Cranks, Fires, Dies - 1991 Briarwood Restoration

[Jam Master Jay]

I'm back seeking help with my restoration of a 1991 Briarwood.
It's been running great until I left it parked for awhile. Now when I crank it, it will fire off and then immediately die. If you try repeatedly it may occasionally stumble for a full second and then die. Holding down the gas pedal it may rev for a second and then die.
It was doing this a while back after being parked for awhile. I thought it was the CPS so I pulled it onto my driveway with my truck and before changing the CPS I tried to crank it and it started and ran normally. I went ahead and changed the CPS anyway. I drove it occasionally for several months before leaving it parked for about a month. Now it's doing the same thing again.

Here's what I know:

• It's not the CPS. I changed that and unplugging this one and cranking results in no fire at all. Plugging it in results in that initial fire off before dying.
• I have 35 psi of fuel pressure at the rail. The fuel pump was replaced as part of the restoration project. I checked this with a fuel pressure gauge.
• It's getting spark, at least at first.
• The spark plugs are recent and look normal. No fouling or anything.
• The wires are recent.
• The distributor cap, rotor, and contacts have been cleaned and made no difference.
• The battery is fully charged and kept on a tender.
• I've checked the MAP sensor and it appears to work. When I unplug it, it will crank but not fire at all, similar to the CPS.
• It has fresh gas, I don't think it's gotten contaminated.
• It has brand new fuel injectors. I was worried the old ones were dirty or stuck from the bad fuel that had been left in it. I replaced the fuel tank, pump, and filter, but had not done the injectors. After changing the injectors it behaves exactly the same.

I'm guessing it's a sensor? I just can't think of what sensor it would be. I could be way off though. Any ideas you all may have are greatly appreciated.


Here's a video I made changing the CPS for anyone who wants to see the project. https://youtu.be/CoAY6QqAOyM?si=89WKMIAQCEVHIM1u

 

[Johnnie Walker]

I believe you have a ballast resistor on the driver side inner fender. Check wires, and if connected try jumping them together.
It was used in early XJs for fuel pump noise.
Will work fine bypassed if that is the issue.

Sent from my SM-N986U using Tapatalk

 

[Anak]

Does it have oil pressure?

Might be worth looking into the ASD (Auto Shut Down) relay circuit.

Also might be worth getting a noid light and checking to see if your injector pulse is there throughout this issue, or if it is what goes away when the vehicle dies.

 

[cruiser54]

I believe you have a ballast resistor on the driver side inner fender. Check wires, and if connected try jumping them together.
It was used in early XJs for fuel pump noise.
Will work fine bypassed if that is the issue.

Sent from my SM-N986U using Tapatalk

THIS^^^^^^^^^^^^^^^^^^^

 

[RCP Phx]

Might be worth looking into the ASD (Auto Shut Down) relay circuit.

That's where test relays come in handy!

 

[Jam Master Jay]

Yall mean the ballast resistor for the fuel pump?
I’ve junketed the fuel pump and it runs great and supplies 35psi after a few seconds. It powers on for a second when you first turn the key. I didn’t bother to check if it’s running constantly when cranking. I’ll have to jumper it and then crank it to see if that changes anything. Since the pump does run I think the ballast resistor is still ok.

 

[cruiser54]

If the ballast resistor is bad, it will fire up and then die when the ignition switch is returned to the ON position.

 

[asymptonic]

Just to add a tidbit of information. If I had to guess, the change in resistor values was to be able to use IEC E series resistor values (standard). The previous values were pretty weird looking, while the new ones look very familiar to anyone familiar with electronics.

 

[Jam Master Jay]

Ok, I'll jumper the ballast resistor this evening and try it. I also have a spare I can throw in but I might just leave it off.

 

[Rob Mayercik]

No harm in leaving it out permanently - the only reason Jeep put it there was because some owners thought the fuel pump was too noisy.

 

[Jam Master Jay]

I bypassed the ballast resistor and it didn’t change anything, unfortunately. It still cranks, stumbles, and dies. The pump is running.
I’m going to invest in a spark tester to see if it cuts spark but I don’t think that’s it.

The fact that it did this previously and then worked, then is doing it again makes me think I have an intermittent fault in a sensor (hopefully) or in wiring somewhere (which would be a pain to hunt down)

 

[cruiser54]

Or, the internal hose on the fuel pump is split and the fuel system isn't holding pressure.

I'd test the fuel pressure with a gauge that can be rented from local parts stores.

 

[Jam Master Jay]

I own a fuel pressure gauge. It holds 35 psi.

 

[Anak]

Does the dash gauge register oil pressure for that brief moment when it fires? I still think that ASD circuit deserves some attention.

There have also been a number of folks who have found their coil seemed to work, but turned out to be weak. They could get a spark, but it wasn't enough to run properly.

 

[lawsoncl]

I bypassed the ballast resistor and it didn’t change anything, unfortunately. It still cranks, stumbles, and dies. The pump is running.
I’m going to invest in a spark tester to see if it cuts spark but I don’t think that’s it.

The fact that it did this previously and then worked, then is doing it again makes me think I have an intermittent fault in a sensor (hopefully) or in wiring somewhere (which would be a pain to hunt down)

Put your inline where the resistor would normally go and measure the current. That will rule out an issue of power to the pump. You could just plumb 12-volts to it, but the current measurement will be more helpful. I recall 7 amps was normal when I bypassed mine and 4 through the resistor. It could still be a relay issue or wiring issue still. Cruisers site has a list of grounds to clean up, including the one for the fuel pump.

 

[asymptonic]

Just to add a tidbit of information. If I had to guess, the change in resistor values was to be able to use IEC E series resistor values (standard). The previous values were pretty weird looking, while the new ones look very familiar to anyone familiar with electronics.

Sorry, posted in the wrong thread.

 

[Jam Master Jay]

Does the dash gauge register oil pressure for that brief moment when it fires? I still think that ASD circuit deserves some attention.

There have also been a number of folks who have found their coil seemed to work, but turned out to be weak. They could get a spark, but it wasn't enough to run properly.

It does register oil pressure just fine. The rest of the gauges appear to work normally too.

I will check the voltage at the resistor next chance I get.

I really appreciate everyone’s suggestions.

 

[Jam Master Jay]

I have an update to this saga.

I left the XJ sitting for a period of weeks. Then I finally got around to messing with it this weekend.

I tried starting it and it did the same crank, fire off, then die scenario it's been doing. So I plugged in a spark tester on one of the plugs to see if it had spark. When I cranked it that time it started up and idled.

I let it idle for awhile and then turned it off and then started it again and it started and ran the second time as well. So I drove it around the neighborhood and then parked it.

Then the next day I went to start it and it did the crank, fire, die thing again! This time I got my fuel pressure gauge and in the process of messing with that, before I even had it fully connected, I asked my son to cycle the key to make the pump run and he instead cranked it and it just started and idled.

So I have no clue what is causing this intermittent issue.

I do know that it sparks when cranking even after it dies.

I know that is has sufficient fuel pressure on the times when it runs because I drove it and it performed normally.

I never changed anything between the instances where it ran or didn't run other than disconnecting the battery so it won't die.