Fuel pump relay trouble - Page 2

jeep210 · 11-20-2009, 06:34 PM

The relays are good but the control ground is no good on both. It is pointing more to the PCM. The PCM has to ground these pins so the relays turn on. Then you will have fuel, coil, injectors and alternator.

The PCM grounds the circuit long enough to prime the fuel then they turn off until you crank the engine. When you checked the ground was it within a few second time frame. If not check it again. Have someone turn the key on while you check for ground at the relay socket.

I don't think it is the crank position sensor because if it had failed the PCM would still turn the relays on for a few seconds. That is how I understand it.

Sextiva · 11-20-2009, 06:39 PM

Wire it up on a switch. Redneck mechanics 101.

ZeeJay1997 · 11-20-2009, 06:42 PM

Quote:

Originally Posted by 99grandcheroki

97 wiring diagram is better than non

The 96-98 PCM is different from the 99. It most likely will only cause confusion and probably worse than none. Start by pulling the black plug and looking for the wires I mentioned.

Maybe someone else knows a source for your YM.

99grandcheroki · 11-22-2009, 01:14 PM

I tested the B+, ignition positive and grounds to the PCU. They all seemed in order.

I also did a continuity test on the B and C prongs on the crankshaft position sensor and it was an open circuit....as it should.

Jeep Grand Cherokee Crank, No Start

I feel that I have learned a lot about what the problem is not...but still do not have it solved.

I have to say that I have a hard time believing that the PCU just crapped out.

Does anyone know how the stock security system works? I understand that if armed, it will shut down the car. I no longer have the remote key for this car and just use the old fashion key. The door panels are a bit loose and I am wondering if a pinched wire in the door or the like could cause all of this trouble.

ZeeJay1997 · 11-22-2009, 03:16 PM

Quote:

Originally Posted by 99grandcheroki

I have to say that I have a hard time believing that the PCU just crapped out.

Yup, my confidence in DC cost me about 700 bucks before I finally gave in and changed the PCU.

The beast is sucking you in. You must resist.

99grandcheroki · 11-22-2009, 09:16 PM

Sorry for my ignorance...but what do you mean by DC? Direct current?

ZeeJay1997 · 11-23-2009, 05:09 AM

Daimler Chrysler .... don't drink the kool-aid.

As a side note, my problem was intermittent and in the end was caused by a loose connection at the PCM and a bad PCM.

99grandcheroki · 11-23-2009, 04:17 PM

Ordered the PCM

99grandcheroki · 12-03-2009, 12:15 AM

The PCM arrived.

I installed it, cleaning carefully along the way.

I tried to start the jeep. NO GO.

I checked the fuel rail....no pressure.

I checked the fuel relay ground....still nothing.

I connected the OBD-II scanner....still "no link".

This getting frustrating....I have no idea where to go next.

I even pulled the driver door panel off thinking that I might find a kinked wire that set off the security system.

Any ideas?

ZeeJay1997 · 12-04-2009, 08:54 PM

Bummer...

Sounds like you need a wiring diagram for your YM. Not sure if security system will shut down the bus.

Do the fuel and battery gauges work?

99grandcheroki · 12-05-2009, 01:06 AM

Well I was reading the haynes manual again and discovered that the PCM will not start the car, if it does not recieve a signal from the Crank Position Sensor. I will test that unit more carefully this weekend and post again. My fingers are crossed.

ZeeJay1997 · 12-05-2009, 09:17 AM

I've read several places that the CPS will shut the PCM down, but you said you checked it for short.

jeep210 · 12-06-2009, 06:42 PM

Quote:

Originally Posted by 99grandcheroki

I tested the B+, ignition positive and grounds to the PCU. They all seemed in order.

I also did a continuity test on the B and C prongs on the crankshaft position sensor and it was an open circuit....as it should.

Jeep Grand Cherokee Crank, No Start

I feel that I have learned a lot about what the problem is not...but still do not have it solved.

I have to say that I have a hard time believing that the PCU just crapped out.

Does anyone know how the stock security system works? I understand that if armed, it will shut down the car. I no longer have the remote key for this car and just use the old fashion key. The door panels are a bit loose and I am wondering if a pinched wire in the door or the like could cause all of this trouble.

Here is some basic info on the security system. If you have such a system it may be a problem.

Here

Pm me an email and I will send you some wiring diagrams. What engine do you have?

Was this engine running before? Did you work on the engine and then the problem started? What led up to the problem?

99grandcheroki · 12-07-2009, 12:25 PM

FIXED!

It was the crank position sensor.

Having a scan tool not link to the jeep and work on other cars, made me believe that it was the PCM.

My earlier test of the crank sensor was based on limited info that I found on the web and obviously not thorough enough.

I should have had the haynes manual from the start. Amateur move on my part.

Getting to the crank sensor on a 4.0L 6 cylinder with an automatic transmission is a feat and a half.

Thank you all for the help.

Anyone know of an affordable scan tool known to work on these jeeps?

ZeeJay1997 · 12-08-2009, 05:16 AM

Quote:

Originally Posted by 99grandcheroki

FIXED!
Anyone know of an affordable scan tool known to work on these jeeps?

Anything that is affordable will be generic. Generic will lack the ability to read OEM data beyond the higher level and emissions codes. I have an Actron that I gave 150 for that is minimally suitable. If you get one, be sure it will read live data and save records.