Onan 5500 Backfires and Dies under a load

lakecityemt wrote:
Good Morning.. Im hoping to find the Onan guru's that are here... For the past year I have been searching for answers and replacing parts with no improvement.

I have an Onan 5500 with less than 100 hours in my toyhauler. It began backfiring and then dying when a load was placed on it. I have so far replaced the carb, fuel pump and filter, fresh gas directly from beneath the gen. Once it starts backfiring, if the load is stopped, it continues to "put put backfire" until it dies then gives an overheated exhaust code (I assume from the backfiring?). Plugs were replaced, now currently testing to see if there is spark to both plugs. Please someone help me solve this issue!!! I'm in BFE Alaska in a perm set up, there's no ONAN tech here so I'm on my own... Thanks for ideas and suggestions!!

Backfire through the exhaust is often too rich. Backfire through the carb is too lean.

If no ONAN service I would look for a lawn mower or small engine repair shop.

I would be tempted to remove the carb and apply fuel pressure and see if it leaks. Rich will tend to foul the plugs black and lean will have them normal to extra white.

If an ONAN tech sees your message they will want the exact model number and serial number to avoid playing 20 questions.