Need Help W/random Engine Stalling!

[AustinGT]

I have a '92 LS400 with 208,000 miles, and it has been well maintained, but last Wed. the starter cranked the engine but the engine did not fire. I had it towed (it was sad to see my blue baby on the flatbed :cries: ) to my shop, but they can't find out what is wrong- I am thinking something like a coil or distributor could be the culprit, but I am not sure where to start. The car will run fine for a while, then randomly quit and refuse to start up again. This forum has been extremely informative, so I figured this would be a good place to check!

p.s.- fyi, in the past year, the Lexus dealer has performed the "60k service w/timing belt", plus the shop put in new front struts, rear axle boots, rear tranny mount, steering gearbox,alternator, front pads and rotors, and new fan belt tensioner- so it has been well taken care of (plus Mobil one changes every 3k and always 91 octane!)

[SKperformance]

A single coil or injector would not cause the engine not to start just idle and run badly.

A broken t-belt or an old aftermarket alarm that is acting up.

Do you hear your fuel pump make any noise when you turn the key?

[AustinGT]

The timing belt should be fine, as the local Lexus dealer replaced it about a year ago, and it does not have an aftermarket alarm. The problem is very random- the mechanic started and drove the car many times (although it did die on them once after driving it for a few min.), and it would run fine- but when I went to pick it up, I started it (it fired right up) but when I put it into reverse it died. I was still able to turn over the engine, but it would not start. I hear no noise from the fuel pump, I hope that is a good thing! I am hoping there is someone else who has had this problem..........

[SKperformance]

If it runs fine at times it is not the belt.

If you can start it can you rev the engine rpms at all?

Does it only stall when in gear?

Check the intake tube for a rip after the maf.

Also clean the maf.

[AustinGT]

Thanks for getting back to me so soon- as far as I know, the car will stall when put into reverse or when in drive- and whenever it does stall, it won't start up for a while. The intake tube looks fine, as it was replaced along with the timing belt, plugs, etc. Hmmm, the maf- could that be the problem maybe??? That is easy to check- again, because it is so random it is hard to pinpoint it. Other than this issue, the car runs fine, plenty of power and smooth takeoffs (although it will be time for new O2 sensors soon)

[AustinGT]

I was talking to someone who is more knowledgable than myself on these cars, and they suggested a crankshaft sensor or a "coil pack"- does this sound possible to anyone? They said that the sensors wear out, and that the "coil pack" is mounted way in the engine, so the heat could gradually wear it down- could either of these things cause the stalling I mentioned earlier?

[LScott400]

As SK pointed out above, a coil problem should exhibit some rough running because there are 2 coils. Highly unlikely both fail at the same time intermittently. I would think a missing crankshaft signal would trigger a code. Also, when SK asked about fuel pump noise when the key is switched on that is because you should hear the pump pressurize. So no noise immediately upon turning key to on position prior to starting during an event of "cranking, but no starting" would indicate a fuel pump/fuel pump circuit problem. And did you clean the MAF?

You may want to consider looking for a shop with both Lexus experience and the patience to track the problem down.

Best wishes.

[AustinGT]

When the key is turned to the on position there is a very faint whirring noise that lasts just a second or two- this could be the fuel pump noise SK was talking about. The car has been at the mechanics for the last 5 days (and they are familiar with Lexus)- so I can't say that I have heard the noise recently, but that will be the first thing I listen for when I check on it tomorrow morning. And there have been no lights in the dashboard, so it sounds like the crankshaft sensor wouldn't be the culprit. These electrical problems are a pain in the butt! (and I haven't been able to check the MAF yet, but again, tomorrow morning.....) Thanks for the info- this has been very helpful in eliminating possibilities, and I will keep you guys posted.

[SKperformance]

The crank sensor is easy to diagnois as it either shows or not on a good scan tool.

Is there any smoke when it starts at all?

[AustinGT]

There is no smoke upon startup, and there are no dashboard trouble lights, so it is sounding like the crankshaft sensor might not be a problem. About the fuel pump...... on most other cars, when the fuel pump fails it just quits and strands you. Is the fuel pump in the LS different in that it will slowly start to quit rather than completely failing?

p.s. my apologies for being so uninformed about this... my dad and I have restored some old cars, but they are big American iron from the 60's- far less sophisticated designs than the LS400. And, my mom's ES300 just goes in for oil and filter changes, so this problem is covering new ground for me!