Now I am really frustrated.......
Thread Starter
Rotary Freak
Joined: Jul 2003
Posts: 2,199
Likes: 9
From: Oakville, Ontario
Found It
After much work, I think I found out what happened. I re-plunged the CAS and that helped some, but the car started to run really fat after a while, but it sounded better. So I bit the bullet and stripped everything off the motor to go over everything step by step.
First thing I noticed that the lower back intake manifold bolt had loosened off slightly. Not enough to cause an issue cold, but I could see a place where exhaust gasses and carbon were leaking past the gasket into the intake when hot. This was hidden beneath the heatshield, so it was never checked and it also would have seen the largest swings in temperatures.
The second thing I noticed was that on the bottom of the ITB's there are 4 ports that come out of the bodies that are all connected together into a log for a common vacuum source. All of those were connected, but a small secondary port had the rubber cap cracked open from the heat and the whole end was open to atmosphere on the last ITB. Drawing in air through the open port can't have been a good thing. Same ITB port as above and both were feeding the chamber that the wideband was reading. This means that the back rotor was running at 11.5 - 12 to 1 air/fuels with the air leaks above, but the front must have been a fair bit richer than that as it had no air leaks. No wonder it was fouling plugs so much.
I am also taking this opportunity to clean up some of the welds in the intake. It should be done by this weekend, then out to the dyno for some runs. I am also going to change the eccentric shaft pulley for the Racing Beat one I have that has the timing marks on it. This should give me a good indication if my timing is correct at max advance.
Just need some more time in the day........
Eric
First thing I noticed that the lower back intake manifold bolt had loosened off slightly. Not enough to cause an issue cold, but I could see a place where exhaust gasses and carbon were leaking past the gasket into the intake when hot. This was hidden beneath the heatshield, so it was never checked and it also would have seen the largest swings in temperatures.
The second thing I noticed was that on the bottom of the ITB's there are 4 ports that come out of the bodies that are all connected together into a log for a common vacuum source. All of those were connected, but a small secondary port had the rubber cap cracked open from the heat and the whole end was open to atmosphere on the last ITB. Drawing in air through the open port can't have been a good thing. Same ITB port as above and both were feeding the chamber that the wideband was reading. This means that the back rotor was running at 11.5 - 12 to 1 air/fuels with the air leaks above, but the front must have been a fair bit richer than that as it had no air leaks. No wonder it was fouling plugs so much.
I am also taking this opportunity to clean up some of the welds in the intake. It should be done by this weekend, then out to the dyno for some runs. I am also going to change the eccentric shaft pulley for the Racing Beat one I have that has the timing marks on it. This should give me a good indication if my timing is correct at max advance.
Just need some more time in the day........
Eric
Joined: Mar 2001
Posts: 31,837
Likes: 3,234
From: https://www2.mazda.com/en/100th/
both of those things you found could cause the problem. i had a friends car making detonation noises, and i forget specifically what fixed it, but it was an air leak.
