Help - Knock, LTFT, and low mpg (stock cal) - 3400

[3400-95-Modified]

Well first off, I have 10% ethanol all the time and I've never changed my CL afr value. I'm not sure what tables are available in HPT but I know I have a table for closed loop AFR which I can modify, but I'm not sure how it actually determines if its running anywhere near there since it only has a narrowband O2 sensor. To make that statement more simple, I've never changed that to say 13.0 to see if it would actually idle/cruise at 13.0

I can't say I've seen less MPG due to the thermostat since I did change so much. It wasn't like I was running the 195 and changed JUST that and then did some logs as far as MPG goes. I simply changed that a long time ago when i started modifying these engines and I've been using the 180 ever since.

I can't see the 180 hurting anything since our motors already have a bad cooling pattern resulting in the last two cylinders being the hottest (hence the oil squirter's on the 3500) Also the 180 thermo is a factory item for a 4 cylinder cavalier. The only issues I've heard from a low temp thermostat is when people run a 160 it does not allow the engine to get to a proper temperature to warm up the oil and such, which could result in some other issues.

I've never tricked the ECM to run in OL or anything like that, or changed the afr as noted. I've always worked on getting the trims close to 0, I do both a VE tune and then a MAF tune so there is less correction being made, and then I work on getting the WOT pulls to a good AFR using a wideband O2 sensor. After I have those items dialed in then I look at spark and start to advance that in small increments. Those tuning items are what I concentrate on and I tend to leave most of the other stuff alone since some of it is not vital... Although I've learned that AE is quite important when your running a big cam. I had problems with the engine hesitating when going from 0% tp to 50 or more say leaving the line and after playing with some of the AE tables I'm getting it much better. There is still a bit, but I'm working on it.

[hoosierloser]

If your FPR is seeing low vacuum it sees that as the engine being under load when it isn't. Wouldn't that result in overly rich mixture? Although it doesn't explain the low vacuum readings, just a possible result of low vacuum.

[chri0029]

If your FPR is seeing low vacuum it sees that as the engine being under load when it isn't. Wouldn't that result in overly rich mixture? Although it doesn't explain the low vacuum readings, just a possible result of low vacuum.

Man, good point! That could explain why I changed the AFR to 15.3 in O.L. and all the sudden my car had balls again. I should try a MAP sensor swap just for grins too and see what happens. It perplexes me still that I test drove 2 other Grand Am's of the same year and was seeing very similar MAP readings.

In C.L., it doesn't seem to matter what 'standard' AFR I choose, the engine always runs at stoich due to the 'closed loop' O2 sensor. When I average the O2 sensor voltage read-out, it averages about 530 ish, or 14.5 or 14.6 AFR, probably due to the 'up to 10% ethanol' blend. I think my NB is pretty accurate at the 14.0-15.3 range which is all I probably need for now (except at WOT) until I eventually get my WB.

BTW, I am actually now able to change my CL AFR in HPT now. It was just a setting I had to change (for more advanced stuff). But I still fail to see what it has to do with much anyway since CL defaults to stoich due to the O2 readings.

I might make a thermostat change to 180 next time I'm in that area of the motor since I agree these motors run too hot already. I'm definitely not going to 160 though. My calibration method is basically what you had in mind above. I haven't done anything dramatic yet to the intake system or cam so I shouldn't need to touch the MAF and VE tables. I just am focusing on the AFR (in very small changes) and touching-up the spark tables when I have enough data from logs to intelligently change and rechange it.

[hoosierloser]

I'll be honest and say I dont know alot about tuning yet but have you taken fuel pressure readings from the rail yet and compared them to the service manual specifications? like KOEO and KOER specs? and also that really low vacuum is strange. If anything I would try to fix those oddities first because even though it looks like your finding a way around it, it may make tuning later on easier on you, and still get those mpg's. That's just the path I would take first.

[chri0029]

Yea, I checked the fuel pressure and stuff first. Consistently at ~55 psi (even did a leak-down). I did all the basics, at least all I can think of. But I have to be missing something ... I figure just playing around with cals and stuff I'm learning at the least. I'll stumble onto a breakthrough soon enough with the car and repost an update. Once I fix the main problem, I'll have enough experience to write a pretty sweet cal, especially once I start adding the good hardware.

[86FieroSEv6]

Question: What is the MAP reading at key on engine off? It should agree with your locally reported barometric pressure. This will be an important clue for going forward in this troubleshoot. Remember, MAP is absolute pressure, not a direct vacuum reading.

