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post #1 of (permalink) Old 09-25-2003, 10:28 AM
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4.2 MPFI conversion help

4.2 MPFI conversion help
hey there

i'm doing a conversion on a 87 yj using 94yj mpfi parts, i
got it all wired up, and i know the mechanical timing is right.

but it will not run , it tries but all it does is pops and sputters, it does not matter how i turn the dist, (i broke the tab thats how i can turn it). i changed the coil, tps, iac, i had extras there not new. it has new rotor, cap, wires, plugs, still the same.

i pulled off the fuel rail to watch the injectors fire, they seem to work fine, BUT shouldnt they shoot just one time per rev.????? there shooting 2 - 3 - 4 times per rev., and i dont thinks thats right.

i'm new to the fuel injection world, and i dont have a way to check for fault codes, i dont know what to do.
can you give me any ideas!!!
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post #2 of (permalink) Old 09-25-2003, 03:15 PM
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Re: 4.2 MPFI conversion help

Not sure about any codes. I am in the process of collecting parts for fuel injection using the 258 head with a high output 4.0 intake and throttlebody with a MegaSquirt controller. So I have no experience with the Jeep FI system. This came to mind (you did not mention any work being done to the intake).
If you are using parts off a 94 (not the MPI kit) and a 258 head, did you redrill the intake for the dowel pins on the head that locate the intake? If not it should have a massive vacuum leak. If you are not using a 258 head are you using a High output 4.0 head or a standard 4.0 head. Yes, they are different.
The upper hole is the one that has to be drilled. Aparently, the lower part of the intake flange will have to be trimmed also

Also see http://monsterslayer.com/jeep/40Head/40Head.htm
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post #3 of (permalink) Old 09-25-2003, 06:59 PM
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Re: 4.2 MPFI conversion help

hey everyone
i'm posting this on a bunch of different boards, hopefully sombody can help

this is a 4.2 mpfi & 4.0 HO head conversion on a rebuilt motor

using 4.0 factory wiring
its in proper time (NOT 180 out)
the firing order is correct
all the valves open and close in relation to the dist.
using factory in tank pump
factory CPS
94 4.0 HO flywheel (so i was told)

everything i have tried to do so far makes no difference in the way it TRIES to run

today i figured i would change the plugs thinking they might be oil fouled. i found out they were not even the right plugs, they gave me the wrong ones to start with, i didnt know i had nothing to compare them to.
put the new ones, thinking this would fix it (NOT) it tries to run exactly the same.

i pulled the codes up
here they are

12 Battery or computer recently disconnected
33 Air conditioning clutch relay circuit open or shorted
(may be in the wide-open-throttle cutoff circuit)
41* Alternator field control circuit open or shorted
54 cam sensor inside the dist.

the only real problem hear is #54
so i got another from a parts store, put it in
TRIES to run exactly the same, no change, and all the codes listed above are still coming up, includind 54

i hav'nt actually check the fuel pressure at the fuel rail (no guage) but i had the fuel rail off and watch the injectors shoot, and the seemed fine, even fired in the proper order 1 5 3 6 2 4, i did notice that they fired more than once per rev.
i dont know if that is right or not.

and its firing on all the cyls i can tell the header gets hot at each exhaust port.

but it will not run, i'm stuck thats why i'm posting this everywhere hoping sombody can help.

thanks much
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post #4 of (permalink) Old 09-25-2003, 11:08 PM
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Re: 4.2 MPFI conversion help

That sounds like the crank position sensor isn't quite lined up correctly, or is too close or too far from the flywheel or damper (depending on how you are doing it). Have you played with it yet?
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post #5 of (permalink) Old 09-25-2003, 11:27 PM
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Re: 4.2 MPFI conversion help

i pulled the cps out to look at it then put it back in, want to see if it was hitting.

theres not realy no adjustment it fits on two necked bolts.
post #6 of (permalink) Old 10-02-2003, 07:36 PM
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Re: 4.2 MPFI conversion help

hey everybody

just wanted to let you know it started right up with the RIGHT FLYWHEEL, seems to run perfect, still have a lot more to do before its on the road though.

i know now how to wire up a mpfi with a factory harness, its not hard & its a hell of a lot cheaper than buying a aftermarket harness.

thank you again for all your help.

if i can return the favor let me know.
thx again
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