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View Full Version : Problem with Tune = Low Hp and High A/F


SuperG
06-23-2008, 09:44 AM
After 3 attempts, I finally got my '97 on the dynojet and was thoroughly disappointed, although glad to have the results.

Car dynoed at 336 Hp, roughly 65 Hp lower than my peers' setups. Worse, though was the a/f was 13.5 across the rpm range!! If I remember correctly, this is too lean for normal operations. BTW, the a/f was taken with the shop's O2 sensors.

So...is the tune bad? Could there be something else wrong? Can the tune be erased due to a dead battery?

A few thousand miles have turned over since this tune was installed...What kind of neat things happen to an engine that runs lean for a long time?

Your comments are greatly appreciated!

tcrews
06-23-2008, 11:01 AM
A supercharged engine that runs lean doesn't run at all anymore...that's what happens.

You sig list a Vortech SQ, what tune do you have?

13.5 is blow your engine up lean. You should be at max 12.0:1 on the dyno which will put the ratio closer to 12.5:1 when you are on the road (moving the car vs. turning dyno rollers).

You need to get the car tuned on a dyno where they can check the A/F ratios while tuning.

blk04cobra1
06-23-2008, 11:17 AM
After 3 attempts, I finally got my '97 on the dynojet and was thoroughly disappointed, although glad to have the results.

Car dynoed at 336 Hp, roughly 65 Hp lower than my peers' setups. Worse, though was the a/f was 13.5 across the rpm range!! If I remember correctly, this is too lean for normal operations. BTW, the a/f was taken with the shop's O2 sensors.

So...is the tune bad? Could there be something else wrong? Can the tune be erased due to a dead battery?

A few thousand miles have turned over since this tune was installed...What kind of neat things happen to an engine that runs lean for a long time?

Your comments are greatly appreciated!
It's difficult for a car to just "lose" a tune, but it has happened. Also, for your application, 13.5 is very high (unless your running C16 on a built motor, but even then it's high). If the dyno shop used a tail-pipe sniffer then the readings should have been closer to 12.0 (which is most likely 11.5 downstream). If you haven't experienced any detonation, then I would say most likely your motor is fine. I would definitely give another tuner a chance to get your situation squared away :thumbsup:

SuperG
06-23-2008, 12:18 PM
Thanks guys! The last tune was with an SCT Xcal2 at a reputable shop, for which I am downgrading their service from a B to a C+!!

ausie
07-30-2008, 07:38 AM
If you are planning on getting the car returned, make a request to have the existing O2 sensors replaced. O2 sensors when aged will drop in voltage. Replacing with new one's will allow a more accurate reading.

SuperG
07-30-2008, 09:03 AM
But the O2 sensors have to be wideband, don't they? Or are you sating simply from a computer standpoint...in any case, they most likely need replacing, and that's not cheap if I remember correctly.

red04svtcobra
07-30-2008, 05:20 PM
After 3 attempts, I finally got my '97 on the dynojet and was thoroughly disappointed, although glad to have the results.

Car dynoed at 336 Hp, roughly 65 Hp lower than my peers' setups. Worse, though was the a/f was 13.5 across the rpm range!! If I remember correctly, this is too lean for normal operations. BTW, the a/f was taken with the shop's O2 sensors.

So...is the tune bad? Could there be something else wrong? Can the tune be erased due to a dead battery?

A few thousand miles have turned over since this tune was installed...What kind of neat things happen to an engine that runs lean for a long time?

Your comments are greatly appreciated!That is very lean and would definately stay out of it until it gets tuned again. Alot of people believe that the leaner you go the more power a car will make. Thats true to a point. For example, when I bought my car it was bought to my tuner and it was lean, not really bad but still lean, so he richened it up some to 12.0 and picked up at least 25+ HP.
Neat things that happen to motors that run lean are holes in pistons, vented blocks to name a few. :D

ausie
07-31-2008, 07:53 AM
I was refering to the stock primary O2 sensors that connect directly to the ECU (before the cats, assuming you still have cats). I was not aware that the ECU could operate with wideband O2 sensors.

Depending on the year, the O2 sensors should not be that expensive. I could be wrong on that since I have not priced them.

O2 sensors generate their own voltage in relation to the amount of Oxygen present in the exhaust gasses. They usually do not operate when cold. When they age, the response time falls off. O2 sensors can be affected by moisture (coolant in exhaust), burning of oil and carbon deposits. There is alot of info on how they work on the net. There will be some amount of drift in accuracy over operating time. 60k is the expected maintanance replacement interval. The thought is that with new O2 sensors in place, the tune can be set when the O2 sensors are operating with more accuracy.

I am only offering a suggestion. Talk it over with your tuner when the time comes.

SuperG
07-31-2008, 09:09 AM
Well, I'll have to look through my paperwork...I thought I had replaced them last year, but perhaps it was suggested I replace them!! I'll pull them and inspect them at least...and if it's not too much, I'll go ahead and replace them.

Running that lean is scary and right now I have to as the '03 is still in the shop being reassembled. But I'll head to Triangle next week to have them reflash the 'puter!