Alright guys I got my 98 Prelude H22a swap done and running. However The car runs very rough and feels like its misfiring. I pulled a pending code of p1399 which looks to be a multiple misfire. The only gasoline I had at the house in order to get her started was 87. So my question is could the low octane cause the engine to retard timing enough to make it run rough, and not idle. Also i can start her up and let her heat up for a little and she will run and idle fine. However the second i begin driving the problem occurs. Thanks!

PS. Spark and egr were already checked.

 

Unlikely unless the gas is old, the ecu can change the timing if fuel knock occurs from low octane gas, the compression isn't that high stock.

 

Does anyone know why US has such low octane fuel?

In the UK our standard petrol is 95ron and super is 98, with places like Tescos(our walmart) having 101ron.

 

They are the roughly same octane just rated different. The US uses an Anti-Knock Index (AKI) rating while in the UK you use the Research Octane Number (RON). 87 AK (US standard) is equal to around 92 RON (UK standard). So regardless your super 98 is around the Highest I have seen in my area. (98 RON = 93 API).

 

In the US it doesn't matter ... we have E85 which is 105-110 octane