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bdw18_123 · 01-16-2011

First, I will post the story here that I told Cliff in PM's about why I believe the timing chain breakage was due to excessive driving with a bad misfire:

My ZR-1 currently has 139,376 miles on it, which is what it had when I bought it. I'm almost positive that the timing chain breakage was caused by the previous owner driving it for too long with a bad misfire condition. Here's why I say that:

I had lent my ECM awhile back to tccrabs to help him with some troubleshooting he was doing on his '90 Z. After trying my ECM in his car, he said it made his car run with a bad misfire. Once he put his ECM back in, the misfire went away. At the time, he had already planned to make a trip to see Jeff Flint (jeffvette), so he took my ECM with him and they tried driving Jeff's ZR-1 with my ECM. Same results, bad misfire. So it is a good thing I lent my ECM to Tom or I'd have been tearing my hair out trying to chase down a misfire once I had the Z together and running.

So that confirmed that the ECM that came with my Z was bad. The ECM had already been replaced at least once before, back in December 21, 2001 according to the Carfax report which showed a "Failed Emissions" with 53,657 miles on the car, then on the same day it said "computer system repaired", then a "Passed Emissions" after that. That original ECM was undoubtedly causing similar type of misfire which caused the car to fail smog. The sticker that was on the ECM that came with my Z said "remanufactured" on it.

I have a good ECM now though, I bought a known good original used one from Sgreg, it was out of a 30 something thousand mile Z I think. Paid $275 for it, then sold my bad ECM to Haibeck for $100, so I really only paid $175 for it.

Anyway, back to the story. So the last entry on the Carfax report is on January 24, 2008 which says "Failed Emissions" at 133,074 miles. The bad ECM that was in the car when I bought it is the most likely reason for failing smog. He bought new injectors in October of 2008, which tells me he was probably trying to fix the misfire problem.

Now notice the mileage at the time of the last failed smog - 133,074 miles. The mileage now is 139,376 miles. Which means it is possible that the previous owner drove this Z for another 6,302 miles with a bad misfire condition! If that's true (and it most likely is), no wonder the timing chain broke! Tom Crab is actually the one that suggested that driving it with a misfire could be the cause of the chain breaking and given what I've just said above, it makes sense.

01-16-2011	#2
bdw18_123 Join Date: Apr 2009 Location: Prather, CA Posts: 804	Re: Mystery of the timing chain failure... First, I will post the story here that I told Cliff in PM's about why I believe the timing chain breakage was due to excessive driving with a bad misfire: My ZR-1 currently has 139,376 miles on it, which is what it had when I bought it. I'm almost positive that the timing chain breakage was caused by the previous owner driving it for too long with a bad misfire condition. Here's why I say that: I had lent my ECM awhile back to tccrabs to help him with some troubleshooting he was doing on his '90 Z. After trying my ECM in his car, he said it made his car run with a bad misfire. Once he put his ECM back in, the misfire went away. At the time, he had already planned to make a trip to see Jeff Flint (jeffvette), so he took my ECM with him and they tried driving Jeff's ZR-1 with my ECM. Same results, bad misfire. So it is a good thing I lent my ECM to Tom or I'd have been tearing my hair out trying to chase down a misfire once I had the Z together and running. So that confirmed that the ECM that came with my Z was bad. The ECM had already been replaced at least once before, back in December 21, 2001 according to the Carfax report which showed a "Failed Emissions" with 53,657 miles on the car, then on the same day it said "computer system repaired", then a "Passed Emissions" after that. That original ECM was undoubtedly causing similar type of misfire which caused the car to fail smog. The sticker that was on the ECM that came with my Z said "remanufactured" on it. I have a good ECM now though, I bought a known good original used one from Sgreg, it was out of a 30 something thousand mile Z I think. Paid $275 for it, then sold my bad ECM to Haibeck for $100, so I really only paid $175 for it. Anyway, back to the story. So the last entry on the Carfax report is on January 24, 2008 which says "Failed Emissions" at 133,074 miles. The bad ECM that was in the car when I bought it is the most likely reason for failing smog. He bought new injectors in October of 2008, which tells me he was probably trying to fix the misfire problem. Now notice the mileage at the time of the last failed smog - 133,074 miles. The mileage now is 139,376 miles. Which means it is possible that the previous owner drove this Z for another 6,302 miles with a bad misfire condition! If that's true (and it most likely is), no wonder the timing chain broke! Tom Crab is actually the one that suggested that driving it with a misfire could be the cause of the chain breaking and given what I've just said above, it makes sense.