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Goofy no start?

C

cherokee4fun

NAXJA Forum User
Location
Bend, Oregon
So,,, maybe someone can point me in the right direction.....

As reported yesterday, I go out to my 89 Jeep 4.0, and it does not start!!
I don't hear the fuel pump, so I check the relay, and switch them, still nothing, then I bypass the resistor, still nothing. I short the #30 & #87? terminal on the relay, and I hear the fuel pump, and it will start. I remove the jumper, and it dies. Then I take a break...........

About three hours later, I go out, turn the key, and I hear the fuel pump for a short time, which in my searches, seems normal. But then I hear nothing.

Can this be the CPS or maybe electrical part of the key switch?

Any thoughts would be greatly appreciated!
Thanks,
Bob
 
Have you tried disconnecting the CKP connector and reconnecting it? If that works then that probably means your CKP needs to be replaced.
 
cherokee4fun said:
So,,, maybe someone can point me in the right direction.....

As reported yesterday, I go out to my 89 Jeep 4.0, and it does not start!!
I don't hear the fuel pump, so I check the relay, and switch them, still nothing, then I bypass the resistor, still nothing. I short the #30 & #87? terminal on the relay, and I hear the fuel pump, and it will start. I remove the jumper, and it dies. Then I take a break...........

About three hours later, I go out, turn the key, and I hear the fuel pump for a short time, which in my searches, seems normal. But then I hear nothing.

Can this be the CPS or maybe electrical part of the key switch?

Any thoughts would be greatly appreciated!
Thanks,
Bob
Click to expand...

define your no start problem a little better. Is it cranking?
 
Right,
I know I forgot something!!!
Yes, no problem cranking, the motor turns over easily,,,, and when I short the fuel pump relay, she starts right up.

I have not any issues, except the TPS does not allow me to start in Neutral.

Does the CPS deal with fuel pump? I thought it was only spark........

I was thinking of the ignition switch or starter relay?

Thanks
Bob
 
Last edited:
The fuel pump is powered in different ways at different times.

1. When you turn the key to ON the fuel pump receives 12v from the B Latch relay (later models ASD relay), and that power bypasses the ballast resistor and only lasts for 3 seconds.

2. When you turn the key to the START position, the fuel pump receives 12v from the starter relay bypassing the ballast resistor.

3. When you turn the key to the RUN position, the fuel pump receives power through the fuel pump relay and then through the ballast resistor which reduces the power to about 6v.

4. When at WOT the fuel pump receives power through the oxygen heater relay, a full 12v bypassing the ballast resistor.

Try and determine at what key positions you have power to the fuel pump.
 
So,
I am getting power right when I turn the key on, but nothing after that. I don't hear the pump after that!

If I short the relay, the thing starts, so would that mean the cps is working?

Thanks,
Bob
 
THe fuel pump only runs for a few seconds when the vehicle is not running.
 
Doesn't anybody ever read the FAQ's?

The pump runs for a few seconds then stops. The fuel pressure regulator is supposed to hold the pressure. So either the fuel pressure regulator or the one way valve in the pump assy is bad.
 
SORRY to say, I did read the FAQs, that is where I started.

What I don't understand is why the Jeep ran fine, then went out it did not start.

I have had a few Jeep's, and what I can't figure is what failed.

I understand that the fuel pump runs when you turn the key, to pressure the fuel system, then once you turn the motor over the CPS sends a signal, but I don't see anything that has the CPS sending a signal to the fuel pump relay.

I understand that starter relay also sends a signal to relay to run the fuel pump.

SO, my question is, if the fuel pump is getting power, which it is when I bypass the relay, and it starts, and runs. Does that mean the CPS is fine?

What I might be missing is that the 1989 is the same as 1990 in the electrical starting/fuel pump system?
 
Cool,
so the Jeep will not run if the CPS is bad, so I can rule that out.

I am thinking it is the starter relay mounted up by the battery? Is there a test for that? can I just apply 12v to that post and see if the relay works? It looks like that is what the wiring diagram shows.

Thanks again,
Bob
 
The primary coil of the fuel pump relay is powered by the ignition switch and grounded by the pcm. That's what's odd, if it runs the pump at key on- and the engine will run with the relay bypassed, that indicates the crank sensor is doing its job and the pcm is functioning. Does this Jeep have the infamous C101 bulkhead connector by the brake booster? Sounds like the circuit from pcm to relay coil may have an issue.
 
OK tell me more!!!
Some goofy connector, that makes me feel better. When I get home tonight I will do a search for this connector.

If anyone has more info or links, please feel free to send them over.

Any ideas would be greatly appreciated, as it seems kinda strange to me.

I am starting to miss my 1990 with 284k on it that I sold. This 89 has not been well cared for....................
 
cherokee4fun said:
OK tell me more!!!
Some goofy connector, that makes me feel better. When I get home tonight I will do a search for this connector.

If anyone has more info or links, please feel free to send them over.

Any ideas would be greatly appreciated, as it seems kinda strange to me.

I am starting to miss my 1990 with 284k on it that I sold. This 89 has not been well cared for....................
Click to expand...

i find this to be very helpful

http://www.lunghd.com/Downloads_and_Links/Jeep_Renix_Fuel_Injection_manual.pdf
 
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