No Spark, Fuel Pressure = No Start?

No Spark, Fuel Pressure = No Start?

1991 - 4.0 - auto


I know this has been asked a bunch of time but I'm stuck on a few things that don't seem to add up as well.


I believe it may be the CPS but would i still get the pre-start fuel pressure. The reason i ask is I'm not getting fuel pressure even when the key is first turned.

Could this mean that the ECM could be the problem?

No spark from the coil.

I'm not getting any codes even after unplugging the CPS.

Hallo. It can be a bad ASDR ( Auto Shut Down Relay) or the LATCH relay for your year?
No spark and no fuel when broken.
Check the battery cables and ground cables too.


'92 XJ

You can swap the relays in the front that are the same as the ASD to test the relay. Check with voltmeter to see if current comes into the ASD socket.

I swapped out all relays with my running 92 and every one of them work fine.

The ASD has power with Key off on the two out side slots.

When Key is on the two out side slots loose power but the top slot gains power.

I checked the CPS as specified in the book and it checks out so now I'm thinking the ECM may be it.

Unfortunately my 92 is a 5 speed no power acc. so i can't try that computer.

OK here is where I'm at with this one.

ECM is good! removed the one from the 91 and swapped in the one from my 92 and still no fuel or spark. But the ECM from the 91 ran fine in my 92.

CPS is good! swapped the 91 and the 92 and still no spark or fuel but both worked fine in the 92.

The ASDR and the FPR are both working and both get a good 12V from key power.

I've started pulling the wiring harness apart to look for shorts and other damages but have found nothing.

This thing is really starting to drive me nuts. Any other suggestions would be great.

Mike

What about the coil? Can you swap those? When cranking, can you check for 12 volts going to the coil?

Seems like you should focus on the fact that you have no fuel pressure at the rail...

You should be able to jump the fuel pump relay and get the pump to run and supply about a liter of fuel per minute..

McQue said:

Seems like you should focus on the fact that you have no fuel pressure at the rail...

You should be able to jump the fuel pump relay and get the pump to run and supply about a liter of fuel per minute..

Click to expand...

I forgot that he didn't have fuel pressure, but did you forget that he didn't have spark? Most likely it is one thing that affects both.

You are probably right that it is one thing affecting both...but it seems like chasing fuel pressure is easier ...motor doesn't have to turn over to troubleshoot that...no way you would catch me breaking my azz to change a cps when I don't have fuel pressure.

As long as he's just not confused by the fact that the fuel pump only pumps for 3 seconds with the key in run unless it PCM sees CKP (Crank Position Sensor) signal.

OK let me give you guys a quick history on this 91 XJ.

Bought from the son of the original owner (Not a Kid) for $100.00 do to the fact it had a rap that they believed was the lower end.

Owning many jeeps I new it was the flywheel being cracked and would need to be replaced.

Dove it for six months before the fly wheel finally let go. Replaced the flywheel and every thing was fine.

A few day later it started starting really hard . I would need to cycle the key a few times to get the fuel pump to start working then it would start and be fine for the rest of the day. This only happened first thing in the morning and be fine for the rest of the day.

I checked fuel pressure wile this was happening and it was low, this along with the fuel pump being really loud told me it needed to be changed out. a day or two latter it stooped working all together.

Installed a new fuel pump and now nothing. New fuel pump works i jumped it and it's fine.

No fuel pressure: No power at the pump even when i jump the FPR.
No Spark: No Power to the coil

Swapped out:
all relays- ASD,FPR, Balister relay etc.
CPS
ECM

Ive been swapping all the parts from my running 92 thats has continued to run with all the parts from the 91 that i have swapped out.

According to the wiring diagram (but for my 2000), the ASD should get power to only one socket with the key off, and with the key on, one more socket should get power, but the first one should keep it's power too. You've changed all the parts you can (neat to have the running swapper). It must be in the wiring or ignition switch. Study the wiring diagram for yours on the ASD.

When you jump pin 30 to pin 87 on the Fuel Pump Relay, you are supplying battery power thru the Ballast resistor, then to the pump. Check power at the Ballast resistor. You want voltage between ground and each end of the ballast resistor. Ballast resistor may be open.

OK now this is getting weird.

I checked the power at the FPR & ASDR Key off NO POWER Key on Power at only one terminal. When i checked before this was not the case.


I jumped said mentioned terminals on the FPR and power was supplied to the fuel pump and it cycled fine, But still nothing when the relay is plugged in and key is turned.

I swapped the relay for the one on my 92 and it still did nothing in the 91 but ran in the 92.

Unless my 92 is a miracle XJ that just runs then i have no idea whats going on.


Doing some tests on the 92 to see if un pluging sensors would cause the same problem as my 91 here is what i found.

Unplugging the CPS still allows the fuel pump to cycle on pre-start. The only way to stop the fuel pump from cycling is to remove the FPR.

The only thing that stopped spark was unplugging the CPS, ASDR, or the distributor (Cam Position Sensor)

This thing will be the death of me and it's probably a simple thing I'm over looking. hasta

You need to start out at that fuel pump relay socket. Either you are checking it wrong, or you are on to the problem. Every relay has at least two circuits. That is kind of the definition of a relay. There is a switched circuit and a switching circuit. Think of it as a light switch at home. The switched circuit is your lights, but your finger performs the switching circuit. You know your relay is good (vehicle swap test). When you jumped the circuit, the fuel pump worked. When you tested the socket though, you said you had no power with key off and power to one circuit with key on. You should have power in to one circuit with key off, and power in to two sockets with the key in the run position. Find the fuel pump relay in your wiring diagram to see which pins get power from where.

Hallo. like McQue and Winterbeater suggested, I think that's the way to go.
Did the pump going, when you connected or jumpwired the #30 and #87 in the socket of the fuelpumprelay? When you do that, the pump has to run.




92 XJ

Check all your fuses in the PDC...fuel pump relay and ASD relay get power through fuse F6...Fuse F6 gets power from battery through ignition switch when you turn the key...if fuses are good, and no power at fuse F6 or at the relay, then you either have an open wire somewhere, (Dark Blue) or a bad ignition switch.

OK Now things are getting strange.

my wife went out the other day and tried starting it and it started up. Ran great but when we took it for a test drive the tranny wouldn't shift out of first gear.

I looked up what the problem could be and started to check the TCU out found that it wasn't receiving power.

Continued to check thing over then tried to start it again and nothing.

I'm back at ground zero again.

Hallo. There are a few fuses to check of the TCU.
One 7,5 amp and one 15 amp.
Helpful: AW4 Jeep Diagnoses by Wayne Colonna.

I suspect you have a bad electrical connection...I would start by thoroughly inspect the bottom side of the Power Distribution Center..and inspect the harness as it travels towards the firewall and down into the interior to the Junction block.