure boost for improved performance. This allows for stabilizing
and adjusting fuel pressure as needed for peak performance.
stroker motor with a mild camshaft
and compression ratio, fuel pressure and flow is less of an issue than with a
higher horsepower engine build. Available fuel flow and necessary injector
sizing is governed strictly by horsepower requirements.
It takes a certain
fuel amount (pounds of fuel per hour) to sustain a given amount of horsepower. Each horsepower level requires
injectors of a specific flow capacity.
The milder engine build
that Tony Hewes and I discuss will produce around 240 horsepower. Based upon one six-cylinder formula for
injector flow (horsepower divided by 12 = needed injector flow), it will take 20 lb/hr fuel flow
to sustain the 240 horsepower demand.
Note: This simple formula reflects net fuel flow rating. All
discussions of replacement injectors for stroker sixes recommend 24 lb/hr rated injectors. (There is an 80% duty
cycle on the type of injectors that fuel the Jeep inline 4.0L sixes.) From our own
tests, a Jeep 4.6L inline six with a CompCams 252 grind camshaft and 8.7:1 compression, the
5.0L Ford V-8 24-pound injectors work well. This is Ford part number F1TE-D5A or
Bosch number 280 150 947.
Note and Caution on late coil-pack
ignition engines: The injectors described above are for a pre-coil pack 4.0L
engine application. Coil pack engines typically require 24-pound injectors like the 2000-2003 5.9L
Dodge Ram V-8 square-plug type. These are available as rebuilt types (GB812-12132) from HESCO
and others...Also, the CompCams' 252H grind is discussed in the videos and listed in the parts below...This
camshaft has performed and tested well in pre-coil pack 4.0L stroker builds. We are currently
considering whether or not this is the optimal camshaft for 1999-up TJ Wrangler and 2000-up XJ Cherokee
builds with the late coil-pack ignition and cylinder head redesign. Stay tuned for our findings about
camshaft grinds and tune for the later coil
There are continual
references to 24 lb/hr retrofit injectors used with Jeep stroker inline sixes. We find it
practical to run 24 lb/hr injectors, even in a street-and-trail Jeep 4x4. Although this engine
application typically idles and runs to a maximum of 3,000 rpm, there are occasional "red line" bursts to
4,000-5000 rpm that will demand more fuel flow. The 24-pound injectors are simply a
hedge against fuel starvation, and they do not cause the engine to run "rich". A/F ratio is still maintained
by the oxygen sensor signals and PCM fuel allocation.
Here, we'll share the
experience of several engine builders. (Click
here for a popular website that describes several Jeep inline six stroker engine
buildups.) Injector choices and parts lists accompany each level of engine build.
Note: "Dino's Jeep 4.0L
Performance" website, mentioned above, presents specific dynamometer results for several
stroker motor prototypes. (See the stroker motor page at Dino's site.) Since
dynamometers were apparently used to determine the horsepower and torque output, we might assume that air/fuel
ratio tests were also run on these engines.
At Dino's site, the engine builds closest to
the Tony Hewes approach would be the "rockcrawler" and lower cost builds. For these engines, 24 lb/hr Ford
injectors appear to work. These are common 302 Ford V-8 MPI injectors, available online as new, rebuilt
and even "good used" varieties.
For those who like to "do the math" and validate the reasoning behind EFI/MPI injector
choices, consider Stan Weiss' EFI flow data table. Click here for direct access to
fuel flow formulas, tables and actual part numbers for a variety of injectors—including Ford, Bosch, Mopar,
Holley, Accel and MSD.
There's a lot of work
presented at each of these websites. Dino's effort includes a great deal of commentary on Jeep inline six stroker
motor options and component choices. Such research and the effort to present reliable material is of great value.
Thanks, Dino and Stan Weiss!
Here are camshaft choice and tuning
comments from a Moses Ludel topic post at the 4WD Mechanix
'Tech and Travel' Forums. Join the forums and participate in these
"At the magazine, building a Jeep inline 4.0L six with a 4.2L
crankshaft (stroker motor) is very popular. Tony Hewes (Hewes Performance, Reno, Nevada) and I did a
series of HD videos and shared our favorite components for a 4.6L (0.030" overbore with the 4.2L crankshaft)
stroker motor build for combined street and trail use.
we have received a lot of feedback and continue to address the tuning and camshaft requirements of these
engines. From our testing, the pre-coil pack (1998 TJ and older 4.0L) engines with older style
injectors do very well with Ford
5.0L V-8 24-pound
injectors—no emission quirks, "Engine Check" lights or other issues when tuned correctly. Ford
part number F1TE-D5A or Bosch number 280 150 947 is the specific injector type. These engines work well with
the 252H CompCams grind camshaft and 8.7:1 compression.
