Nightmare Problem....

[Phantom GTZ]

Hey guys I'm posting here in hopes that someone has a helpful tip.

As of right now, I can tell that the 1st and 4th cylinders are not fiing due to the exhaust runners not getting hot.  Also the new plugs in those cylinders were also clean after a few startups but we'll get to that.

OK...  Heres the list:

Parts Replaced:

-ECM
-MEMCAL
-Coils (obvious fix right?)
-Ignition Module
-Coil Housing
-Spark Plugs
-Injectors
-Injector Harness
-New Downpipe and Catylitic Converter
-New 02 Sensor about 2 monthes before the car went down.
-Replaced almost every vacuum line

This car has got me pretty desperate.  I parked outside a local sporting goods store, ate lunch inside with a friend, and when I came out the car ran like hell.  It was a hot day and car was in the sun which prompted all the ignition pieces being replaced.

The turbo prepped motor is all but done, but I couldn't bare to shove that thing in there just to have it run like hell right out of the box and mess up a proper break in.

Does anyone have a stab at this one?  I would appreciate it VERY much.

Thanks,

-Joel

[whitetalonb16g]

i see plugs but I'm sure you've replaced the wires right ?

[spacecadetz26]

were the injectors new or used? did you ohm them out?

[Phantom GTZ]

They were slightly used out of a running car.  I did throw an ohmmeter through them and they checked identically.

[docrodg]

if 1 and 4 aren't firing it is likely that the coil pack or the ignition module are bad.  Those are opposite firing in the order and share the same coil pack.  It will cause the car to run really bad as I had a bad coil (original, on an 88) on those as well last month.  Replaced it at the hotel where I was at the time and ran like a dream.  Check the module too as the failure could harm the module, but the coil pack should fix the problem.  Also check the plugs to the module and make sure they are good.  If you used coil packs from a donor car they may have a bad connection.  New packs are pretty cheap, 50 bucks or so and worth it.

[Phantom GTZ]

(docrodg @ Sep. 07 2006,12:59)Q
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Eif 1 and 4 aren't firing it is likely that the coil pack or the ignition module are bad.  Those are opposite firing in the order and share the same coil pack.  It will cause the car to run really bad as I had a bad coil (original, on an 88) on those as well last month.  Replaced it at the hotel where I was at the time and ran like a dream.  Check the module too as the failure could harm the module, but the coil pack should fix the problem.  Also check the plugs to the module and make sure they are good.  If you used coil packs from a donor car they may have a bad connection.  New packs are pretty cheap, 50 bucks or so and worth it.
These have already been replaced....

Does anyone know some wiring tips?  I think this guy is an electrical problem.

[blindmandesigns]

(whitetalonb16g @ Sep. 06 2006,21:28)Q
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Ei see plugs but I'm sure you've replaced the wires right ?
quad4's dont have plug wires.

It looks like you nailed every thing I would have looked at/replaced.  Did it show any signs before hand it was having an issue starting to develop???

It's the worst when it randomly doesnt work after it seemed to be working fine before you shut the car off... those are the things that drive me up the wall.

[whitetalonb16g]

oops

[rweatherford]

Man that is a tough one!  I'd start looking at the wiring that is inside the coil housing that goes between the ignition module and coil.

[ws90gtz]

My 1990 gtz is doing the same thing, it started with the
car missing when it was cold, and go away when it was
warm, and every once in a while warm at a stop light
it would miss and go away at 2000 rpm. now, cyl. #1&4
will not fire. swaped coil packs, put in new plugs and
new ign. module, but cyl. # 1&4 will not fire !!

any one have a clue for the both of us ?
can anybody give us something else to check ?
please help.

[ws90gtz]

could this be the crank position sensor getting weak ?
if its starting to go out could it possibly see a stronger
target on the crankshaft ? is there a seperate target
for cyl. # 1&4 and cyl. # 2&3 ?

[ws90gtz]

ok,
pulled crank position sensor out last night, and noticed
the target wheel is off to one side of the sensor hole
(sensor only over little more than half the target wheel)
the book said the target wheel is CAST into the crank
so i know it did not slip over. any one know if this is
the correct position for the target wheel/sensor ?

[Phantom GTZ]

OHHH KAAYYY

Well the car ran beautiful this evening. Barked the tires into second gear and everything!

Changed the crank position sensor and it did the trick. The old one tested good and everything but the change when the new one went in was great.... The car still ran like hell until I swapped into a new ECM and MEMCAL, but I'll get to that.  After plenty of time with a multimeter and wiring schematics led to the discovery of this.

I leave the shop and the car wouldn't start!

Turns out that the alternator (guy says bad diode...) was the reason for the old battery dying. It also is a possible culprit for frying the ECM, MEMCAL, and maybe even the crank position sensor and coolant sensor. Think about the battery (plus even more from the alternator) discharging constantly through the car (i.e. GROUNDS).

So after a new alternator tomorrow, hopefully the car will be healthy...

[docrodg]

Hmmmm... guess that makes sense.  The diode only allows electricity to flow one way so rather than going the right direction (negative to ground) it alternated and became AC rather than DC current if the diode failed closed.

[Phantom GTZ]

After a few minutes, the car no longer ran correctly again!

I yanked the car and sent it to another tech in the area.  This guy located the problem in 30 minutes!

There was a faulty injector that was causing a short in the injector harness.

Just swapped in another injector that I had laying around and the car ran great!

Talk about a headache!