Car: 1999 Mazda RX7 S8

Specs: Stock Port, Stock injectors, Adaptronic S8 pnp, CX Racing Tubro kit(please don't shame me, it's all my wallet can afford right now), Blitz BOV, Rotary Run Racing Intercooler, Koyo Radiator, OMP Delete.

So, I just rebuilt my motor, finished the break in tune and got it tuned by Nelson from RRR. Drove it home, no problems at all. Next day, swapped out the stock Radiator for a Koyo, changed out the thermostat for a 180° one, changed the front rotor ign coil(trailing) cause it was going bad and rerouted the wires from the Wideband to the ECU. I did have to remove the battery to get to the radiator so that could've done something(dont know much about ECUs and Tuning). Anyways, we turned the car on to bleed the system and it had a surging idle. No clue what happened, checked all the wires, hoses, etc. Nothing was different from when it was on the dyno. The new ign coil works as well because we had to use it for the dyno session. Since all my gauges were reading normally and the AFR was good, I decided to drive it around. The Koyo kept it cold, maybe a little too cold. Fans off, it ran about 170°, sometimes dropping to 165° even in 95° desert weather. A day later, I'm noticing the car is running really weird. Surging between 1700 and 900, almost dying, getting absolutely terrible mpg even cruising at just below 3K rpms, and on Deceleration, the engine sputters and makes the car jolt and shake, almost struggling for something. AFR reads 14 when cruising, no boost, and 10-10.5 in boost.

I'm at a total loss of what could be wrong.

 

Check how the TPS is set up, could be something there. Or throttle cable or throttle plates could be binding.

Dale

 

Thanks for the advice, Dale! The throttle cable was binding up a bit and also missing the secondary idle screw on the throttle body. Adjusted it and got a new screw, no problems with idling anymore. TPS voltage was within spec.

Unfortunately for my bad luck, I'm now dealing with another problem. Now the car is eating up coolant. No clue where it's going, but it's going somewhere. No smoke or coolant smell from exhaust at all, plugs aren't wet, no bubbles in the filler neck, no visible leaks on the floor, turned motor over when cold with no plugs and no coolant was in the combustion chamber. I did notice my overflow tank leaks, so if that could cause loss of vacuum, then I answered my own question. If it wouldn't matter then the problem still exists. Haven't done a pressure test though, next on my 'to do' list.

Funny thing is, she doesn't get hot at all while moving. Stays around 170-175 while moving, doesn't matter if it's 100° or 50° outside. Stopped or moving slowly, it creeps up. I only noticed the coolant problem yesterday when I got stuck in traffic and it just kept going up and up. Pulled over and the low coolant sensor started blaring so I let the car sit while I grabbed food. After about 2 hours, I grabbed some coolant and started pumping the upper radiator hose. The car drank more than half a gallon of coolant. This was all days after I replaced the Stock Rad with the Koyo and bled/topped off the coolant.

Whenever I fix one problem on this car, 2 more take its place... Not giving up though.

 

Check your radiator caps and the hose to the overflow tank, this has been written up many times. Possible you are pushing coolant to the overflow tank and not bringing it back as the car cools.

Need to figure this out as it's a good way to turn that good engine into an overheated paper weight!

Dale

 

It seems you might be right again! As I was pouring coolant in the filler yesterday, and trying to bleed the system with the engine off(squeezing the radiator hose), I noticed she started puking coolant out of the overflow as I kept pouring. My Overflow was overflowing lol. Also, car was cold too. Is this the sign of a stuck open/bad AST cap? And is the AST cap a special cap I have to order from Mazdatrix or Atkins? Thank you!

 

I've posted on this a zillion times. Here's one thread on the topic -

https://www.rx7club.com/3rd-generati...-tank-1146741/

AST needs a spring radiator cap. The fill port on top of the thermostat housing is supposed to be a flat cap (no spring) but a regular radiator cap works here too. If you swap the caps you'll have a bad day. Mazda is the best source for the caps - cheap and dead reliable, I wouldn't trust a parts store cheapie.

Dale

 

Yea just get the ast cap from Mazda.. my local Mazda dealer had it in stock.

Yep my overflow tank was overflowing and it was indeed a bad AST cap