QuestionQUESTION: My TR6 has a misfire condition at higher speeds under load. I've checked the usual tune-up items (dwell angle, timing, advance/retard, valve clearance, etc), but after driving for a few minutes at a constant speed it feels as though the engine cuts out. In an effort to make it to a safe place to pull off the road, I keep the pedal down. I can hear an intermittent backfire, and for brief moments the engine will put out power again, allowing me to keep it at about 30-40 MPH. Downshifting or stopping the car allows normal running for a short time (maybe a few seconds if downshifting and a minute or two if stopping). I substituted a vacuum gauge for the air hose leading from the manifold to the carbon canister. Vacuum at this point reads about 14 (not sure what the units are or if my gauge is any good) and stays steady. Compression (only had time to check when cold) is higher in 1 and 6 than in the center 4 cylinders by about 15%. The problem was occurring only at highway speeds, but now has presented at 40-45 MPH as well--especially following or during harder acceleration.
ANSWER: Hi Matt,
Install a "T" in the fuel line between the pump and the carburetors and a fuel pressure gauge. (many vacuum gauges have a section for fuel pressure.)
Run a long hose out from under the hood and place the gauge under a wiper arm so that you can read the fuel pressure while driving. (be sure to put hose clamps at every connection)
You MUST be able to read the gauge while the car is in it's failed mode.
A partially stopped up exhaust system can also give you the symptoms you have. However, you have ruled that out because of the 14 in you have read when it was dying in it's failed mode.
Howard
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QUESTION: Howard,
The problem with the TR6 has been worsening to the point where I can now replicate it at lower speeds under load or while the car is stationary by simply reving to 3000 RPM and holding it there after the vehicle has already started acting up. Fortunately, this makes it easier to test! I installed the T-junction in the fuel line again. When I started the vehicle, it ran, showing about 1.5psi of fuel pressure as before. I held the gas until it started acting up. In the process, I noted the fuel pressure dropping slowly to 0, still running smoothly, and then a minute or so later it lost power again. I pulled the gauge from the line (engine now idling) to verify the 0-pressure reading, and no fuel came out of the line, even with the engine running. You recommended against purchasing parts before pinpointing the problem, so I held off from going to Moss Motors, but I did swap out the fuel filter (I had one lying around anyway) which had no effect. What's next?
AnswerRemove the line from the pump that comes from the tank and lower it to a can and drain some fuel (at least two quarts) to confirm that the fuel is freely flowing from the tank and if it flows good put a new pump on the car.
Be sure you get the correct pump as some suppliers get it mixed up. Long arm pump when a spacer block is used on the pump mounting and short arm pump when no spacer block is used.
When installing the pump be sure not to let the arm slip off to one side of it's cam when bolting it up, Keep it straight.
Retest the fuel pressure after installation.
Howard