[SappySE107]

you will lose milage with a 160. I wouldnt use a 180 and I wouldn't say it runs too hot stock other than fan turn on times. Keep the 195. Don't replace the map, its fine. kpa is normal. OL is good for WOT tuning and cold start. KR is normal, when you have that much advance (looking at the old datalog). Have you tuned the MAF yet?

[chri0029]

Have you tuned the MAF yet?

No, I haven't done that yet. The air system is stock except a K&N, so I wouldn't think this should be out of whack..??

What is the MAP reading at key on engine off?

Don't replace the map, its fine. kpa is normal.

I agree, the MAP KOEO is consistent with the local weather man - ~99 kpa or 29.2" of Hg.

[SappySE107]

VE tuning doesn't do much. You can drive for a while with the VE table 0'd out. Not sure why it died on me a few miles down the road like that but I know it wasn't used at all until the engine died and refused to start again until I changed it. MAF tuning is easy with HPTuners if you graph maf hz vs ltft. That can make a big difference right there.

[chri0029]

Cool! I will try a MAF re-cal in HPT and see if that makes a difference.

Regarding AFR and CL, how do I make any changes to AFR in CL since the PCM automatically adjusts itself to stoich per the O2 sensor anyways (no matter what the AFR setting in HPT is)? Can I make the engine run slightly leaner (15.0 or 15.3 AFR) in CL?

[85erbirdie]

hey guys sounds like ur having fun i do agree with the vacum issue should be taken care of first whenever i have ran into a problem that seemed way wierd or overly complicated i try to remember the basics sometimes we tend to overlook them and go to the technical stuff first so things that i feel might be an issues and i might sound a little grade scholl but 1)mpg issue with knock have you check the fuel filter and done a fuel volume test i see you did a pressure and leak down but we know their is a differance between pressure and volume also a amp check on the pump might be a good idea as well 2)vacum issue i remember a lumina van that was running rich that took me for a spin the map was running it rich so i changed that didnt solve it changed the o2 didnt work and finally realized after like two weeks to check vacum ie basics lol and it was low sounds like the same issue here and it was a loose timing chain i saw someone already threw that out and that can and will cause issues with the whole fuel managment system so maybe you can check ur base timing car with the car off then turn the crank back and forth and mesure how many degrees of movement on the crank before the cam starts moving that should give you a idea of timing chain strech these are the things i would check first before changing the parameters on the ecm but let me kmow i still am a rookie compared to some of you guys in here but these are allways the problems that make us better

[chri0029]

Yea, it is kind of fun doing all the tuning and learning along the way. But I agree with you about the basics. No matter what tuning I do, I can't seem to get the mpg's up to where they used to be. I think I have already covered all the basics, but I have to agree that there are a few stones unturned. I already changed the fuel filter and verified fuel delivery, but not fuel volume. I guess since a few people threw it out there, it's good to check chain slop. I previously ruled this out since there were relatively low miles - under 100k. I would expect this more at 200k + miles. But I guess anything is possible. Even the very slight chance it DID jump a tooth, that might explain the vacuum irregularity somehow..?

Once it gets a little warmer in the garage, I will look at some more of the basic mechanical stuff.

[85erbirdie]

i doubt it jumped a tooth if it did it would bearly run so if you do the math 720 degrees divided by 6 cylns is 120 then take in to count how many teeth are on the gear then that will tell you how many degrees the cam has retared which you be noticed by alot more then just bad milage and low manifold vacum but figuring out the problem is the most fun i would love to see what it turns out to be

[bszopi]

i doubt it jumped a tooth if it did it would bearly run so if you do the math 720 degrees divided by 6 cylns is 120 then take in to count how many teeth are on the gear then that will tell you how many degrees the cam has retared which you be noticed by alot more then just bad milage and low manifold vacum but figuring out the problem is the most fun i would love to see what it turns out to be

Cam gear has 40 teeth, so it would be off by 3 degrees.

[chri0029]

I'll let you guys know for sure what I find when I tear into a few things in the next few months when it gets warmer out in the garage.

Thinking more about it, I replaced the head gaskets and LIM gaskets about 40k miles ago. I used the GM parts kit. It's possible that the fuel mileage took a dive around that time. I was thinking about it and can't come up with anything that I could have done wrong that would cause the lower mpg. Can anyone think of anything? I don't think there's a way to install the LIM gaskets backwards. You guys have probably torn into the upper part of the engine a lot more than I have.