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Discussion Starter · #1 ·
I wanted to share this in case it can help somebody out. I changed the fuel pump in my car and in trying to do so broke the little insert that plugs down into the fuel pump, the supply check valve. Should have re-read the DIY threads but oh well. :)

So I ordered another one, and I installed it, by grafting a brass adapter on to the plastic fuel line and adding a piece of 1/4" high pressure rubber fuel line.

That seemed to worked fine, but while the car idled fine and drove fine when driven slowly, it lacked full power after the fix. I was stumped and tried all sorts of things (vacuum hoses, fuel filter, fuel cleaner, tapped on fuel pressure regulator, tried a different fuel pump), all to no avail.

The car ran fine at partial throttle, and idled fine. But when giving 3/4 or full throttle, it would stumble and just wouldn't pull like it should. It struggled on hills. It sure felt like fuel starvation. When I held the throttle pedal down for too long, it sort of stumbled and choked and finally threw the code P0300.

Somewhere in this process, I ordered, sort of on a whim, a new fuel supply check valve. When it arrived, I blew air through it to check its operation, and it seemed to work ok. I removed the other one, blew through it, and noticed it felt really restrictive. Aha! I installed the new one, went for a test ride, and presto full power, no more check engine light are coming on. ;ol; My diagnosis is that the first check valve was faulty and too restrictive, even though brand new.

So two things I found out are:
1. It is possible to get a code P0300 from a fuel starvation problem (inadequate fuel pressure) I know there are other reasons for this code, but hopefully this adds to the knowledge base.

2. Don't buy a cheap fuel supply check valve (plugs into fuel pump assembly) because it may not allow enough fuel flow.
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