No start / no fuel pressure - JeepForum.com
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post #1 of 15 Old 03-10-2019, 06:54 PM Thread Starter
jfiscus
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No start / no fuel pressure

I bought my daughter her first car the other day, a 93 grand cherokee 4.0 liter. When we went to get it it had been sitting a year, but it did start a couple times, and then lost fuel pressure. I assumed a bad fuel pump.

Today I installed a fresh pump and cranked it over, no buzz or fuel comes from the pump....

I also noticed no check engine light came on while I was cranking it and the rpm guage doesn't move either. So, where do i start? I'm not an electrical whiz, but I'm a decent mechanic. All grounds fuses and wires look ok, but I'll check again tomorrow since I ran out of light.


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post #2 of 15 Old 03-10-2019, 08:45 PM
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Check your relays, fuel pump & ASD.
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post #3 of 15 Old 03-10-2019, 09:48 PM Thread Starter
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Checked those and switched them out with the other relays. No difference.

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post #4 of 15 Old 03-11-2019, 07:46 AM
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engine will crank?
You have NO fuel pressure and you are using a gauge to check pressure?
Do not just look at fuses - use a dvom or test light.
With Key On Engine Off (KOEO)
is there 12v at injectors?
Iss there 12v at coil?

Fuel pump FYI the system will only supply 12v to pump for @3seconds if engine does not start. Relay and fuses in PDC.

With KOEO is the CEL on for @3seconds?

When cranking engine is there SPARK?

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 #5 of 15 Old 03-11-2019, 11:19 AM
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Use a voltmeter (and an assistant) to determine if the fuel pump is receiving 12V at key on.

Diagram below is for a '95 but should be same pinout.

Also note that some aftermarket pumps have very low-quality connectors. I put an Airtex pump in mine and I had to secure the plug with zipties to keep it from losing connection, even if it appeared to be plugged in solidly.
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post #6 of 15 Old 03-12-2019, 10:33 AM Thread Starter
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Quote:
Originally Posted by jtec View Post
engine will crank?
YES

You have NO fuel pressure and you are using a gauge to check pressure?
I just replaced the pump, now have the fuel line disconnected right before the filter so I could see if it was spurting gas.

Do not just look at fuses - use a dvom or test light.
All fuses checked out ok. Don't have a test light, wil have to get one.

With Key On Engine Off (KOEO)
is there 12v at injectors?
I will check (after I get a guage)
Is there 12v at coil?
(same answer)

Fuel pump FYI the system will only supply 12v to pump for @3seconds if engine does not start. Relay and fuses in PDC.
Removed/re-arranged fuses in PDC, no corrosion noted.

With KOEO is the CEL on for @3seconds?
NO, no CEL at all.

When cranking engine is there SPARK?
Will check with assistant tomorrow.
I hope my responses (limited as they are) can help.

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post #7 of 15 Old 03-12-2019, 10:35 AM Thread Starter
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Quote:
Originally Posted by CatSplat View Post
Use a voltmeter (and an assistant) to determine if the fuel pump is receiving 12V at key on.

Diagram below is for a '95 but should be same pinout.

Also note that some aftermarket pumps have very low-quality connectors. I put an Airtex pump in mine and I had to secure the plug with zipties to keep it from losing connection, even if it appeared to be plugged in solidly.
I am using the factory wiring harness - I only replaced the actual pump inside of the housing/assembly. (which I am now understanding wasn't even the problem )All pins looked good on the factory harness connectors.

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post #8 of 15 Old 03-12-2019, 12:14 PM
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Quote:
Originally Posted by jfiscus View Post
I am using the factory wiring harness - I only replaced the actual pump inside of the housing/assembly. (which I am now understanding wasn't even the problem )All pins looked good on the factory harness connectors.
Verify power to pump connector at key-on before you start trying to diagnose other things. You can do that with a multimeter/voltmeter or test light - just put the test light probe on the pump power pin and have your trusty assistant turn the key to ON. If the connector is seeing 12V for the key-on prime cycle, then your problem is somewhere in the pump module or associated tank-side wiring - your new pump may be DOA, there may be a wiring problem, etc. Confirm or eliminate that as the problem first and then work your way forward.

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post #9 of 15 Old 03-12-2019, 12:26 PM
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I wonder if a fuel pressure gauge might be easier than crawling around and you can get a look at PSI and leak down all from driver seat. Maybe just being lazy and feeling sore today.

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 #10 of 15 Old 03-12-2019, 12:37 PM
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Quote:
Originally Posted by jtec View Post
I wonder if a fuel pressure gauge might be easier than crawling around and you can get a look at PSI and leak down all from driver seat. Maybe just being lazy and feeling sore today.
OP mentioned he pulled the fuel line at the filter and no fuel was being pumped so I think we can already assume the fuel pressure is zero. Next step is to determine whether power is being sent to the pump or not.
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post #11 of 15 Old 03-12-2019, 02:26 PM
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And my reading comprehension again shows itself.... getting old makes long post even harder to follow. BUT I try.

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 #12 of 15 Old 03-12-2019, 03:10 PM
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Hah, no worries. That in-quote response was a bit difficult to parse.

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post #13 of 15 Old 03-12-2019, 03:37 PM Thread Starter
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With no CEL on KOEO, that indicates more than just a bad pump/pump wire correct?
A bad computer / PDC / other major connector issue?

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post #14 of 15 Old 03-12-2019, 04:26 PM
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SORRY bad grammar :

Grammar the difference between helping your uncle jack off a horse AND helping your uncle Jack off a horse.


ON TOPIC
With Key On Engine Off (KOEO)
is there 12v at injectors?
Is there 12v at coil?

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 #15 of 15 Old 03-12-2019, 04:31 PM
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Quote:
Originally Posted by jfiscus View Post
With no CEL on KOEO, that indicates more than just a bad pump/pump wire correct?
A bad computer / PDC / other major connector issue?
Yes, it could indicate a bad PCM. Or it could indicate your CEL bulb is burned out. Your prior mention of the CEL was that it didn't light up when cranking - that's normal, it should only light up briefly with key-on.

There was an issue with the early PCMs where the capacitors went bad and would lead to a no-start condition and no CEL with key-on. This might be something to look into and is a cheap fix, if a bit onerous.
https://www.jeepforum.com/forum/f13/...51/index2.html
A test for the "lazy" PCM is to turn the key ON... and just wait. If the CEL eventually comes on after a few minutes and the fuel pump finally primes, you almost certainly have bad PCM capacitors.

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