[ReefBlueCoupe]

Hey guys,

I don't have a tweecer yet, but I will probably be getting one soon. I'm not 100% familiar with the tweecer yet, but I understand the concept and am good with computers and math, so I should pick it up quickly.

I will briefly describe the problem I am having, and what I want to get out of this is, is this a common problem that can be fixed by using the tweecer.. I want to avoid having a chip burned that has to be reflashed should I ever make a change and need a new tune.

Ok, combo:

93 LX, 5 speed, stock computer that has never had a tune,
347, 10.9:1
TFS TW heads, unported
TFS Track Heat intake, unported
TFS Stage 2 cam,
1.6 RR, 70mm TB
75MM MAF, cal'd for 30lbers
30lb injectors
1 5/8 headers, 2.5 inch exh
3.73 gear
Base timing is down to 12 degrees BTDC while I am having this problem, but TFS reccomends around 18deg BTDC..

The problem I am having is a little bit of detonation. It happens after the car is warm, and while I am lightly or even somewhat heavily rolling into the throttle below 2k RPM. Even just normally accelerating in say 4th gear at 40mph gives me some detonation. It gets "past" the detonation above 3k RPM and from there on out it seems fine. During normal driving, however, I am rarely above 3k RPM so you can see my dilemma. At WOT I do not hear any detonation, and I can give it a good amount of throttle at a fairly low RPM even in 3rd and 4th when the car is cold, and no detonation there either. I wasn't sure if this is because the parts hadn't heated up yet, or because it's still running a richer fuel curve at that point...

When I go WOT it doesn't detonate, but the engine seems to "break up" around 4500+.. I don't really know exactly where to start with that part.. I don't want to throw ignition parts at it to try to fix that because I'm guessing it's the tune and not the ignition.

I haven't been to a dyno yet. I want to get the tweecer before I do go to the dyno so I can make some adjustments there with the help of some friends who know more about it than I do.

Based on what I've said, is this something that is commonly tuned out with a tweecer? I realize the compression ratio is high at almost 11:1, but plenty of people run that kind of compression ratio in Mustangs with no problem.

From what little I've read so far, this may be because my tip-in settings are either too lean or there is too much timing there..

Thanks for any help! Please let me know if you need anymore information.

Thanks,

Chris

[EFIpunk]

what gas are you running?????

[ReefBlueCoupe]

Ethanol.

Just kidding. 93 octane pump gas....

[Jack Hidley]

Chris,

This will be easy to fix with the Tweecer.

Basically you have one main problem. The EEC is coming up with the incorrect engine load because there are things about the sensors and engine displacement it doesn't know about.

Specifically the use of an MAF "calibrated" for 30lbs/hr injectors means that the EEC thinks the engine load is 19/30=63% of what it really is. At lower loads, the EEC is going to command more spark advance. This is why you are not getting detonation at WOT. Under WOT, the A9L goes to a nonload based function to determine timing.

I don't know the specs on your camshaft, but the duration of it may be narrow enough that the 10.9:1 compression ratio is simply building too much cylinder pressure at low rpms. This is easy to compensate for in the various timing tables.

If you do a search, you can find tons of information on the subject of inaccuarte load calculations from the EEC not having the correct MAF transfer function.

[ReefBlueCoupe]

Thanks for the info. I will probably be getting a LMAF and using it instead of this meter also, but I'm using this one to get me by for now.