TJ Wrangler and 2000-2001 Cherokee engines with coil-pack ignition have square injector connector
plugs. For these engines, stroker builders use the Dodge Ram 5.9L V-8 injectors listed for 2000-up with coil
pack. This is the injector that HESCO calls a "24-pound/hour”. HESCO supplies rebuilt GB injectors,
although new Mopar OEM part numbers are available. This injector also crosses over to the aftermarket Bosch
Fuel Injector #62005 offered at Summit Racing for a significant price per injector.
Here is the GB
website: http://www.gbreman.com/index.html. The 5.9L Ram truck V-8
application is the GB812-12132 injectors for engines to 2003.
I researched further
and came up with the OEM 5.9L Mopar V-8 injector part number: 53031740AA. (I used 2001 as a clear year
for coil-pack and square injector plug.) This OEM Mopar injector is 23.61 pound/hour rated at 43.5
PSI. This is a "high impedance" injector design with a square plug socket.
The OEM injector
on a coil-pack engine rates 22.5 pounds/hour at 49.0 PSI fuel pressure, which may work okay on a coil
pack stroker engine unless the cylinder head, compression or camshaft/head combination is an issue for the
PCM. Fuel rail pressure of 49.2 +/- 2 PSI should be confirmed by factory testing
Click here for
an instructional PDF for running fuel rail pressure tests on Jeep MPI. This is the 1997-up XJ Cherokee and TJ
Wrangler type with fuel tank mounted pressure regulator and single-rail injection.
In the late '90s, my engineer friends, Jeep performance
enthusiasts at Mopar, were talking about 5.9L Mopar V-8 injectors for 4.0L/4.6L stroker engine
builds. This has apparently been a route to go, with a 24-pound/hour injector
I researched the Jeep ZJ Grand Cherokee 5.2L/5.9L V-8 injectors
from the mid-‘90s: 1995 Jeep 5.2 ZJ/Dodge 5.9L V-8 injectors are Part #53030262 and rated to flow
24.6-pound/hour at 39 PSI. By 1996, the Jeep V-8 injectors rated 23.2 pounds at 49 PSI. The 1995 Mopar
injectors (24.6#/hour @ 39 PSI) could be an alternative to the 302 Ford injectors for a stroker build in
a 1991-95 Jeep 4.0L MPI chassis application if the engine demands that kind of flow.
Summing it up, if GB is
accurate, using the right injector cores and parts for this application, HESCO is marketing a “24-pound/hour @
43.5 PSI injector for a stroker inline six. A caution here is that the '97-up Jeep TJ Wrangler and XJ Cherokee
have a 49.2 +/- 5 PSI rail pressure. Flow could be higher than 24 pounds/hour at this 49.2 +/- 5 PSI rail
If the GB812-12132 injector is okay for a coil pack later engine with the later cylinder head casting, the
GB812-12132 square plug injector would be the choice for later coil-pack engines. There are a number of
sources for these GB injectors.
We're still testing the
CompCams 252H camshaft in a later 4.0L (1999-up TJ Wrangler/2000-up XJ Cherokee) engine with the
redesigned head and coil pack ignition. Tony and I will update on these late 4.0L/stroker engines. The
pre-'99 stroker engines and stock PCMs have worked well with this camshaft grind. We're consulting
with CompCams about a possible new grind for later coil-pack ignition stroker engines.
The 1997-up TJ Wrangler
and Cherokees with the tank-mounted fuel regulator use higher fuel pump/line pressure. I would stick with Mopar
53030262 or Ford 302 V-8 type injectors* on the 1997-98 TJ Wranglers and Cherokees through 1999 (without the
coil pack system).
