Open Loop on Hwy

[matt59]

My 93 Atx goes into open loop on the Hwy. The CEL Lights and it looses more than 50% power.
It boggs down to about 25mph.
I checked and there are no stored codes. What am I missing?

 

[luigisho]

Check engine light should always trigger a code. Does it happen every time? Any way to replicate it in a garage?

 

[matt59]

Unfortunately I can't replicate the problem unless it's under a slight load.
I have an Old TECH1-A and have captured the data but the only thing I found was it goes into open loop. But there weren't codes. I have never run into this type problem

 

[luigisho]

Have you used it successfully to retrieve codes on this car before? I have a few code readers/scantool and some do not work correctly on my SHO's OBDI for some reason. Maybe replicate it again on the road and try for codes with the traditional method? Open loop has usually been a faulty sensor or PCM when I have had to hunt it down. The first thing that comes to mind with intermittent open loop when running is a failing MAF sensor..

 

[matt59]

Have you used it successfully to retrieve codes on this car before? I have a few code readers/scantool and some do not work correctly on my SHO's OBDI for some reason. Maybe replicate it again on the road and try for codes with the traditional method? Open loop has usually been a faulty sensor or PCM when I have had to hunt it down. The first thing that comes to mind with intermittent open loop when running is a failing MAF sensor..

The Tech 1 in its day was one of the best. I am sure it's not anymore but it is all I have. I'll try the MAF and let you know. Thanks for the input.

 

[luigisho]

They are great when they work properly on a specific application. That's why I asked if you have been able to use it successfully on the SHO for code retrieval before

 

[matt59]

Oh, yes many times. Also on my 92 Supercoupe and 90 Dodge Daytona Shelby. Maybe because I have the big three cartridge, it may not be as good as a dedicated cartridge.

 

[rubydist]

I would try counting cel flashes to be sure there is nothing there.

If no codes with your description, then the pcm is suspect.

 

[luigisho]

I agree with above

Although I think I do remember a time or two having issues with no code but nothing as dramatic as stated in the initial post

 

[matt59]

PCM was swapped out before when the car would die unexpectedly. I never thought it might be responsible for doing this kind of stuff. Just to be clear we're not talking about the ECM right?
I changed the one on the front header above the radiator.

 

[luigisho]

The CCRM is the relay module above the radiator. The PCM or ECM I think are used interchangeably. Either way, we are referring to the computer that's behind the glove box with a large connector on the other side of the firewall. The connector has a long bolt in the middle that runs into the back of the computer so you can't remove it unless you unscrew that first