Limp home mode question

[99Formula]

What sensors are bypassed when the car is placed in limp home mode, i.e. ECM connected with no chip installed? Is there just a basic closed loop table that it follows?
Right now my car will actually run better with no chip in and the SES light flashing than it does with a chip, no matter the type. I'm trying to track down the problem but haven't had any luck yet.

Peter

 

[SubZero350]

Also known as "Back-up" mode, this is the mode in which the ecm uses the CAL-PAC. The CALPAC chip allows the ECM to run the engine using only distributor reference pulse and throttle position inputs to change fuel and timing calculations. The coolant temp sensor may also be utilized on some systems.

Basically, without the PROM, the ECM is running your fuel injection like an ALPHA-N EFI system that only uses TPS and Distibutor Reference Pulses to deliver fuel and spark.

Sounds like your problem might lye in the MAF sensor or PROM itself. The ECM may not set a MAF code if the MAF has a re-occuring intermittent fault. I would try a known good unit if one is available to see if that is your problem.

Hope this helps.

 

[Turbo PeppeR]

my maf is off my car if you want to try it,I live in green valley...

 

[WarpSpeed]

I would agree with the MAFs. When in Limp home mode, the ecm runs the engine very rich,,, so, it seems in normal closed loop it's not getting enough fuel,,,,,,,if it runs better in limp mode.

 

[99Formula]

Originally posted by Turbo PeppeR
my maf is off my car if you want to try it,I live in green valley...

Thanks, you have email.

Peter