Occasional Starting issue

[SHOmaniac1975]

I have a 92 MTX, all maintenance is up to date. Occasionally I will go to start the car and it will crank but not start. Sometimes if I push down on the gas while cranking it will start. Every once in a blue moon(like when I had it up on a lift checking the tranny fluid) it would not start even when pushing on the gas pedal. I checked spark and thats good. brand new +4 plugs and new wires. I checked fuel and its getting plenty ( it has new fuel pump, sender, and filter) yet the problem is still there. The TPS and CPS are new. I bought a spare DIS module, but I havent installed it yet because I dont think thats the problem. No codes in the computer. I was thinking it might be the computer starting to go (car has 148,000 miles) or maybe the air by pass valve? Anyone have any ideas?

 

[NiNeTy Fo SHO]

This guy has the same kind of problem...

http://www.shoforum.com/showthread.php?t=33331

I would say, like to him, check the IAB (idle air bypass) and try to clean it to see if it helps...seeing as how you seem to have good fuel pressure and good spark, air is hte only thing left...taking for granted all your new parts are working properly..

 

[SHOtimer]

Also, you didn't mention in your replaced parts the CID (Camshaft positioing sensor). This sensor can cause symptoms as you are describing and when it begins to fail can be very sporatic. It is a rather cheap part and sounds like what may be ailing your SHO.

Just some more info. It is what indentifies the timing of spark, so if it goes out the computer will send the spark at the wrong time or have to default to different mixes untill one fires the car. Hence the car not starting.

Doug

 

[SHOmaniac1975]

Where is the CID located on the motor? The IAB is on the back side of the throttle body?

Thanks

 

[SHOtimer]

Someone may have an engine bay pic of the CID, I don't. It is located on the back corner of the motor right above the power steering pump. It is located on the rear head, it is a circular sensor that screws into the side of the head with 2 7.5mm bolts next to the end of the valve cover. It has one plug going into it on the top. It measures the location of the rear cam and by doing that sets the timing for the motor.

Doug

 

[projectSHO89]

Clarification: The CID sensor is used to establish fuel injector timing.

If it is unplugged, the engine computer has a one-in-three chance of guessing the correct synchronization for the inijectors. This can be useful for getting around for a few days in the event that the CID sensor fails and kills the CID signal to the DIS and the ECM. No tach with CEL will be the operating mode...

The IAB/IAC is mounted on the intak just opposite from the throttle body.

Steve

 

[SHOtimer]

Ah, my bad.....fuel injector timing, not spark timing. But, still - important and can cause starting problems...

Doug