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Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

 
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post #1 of (permalink) Old 06-02-2001, 10:33 PM
Mudman
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Hey LEVE

Hey LEVE, I have a friend who is rebuilding his engine in his 90 wrangler and wanted to put a more radical cam in it, more along the lines of an RV cam but is wondering if he will have to get the computer reprogrammed or will it be able to adapt to the change in the engine. Thanks ahead of time.
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post #2 of (permalink) Old 06-02-2001, 10:43 PM
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Re: Hey LEVE

1990 YJ with a 258, non EFI/MPI engine? If the BBD Carb and emissions are all stock then there is no re-programming that can be done to the computer. The computer only controls about 3 degrees of timing by use of the knock sensor. So your buddy should be OK.

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post #3 of (permalink) Old 06-03-2001, 08:50 PM
Mudman
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Re: Hey LEVE

My mistake for not having him herewhen writing to you. Hehas a 94 with an inline six with efi. Will the cam effect the computer?

if its clean, I aint having fun!
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post #4 of (permalink) Old 06-03-2001, 09:59 PM
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Re: Hey LEVE

Yep, he's toast. From what I've heard HESCO has recently started to modify the computers to take different cams. That's going to be a very, very expensive process of trial and error. Howell has found it to be a "one of a Kind" effort with every modified Jeep. I suspect HESCO will also find the same thing. I'd not advise using a non stock cam.

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post #5 of (permalink) Old 06-03-2001, 10:06 PM
Mudman
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Re: Hey LEVE

could you explain why a non sock cam will mess up his computer that much. sorry this may sound stupid but I will need to explane this to his as to why.
Thanks again

if its clean, I aint having fun!
post #6 of (permalink) Old 06-03-2001, 10:56 PM
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Re: Hey LEVE

Fuel injecton is all "Best Guess" by the computer. The computer takes several inputs from the sensors and figures out just how much fuel to let flow through the injector. The injector on-time becomes the greatest variance.

The computer knows the characteristics of the engine. In most case the comptuer is pre-programed to know at 25 rpm steps just how much fuel is needed. The MAP and TPS sensor adust each step plus or minus for a better delivery. So, if the internals of the engine have been thrown off from stock, the computer must be re-programed to take the new specifications into its memory.

As example if the intake valve's open duration is longer than stock, the engine can asperate more fuel mix. Now the engine's running rich.. and the computer can't lean it out becasue it's outside of the parameters of the program. The re-program can be done on an Eprom, but the programmer must then re-program for the new specifications. This unknown will then have to be veiwed at each step on a readout and then adjustments made. It will take some time to find the right mix for EACH RPM step. That's going to take some time, sophiticated equipment and trail and error.

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post #7 of (permalink) Old 06-04-2001, 09:04 PM
Mudman
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Re: Hey LEVE

thanks for the info LEVE I will pass it on

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post #8 of (permalink) Old 06-04-2001, 10:11 PM
 
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Re: Hey LEVE

Following LEVE's train of thought ...
if you DO still want a little more 'umph' via a little more liberal cam I'd call Bennie at Hesco and ask him for a grind that has proven out on the dyno for your particular setup.
The grind they sent me was way different than a lot of the 'RV' grinds out there and when I protested to him about the specs he said ... "John, just do it".
I was smart enough to listen ... and I'm sure not sorry !

JAF
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post #9 of (permalink) Old 06-05-2001, 06:06 PM
brendan
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Re: Hey LEVE

I've read on the yahoo stroker list that all the computer can do is try to optimize mixture according to the power curve that it has it it's eprom chip. When you change the camshaft, you have changed the power curve, and thereby making the computer unable to optimize the spark and injection(the computer has a big role in the ignition on the 4.0).

My question is : is this because the mopar mpfi is a speed density system, not a mass air system? Back when I was into mustangs, it was when all the hipo parts really started pouring into the market for the 5.0. I don't recall anyone having to change their computer out every time they put on a new throttle body or camshaft. The mass air system can compensate for this, while the speed density cannot? Thanks, Brendan

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