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Discussion Starter · #1 ·
hi all, just finished my real first test drive after the hughes air gap install. car run fine for 5 miles. i parked and just while i was parking i noticed the voltage indicator being way low. i tried to give it some gas and it did not climb back up. i shut it off and now every time i try to start it blows this lil yellow 20 fuse up. it starts, runs for a fraction of a second and immediately dies and blows the fuse. i stopped trying after the 3rd blown fuse.
what am i looking for? any advice?
Vehicle Gauge Measuring instrument Car Personal luxury car
Motor vehicle Hood Trunk Automotive exterior Electrical wiring
 

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That fuse powers the PCM first, then the ASD Relay, which powers the Injectors, Ignition Coil and O2 Sensors. You could pull the ASD Relay and see if it still pops. If it does then it's PCM or wiring related, if it does not pop then it's after the ASD and you'll need to hunt a bit. Could be a pinched or melted wire somewhere that finally rubbed thru after the test drive and is now shorted.

Could also be the internal regulator in the PCM as that is also after the ASD.
 

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95ZJ dd 303122K
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Well it's definitely a short. Question is does it blow the fuse as soon as you energize the key? Or, once you've started cranking the motor, or does it pop after the motor has already started?
 

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I am looking at thre 97 diagram and fuse 20 is different than what RDC_ZJ is seeing SO i'm lost WHAT year is the jeep?

PS - what is a huges air gap?
 

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98, according to his profile. There is a Fuse 20 in the PDC (under hood) as well as a Fuse 20 in the Junction Block (inside).

Hughes Air Gap is an intake manifold, why I'd suspect some pinched or melted wiring issue since a good bit of that would have been messed with doing that swap.
 

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95ZJ dd 303122K
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Agreed! Something got caught, or gave way when the work was done. Usually the first thing I think of when a "new problem" arises after a repair. Really want to know what exact conditions are blowing the fuse. If he's lucky and it's poping once the engine is running then maybe it's in the charging system/voltage regulator or something similar, and not the PCM
 

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I'm definitely suspecting a pinched 12V wire which causes the fuse to pop. I need to check the wiring diagrams from the FSM for most likely causes after the intake swap, but start going through what RDC_ZJ mentioned. I'll check in a bit, I'll get back to you.
 

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95ZJ dd 303122K
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Mark-318-IT, just found this post, it might prove helpful:

 

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The TL/DR of that one is check your O2 sensor wires. They may be shorting out somewhere under the vehicle.
 

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got it a 1998 - first suspect COIL

Yes o2 sensors are usually a 1st suspect but having done intake I focus on wires at work site..

looking for a way to split all the circuits after ASD closes...
 

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If I looked correctly, the fuse #20 in PDC that blows feeds two things: powertrain control module B+ (12V feed) and ASD relay. ASD relay feeds the O2 sensor heater circuit, ignition coil and fuel injectors. ASD relay feed is hot, it's output is hot ONLY after PCM is powered up. So as RDC_ZJ mentioned, pull the ASD and see if the fuse blows. If it does, short is in the wire harness B+ feed to PCM/ ASD or bad PCM. If it does not, it's somewhere in the ASD system.
You may have a short in any of the circuits fed by ASD, and ALL of those are hot wires when you turn the ignition to run or starting positions. Coil and fuel injectors are ground controlled so a short to ground in the 12V feeds will blow a fuse.

Check if you have pinched or damaged a +12V feed wire on any of those, most likely focus on coil and injector wires because that's where you work with the intake swap.

Just to be sure - especially if you unplugged it during intake swap - check the connector next to/ behind passenger side valve cover at the firewall (two black connectors on the bracket), that's C131 (and C132) which has the RD/YL wire.
There is also the S100 splice which splits the feed from the #20 PDC fuse in the injector wire harness - name is a bit weird - splice is at the passenger side inner fender. That harness doesn't need to be touched so I doubt your problem is there.
 
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I'll just chime in to second the pinched wire. Once knew a guy that started having charging issues after installing a new engine (not a ZJ). Turned out he pinched a bit of harness between the engine and trans. On my 93 someone had pinched the oil level sensor wire in the oil pan gasket and fixed it by cutting the connector off and installing a new connector. Or I assume so. There was a bit of wire stuck in the gasket for years. When I replaced it the connector was inside the pan.
 

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Discussion Starter · #13 · (Edited)
hey all,

been playing around with relays , fuses and wires. obviously found nothing wrong with it.

i followed the advice to attempt to start the car without the asd relay. this did NOT blow the fuse. i switched the asd relay with the horn one and the car fired right up. it's now working correctly. also the horn is working so the relay i suppose is fine...??

took a look at the o2 sensors wiring, it's fine as long as i can see the wiring itself. o2 sensors are new though. same thing for the coil/coil wire.

it is a 98, was a 5.2 but now has a 5.9 in it.
the air gap is the air intake manifold.

i'll try follow everyone's advice in order to get this issue solved.
 

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Discussion Starter · #16 ·
yup, when it blows i have the same issues with the gauges.
 
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