Hey guys, I took one of my first recorded runs with DataMaster the other day and got knock retards of up to 9 degrees at high MAP's. So I figured I should stop being a cheap SOB and switched from 89 to 93 fuel. The next day (a few hours of driving time,) I did another full throttle run through first gear and let it shift to second and got retard of almost up to 6 degrees. Is 6 degrees normal or should I be getting 0 degrees at all times? The engine does have 107K miles on it... do you guys think it has lots of carbon buildup inside? Do any of the cleaners work that you pour into the tank or anything? The heads may be coming off in the summer if I do the cam for a cleaning and valve/spring job. What do you guys think?

 

BlackCamaro, may be winter time and the cold. Sounds weird, but your car will run leaner in the cold weather. And i'm sure it's cold out there on the island. Used to live in Elmont. Now out here in New Mexico and i'm sure it's just as cold here as it is there right now. In the summer I did some scans on my ride and I never got any KR while I was rapping that thing out. Did some scans last week before my PCM frying session and I was getting anywhere between 2 to 9 for KR. I'm thinking it's due to the cold and that I may be leaned out. I wouldn't mind hearing other opinions on that from other people out here. The temp out here was between 35 and 45 at the time. Lets see what everyone else has to say.

Ken R 95Z

 

I can understand why the engine would lean out in cold weather, because the fuel doesn't vaporize correctly, but isn't that why the PCM sends more fuel to the engine in colder temperatures? I can see this situation from both sides but maybe the cold does have something to do with it... any more opinions?

 

That is a ton of KR, the problem is, once the KR starts it gets bad fast, so removing only a little timing may help, or adding a little fuel, but there can be many possible reasons for KR. Long tube headers would be one example, with myster knock on these cars.

 

So Dr Mudge, do you think I should remove a degree or two of timing on the tables where it's high map and tps? What did you mean by "add fuel" ... increase the duty cycle on the injectors?

 

I think he's talking richening up the AF mixture when he's talking add fuel. I would probably try that first and see if your KR goes away. If your not on a dyno, it's just a shot in the dark and I don't know exactly how much to add even on a shot in the dark adjustment. By the sounds of what i've read hear, 5 to 10% would be a good place to start probably and if that didn't work then you'd have to try the timing route. I'm not too experienced in that stuff, but i'm an expert in trashing your PCM if you want advice on that. Haha. Lets see what the input from the others are. Good luck and post what you find since I seem to be seeing the same thing on my ride. Later.
Ken R 95Z

 

I'm beginning to feel it's just the three of us on this board .. you me and Dr Mudge. LOL...

 

I have pretty much the exact same problem.
I done a little bit of scanning and found that my knock appears to be associated with high MAP.
My next step was to drop the timing by a degree where I see knock. Unfortunately winter came before I got it done so I'll have to wait until spring when the car comes back out.
I'll keep watching and see what you come up with.

 

There is no reason cold air would cause the mixture to lean out. In the MAF engines, the MAF sensor reads "mass air flow".... that means it is measuring the pounds of air that enter the engine, so temperature is, in effect, compensated for. In the speed-density engines, the ECM is using MAP and air temperature to calculate the density of the air, and then uses rpm, displacement and VE to calculate the mass flow, so again, temperature changes are easilly accomodated, and the A/F ratio is maintained.

In fact, cold intake air REDUCES the tendency to detonate, as does lower coolant temperatures.... both things you see in cooler weather.

I wouldn't ascribe excessive knock to colder air temperatures.

Detonation is generally encountered at high MAP, because MAP is a measure of engine "load".

The question I have for "ablackcamaro" is WHEN do you see those retard values? Would it happen to be ONLY at the shift points? Or does it continue for an extended period of the run?

 

Well on my first recorded run the knock seemed to come whenever the MAP was high. This run was recorded on my way home from the bank, btw... so it was stop and go driving that never made it out of first when it was at WOT.

After switching to the 93 fuel, I recorded a run that started at 17 mph, and went to 70 mph on a WOT run, and the only shift in the run was from 1st to 2nd. The knock was always there, in the 1 degree range, and a short bit after the shift, it went from 1.9 to 5.9 in one record (using DataMaster.) There was no significant change in map when it shot up, either.

I have the datamaster files saved, should I post them so you can see it yourselves?

 

Injuneer, if air temp is somewhat accounted for in a MAF setup, then why is there a tempature sensor in the air inlet before the throttle body (don't know if a speed density set up has one or not)? Doesn't the PCM change AF ratio somewhat based off the temp sensor readings (like making the mixture richer as tempature decreases)? If not, then why have a temp sensor in the air intake? Not saying that cold is definitly blackcamaros problem, but just figured i'd throw it out there. Not sure if the PCM would easily compansate for that or not. All I know for sure it that on a non fuel injected engine, the mixture will lean out in cold weather.

Ken R 95Z

 

Is the pcm tune stock? I've seen a few mail order tunes with low rpm timing tables that have 3-4 degrees added over stock. That much advance gave me 1-3 degrees retard, I backed them down 1-2 degrees and it helped a lot. I may see 1 or 2 degrees retard right at my shift point.

 

Ken,
IIRC (and that is an if been out of the loop for a good 6-8 months) the IAT sensor is primarily there in case the MAF should fail. In that case the PCM reverts to Speed Density in which case it must know the temperature of the air entering the engine.

I'm too rusty to go more into depth, maybe Fred will give a bit more scientific explanation of how the MAF functions (hot wire determines how much air and what temperature is flowing over it IIRC).

HTH.

 

thats sounds about right...you should always use premium unleaded in these cars. also...does knock retard appear just at high RPM or high MAP or does this only occur during shifts? i rearly get knock just running the car hard...until i shift. and if you get it when you shift then i dont think theres a whole lot that can be done about that IMO...only when knock shows up before you shift is there a real good chance of illiminating it with better gas or subtracting some timing.

 

It was happening more w/ high map than at shift points (the car is also an automatic BTW, not sure if that matters,) and at the same times the RPM's were either high or on their way up (due to the high MAP.) I'm gonna test it again in a few days, now that I've been using the 93 fuel for a while.