CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

1994 Buick LeSabre Problem making me chase my tail

ok, try this… real poser…ha ha ha… checked coil, emits spark to plugs and gets good pulse to injectors - acts like it wants to start, pulse and sparks 1 time when u turn key to crank engine and one time when u release key… unplugged crank and cam sensors and turn key to on position, check with scanner and it reports (without engine running) 20RPM (reboot scanner and does not change)… it sets no codes to check out either… also changed Ignition module (IGM)… what am I missing on this as it will not start and how’s that for a good one?..
HAVE TRIED
1.) Replaced IGM (used IGM, presumed good, b4 buying new one)…
2.) Checked for codes with scanner (no codes set)…
3.)Checked for spark to plugs and pulse to injectors (good, but only sends 1 spark and pulse when engine starter is engaged and disengaged respectivly)…
4.) Checked with scanner while Crank Sensor and Cam sensor are unplugged - strangest thing, registers 20RPM with key on and engine not running while sensors are unplugged…
5.) Checked and getting fuel to injectors…

Are you loosing contact with the actual key switch internals causing power to be lost during the actual cranking event? I’m talking about the switch not the key tumbler.
Or maybe it is an issue with the VATs system on that car. I know my 92 Lumina had a chip thing in the key and would wear. It would start better on one key over the other if you have a spare.

W30post - "maybe it is an issue with the VATs system on that car"

The key and switch was the last thing I was going to look over as it was the only thing I could think of that might cause the plug and injector thing, I just don’t understand about the RPM problem though…I have never seen an engine set RPM value with out the engine running and/or sensors unhooked… I am assuming that I am not loosing power as the engine cranks fine and everything works, just has the pulse and spark thing, wonder if the ICM or Coils are just intermittenly bad and that is why I can’t narrow it down…

What does the RPM on the scanner read with everything hooked up and the engine cranking?

will have to get back to u on that… don’t remember checking it after we found the RPM thing… ty for the input…

Have you checked the timing chain? When it fails the cam sensor often goes out.

Why’d you change the ignition module? After all, you have a good spark…
When you unplug the cam and crank sensors the input to the computer is floating. Those things are magnetic inputs so are fairly high impedant so it picks up all sorts of noise that it may interpret as signal. It basically acts as an antenna.
I don’t think it is an an indication of anything.

I’m with Rodknox: check the timing. Put a timing light on it and see if it skipped.

I’m pretty sure that a 94 has an actual distributor and the single spark when the key is turned on and off indicates that the ignition system is good. The next thing I would check is the wear on the distributor shaft bearing. Turn the engine until one of the vanes on the distributor shaft lines up with the line in the ignition module in the distributor. Use a feeler gauge to check the gap, it should be 0.010". With the feeler gauge in place, push the distributor shaft away from the ignition module. If the gap opens up, replace the distributor.

BTW, crank the engine with the distributor cap off and see if the rotor is turning. If it is not, you need a timing chain. Also turn the engine until the timing mark is at top dead center. A vane on the rotor should be just past the line on the ignition module.

ok asemaster, the RPM is changing when u crank the engine over but it won’t zero out when ignition is released, it just returns to 20RPM… it was running when it was parked even though it died in the street when brought home, it started long enough to b parked after cooling down, but now it simply won’t start… Rod Knox, keith, it has no distributor so that is out… RemcoW, will check the timing, but since it was running once would it give out after from just sitting?.. ty for the input all, am going to try a different scanner and see if maybe that is the cause of the 20RPM glitch… I just can’t afford to start replacing parts blindly and see what fixes it that way…

You may need to check continuity to the crank sensor. It almost seems like it is picking up noise. Check to see if that connection consists of a shielded cable of sorts. Maybe the shield is not there.

RemcoW, ok, ty will check it out… sounds like it is a good possibility…

Not saying that’s “it”, but it is worth a check. I’ve never seen any RPM with my reader with the car off.

PS. - W30post, have 2 other keys, checked using them and it is not the problem…

RemcoW, yeah, I was pretty astounded by the RPM glitch myself as I have never encountered it either… will check it today and get back with u on it…

If your scan tool shows 150rpm or so when you crank then the ecm is seeing input from the crank sensor. But this crank sensor sends out 2 signals so it still could be bad. If you had a jumped timing chain you would still have steady spark just at the wrong time. If I read your post correctly you have no spark when the engine is cranking, right?

did the magnet fall of the cam gear and is the harmonic damper in one piece there is a toner ring on its back side for the crank senser.

Check the timing chain…