4.2L Fuel Injection and Build - Page 7 - JeepForum.com

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post #91 of 620 Old 12-25-2010, 02:07 PM
unclewilson2
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nice thread doing a 90 sahara with a complete 4.0 down to wiring ! 1 more trip to junkyard and ill be ready........

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post #92 of 620 Old 12-25-2010, 09:07 PM
Lyterx
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Great info. This is my first jeep, 89 wrangler shagged tranny, sat outside with no top for years....$600. Swapped ax15 in and the carb did not work good and motor smoked a little. Didn't want to mess with carb. Found a 91 parts jeep with 4.5 stroker. Swapped motor and all wiring, dash, rear, and engine from the 91. It runs like a top! So glad I did the swap. Have a few questions.

What kind of gains are to be expected the Unichip and what is the cost? HP? Better MPG? Other chips to look into?

I don't think there is any head work done. It has the brown injectors #33007127. Are these injectors the correct size for the 4.5? Motor runs fine. Can I get away with 87 octane fuel? Finally any idea on estimated HP and torque for a 4.5?

Thanks
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post #93 of 620 Old 01-20-2011, 08:16 PM Thread Starter
cevans87
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lyterx - run mid grade or premium ... never regular... and i love the unichip... i get about 2 mpg more and about a 20-25hp gain... and around 40lbs torque... and just depends on what the motor has done to it... cam, lifters, bore, stroke, pistons, a lot goes into calculating it

Built Not Bought #447, 1992 Jeep XJ Supercharged 4.7, 1988 Jeep YJ Auto 4.2L, 2008 Commander Limited HEMI, 1990 Jeep YJ 4.7L Fuel Injected AW4, 1981 Scrambler 304 Auto

I Am The Jeep Surgeon!!!
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post #94 of 620 Old 02-18-2011, 09:12 PM
mdrobb
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I am trying to figure out how to trick the computer into thinking that the alternator is hooked up so that I do not get an error code 41. Any help?
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post #95 of 620 Old 02-18-2011, 10:48 PM
lclark2074
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Quote:
Originally Posted by mdrobb View Post
I am trying to figure out how to trick the computer into thinking that the alternator is hooked up so that I do not get an error code 41. Any help?
I have herd you can put a resistor in to fool the computer but what size ohm and what watts I do not now?
but you can put a 4.0 alt upside down and it will fit. and this will solve your code problem.
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post #96 of 620 Old 02-19-2011, 12:00 AM
Douglas S.
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Quote:
Originally Posted by mdrobb View Post
I am trying to figure out how to trick the computer into thinking that the alternator is hooked up so that I do not get an error code 41. Any help?
That code will have no effect on engine performance, so if you don't have a CEL hooked up I wouldn't worry about it.

1991 Land Cruiser HDJ81
1987 YJ Laredo
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post #97 of 620 Old 02-19-2011, 07:41 AM
mdrobb
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Thank you for the feedback, this is a great place for information.

I am mostly concerned about the check engine light and emissions. Maybe this won't be an issue.

Not sure what a CEL is?

I know that codes can be cleared with a scan tool, is there any way to clear codes without one?

Thanks.
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post #98 of 620 Old 02-19-2011, 01:00 PM
Douglas S.
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CEL is check engine light.

1991 Land Cruiser HDJ81
1987 YJ Laredo
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post #99 of 620 Old 02-20-2011, 12:30 PM
mdrobb
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Finally got the codes to clear with 1K Ohm resisters (one for the A/C and Aux fan and a separate one for the Generator Driver). Thank you for the help.

This is a fantastic mod, I still cannot believe how well it runs, idles and how much more power I have. I am afraid that I won't see the fuel savings for a while as I still love to accelerate up hills, just because I can.
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post #100 of 620 Old 02-20-2011, 05:25 PM Thread Starter
cevans87
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sorry i haven't responded to my own thread have been out of town, unless you put in the 4.0L alternator you will have a code 41, the reason for this is that the power distribution box and ecm both use a "system fail" component, this component is in the form of a green wire with an orange tracer, this wire is present on each injector, the coil, the alternator, and a few other things, basically the computer uses the wire to see what is not completing a loop when it doesn't see a signal from that wire it throws a code... in your case 41 for shorted alternator field wire... since i pioneered the use of a 4.0L alternaor on the 4.2L block and alternaor mounts i can tell you your options...

you can leave the 4.2 alternator in and put a diode on the field control wire, the reason for this is because the alternator will back feed a electricty into the system and when you turn the key off it will keep the motor running because the ecm is still recieving power... if you don't do this... there is absolutly nothing you can do about it... other than putting the check engine light on a switch so that it will only come on when you want it to, or you want to read codes...

you can put the 4.0L alternator in by flipping it upside down and bending the original bracketry to fit the alternator, upon doing this, the system will function like it should and you will not have trouble codes unless the system fails... you will not have to use a diode if you go this way....

to clear the codes on OBD1 systems, you can take the positive battery cable and put it to a ground for 30 seconds... NOT THE BATTERY GROUND !!!! put it against the motor or something else metal... this is discharge the capacitors in the ecm, as they store power to keep EPROM which is memory of driving habits... an EPROM is the system within the ecm... it's like windows to a computer...

Built Not Bought #447, 1992 Jeep XJ Supercharged 4.7, 1988 Jeep YJ Auto 4.2L, 2008 Commander Limited HEMI, 1990 Jeep YJ 4.7L Fuel Injected AW4, 1981 Scrambler 304 Auto

I Am The Jeep Surgeon!!!
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post #101 of 620 Old 02-20-2011, 06:05 PM
Douglas S.
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You can get rid of the code with a resistor, just like he did.

1991 Land Cruiser HDJ81
1987 YJ Laredo
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post #102 of 620 Old 02-20-2011, 06:33 PM Thread Starter
cevans87
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and I quote CEvans87 : "you can leave the 4.2 alternator in and put a diode on the field control wire"

a diode is a form of a resistor... so before you post, read the reply

Built Not Bought #447, 1992 Jeep XJ Supercharged 4.7, 1988 Jeep YJ Auto 4.2L, 2008 Commander Limited HEMI, 1990 Jeep YJ 4.7L Fuel Injected AW4, 1981 Scrambler 304 Auto

I Am The Jeep Surgeon!!!
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post #103 of 620 Old 02-20-2011, 11:07 PM
Douglas S.
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Quote:
Originally Posted by cevans87 View Post
unless you put in the 4.0L alternator you will have a code 41

there is absolutly nothing you can do about it... other than putting the check engine light on a switch so that it will only come on when you want it to, or you want to read codes...
You do NOT have to swap in a 4.0 alternator to get rid of code 41.

1991 Land Cruiser HDJ81
1987 YJ Laredo
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post #104 of 620 Old 02-21-2011, 07:56 AM
mdrobb
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Yes, the resistor worked to remove the code 41 and I am using the 4.2 alternator with a diode between a 12 volt circuit and the alternator.

I also used a 1K Ohm resistor between the new(4.0 cpu) generator driver wire (that was not connected to the alternator) and a 12volt circuit.
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post #105 of 620 Old 02-21-2011, 10:17 AM
lclark2074
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Quote:
Originally Posted by mdrobb View Post
Yes, the resistor worked to remove the code 41 and I am using the 4.2 alternator with a diode between a 12 volt circuit and the alternator.

I also used a 1K Ohm resistor between the new(4.0 cpu) generator driver wire (that was not connected to the alternator) and a 12volt circuit.
do you mean by generator driver wire pin 57 then to pin 20 witch is alternator field ground.
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