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Detailed fuel pump problem on my 93 - humming n worse

THANKS to ALL NAXJA'ers for the help on this one-good cause.
:cheers:


(I suspect the old owner misdiagnosed the fuel pump, to start with, and that led us ALL astray... oh well, its running now, so he can job hunt -Thats the Big Thing.)
----
Now back to all them ole "The Cooling System Blues" threads!
:rolleyes:
:cheers:
 
Quote:
Originally Posted by xjbubba
I'm sorry, but I don't buy it.
The pump's operation, other than not running if the ECM is not getting an input from the ignition module, is not affected by the CPS.
If so, I'd appreciate the "science".

Quote:
Joe_peters
I think the "science" is there for the major part of his trouble--did you read his original post on 2-10-2009?

I don't know why his pump is less noisy now, but at least his xj is running, which I think was the major part of his goal.
__________________

What I meant by "science", was, what is the possible causal link between the CPS being marginally inoperative and the fuel pump humming?
Easy to see how an intermittent CPS signal would cause misfiring, and even cause the fuel pump to momentarily cease pumping, but cause humming?
 
I'm sorry I have not been on to update this.

This is confirmed, my Jeep is fixed.

The Crank Position Sensor was the problem.

Again thank you all for your help, you can move this into a fixed or closed state.

I have this same problem and just found this post. Thank you all for all the support and thank you nick for the leg work. I will be tackeling this this weekend.
 
I'm sorry, but I don't buy it.
The pump's operation, other than not running if the ECM is not getting an input from the ignition module, is not affected by the CPS.
If so, I'd appreciate the "science".

I am not a mechanic or an electrical engineer, so I have no idea what the exact connection is but...

After talking to at least 8 different mechanics about this problem, a backyard mechanic is who told me the fix. He claims he has worked on at least 5 other jeeps that had the same problem with the same solution (2000 and newer the problem would be the Cam Position Sensor since it took over part of the job of the Crank Position Sensor according to my Haynes Manual + description from the mechanic). I myself was also skeptical about this so the mechanic gave me this simple description:

The CPS reads the RPMs of the motor and tells the computer to send more or less voltage to pump more or less fuel. If the CPS goes bad it will throw a code, but if it's faulty it will not throw a code, but rather miss calculate the RPMs and send too low or too high of voltage to the fuel pump, causing it to overheat. (overheating is what caused humming and the pump to give out)

Other than that simple explanation that I was givin, all I can say is that it solved my problem. I would not recommend this as your 1st choice for a part to replace in this situation, but if you have gone through all other solutions (replacing the pump, checking your grounds, replacing the ballast resistor, checking or replacing your fuel pressure regulator, replacing your fuel filter, cleaning/replacing your fuel tank, filling it full with gas, checking all the fuel lines and vaccum lines to make sure nothing is pinched or kinked) then maybe this solution will work for you?
 
Thanks for the "science". It sounds logical, if in fact the PCM does directly control the fuel pump's output via voltage modulation. Not sure how the PCM knows the pressure, unless there is a pressure transducer in the fuel pump's output; could be. Anyone confirm the PCM's ability to control fuel pump output?
 
My fuel pump is still under warranty, I am not going to buy another pump for it.

here is a picture of the 1st new pump I installed after i pulled it out of the tank:

b51yqh.jpg

Can someone do me a favor and confirm that of the two tubes that come out of this pump, the longer one is the fuel out to the engine, and the shorter one is the fuel return from the engine. I forgot to label them when I disconnected it and want to make sure I'm putting it back together right.
 
Just an update for all the questions about CPS vs fuel pump issues... no, the PCM cannot control the exact voltage to the pump. There are three modes - pump off, no power at all. Pump on in start position with ballast resistor shunted, giving full power to the pump. And last, Pump in run mode with the ballast resistor in the supply wire to keep noise down. Any extra fuel is either sent back down the return line to the tank (my 96 is like this) or never goes to the engine in the first place, the pump just sees more backpressure.

I have no idea how replacing the CPS made the fuel pump quieter, but I think it's something similar to how I fixed my TPS/IAC issues by buying spares at the junkyard and keeping them in my glove compartment. I blame the stock market.
 
I recently have had these exact issues but I have already replaced cam sensor 2x once autozone and once mopar no change, her is list of parts that have also been replaced:cam,crank,map,coolant temp,coil,distributor all on a 93 jeep xj I'm out now pulling fuel rail, lines,and injectors to rule out those I'm losing my mind I also changed about 6 fuel pumps thinking they were trash finally settled with a carter
 
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