400SE suddenly running weak
Discussion
To cut a long story short, I ran out of fuel recently and damaged the fuel pump. I got my local garage to change the pump and drove the car the short distance home with no problems. The next time I started the car it idled ok while I got it out the garage. I stopped the engine, closed the garage doors and when I restarted it, it was running very weak (AFR about 18-20 cold). Since then it has done this consistently. It runs weak and misfires a bit. I think maybe the filter has become blocked or the fuel regulator has packed up. I put a pressure gauge in the fuel line and primed the pump. The pressure showed as 38 psi. When the pump stopped after 5 seconds the pressure showed 30 psi. This is where it gets odd. I started the engine and the pressure showed a constant 30 psi with it running weak. But when I switched the ignition off, the gauge slowly crept up to 35psi and stayed there. Should it do that if the pump isn't running and what pressure should a 400SE be showing when the engine is running. So what do you reckon folks, is this a faulty pressure regulator, a blocked filter or something else? Could the new pump be under rated for the system. I don't now what pump was fitted. TIA for any help/ideas.
I'm not sure this is going to help much, but you never know.
My fuel pump failed and a while later I noticed the replacement had become noisy. I clamped the rubber fuel line to it to save draining the tank and inside the inlet side is a small nylon gauze filter. It had become clogged with fluff and other stuff from the bottom of the tank. Replaced it and all was good. It makes me wonder if your pressure is ok when you are testing it but you're not getting enough flow and pressure when actually driving. Just a thought.
My fuel pump failed and a while later I noticed the replacement had become noisy. I clamped the rubber fuel line to it to save draining the tank and inside the inlet side is a small nylon gauze filter. It had become clogged with fluff and other stuff from the bottom of the tank. Replaced it and all was good. It makes me wonder if your pressure is ok when you are testing it but you're not getting enough flow and pressure when actually driving. Just a thought.
Update: I've managed to track down the problem. Despite the AFR suggesting it was being starved of fuel, it turns out the HT lead from the coil had worked its way loose so that it was making a poor contact at the coil end. This must have led to various plugs intermittently not firing and giving a high oxygen content in the exhaust hence a lean mixture. Strangely there must have been enough contact with the coil that it would start first turn of the key every time and rev easily. I've adjusted the lead connector and full power has been restored. It just goes to show just because I had recent fuelling problems it's worth checking everything logically and not making assumptions like I did!.
lancepar said:
If it's the same pump as a Chim or Griff you can do it no harm by running it backwards, might be worth a try if it's partially blocked.
This is exactly what a garage did to mine in Southern France to clear it of debris.Edited by lancepar on Wednesday 26th October 20:05
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