I am having a starting problem, not a cranking problem - starter turns fine on my '93 XJ6. Anyway, I want to check fuel pressure but can't find a shraeder valve anywhere. Can someone tell me specifically where it is or if it is really there? If not, where is the best place to check fuel pressure so I can determine if that is where the problem is?

The car runs fine when it starts, but occasionally, the starter turns good but it will not run. This is usually after I have driven it a bit. After 20 minutes or so, it will start right up and run fine.

Any other suggestions as to what to check? The intermittent nature of the non-starting makes it really difficult to check.

 

Not aware of a schreader on the XJ40, but then the USA market did get stuff we did not.

In the hose "before" the inlet to the rail is the place for a gauge. You may have those "lined" fuel hoses on that year, so splicing in will be awkward. Finding an adaptor to use the actually 2 nut fitting on the rail will be equally awkward I reckon.

A simple quicky test for "fuel or no fuel" would be to crank it, it wont start as you said, so get some rags, and TAKE CARE, and CAREFULLY crack the inlet fitting at the rail. If you get a "spurt", then you at least have fuel and some pressure. If you get zip, then you know that answer.

Since fuel spillage happens here, use the brain, and take all the precautions required. I have done this simple quicky on V12's just to establish the presence of fuel and at least some pressure, which should have it fire and run, and indicate the issue is maybe spark related.

Then I would find an old spark plug, any old spark plug will do, and plug it into one of the plug leads, and earth the body of the spark plug on the exhaust manifold, and crank the engine, and observe the spark. You are looking for a nice fat Blue spark, with a "crack" as it fires.

The resistance in oldish spark plug leads increases as they get hot/old, thats why some engines start fine cold, but are a mongrel when warm/hot, especially when cranking, when the starter is drawing a lot of the energy, and the engine needs a good "fat" spark to actually START, but not so "fat" once its running. The actual lead from the coil TO the distributor cap is highly suspect in my opinion again.

More suggestions will arrive in due time.

 

Grant,
Thanks for the suggestions from Down Under. Will see what I can find there. Upon thinking about the difficulty of hooking up to test fuel pressure, I think I will first change the fuel filter and see if I can check the fuel pressure there so I will at least know if the fuel pump is working. Then I can move on to other things. The bad, or good, part depending on how you look at it, is that the car does start most of the time even when hot which makes it really hard to troubleshoot.

Thanks again. I remember well my trip to Stralia and NZ a few years ago. Really enjoyed it and took lots of pictures, but it is a LO-O-O-ONG way though!

 

When it is not starting, see if the tach is moving at all or stuck on 0. If stuck on 0, your "crank position sensor" is going bad. It will fail when heated up, then work again once it's cooled down. For a little while. It's somewhere on the front of the engine and "possible" to change yourself, unless you're driving to Florida and it finally gives out in the parking lot of the Jag dealer in Nashville.

There's a diagram of a fuel pressure setup, maybe on Jag-Lovers. I've got a copy but it's at home. Basically a T, an adapter or 2, and a gauge (glycerine filled?).

 

Also, my above note is from my '88. any similarity to your '93 should at best be presumed.

 

Update: The Jag would not start this morning yesterday at my house even though I tried it at several times. Obviously, air/gas/spark mixture not working. I tried it again this morning and still no start so I changed the fuel filter. Actually easier than I thought it might be and did not leak nearly as much as I expected -- seemed to mostly be just what was in the fuel filter itself. I blew through the filter, and it did not seem restrictive at all. I can hear the fuel pump for a couple of seconds each time I turn on the ignition and wanted to test my fuel pressure at the fuel pump. Unfortunately, I could not attach my fuel pressure gage so I put it back together. Then I tried it and though it seemed to crank fine, it still did not start up. So then I checked the battery which showed 12.3 volts so I charged it for several hours even though it seemed to be cranking fine. After it was fully charged, I tried it, and it started right up. (I was actually kind of disappointed that it started since the intermittent nature of the starting makes it hard to troubleshoot. This makes me wonder if it is the slightly reduced voltage that is causing it not to start. My plan at this point is to try to make sure it has a good spark and double check the wiring. If I don't spot an obvious problem there, I plan to rig up a connection so that I can check the fuel pressure at the fuel rail. Any other suggestions as to other troubleshooting?? It is really frustrating for it not to be reliable because it drives and rides SO GOOD when it runs, and looks good, too!

 

Sounds very similar to what was happening with one of my XJ40's would run for weeks with no problem and then just wouldn't start. For the first few times I was able to get it started by checking several conections in the engine bay. I got progressively worse over time. Someone suggested it sounded like the ignition module may be on the way out. I had already replaced spark plug leads, distributor cap and rotor button with no change. I replaced the ignition module (located under the coil) and have had no problem since (35,000 kms). Not saying that this is what it is but sounds identical to what was happening with me.

 

Leigh, Thanks for the suggestion. That would seem to fit. Since you did not mention a way to check it, I assume that there is no reasonable way to troubleshoot and determine this is the problem without just replacing the module and seeing what happens?

 

I haven't seen a response regarding the above post on the CPS. I know the old adage of the the 3, Air/Fuel/Spark but your car has a 4th, the CPS. If it isn't working properly you will pull your hair out. It's easy to get at with a long extension. That's your next step. Search the XJ40 section on CPS, it will answer all your questions.

 

Update: I turned the starter and the tach moved slightly, maybe 100 rpm's, so if I understand right, it should not be the cps. Later, it started right up and ran smoothly just like it usually does. I inspected all of the ignition wires and saw no loose wires or anything amiss. So I came back last night and started it to check for arcing across wires. Saw nothing there either.

So now I got an ignition tester that goes between a spark plug wire and spark plug so that you can easily check for spark. It started right up and spark looks good, consistent, bright, and increase in frequency as you rev engine. I will check again WHEN it doesn't start. If no spark then, at least I will know it is in the ignition system so will try to also check the coil resistances. If no problem seen there, looks like I will have to replace the ignition module and drive it a while to see if works. Really want to get where I can trust it again so my wife can drive it. She loves driving it and is always talking about how it rides, but she doesn't want to be stranded and not be able to go. Any other suggestions as to what I can check? At least all of this has gotten me to change the fuel filter so I won't need to worry about that maintenance for a while!

 

FWIW, my '88 XJ40 would not start for a couple days after it rained. Crank and crank but no fire. Put in a new dist cap and rotor, only rained once since but it started fine. Not ready to declare it fixed, but definetaly seems better.