No Start, No Fuel Gauge, Low Pump Voltage, 5.2L - JeepForum.com
 
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post #1 of 9 Old 06-06-2021, 08:12 AM Thread Starter
Christopherrto
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1996 ZJ 
 
Join Date: May 2016
Posts: 5
No Start, No Fuel Gauge, Low Pump Voltage, 5.2L

Hey guys, trying to get my ZJ 5.2L started to no avail. Last ran a few weeks ago with no problems. Cranks and cranks, won't start. If I add some quick start it'll catch for a moment. So that leads me to a fuel issue. There's 12V at the relay supply, and while there is no voltage difference between relay signal + and battery +, and relay signal ground and battery ground, there is only 7V between relay signal + and -. With the relay in or the relay supply shorted, there is only 5V to the pump (measured at the plug at the rear axle), and it's not going. I checked with relation to body ground nearby and it appears to be 5V on + and 0V on pump - as well. I know that the crankshaft position sensor could cause no gauge and no start, but I tried unplugging and no difference, and no difference after replugging either. Note that the voltage gauge is working about as expected, though showing a touch low. Unplugging the crankshaft position sensor seemed to bring back the fuel gauge momentarily, but that may be unrelated because it was not repeatable and plugging the camshaft sensor back in did nothing. I also tried the MAP and throttle position sensors because I heard those could also be the issue. I tried cleaning the main ground, as well as what I believe is the PCM ground (just below and passenger side of the alternator) and no difference.

If I pop off the terminals and connect a weak booster pack (putting - on an engine ground) it seems the fuel gauge wants to work after a stort attempt, where voltage is dropping pretty low.

Honestly this is making no sense to me. If there is a break, there should be 0V or 12V at no load to the pump. The 7V to the relay doesn't make sense either. I would assume it's a PCM issue or sensor issue, but I can't seem to narrow it at all, and the seemingly random function of the fuel gauge is also confusing.

I did check fuel rail pressure, there is none.

For clarity, it's a 1996 Jeep Grand Cherokee Limited, with a 5.2L. Only 144,000kms (90,000 miles).

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post #2 of 9 Old 06-06-2021, 11:38 AM
Skye Covington
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1998 ZJ 
 
Join Date: Mar 2021
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I ended up replacing the PCM on mine when I had the same issues. I searched Amazon and Ebay and found one with the same option code as the one I had and dropped the pennies for it. Even then, not everything is working so it's still kinda a crap-shoot. I'm eventually going to try and take the original one apart and see if I can repair it. There are videos out there showing how to fix the notorious cold solders they are famous for so you may want to look at them as well and try to fix yours.
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post #3 of 9 Old 06-06-2021, 12:08 PM
jtec
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2014 JK Wrangler 
 
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KISS
Do you have spark at several plugs?
Fuel pressure - PSI? 49 (+or-2) PSI
Scanner post all codes.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 9 Old 06-07-2021, 12:02 PM Thread Starter
Christopherrto
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1996 ZJ 
 
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Posts: 5
Quote:
Originally Posted by jtec View Post
KISS
Do you have spark at several plugs?
Fuel pressure - PSI? 49 (+or-2) PSI
Scanner post all codes.
I assume I have spark as it'll run briefly with starter fluid.

There is no fuel pressure as I can tell. I don't believe I have a fuel pressure gauge, but when I pushed on the test valve no more than a drop seeped out. I believe when the fuel pump is working properly it should spray from there.

The scanner says no codes. This is using an Innova 3030e. It may be because the battery has been disconnected prior to the latest start attempts. It has an unresolved tailgate ajar sensor issue that's eating batteries so I have to disconnect the battery when not daily driving it.
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post #5 of 9 Old 06-12-2021, 04:24 AM
mpgmike
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Location: Sussex
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The low voltage to the fuel pump may be due to a shorted pump or bad wiring connections. I'm on my 4th fuel pump in our Jeep. The alcohol (E-10) kills them.

Check voltage at the fuel pump relay load supply with the relay removed. Then jumper across the load circuit (instead of the relay). If you get fuel pressure, the contacts in the relay are the bad connection. Hope this helps.

'95 ZJ, NV3500 5-speed conversion, 4.0 (soon to be 4.6 Stroker)
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post #6 of 9 Old 06-12-2021, 09:30 AM
V8GCZJ
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Quote:
Check voltage at the fuel pump relay load supply with the relay removed. Then jumper across the load circuit (instead of the relay). If you get fuel pressure, the contacts in the relay are the bad connection.
This! Make sure you have power and jump the correct terminals. You should be able to hear the pump run.
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post #7 of 9 Old 06-12-2021, 07:35 PM Thread Starter
Christopherrto
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1996 ZJ 
 
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Posts: 5
Quote:
Originally Posted by mpgmike View Post
The low voltage to the fuel pump may be due to a shorted pump or bad wiring connections. I'm on my 4th fuel pump in our Jeep. The alcohol (E-10) kills them.

Check voltage at the fuel pump relay load supply with the relay removed. Then jumper across the load circuit (instead of the relay). If you get fuel pressure, the contacts in the relay are the bad connection. Hope this helps.
Like I said in the original post, I tried shorting the relay and I still have only 5v, fuel pump does not turn on.
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post #8 of 9 Old 06-13-2021, 05:17 AM
V8GCZJ
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Are you sure you jumping the correct terminals and made sure you have power at one of them? The relay is fused so did you also check the fuse?


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post #9 of 9 Old 06-13-2021, 01:36 PM
Mark-318-IT
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1998 ZJ 
 
Join Date: Sep 2011
Location: Desenzano del Garda (BS)
Posts: 775
there's a lil fuse in the engine bay, a yellow 20 one, try to see if it's shorted.
mine was doing the same and that fuse was shot.

360swapped:np242swap,shift kit,BOLT ONs,ome HD coils,aussie locker,dana30hp trussed
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