LT5 Ignition Systems Question??? - Page 7 - ZR-1 Net Registry Forums

LT5 Ignition · 03-15-2011

I can now appreciate the concern with the IM availability. Also, I apoligize I got my dates mixed up on LS introductions in post 56. It was the Gen 2 small block LT1 in 1992 (ABITS). The Gen3 LS ~ '97 and Gen 4 ~ '05. I agree that if you can keep the IM module from sinking the primary current it will run cooler.
Now, if someone can come up with a way of turning the 9x VR signal into into a 4x logic signal and also take the single EST signal from the ECM and steer it to the 4 coil pairs in firing order it seems the IM can be eliminated. For sure the LS systems have dwell overlap starting around 4000 RPM. Perhaps the Lt5 does too. In the run mode the IM could have been designed to follow the falling 4x EST signal from the ECM for end of dwell spark timing but control the start of dwell ahead of the rising EST pulse. I can not remember if it actually was. Would it be worthwhile to put a couple of current probes and a scope on the coil primaries to see if the dwell overlaps on a LT5 at higher speed? I wish I had one!!

POWERBRAKEBOB · 04-12-2014

Does anyone know if the MSD DIS-4 box will replace and remove the factory DIS Box?

XfireZ51 · 04-12-2014

Quote:

Originally Posted by POWERBRAKEBOB

Does anyone know if the MSD DIS-4 box will replace and remove the factory DIS Box?

Nope. Just an amplifier.

POWERBRAKEBOB · 05-25-2014

I'm still chasing this "cranks but won't fire" problem on mine. I have changed the IM, the CPS, tested the harness between CPS and IM, all fuses, tested the ECM and Jet chip, new battery, coils are new MSD 6 months old, all new injectors, have key on power to the coils, IM, and computer. NO trouble codes. Had the plenum off a dozen times.. Checked for bent pins on the IM. really causing me some problems. Any OTHER ideas?

Tyler Townsley · 05-25-2014

Fuel pressure? No spark across the plugs when cranking?

Tyler

XfireZ51 · 05-25-2014

Quote:

Originally Posted by POWERBRAKEBOB

I'm still chasing this "cranks but won't fire" problem on mine. I have changed the IM, the CPS, tested the harness between CPS and IM, all fuses, tested the ECM and Jet chip, new battery, coils are new MSD 6 months old, all new injectors, have key on power to the coils, IM, and computer. NO trouble codes. Had the plenum off a dozen times.. Checked for bent pins on the IM. really causing me some problems. Any OTHER ideas?

Have you installed a stock chip? When you turn KEY ON, does the SES light blink once? You won't get trouble codes till the motor runs. Are the pumps coming on?

POWERBRAKEBOB · 05-25-2014

I set a plug out on the engine with wire and cranked. NO spark. NO flash of the noid light. Sec light flashes, then goes out by turning key to ON. Key on, pumps run two seconds. Cleared door alarm. I did find a fuse burned out under the right dash. It looks to be marked "conx" or "cone" . I replaced ALL fuses on the right side of dash. VATS by passed. It was running when I parked it one night, next day, nothing. I bought a used IM from Brett. Replaced CPS, which did test "open". Tested the harness from CPS to IM for shorts. None. I'm sure it's something simple, but I can't find it, and my FSM's are buried in storage. Frustrating, and I need the car. It does have 268,000 miles on it, which I am sure is a record. No one has ideas on when things fail at what mileage.

03-15-2011	#61
LT5 Ignition Join Date: Feb 2011 Location: Sterling Heights, MI Posts: 11	Re: LT5 Ignition Systems Question??? I can now appreciate the concern with the IM availability. Also, I apoligize I got my dates mixed up on LS introductions in post 56. It was the Gen 2 small block LT1 in 1992 (ABITS). The Gen3 LS ~ '97 and Gen 4 ~ '05. I agree that if you can keep the IM module from sinking the primary current it will run cooler. Now, if someone can come up with a way of turning the 9x VR signal into into a 4x logic signal and also take the single EST signal from the ECM and steer it to the 4 coil pairs in firing order it seems the IM can be eliminated. For sure the LS systems have dwell overlap starting around 4000 RPM. Perhaps the Lt5 does too. In the run mode the IM could have been designed to follow the falling 4x EST signal from the ECM for end of dwell spark timing but control the start of dwell ahead of the rising EST pulse. I can not remember if it actually was. Would it be worthwhile to put a couple of current probes and a scope on the coil primaries to see if the dwell overlaps on a LT5 at higher speed? I wish I had one!!

04-12-2014	#62
POWERBRAKEBOB Join Date: Apr 2010 Location: HUNTINGTON BEACH, CALIF. Posts: 38	Re: LT5 Ignition Systems Question??? Does anyone know if the MSD DIS-4 box will replace and remove the factory DIS Box?

05-25-2014	#64
POWERBRAKEBOB Join Date: Apr 2010 Location: HUNTINGTON BEACH, CALIF. Posts: 38	Re: LT5 Ignition Systems Question??? I'm still chasing this "cranks but won't fire" problem on mine. I have changed the IM, the CPS, tested the harness between CPS and IM, all fuses, tested the ECM and Jet chip, new battery, coils are new MSD 6 months old, all new injectors, have key on power to the coils, IM, and computer. NO trouble codes. Had the plenum off a dozen times.. Checked for bent pins on the IM. really causing me some problems. Any OTHER ideas?

05-25-2014	#65
Tyler Townsley Join Date: May 2005 Location: Nichols, FL Posts: 615	Re: LT5 Ignition Systems Question??? Fuel pressure? No spark across the plugs when cranking? Tyler __________________ 55 Polo White (Project) 61 Jewel Blue (Sold to buy above) 66 Nassau Blue 68 Torch Red 88 ZR1 Blue 90 ZR1 White

05-25-2014	#67
POWERBRAKEBOB Join Date: Apr 2010 Location: HUNTINGTON BEACH, CALIF. Posts: 38	Re: LT5 Ignition Systems Question??? I set a plug out on the engine with wire and cranked. NO spark. NO flash of the noid light. Sec light flashes, then goes out by turning key to ON. Key on, pumps run two seconds. Cleared door alarm. I did find a fuse burned out under the right dash. It looks to be marked "conx" or "cone" . I replaced ALL fuses on the right side of dash. VATS by passed. It was running when I parked it one night, next day, nothing. I bought a used IM from Brett. Replaced CPS, which did test "open". Tested the harness from CPS to IM for shorts. None. I'm sure it's something simple, but I can't find it, and my FSM's are buried in storage. Frustrating, and I need the car. It does have 268,000 miles on it, which I am sure is a record. No one has ideas on when things fail at what mileage.