Ben, I had almost identical results a year ago on my '97 C2S. The problem turned out to be a hair-line crack in the fitting where the main vacuum line originates. At times it would leak, while at other times it would not (I guess due to engine movement, etc.). Drove us nuts finding it.

BTW, another clue we had was that the HVAC airflow direction "flaps" would work properly sometimes, other times not......

 

Thanks Bob,

Vacuum leaks are where we're going first - and my A/C does act up on Max A/C setting. Funny thing is that 4 vacuum leaks were found about a year ago - guess we needed to keep looking.

Ben

 

Damn Steve, you have to temp me like that. I wish mine wasn't a '96 with the funky box that can't be chipped. I don't feel like shelling out for another ECU. Maybe one day and I'd definitely send it to you.

I don't want to get into the exact numbers of the air/fuel mixture, as I think they are not extremely accurate, what I want to know is why our curves are so different? Could it be that they just didn't place the probe properly in the exhaust?

Scott, I don't remember if I asked but did you get the dyno run files electronically? BTW, it was nice meeting you.

Deltawedge, your rev limiter didn't kick in, it was the shop that stopped it at 6K. They did that to me on my first run and I had to convince them to rev it up to 6750. Remember, these guys are use to dynoing small/big block cars that don't really go over 6K.

George

 

Thanks again Steve for your insights. It surprises me somewhat that the difference between 285hp and 272hp really is no difference at all. Makes me feel a little better about buying a 1995! (except for that torque thing...)

 

I'd need a great deal more detailed info about your car to know why yours runs leaner. It might also be due to how the sensor was positioned in the tail pipe.

 

Steve, my question is not about my car running leaner, it's about why the shape of the curves looks so different. Mine looks almost linear, while Ben's looks concave.

But since you mentioned my car running lean, I’ll ask one more question. Wouldn’t my engine run hotter if it was running lean? The reason I ask is that my engine never gets close to the red mark on the engine oil temp, even on the track, and 110 degree days are not uncommon during the summer here. Also, I don’t have the additional oil cooler. I’ve helped a couple of my 996 friends put third radiators on their cars and always tease them about how cool my car runs.

George

 

There are many factors that influence the shapes of the curves; some are environmental and some are mechanical. We've found that cam timing disparities can account for the reason why some 993's run harder than others. Engine running temps account for some differences as well.

Running lean doesn't ALWAYS result in a hotter running engine. Once again, its a question of degree,....... I've seen a good number of these cars with partially obstructed front oil coolers from road dirt, grass, leaves and things like that. With the lower third of the cooler partially blocked, these cars will run hotter. I like to pull the front bumper cover and clean the whole cooler to ensure that its doing the best job it can to keep the motor cool.

It would be interesting to be for you and some others to have compression & leakdown tests performed at the same time to see the differences.

 

I have preliminary information from my tech on leakdown & compression.

Cylinders 1-5 all have < 10% leakdown and compression of 185 (units?).
Cylinder 6 has 18% leakdown and compression of 160.

Cylinder 6 is not happy - any chance this valve spring or lifter issue (valve not making good seal). I'm not using much oil (quart every 1000-1200 miles) so piston rings don't seem likely.

Ben

 

Ben, I wounder if Hans would let me take my car there so that he could compare the two?

George

 

Ben,
The units are psi. I'm not convinced that the magnitude of the numbers are all that meaningful because my previous 1996 C4 measured about 240 psi with one about 10% lower. Although the numbers were high, the car pulled 215 hp on a 4-wheel dynojet, which was disappointing. Some have said that you want numbers at 200 psi or higher, but I don't think that's a rule to live by. My current car measured at 200 psi on all but one cylinder which measured 190 psi. This car feels much faster than my prior.

But still, your numbers DO seem low, and your weak cylinder surely doesn't help.

 

Eric,

I'm sure I don't understand the compression test correctly but it seems to me that it would measure the maximum pressure attained during the 4-stroke cycle. Atmospheric pressure at sea level is 14.7 psi and the compression ratio is supposed to be 11.3:1 (optimistic) so that would either be 14.7 + 11.3*14.7 (psia) or just 11.3*14.7 (psig) for a maximum pressure of ~180 psia. So it seems like the cylinders registering around ~180 are good and the one down at 160 is definitely low.

I suppose the slop in the magnitude of the numbers could simply be pressure gauge calibration. I'm betting most shops don't use annually NIST certified gauges ;-)

Ben

 

I wish that was the case, but it looks like it's the chip. The first run went to 6700, but the subsequent runs cut out at 6000. The cutting out at 6k also happens while driving more often than not. Andial said they had issues with their chips and as a result they don't produce them anymore. Oh well, time for a chip from Steve.

P.S. From the looks of their shop they are used to the Civic and Celica crowd (Japanese auto tuner). They did ask which end had the motor(to hook up the tach) on my C2, amusing.

 

Sorry Ken, I thought your experience was like mine.

I would definitely change out that chip. 6K is where all the fun begins.

George

 

Like Greenspan would say, it's like taking away the punch bowl just when the party's getting started. It's new chip time.