Rough Idle, low power, and engine dies at stoplights

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Re: Rough Idle, low power, and engine dies at stoplights

Post by rconlon@ou.edu » Thu Jul 12, 2018 11:18 am

These exact symptoms are so similar to another Pinin that I know. It was fixed by a shop who replaced a lot of parts and thinks it was replacing the AFM that fixed it.
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Re: Rough Idle, low power, and engine dies at stoplights

Post by bartigue » Fri Jul 13, 2018 7:03 am

AFM and the rest of the FI system is fairly easy to test with a multimeter - I tell folks to make sure to test it dead cold and after running. Electronic devices that behave erratically in the extremes are failing The AFM is a very reliable device, but modified ones and those that have been in service for 20+ years are certainly suspect.

Another issue related to the AFM is related to the fuel pump being turned on and off, and really has nothing to do with the AFM. If the idle is set wrong or an air leak occurs post-AFM the result is the AFM door not opening enough at idle. When this happens the chrome rod in the AFM that opens the fuel pump switch triggers on and off. The result is (to borrow from the title) - rough idle and the engine dying at stoplights. It usually does not result in low power though.
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Re: Rough Idle, low power, and engine dies at stoplights

Post by searya » Sun Jul 15, 2018 12:53 pm

So got a timing light and am running through a bunch more checks as well using the maintaining the Italian roadster book (pg 133 double relay tests)

Here is what I got and wondered if #2 and #3 were a problem? This is testing at the double relay under dash on the passenger side.


Double Relay Test Results:
1. General voltage was 11 to 12v
2. Voltage yo fuel pump was 12v if I gave it more gas. Without more gas it was 1-2v
3. Voltage from input ingnition was 9v
4. Voltage into fuel pump was 12v
5. Voltage into control rely was 12v
Y. Output voltage from control rely was 12v
Last edited by searya on Sun Jul 15, 2018 3:54 pm, edited 1 time in total.
Sean
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Re: Rough Idle, low power, and engine dies at stoplights

Post by rridge » Sun Jul 15, 2018 2:38 pm

If the voltage at the battery terminals is between 11 and 12v then you have found the problem, an almost dead battery. You can't troubleshoot electronics without first charging the battery. At 72 degrees F, a fully charged battery should be 12.6V. By the time its down to 12.0 it's lost 90% of its charge. Harbor Freight sells cheap battery chargers and digital VOM's.
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Re: Rough Idle, low power, and engine dies at stoplights

Post by searya » Sun Jul 15, 2018 3:22 pm

At the actual battery in the trunk I do have 12.6 so thinking the battery is good. Just odd that I had less at the double relay for tests 2 and 3.
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Re: Rough Idle, low power, and engine dies at stoplights

Post by searya » Sun Jul 15, 2018 3:32 pm

Also I just did the timing test with someone keeping the throttle open enough to keep 1000 rpm. Timing was showing way before the 10 btdc

Not sure why it would change overnight though.

Any I am going to loosen the distributor nut and turn it. To get less advance which direction do I twist? Clockwise looking down at the distributor?
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