4-7 firing issue; posting for a member

[LGAFF]

Got somone in the registry having issues:

4-7 not-firing

Has replaced the DIS with no change


If I were guessing, and coil has been changed, I would think he has a bad wire from the bottom the DIS(Dark Blue Cir #932)....he was informed 2nd DIS was bad, but I would think thats a long shot...

Thoughts?

[phrogs]

wiat a second,

Does he get spark?

I had a missfire and it ended up being the ECM was not firing the injectors.

I had spark but no fuel took me a while to figure it out.

[scottfab]

Simply not enough to go on.
Guesses would be
Bent pin from DIS
bad wire on 4 or 7
bad coil
Bad connector at coil
shorted plug on 4 or 7

How is it that 4 and 7 were diagnoses as not firing?

[LGAFF]

I had bent pin on my list also, car was checked out at a GM dealer, however I am guessing that does not always mean much. Was curious to see what else other thought....I just cannot see it being a bad DIS

[XfireZ51]

Originally Posted by LGAFF

Got somone in the registry having issues:

4-7 not-firing

Has replaced the DIS with no change


If I were guessing, and coil has been changed, I would think he has a bad wire from the bottom the DIS(Dark Blue Cir #932)....he was informed 2nd DIS was bad, but I would think thats a long shot...

Thoughts?

2 DIS modules bad?? And on the same coil???

[LGAFF]

thats exactly why I think something is not right here, has to be something else...I almost have to take bent pin off the list due to the fact 2 DIS used....thinking wire

I want to say they tried different coils

[scottfab]

Originally Posted by LGAFF

thats exactly why I think something is not right here, has to be something else...I almost have to take bent pin off the list due to the fact 2 DIS used....thinking wire

I want to say they tried different coils

I think I'd be swapping plugs, wires and coil with
one of the other pair in the car.
Bad DIS again? Maybe especially if it was forced
to fire into a shorted coil.
This could be annoyingly time consuming to isolate.
Fortunately you can do end to end wire tests on
the harness that runs to the coil from the DIS.
I take it there is no spark at all on 4 or 7 ?

[LGAFF]

Sounds like it had been some time since he tried to address, I will see what notes he has....

[XfireZ51]

Some of you may recall that a few years ago I played around with using LSx coils on the LT-5. Basically I subbed LSx coils for the LT-5 coils and used the DIS module as the sequencer. Went through several iterations of that and actually got the motor to idle (and smoothly btw) for about 30-45sec before I blew a fuse for the Inj 2 circuit which supplies power to our coils. I tried 2 different types of LSx coils including the more "powerful" truck coils w heat sinks. Those did not work. When I first started the motor with the LSx coils it ran like crap until I discovered that the coils where cross wired. 3-5/4-6 were flipped. Motor ran albeit missing badly. With that cleared up, motor started great and ran until power blew out. I thought I may have had a couple of shorted coils also and subbed the upgraded truck coils along with some changes to the circuit including separate BATT (20a) and GND circuits for each bank of coils. It would start but not run. IOW, the DIS was starting the motor but the handoff for timing control to the ECM wasn't happening once it would reach 400rpm.
Got everythng back to stock eventually and DIS has been running ever since. The DIS should survive firing even a shorted coil because it is "current limited". Obviously the engineers that designed the IM took into account contingencies and malfunctions and safeguarded the IM from them. If all else fails the IM is what provides the "limp home" capability since it is essentially a CO-ECM. That's also what makes it difficult to substitute for without some great expense. Anyway, I bring this up to illustrate the ruggedness of the DIS module. Its probably the last thing to consider when having ignition problems since everything else will fail before the DIS does.

BTW, here's a shot of the LSx coils installed:

[LGAFF]

Looks like the things to check for this member

#DIS to Ign coil wire circuit 932(blue) for short(highest probability)
#swap ign modules
#make sure there are not too many rubber gromments on the module housing
#check continuity of module housing..