3.3L. Intermittent, brief stall

I have a 1993 Voyager with a 3.3L engine. 102,000 miles.

Sometimes on acceleration, it will stall very briefly, and then
continue acceleration. One shop suggested an intermittent coil pack. I
pulled the codes with the key on / key off procedure. Nothing other
than "55" is reported.

I am going to take it in for more extensive diagnostics. Could a bad
crank or cam sensor cause something like this? It seems more like an
ignition problem as opposed to fuel delivery.

Thanks,

KM

 

From the description of a slight bogging during acceleration, I would
suspect either a fuel delivery problem (clogged fuel filter or fuel pump
starting to fail) or more likely, bad ignition wires or plugs. Ignition
wires seem to fail fairly frequently on the 3.3L engine and you do not
indicate how old they are so I'd start there if they are over 5 years/50K
miles old. Does the engine also backfire at all when you accelerate after
this occurs?

I would doubt it is a sensor since no code was set. Good luck

Bob

 

Check the fuel pressure as recommended, but another problem that can
cause a hiccup during acceleration is a bad throttle position sensor,
and it won't ALWAYS set a code. Cam or crank sensors, at least in my
experience, tend to either cause a complete shut-down or a longer
duration cut-out. And the cam sensor will definitely set a code, not
always the crank sensor though.

 

Thanks for all the help. The plug wires, and fuel system components
are all original from it's Sep 1992 assembly. The TPS was replaced two
years ago to correct a surging problem at idle. The fuel filter was
replaced then too. Looks like a lot of things to check.

It does not backfire during acceleration.

-KM

 

One last and simple thing you might wish to check are the battery
connections. Check to be sure they are clean and tight and that the clamps
are in good condition.

Thanks for all the help. The plug wires, and fuel system components
are all original from it's Sep 1992 assembly. The TPS was replaced two
years ago to correct a surging problem at idle. The fuel filter was
replaced then too. Looks like a lot of things to check.

It does not backfire during acceleration.

-KM

 

hook up a fuel pressure gauge to it and drive it and watch the fuel
pressure then you will know for sure

 

When were the plugs last changed/checked?

I would pull one of the front plugs and check it with a plug gap
tool. If the plug gap is significantly off then replace ALL plugs.
A larger plug gap can throw off ignition timing.

Ted

 

I don't understand that. Can you explain?

 

Larger gap means the firing voltage must be higher before the
spark happens - when the mag field is collapsing in the coil
as the field collapses the voltage is rising in proportion - it
isn't an instantaneous thing - it takes slightly longer to reach
trigger voltage.

I've observed with a timing light on my MC engine (which
has electronic ignition, but manually adjusted timing) the
timing marks changing position after simply re-gapping the
plugs. Now, maybe a modern engine computer can compensate
for this....

Ted

 

I would have thought the rise time of the coil output would be extremely
fast, and therefore the delta T extremely small, relative to the motion
of the engine - but that was an assumption on my part.

Let's do some Googling and some math: I found that it is accepted that
coil output rise time is typically 50 to 100 microseconds. At 6000 rpm,
the crank rotates a full revolution every 10 milliseconds. That's a
degree of crank rotation every 28 useconds, or a degree of distributor
rotation every 46 useconds. Lets say a gap change could give a delta T
of 1/10 of total rise time, so we're talking less than a degree of
distributor timing change, about a degree of crank timing change. To be
honest, I don't know if what we traditionally talk about as degrees
relative to TDC is crank or distributor rotation - probably crank, but
thats a guess.

Anyway - so - there is some measurable effect (assuming my assumptions,
like 1/10 of total rise time delta T, and that I didn't make any
mistakes in my calculations) on the order of a degree or so. The better
the ignition (faster rise time), the less that effect. And - yes - I
think you're right, a modern engine would definitely compensate for that
since it controls timing based on the effects of ignition (like knock).
If that's the case, then it's a moot point.

Would the hotter spark resulting from the wider gap (higher firing
voltage) offset that with faster pressure build? All the ad copy for
the rip-off devices on the internet would lead you to believe that. Not
sure if it's true or not (I want to say not, but that's an uneducated
guess).

Related to the OP's original problem and your comment about plug gap:
Excessively high plug gap puts undue stress on the coil insulation and
can cause coil failure (insulation punch thru and/or carbon tracking)
for the reason you cited: higher voltage before the spark gets
initiated. That's why you don't fire a coil without its output either
being grounded or going thru an appropriate spark gap.

 

Ah, that also depends on HOW it's compensating.

It's been my observation that plug gap doesen't wear equally in the
engine - after wear, in some cylinders the plug gap is larger than others.
If the compensation is of an average of the change...

Ted

 

Then that would simply be an argument for changing the plugs before
significant wear (which would create those differences) occurs and
accurately gapping them initially.