1989 240 b230f engine I love dearly.
My problem occurs when the weather ouside is below 40 degrees F. The car will always start and idle fine, but sometimes the engine has no power and backfires when I hit the gas. When I let off the gas it returns to normal idle. The problem goes away for a varying amount of time if I shut the engine off and restart. I have noticed when this happens, the primary fuel pump makes an abnormal growling type noise and seems to lope (rrrr r r r r r rrrr r r). The fuel pump is only about a year old. I have replaced the pre-pump, both filters, fuel pressure regulator, fuel pump check valve and relay. The hose on the pre pump looks good and I dont think it could be collapsing. Could this be due to a faulty ground? Where is the fuel pump ground located?