Random low idle and loss of power (12A Weber DCOE)
03-04-22, 11:42 AM
#1
Random low idle and loss of power (12A Weber DCOE)
I'm a little stumped. Car has a 12A with Weber DCOE, and an old MSD Streetfire drives the leading plugs.
The engine has developed a problem where the power drops, idle is low, engine shakes a little, but then it comes back and acts normal.
This started last weekend after the car sat for 2 weeks. At that time it had trouble starting until I cleaned the corrosion off the battery terminals.
What I've tried in order:
Replaced fuel filter.
I've had trouble like this before and it was dirt near the idle jets, but cleaning them did nothing this time.
Also took off the top cover and saw a dirt spec at the float needle seat so I switched it with another in case the seat was worn out. Float level was checked at the same time.
Replaced plugs since I was ordering stuff from RockAuto anyway.
Checked for vacuum leaks, nothing obvious found.
So today after doing the above, I drove it for a half hour, up and down the freeway, and it was fine but on the way back the power dropped again.
Engine started fine when warm after that trip. Caught video of it shaking at idle (see below), and the revs dropped, but right after I stopped recording it went back to idling smoothly.
When troubleshooting last weekend I *thought* I heard noise from the fuel pump driving in a parking lot. Before I mess with that is there anything obvious I'm missing?
Fuel pump is an Airtex E8004 that was installed in 2019. The similar spec Carter it replaced lasted a year, that's why I'm leaning towards the pump and believing all the low pressure/high flow pumps are made poorly now that there's barely a market for them. However, my experience is that they just quit instead of burning out slowly.
The engine has developed a problem where the power drops, idle is low, engine shakes a little, but then it comes back and acts normal.
This started last weekend after the car sat for 2 weeks. At that time it had trouble starting until I cleaned the corrosion off the battery terminals.
What I've tried in order:
Replaced fuel filter.
I've had trouble like this before and it was dirt near the idle jets, but cleaning them did nothing this time.
Also took off the top cover and saw a dirt spec at the float needle seat so I switched it with another in case the seat was worn out. Float level was checked at the same time.
Replaced plugs since I was ordering stuff from RockAuto anyway.
Checked for vacuum leaks, nothing obvious found.
So today after doing the above, I drove it for a half hour, up and down the freeway, and it was fine but on the way back the power dropped again.
Engine started fine when warm after that trip. Caught video of it shaking at idle (see below), and the revs dropped, but right after I stopped recording it went back to idling smoothly.
When troubleshooting last weekend I *thought* I heard noise from the fuel pump driving in a parking lot. Before I mess with that is there anything obvious I'm missing?
Fuel pump is an Airtex E8004 that was installed in 2019. The similar spec Carter it replaced lasted a year, that's why I'm leaning towards the pump and believing all the low pressure/high flow pumps are made poorly now that there's barely a market for them. However, my experience is that they just quit instead of burning out slowly.
Last edited by j_tso; 03-04-22 at 02:03 PM.
03-07-22, 09:35 PM
#2
Last week while troubleshooting, I found gas pouring out of the carb with the fuel pump on. Since the needle was already changed, I changed out the float.
Gas stopped spilling, but the bogging and low idle persisted.
I decided to say "screw it" to rational problem solving and swapped the carb out with another DCOE I have.
Kept the same jetting, venturi was 1mm bigger. I didn't feel any power loss and the idle didn't fall while doing a mix of street and highway driving.
I had a spare DCOE because the next engine is going to use both, so I'll be in for twice the fun should this happen again.
Later I'm going to do a thorough cleaning and check over on the bench.
Gas stopped spilling, but the bogging and low idle persisted.
I decided to say "screw it" to rational problem solving and swapped the carb out with another DCOE I have.
Kept the same jetting, venturi was 1mm bigger. I didn't feel any power loss and the idle didn't fall while doing a mix of street and highway driving.
I had a spare DCOE because the next engine is going to use both, so I'll be in for twice the fun should this happen again.
Later I'm going to do a thorough cleaning and check over on the bench.
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