The car is very hard to start cold and sometimes when warmed up. I can turn the key to the #3 position and not start it a few times and let it stay there a few seconds and it makes it easier. I am not sure if it is a fuel pump issue or a FPR issue or is there something else causing the problem? Any ideas?

 

I think hard cold starts are often due to a combination of issues. Some of the basic things are:

How long since your last full tuneup (plugs, wires, all filters (air, oil, fuel), MAF cleaning, injector cleaning, throttle body cleaning, etc.)?

If your car is still on its original FPR, then I would definitely recommend replacing it. Over time it loses its ability to maintain pressure in the fuel rail, requiring the fuel pump to repressurize the system at every cold start. Another FPR problem is that if the diaphragm has failed, raw unmetered fuel can leak into the vacuum hose that is connected directly to the intake manifold, allowing unmetered fuel to overly-enrich the fuel mixture. You can check for this by pulling the vacuum hose, cranking the engine and checking for any fuel at the hose fitting on the FPR.

The system also has a check valve between the fuel pump and fuel filter, which works in conjunction with the FPR. The check valves also fail. I don't know whether the XJ81 has the check valve in the fuel pipe just ahead of the filter, or in the fuel tank. You can add an inexpensive check valve to the fuel line:

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Another prime suspect is the Coolant Temperature Sensor (CTS). It's a temperature-dependent resistor and its signal tells the Engine Control Module (ECM) when the engine is cold so the ECM can apply cold-start fuel enrichment. If the CTS has failed or there is a problem with its electrical connector or wiring harness (all common issues), the ECM may not be enriching the mix, leading to longer start times.

Another suspect is a failing Crankshaft Position Sensor (CPS) or looseness of, or corrosion on, its electrical connector. If you haven't replaced the CPS in a while, I would recommend installing a new one and keeping the old one in the trunk as a spare, since the most common failure mode is "suddenly with no warning."

Hopefully others will offer some additional possibilities. Please keep us informed.

Cheers,

Don

 

Thanks Don. I just recently purchased the vehicle and haven't driven it much so I can not say how long any of the items you mentioned have been addressed. I know the previous owner seldom drove it so it sounds like I have a lot of things to take care of. I will keep you informed on progress.

 

It's been a while since I was here but I did everything DonB suggested. I still have the same issue of intermittent start. I replaced fuel pump relays. The fuel pump only comes on intermittently. The relays did not fix this issue. I have power to one side of the normally open contacts on the relays but no power to either of the normally closed posts. Where does the power come from for this?

 

Late cars like ours are particularly susceptible to cold or cracked joints in the footwell fuseboxes.

Reflowing the joints is the accepted remedy, worked for me!

Replacing all the unsealed relays in the engine compartment (particularly the blue units) with sealed equivalents isn't a bad idea too, aftermarket relays are fine btw.

Basically these are electrical cars so you have to ensure all the connections and grounds are in top shape to have the reliability they can deliver. That's been my experience anyway!

Larry

 

Thanks Lawrence, I will do that and see if it helps.

 

Lawrence, I have the fuse box out and have the cover taken off. I can't get the circuit board to come out to reflow the solder connectors
. Does the main power post unscrew so it comes out? It is very tight and I don't want to break it if it doesn't come out like that.

 

You don't necessarily have to dismantle (separate) the circuit boards if that's what you mean ...when I did mine I simply reflowed the connections on the top face.

I'm not too sure if that is what you are asking? If you're talking about the large post that holds the big cable, well yes, you have to undo the nut to release the big cable then iirrc the fusebox can be removed from the car.

It was several years ago that I did this job but as far as I can remember it was fairly straightforward to take out the fuseboxes?




remove the rear harness plugs and the large brown cable to remove the fusebox



Larry

 

Thanks Lawrence. I got the fuse box out. From what you are saying I only need to reflow the connections I can see after I separate the fuse box. I guess I was trying to go too deep with the repair. I did try metering the connections and some of them are definitely not making. I will reflow them this week and let you know how it goes. Thanks again for the info.

 

I didn't need to split the boards as I could see the dry (cracked) joints on the surface ..some folks do go deeper if necessary ...probably the easiest way to separate the boards is to cut them apart with snips and solder them back together when you're done.

My footwells and fuseboxes were in pretty good condition and didn't show any corrosion - not all cars are as fortunate and can be heavily corroded.

I've heard if the box has a problem with the main cable stud you need a very powerful soldering iron to resolder it - a small iron won't heat it up quickly enough and you run into the problem of burning the boards before the stud solder reflows...

anyway, I hope it works out

all the best

Larry

 

94XJ12,

Sorry for the late reply. Larry has already given you great info, but just in case the photos at the following link may be helpful, you might have a look. I found cold or starved solder joints in all three of the fuseboxes in our '93 six-cylinder.

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Please keep us informed!

Cheers,

Don