The engine is old but fine.
Timing chain is okay, the sensor on the air intake(forget the name)
is fine as well. Diagnostic codes - the computer spit nothing back.
Service engine light went on - and the computer generated no codes,
just a cyrptic "do not drive" with no explination. All measurements
were normal. (yes - the tester was properly configured)
It appears to be a normal engine.
BUT - it won't start.
Well - I should say it's *almost* impossible to start. One in every 30 or
40 tries, it starts and runs a bit rough but fine. Obviously that rules
out anything mechanical - as it does start and run.(ie - timing chain is still
attached and the crankshaft sensor is working - otherwise no starting at all)
I talked to my friend - and he said it sounded like the distributor
was shot - that the gear on its shaft had sheared off its retaining pin
and was randomly flopping around. He said it happened to him and his
father three times over the years - car fine - then random timing and
The tech at the shop verified that the engine's timing is all over
the place - completely random - so this made sense. Some electrical
or distributor related gremlin.
Except - this engine - has no normal distributor. ???
Leave it to Buick to try to reinvent the wheel.
I see three little modules and wonder - are those three things on
top of the engine the distributors or are they only half of
the equation. Where do they get the information from as far as
firing order and timing? In a normal distributor - that I understand.
There's a mechanical connection to the engine. This thing - I see
nothing - just control wires and a mounting plate.
With this - where should I start? How robust are those modules?
If I swap them from a running car - do I run the risk of frying
some electronics inside them(my sister has a 1988 Park Avenue with
the same engine. She'd be a MITE upset if her car didn't run)
Those three squares you see with the spark plug wires connected to them
are the Coil Pack. Each one I believe controls two cylinders.
1991 Pontiac Bonneville LE
Underneath the coil packs is the ignition module. The ignition module
receives data from the ecm computer, which takes the data from the
crankshaft position sensor, coolent temp sensor, maf, o2, etc, and modulates
the timing to the coil packs. Each pack controls 2 cylinders. You can test
these with a ohmmeter once they are off the car, if I remember right. (Maybe
someone can jump in here, I don't remember the values you need) They are as
common as hell on 3800 engines, and on alot of 2.8 litre GM engines too...
If it were my car, I'd start by swapping the crankshaft position sensor out,
I've seen these fail in really weird ways.... Or kinda "half work", or work
sometimes, or work on a cold engine then die, etc etc etc etc.... It's a
cheap part, and not THAT bad to install, if you are patient.
I don't have a shop manual - where is the position sensor located?
My guess is that it snapped off the center shaft and is rotating
when it feels like it - kind of like how many odometers break)
Underneath the coil packs is a plastic tray type assembly. No computer
that I can tell - perhaps it's just moved a distance next to the other
computers? OTOH, it was generating no codes. Electronics seems fine,
is it's definately some mechanical aspect of a sensor - where the two
Is it safe to swap the coil packs with a working set - or is there
a chance that something might mess up?
The way the crankshaft position sensor works is not mechanical, it's
magnetic. It uses a hall effect sensor, which measures the depressions which
are manufactured into the crankshaft. Look underneath the car, center, right
behind the oil pan for a guess (I can't recall excatly, but it's one of the
few things that is screwed into the block with a wiring harness attached.)
Thanks. Um - question - if the magnets are all buggered up that's pretty
obvious - how common is it to have the crankshaft worn down? Is the sensor
something that I can remove and leave off for a while until I get a replacement
or do I have to get the part first?
Also - my sister is very wary of swapping her coil packs with mine - is
it possible that my engine could damage them?
My bet is the sensor and one of the coil packs is shot or nearly so.
Oh - what do the packs and the sensor generally cost?
I had a similar problem on a 1986 Delta 88 with the 3.8L engine. The
crank position sensor is on the front of the engine next to the harmonic
balancer. There is a ring on the balancer that run between the crank
position sensor (CPS). Sometimes the harmonic balancer loosens up and
starts wearing down the CPS or even breaking it. Also, the harmonic
balancer could be falling apart (the rubber inside) causing it to rub on
the CPS. It is a fairly cheap part, and all you need is a business card
and/or a matchbook to set the gap correctly.
On the coil packs, there are two different types. The Delco version is
three individual coils with two plug wires attached. You can measure
the resistance between the posts on these coils. They should be between
5K and 6K ohms. The other type of coil pack is the Magnavox, and it is
one piece that looks like there are three blocks. The resistance for
this type of coil pack should be between 11K and 13K ohms. But, just
because the resistance is good, it is still possible that the coil pack
is bad (they tend to open up when they get hot).
The cost of an AC Delco Coil Pack for my car in September 2000 , listed
for $121.38 My cost was $91.77 including tax. I have a friend that works
at a Chevy parts department so I get parts for his cost.
The Camshaft Sensor lists for $33.33 at the dealer.
I still have the original Crankshaft Sensor so I'm don't know its cost.
1991 Pontiac Bonneville LE
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