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blessed

91 Ls With No Spark

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Hey guys,

Happy New Year! I'm celebrating by watching a little football and trying to figure out why my 91 LS refuses to start.

Initially thought it was the fuel pump, but replaced that yesterday and still not starting. Check to see if fuel is getting to the motor and yes it is. Then I pulled the High Tension Cord from one of the distributors and held it about an inch away from the valve cover and cranked it over. NO SPARK! (I think this is the best way to check for spark) So, now what? I'm at a loss as to why I don't have spark.

Previously (see my previous posts), the car would run well, but after I turned it off from a 30 min. or so drive it would not start (just cranked over strong) until about 30 minutes later then it started fine. Additionally, when I would be driving and punch it hard to pass a car on the highway it would die in the middle of the highway (I just coasted to the side of the road). This happened about 3 times. So I thought it was a fuel issue.

So, any suggestions as to why I'm not getting any spark?

Thanks for your advice in advance!

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check your coils?

check your cable?

check your spark plugs?

are you not getting a spark from both coils?

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Thanks....I just pulled one plug from each side and... no spark. I pulled the High Tension Cord from each distributor and no spark. Not sure how to check the cables other than just making sure that they're well seated.

Can both coils go bad at the same time? That would seem strange.

?

check your coils?

check your cable?

check your spark plugs?

are you not getting a spark from both coils?

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also check rotors and rotor caps, they might have carbon deposits on them which would decrease the strenght of the spark.

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Hey Blessed –

Re: your coils. While it is indeed incredibly unlikely that BOTH coils are shot, one failed one would prevent the car from starting. If you wanted to check them both, you’ll want to minimally check for spark from a wire from each coil.

Not sure if you have an OEM shop manual or not (worth every penny despite the cost, btw, I got my set on eBay (surprise, surprise). Once you have this, you’ll NEVER use a Chilton’s manual again), but dcfish had previously posted a pic of the cord layout at http://us.lexusownersclub.com/forums/index...ost&id=8189. If you’ve messed with the wires at all in your troubleshooting thus far, I’d make CERTAIN that the layout precisely matches this image.

As far as HOW to check for spark, the most foolproof way would be to disconnect a spark plug wire from the spark plug (being sure to hold the boot and NOT the wire to separate the two), remove said spark plug, re-insert the now loose plug into the wire that it came from and watch for a spark as someone else turns the key. You are looking for a white or blue spark (not sure on the LS, the color is indicative of the electrical output of the coil and really is the phenomena of ‘color temperature’) with a good loud ‘snapping’ noise to it. Reddish, yellowish, or orange spark is weak and indicative of a problem with wires or, more likely, a coil. So long as the plug is out, I’d go ahead and make sure it is clean and dry and the gap is set correctly at 0.044”. If the plug is fouled, that in and of itself could be the trouble (long shot, I admit) and likely a sign to check the others.

Another way to check for spark would be shove a metal rod (I’ve used completely metal screwdrivers [no plastic handle] and even the occasional screw) into the plug holder on the wire and hold the ‘rod’ so that it is almost touching a valve cover to watch for spark (the spark should be able to jump about 3/16” to maybe 1/4”). I’m not sure just HOW much juice it would take for a spark to cross the 1” divide that you mentioned, but it would reasonably be way more than our little coils produce.

Word of caution: if your plug wire is shorting out, it could mean that you get zapped at this step. To avoid this, either just set the plug and wire down on the valve cover or something while it is being cranked (if you use the first idea for checking) or wear/use something to insulate you from the wire as you hold it (special insulated gloves or even a rubber can opener from the kitchen [just be sure to clean it up later to keep the missus happy ;) ]. Having been zapped before on prior cars (so THAT’S what’s wrong with me…), I can tell you it is not a fun experience. Remember that your coil is developing somewhere around 55,000 volts to bridge that gap (can you say ow?).

Checking the wires involves a physical inspection looking for cracks, etc. along the insulation, but most importantly involves using an ohm meter to check for resistance. I don’t have my shop manual handy at present, but perhaps someone else could chime in with what the resistance specification is. A nice write-up can be found at http://www.inct.net/~autotips/plugwire.htm.

Regardless, when you put everything back together, don’t forget to squeeze some dielectic grease back into the wire holder part of the wire to protect against water and corrosion of the electrical contacts.

As for the cap and wire carbon comment, this is pretty easy to check – just pop the rotor off (I’ve never done this on my LS, but on other cars it has been held on with a screw or clip of some kind) and take a peek in there. If you want, you can use a Dremel or other moto-tool of your choosing with a wire brush attachment and clean up the contacts on the cap and the contact on the rotor in lieu of simply replacing it for now. Really fine (220 grit or more) sandpaper could also work, but would just take longer. Of course replacement is ALWAYS better, but if money were no object we’d all be driving ’08 models, eh? :)

Of course, re-seating all of the wires (one at a time, mind you) at the coils is always a good idea, too. Again, be sure to use dielectric grease on the re-connect.

Good luck!

Ed

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What about a crank sensor going bad? I had one going bad the car would not start but would crank normally. Also inpect cables in areas close to the the said sensor and in the engine in general.

CPR

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Hey guys,

Happy New Year! I'm celebrating by watching a little football and trying to figure out why my 91 LS refuses to start.

I'll apologize in advance if this seems incredibly sophomoric, but bear with me.........

Your LS turns over, but it doesn't start. You've checked each spark plug wire, each coil wire, but no spark anywhere (?.....).

If memory serves me correct.........a '91 LS is a "non-interference" engine. The (distributor) rotors are attached to the timing belt pulleys on the front end of each of two camshafts. Have you removed the timing belt cover to see if your timing belt is intact? If it's broken, your distributor rotors won't turn.........no sparky sparky. You wouldn't necessarily know it's broken because the engine is non-interference; you wouldn't hear any nasty "smash/bang" when/if it broke.

Pull the timing belt cover around one of the distributors and have someone turn it over while you watch.

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