I am bringing my car back from being a little used garage queen, and have a problem I can't seem to solve. The car starts fine and runs well, but with a frequent misfire(a miss every few seconds). It will go for 10+ miles, running well at speed, but it starts to misfire increasingly at low speeds. Eventually it will get to the point where it dies when pulling away from a stop, normally leaving me in the middle of an intersection with oncoming traffic. After a few seconds (to a few minutes) I can get it started, but it runs rough until it is stopped and cools down. The mystifying thing is my Austin Healey 3000 does the same thing, it just takes a shorter distance to start happening. I have a Pertronix ignition, new coil, plugs, wires, cap & rotor, clean carbs, 3# fuel pressure cold dropping to 2# pressure when the engine is running its worst. All I can figure is the ethylene in the gas is causing problems. Any ideas? Any Jag experts near Rochester, NY?? Thanks.

Submitted by lincmgmt@hotmail.com on Mon, 08/09/2010 - 15:02

Brian - you helped solve the puzzle. Both cars showed lack of spark when hot, especially when accelerating. I checked for continuity of power to the coil, and it was stable. An MSD coil (high performance) from another car cured the Jag. It now runs better than ever, starts faster, and runs well even when quite hot. I can't quite understand why accelerating would have made the missing worse, but is sure did. That's why I was focusing on the fuel before.

A new coil didn't work on the Healey - it ran a couple miles and conked out completely. The mystery continues! Just back from being towed.

Best Regards,
George

Submitted by DavidBarnes71@… on Wed, 08/04/2010 - 20:48

Some times on hot days after running for awhile my '68's fuel pump will start making noise like it is cavatating or trying to vapor lock and having trouble to pull fuel out of the tank. After it cools down all is fine. I have not positively nailed down the cause or solution to my problem but maybe your fuel pump is acting up when it gets hot ?? I have spliced an after-market soild state pump pump into the plastic lines and located it down below the stock unit at the same level of the tank so it is not having to draw fuel higher than the tank level. So far have had no more trouble but have not driven it too much since I did this.

David Barnes
'68 FHC

Submitted by bblackwell@jcna.com on Wed, 08/04/2010 - 18:51

When I first started reading your note, I thought plug wires, but you indicated you replaced the coil, wires, plugs, etc. 'Bad gas' is a red herring most of the time, and it is something else. What I usually do to isolate spark or fuel is do a test drive and do two things:

1. when it starts running rough, momentarily pull out the choke lever, if it runs better, look to fuel or fuel system. if you are running totally out of fuel due to no fuel pressure that won't help the engine, so this is not a conclusive test. 2 psi sounds kind of low even for twin Strombergs, but don't go putting a 12 psi pump on it or anything. My father did that on a Sprite in 1975 and 'crowned the jets' in the carbs with fuel leaking everywhere.

2. if you have a timing light that runs off 12V, connect it and run the lead out the bonnet louver or run it out under the trailing edge of the bonnet into the dashboard. Ensure the wire does not hit the exhaust manifold or heatshield. Put it on any spark plug, probably no. 1 (aft most). As you drive to a point where you expect it to misbehave, pull the trigger on the timing light and see if you get steady flashing, varying only with engine RPM. it should start to miss flashes just before the engine falters if it is spark.

Once you know the culprit, you can probably figure it out.

Submitted by howardbollinge… on Wed, 08/04/2010 - 17:59

George,

Have you looked at the fuel filter for water? Do you buy gas for both cars at the same place? If you do and the fact that both cars are doing the same thing might tell you something. Do they backfire in addition to the missing?

I had issues with water in the tank and the more agitated things got as I drove, missing occurred more regularly. Wasn't heat, it was agitation. Your "cooling down " period may also be a "settling" period.

I had the last episode going to the NC. mountains for CJC Concours last year. Starting up the mountains, the steeper it got the more it would miss until it would just stop. Put it in reverse, let it roll back, let the clutch out and the jerking motion would allow the fuel pickup in the tank to gather in enough gas to go about 4 more hairpin turns. Die again. Seven or eight times before I made it up sputteringly and parked the car. This was on a Thursday night before the show on Saturday, had to scramble.

Friday morning car wouldn't start at all. Opinions offered were: Fuel pump, Coil, Plugs. Tried them all day Friday, no luck.

Finally check fuel filter. Water in the bottom. No possible way to drain the tank. So,pull off carb feed hose at carbs to drain carbs, with it off, let electric fuel pump push out a couple of hotel ice buckets of gas from tank. Dispose of safely. Clean out fuel filter bowl. Roll car down to flat spot. Go get and put in DriGas. Mash accelerator to the floor, crank it, crank it, some more and finally ignition! When car had been parked with front end up hill, the fuel pickup in the back of the tank was down in the water. That's why it would stop running coming up the mountain. Took a while to dry up the gas but I drove home 350 miles with no further issues.