donch@teklabs.UUCP (Don Chitwood) (03/28/84)
My wife's '74 2002 has a very strange stalling problem. SYMPTOMS: When driving at highway speeds, engine begins mild stuttering. The car begins to slow down, so more throttle is given to maintain speed. tuttering usually gets worse, necessitating more throttle, until the throttle is fuly open. Usually near full throttle, the power comes on full again, so when the throttle is backed off (because we just got up to 80 in a real hurry) it feels like the ignition has been shut off; flooring the throttle gives us full power again--usually. On one occasion, the car simply died. During all of this, engine temperature is dropping significantly. OBSERVATIONS AND CAR HISTORY: This problem has persisted for 3 years with random occurance. It happens in spite of a new 2-barrel Weber carb, a head rebuild, new spark plub wires and distributor caps, installation of an Alison breakerless ignition. The electronic tach never twitches as it would if the signal to the coil was flakey. It occurs on the level, uphill, downhill, high or low altitudes, usually during our rare and precious vacations, and almost always after an hour or more of continuous highway driving. Fuel filters have been changed, the carburetor float bowl has been examined for water or debris--none. Also, but not necessarily related, when riding around town the engine occasionally spits and bucks and the idle has spells of being erratic-- always in the direction of engine dying. Once when the car simply died at the end of a particularly bad stutter spell, I pulled the plugs. They were extremely black and sooty. Replacing with new plugs solved the problem. Around town type driving reveals normal plug appearance. THEORIES: I suspect a polution control device which diverts fuel pump pressurized gas to the carb when the engine is off. Also, it could conceivably be some electrical gremlin like the coil. I've had a few weird coil problems in the past. Mind you, I haven't teken this problem to a "qualified" service dealer or local guru. I like to solve my own problems for the challenge and the savings of bucks. This one has me buffaloed. Any thoughts greatly appreciated. Don Chitwood Tektronix, Inc. Imaging Research. teklabs!donch
rctracy@uokvax.UUCP (04/04/84)
#R:teklabs:-278700:uokvax:1100016:000:1954
uokvax!rctracy Apr 2 12:32:00 1984
/***** uokvax:net.auto / teklabs!donch / 7:25 am Mar 30, 1984 */
... It occurs on the level, uphill, downhill, high or low altitudes,
usually during our rare and precious vacations, and almost always
after an hour or more of continuous highway driving...
Any thoughts greatly appreciated.
Don Chitwood
Tektronix, Inc.
Imaging Research.
teklabs!donch
/* ---------- */
It sounds an awful lot like vapor lock to me. I wouldn't be surprised
if the problem gets worse during warm weather, although how well your
engine compartment retains heat might make the effects of ambient air
temperature negligible. I'll also hazard a guess that in-town driving
after a while on the highway is not a pleasant proposition... Heat
buildup due to lack of airflow at slower speeds compounds the problem.
Driving with the throttle WFO (i.e., fast :-) would tend to clear the
condition since the fuel would be flowing through the lines fast
enough to keep it from vaporizing. I have a station wagon that
exhibited the above behavior, and as long as I drove >= 90 mph, no
problem!
Three rememdies suggest themselves:
(1) Insulate the fuel system from potential sources of heat.
Granted, aluminum foil looks attrocious, but it has been known
to work.
(2) Increase under-hood ventilation (assuming the problem is heat
pick up from this area, and not from the road). I've seen
nicely fabricated air diverters installed which do a wonderful
job of cooling off carb fuel bowls, lines, etc.
(3) Install an electric fuel pump near the gas tank end of the
fuel line (so that the pump is pushing the fuel through the
fuel line instead of pulling it through). This will maintain
pressure on the fuel in the line, and help prevent vapor lock.
Hope this helps.
(Solution 3 was what I ended up using for the station wagon, with
completely satisfactory results.)
Bob Tracy
AT&T Technologies, Inc.
...!ctvax!uokvax!rctracydhk@hp-pcd.UUCP (04/08/84)
If it is vapor lock, try clipping some wooden clothes pins to your fuel line under the hood (providing that it is metal). They do a nice job of acting as a heat sink. Another suggestion is to try to reroute the fuel line away from exhaust manifolds and other sources of high heat. Dustin Kassman !hplabs!hp-pcd!dhk
jwb@mcnc.UUCP (Jack W. Buchanan Jr.) (04/12/84)
I recently had a very similar problem on a '78 280Z. The problem turned out to be a worn distributor bearing. If you can wiggle the distributor shaft more than just a little, it is worn out. A related, and perhaps more likely problem would be timing error with or without a problem with the advance. Jack Buchanan UNC-Chapel Hill