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1989 YJ 4.0L Engine Swap question

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oorin

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Jun 17, 2003, 4:28:57 PM6/17/03
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I have finally gotten my shiny (not really) 4.0L engine in my 89 YJ. It
turns over and trys to start, it runs for about 5 - 10 seconds and dies.
It feels to me like a timing issue, or power is getting cut after that
time period. I'm out of ideas. Does anyone out there who knows their
4.0 well have any ideas? I'm using the computer and wiring harness from
the donor YJ, and I'm using a CPS conversion kit that mounts the sensor
up front. I suppose the other option could be the computer is flaky, I
hope that is not the case.

Thanks for any help,
Mike

Mike Romain

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Jun 17, 2003, 4:47:50 PM6/17/03
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I would be checking the fuel pressure after it dies.

Maybe there is a cutoff relay that needs power?

When you have the key in start, power goes directly to the pump, when
the key goes to run, the power feeds through a ceramic ballast resistor
on our 88 4.0 engine's pump.

The resistor sits on the drivers side fender out near the rad on our
Cherokee.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Mike Romain

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Jun 17, 2003, 4:51:32 PM6/17/03
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I am thinking the resistor might be on the firewall in a YJ, not sure.

Mike

L.W. Hughes III

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Jun 17, 2003, 6:18:38 PM6/17/03
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Hi Mike,
Congratulation.
That's length of time the fuel pump runs on the initial startup,
then something else powers it. could be the regulator, does it have it's
wire and vacuum line connected? May check with Doug's sensors for an
idea: http://members.cox.net/wilsond/Fixes/diagnostics.html
God Bless America, ßill O|||||||O
mailto:LWHug...@aol.com http://www.billhughes.com/

DougW

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Jun 17, 2003, 9:24:28 PM6/17/03
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L.W. (ßill) Hughes III wrote:
> Hi Mike,
> Congratulation.
> That's length of time the fuel pump runs on the initial startup,
> then something else powers it. could be the regulator, does it have it's
> wire and vacuum line connected? May check with Doug's sensors for an
> idea: http://members.cox.net/wilsond/Fixes/diagnostics.html

Fuel pump should run all the time once the engine has started. Only exception
is startup where the computer runs the pump to pressurize the fuel rail.

Hard to tell without an ODB-II scanner. Does ignition on-off-on-off-on
blink the check engine lamp... I guess, do you have that circuit hooked up?

In the 93 I would check the fuel pump relay and the ASD relay.
ASD = Automatic ShutDown. When that relay gets old the engine may die.

If the computer is getting bad sensor readings (overheat, no CPS, or Camshaft
position sensor inputs) it probably will shut down.

My inner greasemonkey says you might have a sensor that's not working or not
hooked up properly. I know that if the CPS is faulty the engine will not start,
so that sensor might be fine. Now if the CPS and Camshaft PS (the one in the
distributor) disagree, the engine will shut down, but it will also stumble like hell
before it does. Yours sounds like it's running properly then the computer is
killing it because of a bad sensor input. i.e. the computer thinks your engine
is going to grenade.

Best suggestion I have is check your wiring again. Make a copy of the schematics
your working from and mark each connection off as you check it.

Good luck.

Will Honea

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Jun 17, 2003, 11:05:37 PM6/17/03
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Gotta go with Mike on this one - that sounds just like mine when the
fuel pump crapped out the first time. Had enough pressure to start
and run for a few seconds, then just faded away because the pump
couldn't keep up even at idle. No stumble, just a smooth, certain
death after running for the same 5-10 seconds.

It could be all the other things like the ballast resistor or a relay,
even a plugged filter rather than the pump itself, but the fuel
pressure sounds like a good place to start since that's the end result
of all of them.


--
Will Honea <who...@codenet.net>

DougW

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Jun 17, 2003, 11:12:37 PM6/17/03
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Will Honea wrote:
> Gotta go with Mike on this one - that sounds just like mine when the
> fuel pump crapped out the first time. Had enough pressure to start
> and run for a few seconds, then just faded away because the pump
> couldn't keep up even at idle. No stumble, just a smooth, certain
> death after running for the same 5-10 seconds.
>
> It could be all the other things like the ballast resistor or a relay,
> even a plugged filter rather than the pump itself, but the fuel
> pressure sounds like a good place to start since that's the end result
> of all of them.

Slap a pressure gauge on it. R-12 Low side gauge works fine.
Look for about 32PSI at all times. With the vac line off
the regulator it should go up to about 41.


oorin

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Jun 18, 2003, 9:23:36 AM6/18/03
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Man that is a lot of info to digest.....
The only thing I can respond on with a certainty is the fuel pressure
with the switch on before being started sits at 40psi, during the 5-10
second running period it fluctuates between 34-35psi. I'm thinking it
is something like a sensor as well although I'm going to recheck my
wiring first.

Thanks a lot for the help guys.
Mike

DougW

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Jun 18, 2003, 5:42:19 PM6/18/03
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oorin wrote:
> Man that is a lot of info to digest.....

yep. :)

> The only thing I can respond on with a certainty is the fuel pressure
> with the switch on before being started sits at 40psi, during the 5-10
> second running period it fluctuates between 34-35psi.

That's within spec.

Hope you find what's b0rked.


Will Honea

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Jun 19, 2003, 12:02:14 AM6/19/03
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That answers part of the question. Now, what does it read AFTER it
fires and dies? That would help isolate the relay/ballast issue if it
exists and allow you to get on to the next step. With all the
electronics around, I usually wind up working that way with
fuel/ignition issues.


--
Will Honea <who...@codenet.net>

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