1992 Ls400 Engine Missing

[Daniel24]

I am experiencing hard missing at highway speeds under acceleration. This is not occurring at city driving speeds at all.

The plugs, plug wires, fuel injectors and fuel filter have all been replaced as they needed to be anyway and seemed the logical place to start on this problem.

For the first time I experienced a backfire when starting the engine cold the other morning. Don't know if this is related either, but it hasn't occurred before or since.

I would very much appreciate suggestions about this from the forum members.

Thank you

[steve2006]

Been posted a few times and a search would reveal this, common problem is failing coil packs usually the one on the driver's side,also check the routing of the HT lead from this coil to the distributor if the grommit on the top cam belt cover isn't fitted correctly the lead can be damaged.

Another possible is the crank sensor on its way out,they become thermally sensitive.

[Daniel24]

Been posted a few times and a search would reveal this, common problem is failing coil packs usually the one on the driver's side,also check the routing of the HT lead from this coil to the distributor if the grommit on the top cam belt cover isn't fitted correctly the lead can be damaged.

Another possible is the crank sensor on its way out,they become thermally sensitive.

[Daniel24]

I should have tried a search, but I've only used this site few times and am not all that good with computers. I aplogize.

I do appreciate the coil suggestion and will look at the other issues you indicated as possibles.

Many thanks.

[fsuguy]

Daniel24,

I am also experiencing occasional missing - it is not my coils, since after replacing them both, the problem still persists. I find that while in park, if I rev the engine to about 1600 RPM and hold the pedal at that point, there is a miss about every 6-7 seconds for about 1 second; the RPMs drop and then climb back, drop and climb back - almost as if a switch is being thrown off and on. Also, after warm up, my idle is lower than specs -450 instead of 650. I still have to check the Vacuum Switching Valves to see if they are faulty. Would like to know what you find out from your efforts as well. Just hoping it is not the ECU!!

I have replaced the following, since this was part of my routine maintenance (all parts are genuine Lexus/Toyota parts):

1. TPS

2. FP resistor

3. Rotors, Caps, Wires, Coils

4. Spark plugs

5. Thermostat

6. Water pump

7. Timing belt

I still need to change the fuel filter and ECU Water temperature sensor. Also think that the FP may be on the decline.

Thanks In advance.

[jtbel]

While trying to fix a cam sensor problem on my car, in which one of the symptoms was a miss on the highway, I cleaned the crankshaft sensor. I was changing the timing belt at the time, so I don't know exactly what was making the cam sensor code come back even after I had changed it, but my crank sensor was caked with about an 1/8th inch of gunk. It may not make a difference, but it is fairly easy to get to, from the bottom front of the car.

[fsuguy]

jtbel,

Thanks for the tip. Will try that and let all know what happens.