Troubleshooting Poor Cold Start on a 3.2

[wazzz]

If you disconnect the CHT from plug connector in the engine bay and measure voltage on connector from ECM harness, you should read about 4.3 volts.

[mysocal911]

Originally Posted by et cetera

What would be the best way to check the voltage for the CHT when its plugged in? Open up the ECU and check from there or at the plug connector in the engine bay?

No! Do as Wazzz said, and try to back-probe it when plugged in at the sensor. Since you don't have a break-out box, you really need to remove the ECU connector shell and back-probe the ECU connector.

[et cetera]

Originally Posted by mysocal911

No! Do as Wazzz said, and try to back-probe it when plugged in at the sensor. Since you don't have a break-out box, you really need to remove the ECU connector shell and back-probe the ECU connector.

I plugged in the ECU and checked power at the connector for the AMF, voltage read 4.95.

I then checked the connector for the CHT and it read 1.88.

Figured out how to get the back off the ECU connector.

Port 13 read 1.67
Port 7 read .20 at closed and 3.65 at fully open. Voltage progresses smoothly as the barn door was opened
Port 24 read 0

[et cetera]

I purchased a smoke tester just to double check the vacuum lines, figure it wont hurt and its a good tool to have around. Should get here later today.

I'm also going to find some time to go rent a fuel pressure gauge so I can check that off the list this week.

[et cetera]

To add a bit more context here. I had this 3.2 put into my car after the original 3.0 spun a rod bearing. The metal in the oil system meant that we replaced everything, including the oil tank. The oil tank is the screw on cap style so we also needed to put on a new oil cap.

I performed the smoke test on the vacuum system just now and guess where smoke was pouring out of… that’s right the oil cap. The new oil cap was never installed with the proper gasket. I’m ordering one now and hopefully that will be the last of my problems.

I just want to extend a huge thank you to everyone who gave me pointers. I was pretty familiar with the CIS systems, and I’m happy to have gotten a quick education on the motronic setup. At least now I know what the common issues are and how to troubleshoot them in the future.

Hopefully this thread will help others find answers in the future.

[proporsche]

glad you got it fixed..but..for the future readers
It would help to add all what you did to your 911 to help you solve the problem
As in this case -new oil tank and missing o ring in the cap...;-)

Ivan

[mysocal911]

Originally Posted by et cetera

To add a bit more context here. I had this 3.2 put into my car after the original 3.0 spun a rod bearing. The metal in the oil system meant that we replaced everything, including the oil tank. The oil tank is the screw on cap style so we also needed to put on a new oil cap.

I performed the smoke test on the vacuum system just now and guess where smoke was pouring out of… that’s right the oil cap. The new oil cap was never installed with the proper gasket. I’m ordering one now and hopefully that will be the last of my problems.

I just want to extend a huge thank you to everyone who gave me pointers. I was pretty familiar with the CIS systems, and I’m happy to have gotten a quick education on the motronic setup. At least now I know what the common issues are and how to troubleshoot them in the future.

Hopefully this thread will help others find answers in the future.

Yes, it was that simple!

[et cetera]

Well, I guess I was wrong. