Yeah.. this is a fun one.. Working on a 99 Miata for my friend, has a turbo on it.

Basically, he had his engine redone by this shop with forged pistons, rods, lowered compression, etc to beef it up. The first thing I noticed when he got it back was that they snipped the wire leading to his AFR gauge inside the car (odd.. I thought.. why would they do that). So I hooked up a WB02 sensor and a wideband gauge, sending the 0-1v signal to the stock ECU. As I had thought, the stock ECU could not provide enough fuel to the engine even at 3psi boost, as it would go lean enough to keep the engine from revving at that point. Only did that maybe 2-3 times, not even getting on the gas hard, just to test the AFR's on the new engine.

Turns out his engine had some internal damage (keep in mind, this is less than stock horsepower with the lowered compression, and with forged rods and forged pistons). They claimed it was his rods that needed replacing, but would not say why, and they said his pistons were fine. They blamed the entire thing on "detonation due to changing the oxygen sensor from NB to WB" and it was "making the stock computer not give enough fuel", which is cannot give in either case, since he has stock injectors, stock fuel, stock ECU.

Now they are trying to charge even more $ for valves, etc, basically saying the entire engine was messed up.. and all because of what?? "the oxygen sensor did it".

Let me know your thoughts. If anything, all I can think of is the ECU was getting too lean of a signal (due to the faster response of the WB), and was trying to give it more fuel, and it could not. However, I thought about it more and realized that the stock ECU's fuel mixture is probably controlled by air temp/water temp/MAF readings to provide the fuel, and may not even use the stock O2 sensor to adjust fuel at all, and at least not in that much that would cause that kind of damage.

Let me know what you think.

 

Update - now the shop says the heads need to be redone as the bearings failed and they can spin the cam inside the head freely - again with no explanation besides "detonation". They now said the rods are not damaged, pistons are not damaged, but they need to replace the rods anyways because of the bearings inside the head.

I'd love to hear your replies to this one and what you think of the shop and if what they say is even possible. We did ask to have the old parts back that they were going to replace and they were pretty reluctant to do that but said they would.

 

Bring it to another shop.... There aren't even bearings on the cams....

And please post the shops name so that nobody goes to them again.

Edit: and why doesn't he have any engine management?

 

To put it bluntly, "O2 sensor is king" when it comes to fuel. If there is no O2 sensor signal, the ECM is going to think the engine is running at about .45v, or about stoich. Under power the ecm is going to see this as lean, as it is programed to want to see a richer mixture under load, therefor it will be adding fuel.

Lean and detonation will not harm cam bearings, or saddles. My bet is they sandblasted the head, and did not get all the sand out, if there is indeed a cam bearing problem. If the valves are out, (or just the followers) the cam had dam well better spin free, or it will eat the cam in a hurry! If it spins free with the valves and followers still in place, the valves are all bent and staying open, = timing belt was off, or again the sand thing!

Was it running when it went to them?

I'm with the above comment, FIND A REAL SHOP TO DEAL WITH!

Ron

 

 

get a lawyer. No, seriously.

 

The engine started knocking the night before we would have been installing the new injectors and microtech ecu on the car. The car had previously been taken to someone who did not know what they were doing with fuel injection, engines, and boosting in general and it required a complete engine rebuild before I could even touch it with the new injectors + computer.

 

So are you agreeing with me when I say that even if there was lack of an O2 signal or receiving too lean of an O2 signal would make the stock ECU give it MORE fuel instead of leaning it out, as the shop is saying? It sounded like they were smoking something from the beginning but I needed some backup to my thoughts.

 

B & M Automotive Specialties Inc
Tucson, AZ

I'm convinced there is not a shop in Tucson that has any clue what they are doing.. Kind of worries me since I am sure they've destroyed other cars as well.

 

Yes