1. Home
  2. General Motors Forum
  3. 1987 LeSabre - random timing gremlins - intermittent starting.

1987 LeSabre - random timing gremlins - intermittent starting.

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 no starting.

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)

Ideas?

Reply to
Joseph Oberlander
Loading thread data ...

Which engine?

---Bob Gross---

Reply to
Robertwgross

3800 series. I figured the three modules on top was pretty unique.
Reply to
Joseph Oberlander

Those three squares you see with the spark plug wires connected to them are the Coil Pack. Each one I believe controls two cylinders.

========= Harryface =========

1991 Pontiac Bonneville LE ~_~_~270,000 miles_~_~_
Reply to
Harry Face

Crankshaft posistion sensor? My dad's 95 LeSabre did the same sort of thing, as did my Celebrity, and it was the crankshaft posistion sensor or whatever it's called each time...

-Sam

Reply to
Sam Tosi (lovin' yo momma)

So - what tells them when to fire? Also - if I swap ones from my sister's car - am I going to fry anything?

Reply to
Joseph Oberlander

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.

Reply to
Tony

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 interface.

Is it safe to swap the coil packs with a working set - or is there a chance that something might mess up?

Reply to
Joseph Oberlander

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.)

Reply to
Tony

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?

Reply to
Joseph Oberlander

Joseph,

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).

Good luck, Bill

Reply to
William F. Yehle II

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.

========= Harryface =========

1991 Pontiac Bonneville LE ~_~_~270,000 miles_~_~_
Reply to
Harry Face

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.