Closed loop pinging

[apwatson50]

Basically I get a little pinging when the ambient temperature is hot, above ~80deg F, when the engine is under load going up a hill and around 2500-3k rpms. If I manually down shift to raise the rpms the ping goes away. During the winter I can even run 87 octane, during the summer its 91. Keep in mind here in Denver, 91 octane is "premium".

So basically is there anything I can do, short of a Unichip, to get a little richer mixture during closed loop operation.

Thanks for any ideas.

Aaron.

[92tank]

ARE YOU RUNNING STOCK INJECTORS? MAYBE A SET OF BIGGER INJECTORS WOULD HELP. IT HELPED MINE BUT I DIDNT HAVE THE PINGING JUST LAZY ABOVE 3,500 RPMS. BUT IM IN MI SO THAT COULD MAKE A DIFF

[apwatson50]

Thanks for the response, I do have bigger "lt1" if I remember right they are ~28lb/hr injectors.

[lafrad]

No matter what injectors you use, closed loop operation is a "dance" around 14.7:1 AFR. only way to get rid of pinging is to add more octane, add more quench, or pull timing.


*OR*... get colder air inlet. so... snorkel? Cowel? etc.

[4.whoa]

When I built my last engine (not a stroker) I checked and found the chambers(NOT ported) were overhanging the bores. That's a HOT spot. I used a dremel to knock the edge off and smooth the flow. Need to be careful -use the hg and top ring depths to be sure you don't ruin anything. I haven't had issues with any level of gas, but when I'm going through the mtns, towing or beating on it I always run super.

[4.whoa]

Forgot to mention, its .060 over and the stock chambers STILL hung over even after .040 milled off the head

[apwatson50]

Mine is .040 over and I did chamfer the chamber edges and the edges on the piston top, etc... So I think i did pretty good considering its a 10.25 SCR engine. I can run mid grade in the winter, and even in the summer I could except for the closed loop ping, which is very minor.

Anyone know a way to pull timing on a 97 OBD 2?

Also I think I may try a heat range 7 NGK plug. will probably end up with a projected nose plug rather than a stock style "extended projected nose".

[lafrad]

One way you can "accomplish" this, is by getting a Map sensor adjuster.

tweak it so that it INCREASES the voltage that the ECU sees. in ALL parts of the timing table in the ECU, more voltage from the map sensor = less timing.

you can get *real* tricky and get a Split Second PSC1 programmable map adjuster. http://moesperformance.com/index.php?ma ... ts_id=1143

With that you can program the map adjustment at different rpm and input map voltages, so you can tweak your mid-load areas but still keep WOT in check.

[apwatson50]

Lafrad, not to question you, but are you sure that the map adjuster will affect timing even in closed loop? If so I have a map adjuster that I had installed for a while, but I took it out because it always caused the CEL to come on. But I would be willing to put it back in to get rid of ping!

[lafrad]

It will affect timing.


How much? unknown.


ALL modern ECU's base timing off of RPM vs Map Sensor voltage. (some of them are using airflow, but thats calculated from map sensor on a speed density system like this)

The higher the MAP voltage, the lower the spark needs to be. you can run 30* of timing if you are drawing a ton of vacuum, but you can't at 1100 rpm and lugging the crap outta it. So, bump the map voltage a bit and it should *help*

[apwatson50]

Thanks for the response, I am definitely going to give that a try, and now thinking more about it, it makes a lot of sense.

thanks again

[lafrad]

Don't go too far, as it can really dig into fueling issues too. However, in closed loop, you are able to be up to 30% off in either lean or rich before you run into problem.s