M20B28 - Pinging/ Smog Questions

[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.

[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]

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.

[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.

[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..

[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.

[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]

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]

So I spent many hours researching, made some phone calls, and figured I just take a small chance and adjust the cam gear a bit. I turned it counter clockwise one tooth, checked valve clearances, and took it for a spin. Pinging was greatly reduced, but still present. For the hell of it, I swapped out my stroker chip and 173 ECU for a refurbished factory 153 ECU and the pinging stopped. The car runs as great as it always has, but no pinging under load or WOT.

What does this mean? Should I leave it alone, play around with the cam timing a bit more and toss the chipped 173 ECU back in? Any thoughts or comments would be appreciated.

[RCM3]

Pretty sure the AFM is solid. It came off of my last e30 where the M20 was pulled in perfect working order. Ill temporarily borrow my bros off his car to confirm with another known good unit. Ill try his 173 ECU also, maybe my unit has some issues.

Ill double check the cam, thought I was told it was stock.

Assuming everything checks out and those items are correct, can this be some sort of timing related issue? Or do all guys have no issues leaving the factory timing at the cam sproket intact? Just wondering if I should retard the cam a bit, or get an adjustable gear? Does that even make sense with my symptoms?

Thanks for the response.

[wilholl]

Are you absolutely sure the AFM is good?
Does this engine have a stock cam?
A compression check might help diagnose a problem with the head or possibly ring issues.

I have used SeaFoam quite often on non EGR engines to get them to pass.
It sometimes helps to pour it in the cylinders and let it sit overnight. Then turn the motor over to clear any remaining liquid before reinstalling the plugs and firing it up. It will still puke out a lot of white smoke for a little while. Also, good to change your oil after the treatment.

I hope you find the problem, in any case it doesn't sound too good.

[RCM3]

Had some more time to work on the e30, here's what's going on now.

Car is back to stock. I ordered a Sssquid chip, installed it into my 173 ECU. Tore back into it, timing is dead on. Took the car for a drive and it pings slightly worse now. Exhaust still smells very rich. If I drive the car under 3.5k rpm it's totally fine, no detonation issues. Once I push it to WOT or go above 3.5k rpm it pings. One observation: going from the chipped ECU to a stock ECU I get a noticeable reduction in pinging, but I still have pinging under engine load at WOT. Is this a timing issue, something else causing advanced spark?

No CELs, most all components are NEW. O2 sensor is not, but it's not triggering a CEL.

Any suggestions? Is it possible to retard the cam sprocket a tooth or two to remove the pinging? I have the front components of the engine off now, down to the timing belt.

Any suggestions greatly appreciated!

[RCM3]

Alright, yesterday I swapped the injectors back for the stock ones (thanks Mark :)) and replaced the ECU with a stock unit. I went for a ride but still noticed the pinging/ rattling sounds. It happens only in 3rd and 4th gear, mainly 4th. It happens only when pulling a hill and at WOT above 3.5k RPMs. I brought it home and parked it. After parking it I put in 6 gallons of 91 but didnt have time to take it for another drive. The exhaust smells much better now, not as rich. Still need to further diagnose the pinging before I further pursue the smog issues. Im thinking about pulling some components off to double check I did indeed set the timing properly I guess.

[RCM3]

Havent made it home yet. The car has just been sitting in the garage :( . Ill be in town in about a week and Ill have an update.

Thanks again Mark for offering the injectors. Ill swing by GC on my way home.

[efficient]

What's the word?