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.
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1984 Pininfarina Azzura
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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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Re: Rough Idle, low power, and engine dies at stoplights

Post by searya » Sat Jul 21, 2018 11:40 am

searya wrote:
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
I am back to working on the Azzura today. Still no luck with the issue. But am still wondering if test 2 and 3 above would lead me to the problem?
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Re: Rough Idle, low power, and engine dies at stoplights

Post by TurboPininfarina » Sat Jul 21, 2018 1:58 pm

Open the double relay to see if you have broken solder.
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Re: Rough Idle, low power, and engine dies at stoplights

Post by rridge » Sat Jul 21, 2018 6:22 pm

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
Re: test 3, are you saying the voltage at double relay terminal 88y was only 9v? If so go back to the in-line fuse that powers the whole FI system. It is usually dangling by itself somewhere under the fuse box or the ignition switch. It should contain a 16 amp Bosch style "bullet fuse". Previous owners often improvise by sticking a common glass fuse in that spot. Check the voltage going into the fuse holder and the voltage coming out at 88y. If it's the original red ceramic fuse it may be on the way out or the fuse holder contacts may need cleaning.

Unfortunately the easiest way to troubleshoot the double relay itself is to plug in another double relay. Since it is a known weak point in the FI system, many Spider owners carry a spare in the glove box. There are other Spider owners in the St. Louis area. Perhaps one of them would be willing to loan one.

As you poke around the FI wiring harness be alert to signs of previous owner rewiring activities. It is common to discover that the fuel pump circuit has been rewired. This is often an attempt to bypass problems in the double relay circuit or in the AFM by powering up the pump whenever the ignition is on, whether or not the engine is running.
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Re: Rough Idle, low power, and engine dies at stoplights

Post by searya » Sun Jul 22, 2018 1:21 pm

rridge wrote:
Sat Jul 21, 2018 6:22 pm
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
Re: test 3, are you saying the voltage at double relay terminal 88y was only 9v? If so go back to the in-line fuse that powers the whole FI system. It is usually dangling by itself somewhere under the fuse box or the ignition switch. It should contain a 16 amp Bosch style "bullet fuse". Previous owners often improvise by sticking a common glass fuse in that spot. Check the voltage going into the fuse holder and the voltage coming out at 88y. If it's the original red ceramic fuse it may be on the way out or the fuse holder contacts may need cleaning.

Unfortunately the easiest way to troubleshoot the double relay itself is to plug in another double relay. Since it is a known weak point in the FI system, many Spider owners carry a spare in the glove box. There are other Spider owners in the St. Louis area. Perhaps one of them would be willing to loan one.

As you poke around the FI wiring harness be alert to signs of previous owner rewiring activities. It is common to discover that the fuel pump circuit has been rewired. This is often an attempt to bypass problems in the double relay circuit or in the AFM by powering up the pump whenever the ignition is on, whether or not the engine is running.

I checked the voltage on both sides of the bullet fuse and it was 12.6. Bummer I was hoping that would be it and an easy fix. I went ahead cleaned the fuse and put dialetic gresse on but same problem. Starts up sounds fine, runs rough then dies (unless I gas it).

I was able to get another double relay but still no luck.

I have access to a bosch computer from an 82 could I try that in place of my computer on my 84?
Sean
1984 Pininfarina Azzura
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