Does faulty CPS shut off fuel pump?

[gsmith]

Have 96 XJ recently was idling in driveway and just died. Wife calls me up I go home and check fuel pressure at the rail. There is none. So as hot as its been in Nor-Cal lately I assume the fuel pump was done since she always runs it low on fuel. I replaced pump and filter only to find it still wouldn't start. I never checked spark at first since there was no fuel no bad relays or maxi fuses. I instantly figured bad pump. Well after that it still would crank and not fire, I then checked spark to find there was none. So the next logical suspect was CPS. I checked it through the helpful advice and specs found here and it was bad. Replaced it and it fired instantly. I dont mind doing the pump and the filter was necessary as P.M. My question is, will a bad CPS cause the fuel pump to not get power and run with the key on? I am just curious and also thought maybe it would help someone else from mis-diagnosing the same problem.

[87manche]

a shorted CPS can casue the ECU to freak, the ECU turns on the pump relay.
Freaked ECU=no pump relay

[gsmith]

Thanks for the reply. I figured that was the deal. Moral of story dont assume . Next time I will check spark and fuel befor drawing any conclusion.

[8Mud]

Same thing happened to me, I had a shorted CPS in the wifes 96. The fuel pump relay would close when I turned the key to the run position (for maybe a second) then open again almost instantaniously, it would build enough pressure for a small dribble to come out of the fuel rail schrader vavle. It wouldn't build enough pressure for a start.
Another oddity was that the check engine light wouldn't light as long as the shorted CPS was in there. A new CPS and the check engine light worked again and I could retrieve the Mil codes.
The test procedure says to check between the B and C pins (with an ohm meter 1K scale) and the circuit should be infinate (open), mine was open like it should be. But mine was shorting (I think it was .2 ohms of resistance) across the A and B pins, which the test procedure said nothing about.
Live and learn.

[langer1]

When you first turn the key on it's normal for the fuel pump to run for 1-3 seconds, It only continues to run if the engine is running, this is a safety requirement.

[Nevada City Sparky]

OK, just had something similar happen on my 89 (also in Nor Cal), only mine's a tad different.

New CPS about 6 months ago, so that's prolly OK.

I can hear the fuel pump do the 3 second moaning thing, but no fuel at the rail. Happened suddenly after a fill up. Hard start one morning (5-7 cranks vs. normal 2-3). Parked it at the office for a day or two and now no start and no fuel at the rail.

Maybe just the filter?

[gsmith]

Could be the filter, pull inlet to filter and check. Mine quit due to a bad CPS and would not pump at all to pressure up the system when the key was on. I realized after replacing the fuel pump that mine still wouldnt cycle on to pressurize the system. At that time The motor would crank, without starting and I would get a dribble at the schrader valve on the fuel rail. So I checked spark and found none. That led me to the CPS. Replaced the CPS, the new pump cycled on and is running just like it always has. I just hoped to find out for my own reference if the CPS can cause the pump to shut off, and not build pressure at the rail under keyed power, and possibly save someone else from buying a pump that they didnt really need for 150 to 180 dollars. thanks for all your replies. Gary

[Nevada City Sparky]

Well, with a new CPS, I suspect either the old, old filter or the 240K mile fuel pump.

I'd rather work on the other Cherokee, which is nearly done and a lot taller. This one's called "Reference 1" for a reason. Toadally Stock