MOPAR ECU performance discussion

[Ben Gratt]

Ben,

Did you ever do a dyno of your car with the hi-flow cats and the stock ecu? It seems likely that your gain of 7 hp and 10 ft-lbs was due to removing the stock cats, rather than any gain inherent in the Mopar ECU itself.

You might even make more power with the stock computer and the hi-flow cats. However, this brings up an interesting problem. Since you are getting a check engine light with the hi-flo cats, will your car really make less power (due to the check engine light)? Does anyone really have any data to prove that the cars go into some type of limp mode with the light on? Does the car run richer on the dyno's air fuel meter? I was under the impression that the check engine light is merely annoying, but doesn't really cause the computer to affect mixture or timing.

I've got a 2000 GTS and I'm about to install Borla 17113 headers and Sean Roe's hi-flow 3 in cats. He said that his cats haven't caused the check engine light to trip on the late model cars, so I'm hoping I won't have this problem. What type of hi-flow cats do you have?

Ben.

 

[treynor]

Ben,
Good questions. First off, the 'check engine' light came on about 1000 miles after I had installed the headers & catback, but while I was still using the stock catalytic converters. I switched to the MOPAR ECU and the high-flow cats at the same time, the ECU to get rid of the engine light and the cats to potentially pick up more power. You are absolutely correct that I don't know the relative effect of the MOPAR computer on power, but without reinstalling the stock computer and running it for several hundred miles to finish the adaption cycle, it's hard to test.
Regarding the actual effect of 'check engine' on the car's performance, it certainly had a large impact on mine! I have Roe Racing's A/F meter on my car, and when the check engine light came on, the mixture would always run full rich at WOT, which means I was down 20-30 HP based on previous experience. Obviously, there are many codes which might set off the check light, and some of them would have different effects on performance, so YMMV.
I don't know which brand of cats I have -- they were selected for me by APEX. You may very well not get a 'check engine' with just cats & catback exhaust -- and there appears to be no reason to change ECUs if you don't...

 

[Fred(DrivingSchool)Kinder]

Stock Cats can reduced HP by 5%. The %loss on your engine may vary depending on engine Mods.

 

[LTHL VPR]

I have done many dyno runs with my check engine light on in my 98 GTS due to no cats. It never seemed to effect hp, tq, or A/F readings.

In fact, several times I would reset the computer between dyno runs and I never really saw a noticeable difference either.

 

[treynor]

... so we now have several data points on the MOPAR ECU and its efficacy:

* On my car, adding the MOPAR ECU eliminated the 'check engine' light I was getting with the stock ECU. I made 438 RWHP and 485 ft/lbs on my '01 with Belanger headers & exhaust, K&Ns & smooth tubes, high-flow 3" cats, and the MOPAR ECU, which was 7 HP and 10 ft/lbs more than I had made with stock ECU and stock cats. My car runs slightly hotter than it did with the stock ECU, and the idle is lower.

* On SoCal's car, the car lost 15 HP and 20 ft/lbs with the MOPAR ECU.

* With Ken's testing at Timberline Dodge, cars lost 10-20 HP when switched to the MOPAR ECU.

Sooo... the question is, what's going on? My car certainly didn't lose HP at the dragstrip when I switched to the MOPAR computer -- I picked up 0.5 mph between running with the stock ECU and stock cats and the high-flows / MOPAR ECU, even though it was a warmer day and I had a headwind.

I've done enough dyno runs with an A/F meter attached to reach some tentative conclusions:
(1) the ECU adaption cycle takes time. Right after switching ECUs, I can't get the car to run less than full rich (<12:1) at WOT. Running rich kills power & torque; I lose 25-30 HP when the A/F dips down. 100 miles later, the ECU will lean out to about 12.5:1, and the HP comes back.
(2) Vipers are very very sensitive to heat & coolant temp. If I run without a fan on the car, and the coolant temp rises much above 195, peak HP drops below 400 and the car runs very rich. My best run (438 RWHP) was achieved when the car was at exactly 190 degrees.

My sneaking suspicion with all this is that the MOPAR ECU is running more ignition advance than the stock ECU, raising temps a bit. However, like the stock ECU it will retard ignition and richen mixture if the car starts to run hot. This would combine to make the MOPAR ECU underperform on a dyno.

Question 1: on the dyno runs comparing stock ECU with MOPAR ECU, was any record kept of the coolant temps before / after the runs?

Question 2: has anyone run on the dyno using a 180-degree thermostat and a fan and/or radiator sufficient to reduce temps to ~180? That would be very interesting data, especially if combined with a stock / MOPAR ECU swap.