QuestionQUESTION: Howard,
To refresh you a bit, I have had my XJ6 for two years next month, and early on, you gave me instructions on several tests to perform for a rough idle/stall/no start condition. This is also the car that I plan to submit a short story about a fiasco that occurred in March, which led to me completely repainting the car at home here myself. That all went well enough, taking nights and weekends, I finished wet-sanding and buffing a couple of weeks ago. Now, this car that was driven fairly regularly before March sat in a garage for three months of body work and paint, and when I was to take it for windshield replacement, it backed out of the garage, died and after 20 or more attempts, started again. I tested fuel pressure, which was good, vacuum was good as well, but stark with an inline tester was erratic at the No. 1 cylinder. The cap and rotor had seen better days and after replacement, the car started right up and ran well. Car was driven to glass shop for windshield replacement, they moved it around a bit, and the next day, I drove it about 40 miles of leisure once I picked it up. That was last Thursday. Saturday, I took it to a carwash to apply several coats of hot wax, filled each tank to half, and back home. Later in the day, took it out on a couple of errands and walked out of a store to start it, it ran for 10 seconds and died. After another 10-15 attempts at starting, I had my wife bring my inline spark tester to me, which showed no spark between the coil and cap. Bought a generic coil at Autozone (matched the specs and tolerance) and it fired right up and drove home. Later, took it to show friends, and when leaving, once again, it started and ran for 10 seconds then died. Only this time, it started again after a couple of tries and took us to dinner and home again afterwards. Without having tested since, but seeing consistent fuel/vacuum readings before, I am suspecting perhaps a coolant temp sensor. I know you will only recommend I test for this, so, what is a way to test this, and does it even sound like I am on the right track? That it is dying/having trouble restarting after warming up - on these hot TN June days?
Thanks,
Michael
ANSWER: No, I don't think you are on the right track. Of over 100 things that can cause it to occasionally not start why have you picked a coolant temp sensor?
Any time an engine does not start one or more of only three items is missing. Compression, Fire or fuel. It is unlikely compression because if compression goes away, it will not return. So that means Fire or Fuel. These both can be easily tested (but only at the time of failure)by just carrying a can of starter fluid with you and when it don't start, spray starting fluid into the intake air horn. If it fires off but quits and will only run while spraying then it is a fuel related problem which requires a series of tests. If it don't fire off at all then you have an ignition failure and a different series of test for that is required to pin point the problem. You should not purchase any parts until you know what is wrong or you may run out of money before you find it.
Howard
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QUESTION: I only began to suspect the coolant temp sensor as faulty perhaps due to the common denominator being that it will always start on first try cold, and with my vacuum and fuel pressure gauges attached, all readings you had previously provided me with are in check at idle, with/without vacuum to fuel pressure regulator, etc. The distributor cap and rotor offered an obvious improvement, as did the coil. There was at first a strong spark between the coil and cap, but erratic spark at the No. 1 plug. The cap and rotor cleared that up when cleaning the old, tarnished pieces did not. When it failed to start on Saturday, I was able to do the quick test of fuel by turning key on and opening the flap in the intake and hearing the fuel running in the fuel rail. The inline spark tester revealed no spark in between the coil and cap, hence the coil being replaced and the vehicle starting right up. I don't believe I said anything in my question that should indicate I was merely throwing parts at the issue. The only times I was now seeing any failure had the common denominator of being a restart attempt after having driven some distance and reaching good operating temp and unfortunately, in those two instances, I did not happen to have my test gear with me. I seemed to recall reading before about a coolant temp sensor possibly causing this type of havoc and was asking if there is a way to test it. Of over a 100 things that may cause a no-start issue, do you mean to say you always go back to the beginning, basic test, ignoring any clues as to the conditions present, as in noticing a trend for a hint to hone in on the issue?
AnswerNo Michael, you don't need to go back to the beginning for a no start. Sorry about that, as I answer some of these very late at night and I often don't remember everything that proceeded.
It does sound like you are proceeding correctly and in detail. (more so then most) It just tossed me for a loop when you wanted to suspect the temp sensor. A temp sensor can make one not start but if it fails it stays failed and can not start working again like a mechanical device.
You can test it with an ohm meter as follows.
0 degrees C = 5.9 K ohms
+20 Deg. C = 2.5 K Ohms
+40 Deg. C = 1.18 K Ohms
+60 Deg. C = 0.60 K Ohms
+80 Deg. C = 0.325 K Ohms
It wouldn't hurt to ohm you plug wires while you are at it. I use a 5 K ohm per foot as a rough bench mark. I ok anything close to that.
As far as a hot restart problem. It can still be fire or fuel so a quick test of spark would tell you to chase fire or fuel as a fault.
The design of the intake manifold causes excess fuel to puddle which can cause a flooding on a hot restart so I would carry a plug wrench to look for a wet plug when you get a no-start. If it is wet you could have a cold start injector that is supplying fuel when it should not or leaking injectors or even a leaking diaphragm in the regulator putting fuel into the vacuum hoses.
If the plugs are dry on a hot no-start condition and if you have established spark you may have a one way valve in the fuel pump not maintaining fuel pressure on the system.
The series III is noted for a very quick start hot or cold when everything is working.
When diagnosing a problem I try to block out of my mind any possible part and look only at systems first, then when I ID a system failure I bracket that down to a smaller part of that system and continue cutting that into smaller and smaller areas until I arrive at the failed part. I am surprised at what I find as many times as not. But that method of diagnosis has served me well in several dealerships over the years.
If you can get the no-start condition at home try putting a jumper battery to the car as though it has a dead battery. If it starts right up you may want to opt for a deep charge battery. I don't remember if we talked about this but the Ser III had an odd problem of the need for a deep charge battery. Even though it would spin the engine over fast there was not enough left over for the injection system at times. The only test was the jumper battery connection. A battery that stops working in a ser III Jag can operate well in other brand cars for sometimes years. I use to have a stock pile of series III Jag batteries from the local Jag dealership in Nsahville.
Howard
