M20B28 - Pinging/ Smog Questions

[squidmaster]

The M20 can handle a huge deal of timing before anything really pops up, and that you were still getting pinging with the stock 173 chip leads me to believe that it would be some issue outside of the tune. But who knows.

If I'm reading right, the stock 173 ECU gave you slight pinging, but the 153 gave you none? And you only went 1 tooth over? IIRC 1 tooth is about 3' of timing.

[RCM3]

Yes the 153 ECU with the added tooth and I have no pinging. I think youre right on it being outside of the engine tune, maybe my 173 unit was wacky to start with. I just grabbed another 173 and Ill swap it in with your chip and try that. Im scratching my head as of now though. I appreciate all of your help also squidmaster.

I might take away another tooth just to see if anything changes better or worse.

[squidmaster]

One thing to think about is: if you have to move the timing off sync (rather than both cogs lined up to tdc in tandem) then something doesn't seem right and might cause a larger problem down the road.

I wonder how the 153 would have performed without the tooth adjustment.

The timing on the 153 and 173 are the same, however the fueling in the upper range (5k+) on the 153 is about 10% higher than the 173. That's all.

[nando]

you have a stock cam? what's the compression ratio? a stock cam + high CR could cause pinging. you shouldn't ping with a stock chip though..

[RCM3]

One thing to think about is: if you have to move the timing off sync (rather than both cogs lined up to tdc in tandem) then something doesn't seem right and might cause a larger problem down the road.

I wonder how the 153 would have performed without the tooth adjustment.

The timing on the 153 and 173 are the same, however the fueling in the upper range (5k+) on the 153 is about 10% higher than the 173. That's all.

I understand. I was hoping this info could help diagnose an issue more than be a permanent solution.

I did run the 153 ECU befor changing anything else at one point. Pinging was present, but much less than with a chipped 173 ECU.

These are just so many unknowns on this engine from the PO that I'm still working to figure out.

you have a stock cam? what's the compression ratio? a stock cam + high CR could cause pinging. you shouldn't ping with a stock chip though..

I checked adjustment on the valves and looked the cam over. I never found a BMW stamp or part number but I figured it could be hidden on one of the ends of the cam. I noted I believe 4 digits stamped on the cam between cylinders 4/5, and then between 1/2 three white "K"s painted around the cam.

Compression ratio, I have no idea what it is on this build. I left a message with supposedly the shop that did the build in the Bay Area. They're going to look it up and get back with me with any records.

[RCM3]

I forgot to mention that I did find one odd discovery when adjusting the cam timing the last time. The CPS line looks to have been cut twice a while back in the past by the water pump pulley. One was repaired and taped over, the other was not repaired elegantly at all. I did order a new CPS last night.

[wilholl]

you have a stock cam? what's the compression ratio? a stock cam + high CR could cause pinging. you shouldn't ping with a stock chip though..

^This^
I would also question the compression ratio if this engine was built by someone else. Also, if the cam timing is an issue, the head may have been milled substantially causing cam timing issues and higher compression.

[RCM3]

Everything is sorted now. Pinging went away with the new CPS! The old sensor had been worn through in 3 places from one of the pulleys. In addition to this, the gaping on the old CPS was out of spec. New sensor and timing set back to factory and she runs great now. I'm using the 153 computer still, the chipped 173 unit gives the car some issues, O have not tested the car with another 173 still. Ill try that soon to see if the ecu is the problem.

Thanks for the advice guys.