24-pound 302 5.0L V-8 injectors fit the pre-coil pack engines; coil pack engine injectors have a square plug
are some useful links and comments at the magazine site:
[I detail pressure ratings and designs for Jeep engines equipped with MPI/EFI. 1997-up single rail systems
with tank-mounted pressure regulator are higher pressure, running rail/injector pressures typically around
49.2 PSI +/- 2 PSI. This includes the coil pack engines with square wire plug injectors.]
http://www.4wdmechanix.com/Jeep-TBI-&-MPI-Advanced-Troubleshooting.html [Overview of
OEM tuning methods and factory diagnostic tools required.]
http://www.4wdmechanix.com/Vlog-Why-Build-a-Jeep-4.6L-Stroker-Inline-Six.html [Video vlog
useful third-party website for every popular OEM fuel injector’s flow ratings.]
http://www.4wdmechanix.com/Vlog-Road-Testing-Jeep-4.6L-Stroker-Inline-Six.html [My video
comments on Brent H.’s Cherokee 4.6L build and its drivability. This is a video vlog plus a list of key
components used in this Hewes Performance buildup for a 1998 Jeep XJ Cherokee chassis.]
Of course, there’s also the entire 4.6L Tony Hewes interview series of HD videos,
six individual videos covering the build of a stroker inline six-cylinder Jeep engine!"
For the moderate
compression ratio, mild camshaft engine discussed and recommended in the Hewes Performance interview, there are few
tuning changes required. The 4.6L stroker motor described will work with the stock 4.0L electric fuel pump; an
adjustable pressure regulator (if necessary) for '91-'95 two-rail systems; the factory PCM; and retrofit 24 lb/hr
The Ford injectors seem
readily available and inexpensive. (Ford injectors were mentioned in several prototype engines at Dino's website.)
24 lb/hr injectors are also available from other sources.
troubleshooting will be possible with a DRBIII scan tool or a quality generic scanner—if the engine build is
It's not until horsepower creeps into the 275-300 horsepower realm that the PCM needs
programming changes. At higher horsepower levels, injector flow requirements move to 26 lb/hr and the PCM
will need program changes. Unless you have plans for a high compression, "big camshaft" build, something
in the line of an off-road racing prototype, these extra measures should not be
Note: Mopar Performance supplies injector recommendations for its 4.7L stroker
long-block. This engine design has a higher compression
ratio and a "bigger cam", which warrants more fuel flow. Consider Mopar's 4.7L build and the injectors
recommended. Compare to your planned engine build.
For the Renix (1987-90
XJ Cherokee 4.0L) and Chrysler two-rail systems (1991-95 4.0L engines), it is practical to use an adjustable
pressure regulator. This offers fine tuning and the option of both flow increases and a means for PSI adjustment.
Both the 4.0L Renix and the two-rail Chrysler MPI systems can be regulated. See the HESCO website (www.hesco.us) catalog listing for pressure
If your engine must pass emissions inspection, be conservative on the
buildup. You best likelihood of passing is a lower compression ratio and mild camshaft, stock PCM calibration
and a fully legal exhaust system. All OEM emission devices must be in place and
Note: To pass the visual inspection, make sure the entire emission package is
intact and compliant, with all OEM emission control pieces in place. A stroker crankshaft is not part of the
visual inspection—however, any visible, non-compliant parts will be! The vehicle will likely need to pass a
clean tailpipe test as well.
Any modifications must
not affect air/fuel ratio readings or tailpipe polution levels. Increasing engine displacement does not matter to
the PCM, it will still strive for clean tailpipe air/fuel ratios and emission-compliant
If you're looking for a
49-State catalytic converter solution, see the Random Technology how-to article. These units work, cleaning up the
downstream readings while offering the least restrictive exhaust flow.
A Borla, Banks,
Edelbrock or Clifford header will help, too. In most cases, the Jeep OEM exhaust manifold is cracked and needs
replacing, anyway! Make sure a header is emission compliant if your vehicle requires pollution control
As for spark timing,
the PCM has this handled with feedback from the stock engine sensors. Using the 1991-up 4.0L stock cast iron head
or an aluminum HESCO head, there should be no detonation (ping), especially if you run a lower compression ratio
with a stock or milder camshaft.
For those wanting a
streetable, trail-ready stroker motor for better torque and decent fuel efficiency, a mild engine build holds the
most promise. A camshaft that keeps manifold vacuum high at low and cruise speed rpm will always improve engine
efficiency and usable torque.
The milder engine
build, with a stock PCM and sensors, also offers a high likelihood of passing an emission test. The wild card is
injector flow rate changes and fuel pressure settings. Minor modifications create the least