The Problem

Michael Frank was experiencing rough running on his E-type. Basically, the car started running rough gradually and got to the point that he couldn't make it back up the hill although the car would seem to idle fine. He posted a message to this list and here are some of the suggestions that were offered as well as his final solution to the problem.

Tonight I will begin by checking the electrical system again by the numbers, just to be sure. First, a new set of plugs. Next, I will dress the points. I will inspect all the wiring. I will also try new plug wires. I expect this will not be fruitful, so it's on to the fuel system. First thing I will do is temporarily disconnect the suppression condensor from the fuel pump. If this doesn't't do it, I will drain the tank and check the pickup (this will be the second time, but who knows?). Next, I will replace the fuel filter. If all this fails, it HAS to be the carbs, and they will have to wait until I get new gaskets.

I'll share one interesting thing I have discovered. I wanted to see if there was a high-resistance short to ground in the coil primary. So I blocked the points open and attached an ohmmeter to the positive side of the coil (let's not get into a discussion of coil polarity). When the ignition switch was 'on', the reading was infinity, ie, no short :-). What was odd is that with the key in the 'off' position, the meter read 3.5 ohms, ie, the coil was now shorted to ground. Not sure if this is to prevent theft, or an indication of a problem (ie, it's not a bug, its a feature)- any thoughts?

I have some great clues, thanks to all of you! Here were some of the responses, and my evaluation:

The Diagnosis

• Maybe you have a loose wire on the fuel pump but you checked the fuel pump!!
  

  I have been concentrating on the ignition, fuel system is next

• Maybe your distributor "hold down bolt" is loose and the distributor is moving slightly
  

  I had this problem a while ago. Found and fixed. It tended to cause erratic performance, and backfiring, since the timing would change on its own.

• Ballast resistor connection is bad.
  

  Ballast resistors were introduced on 1970 Jaguars. Otherwise, this would have been my guess too.

• Check the wire from the points real carefully.
  

  This wire has been repaired by PO. To be sure it was ok, I disconnected and jumpered around it.

• Distributor cap on securely?
  

  I have a Mallory distributor. The cap is so tight, it can hardly be removed or installed. They are prone to cracks, but I have checked it thoroughly

• Can you drive around your driveway with a timing light snaked out into the cockpit? This'll tell you if the spark is gone.
  

  One better: I used a Colortune. Looks to me like the spark is intermittent, but you would be surprised how hard it is to be sure. It seems that the cylinder goes 'black' just before the engine cuts out...no spark, no fire. But this happens just as the engine is dying, so it is not obvious whether I am seeing cause or effect. Wish I could film it in slo-mo.

• Maybe a collapsed muffler?
  

  This was a great suggestion. As it happens, I crushed one muffler on a speed bump a couple of weeks ago. I don't think this is the problem, since I seem to have good exhaust pressure at both pipes. I have a spare muffler which I will install if nothing else works.

• Check filters, etc If they're clogged, it might give you the OK no load, lousy under load symptom.
  

  Air filter and fuel filter are brand new. I will change the fuel tomorrow, on the chance that something is blocking the flow.

• Is air getting into the fuel tank properly? If there is no air vent, you may be fuel starving.
  

  This is a pre-charcoal cannister car. Tank is vented thrum the cap, not a lot to go wrong. I will check the cap to be sure.

• Check the floats and needle valves.
  

  I will order up some new gaskets and check the carbs.

• The problem may not have been around long enough to cause the spark plugs to go south.
  

  They are now south. As the problem has gets worse, there is plenty of carbon fouling going on. Looks more and more like a fuel problem.

• I had a car with a capacitor across the fuel pump points, to reduce electrical noise in the radio. Had an intermittent in the capacitor,
  

  I will check this capacitor tomorrow. I suspect that it is original to the car. Good tip.

• Grosse-Jet captive-ball float valve replacements solve this once and for all!
  

  Been there, done it.

• One of the floats had a pinhole leak.
  

  Fuel system comes next.

• Check fuel flow rate, not static pressure.
  

  While I was checking pressure, one of the temporary fittings 'popped'. I had 1/4 tank of gas on the driveway before I knew it. Still could be something intermittent, tho.

• Fuel inlet might be clogged.
  I think I have had all possible problems with this car, at one time or another. I drained the sump last month and found a blob of solder caught in the intake. I think I'm clean now, but the original intake screen is still unaccounted for.

• I would suggest changing the condensor.
  

  Done this summer.

• Did you check the gas and fill'er up with good high octane? Use a bottle of STP octane booster?
  

  Not an octane issue, this I am sure of.

• Try checking the flimsy wire internal to the distributor that runs from the white/black wire connector to the points.
  

  As I mentioned, I have a Mallory dual point. This has two flimsy brown wires that connect to the points. These will be inspected tonight.

• The needle at the base of the carb's piston had come loose. It was a matter of removing the top of the carb, realigning the needle and then tightening the screw.
  

  Hmmmmmm. Don't need gaskets to check this, either. I will look into it tonight.

• I seem to recall a while back someone describing a similar problem. It turned out to be gunk in the fuel sump in the tank. The sump unscrews from the bottom of the tank.
  

  Yup. That was me...first time I had a problem like this, it was a blob of solder stuck in the intake pipe. The difference is that this time the problem is progressively growing worse, last time, it was binary: either I had the problem, or it was fine. The solder had a shape which allowed it to intermittently block the pipe.

• Did you get some water with your last fill of gas?
  

  Just a can of Diet Coke....sorry, couldn't resist. The sump is coming off again tonight. We shall see.

• Check the little wire that goes from the distributor splash cover (under the distributor cap) and the points mounting bracket. It seems that you are getting cut-out when under load, ie higher vacuum, so the points mount will have moved.
  

  Will check this tonight....Mallory dual point = twice the probability that this will happen...and let's not start up the debate about vacuum advance again!

The Solution

Group..

I should have done this first. I know I should have, but didn't.

I put in a new set of plugs tonight, cranked the engine and.....nothing.

Bypassing a bunch of steps, I replaced the fuel filter. I turned the key without cranking, and listened to the click, click, click of the fuel pump, until it stopped. I then looked at the fuel bowl, it was full of .... air. This is actually OK, as it indicates that the fuel system has integrity, and there are no leaks. Those Grose Jets are working well. I then cranked and watched as the fuel bowl quickly filled up. This told me that the fuel system was basically OK.

Then I tried an old trick. No timing light. No Colortune. Just a spare spark plug. I plugged this into a cable, and set it down on a suitable surface. I then turned out the lights in the garage, and cranked the engine. It is amazing how clear the problem became at this point. The spark was very weak, and frequently non-existent. Bingo! Back to the distributor. I removed the points, dressed them down, washed them in alcohol.

Bill Lyon's Sixth Symphony! :-).

I think that the Mallory distributor has caught a virus from all of the Lucas components which surround it. Any thoughts on electronic conversion?

Thanks again to everyone who responded!

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