99' ih 4700 truck 444e engine
 

Hoping someone will have seen this. On the listed truck, have encountered an active code with service max that comes up as unknown. Dtc is -1 Spn 21 Fmi 4. Have talked to IH dealer and they tried but were not able to help. Other active code is for baro sensor and will replace upon receiveing part. Truck starts and runs but has no power and acts like missing at speed under load or driving. Grateful for any info.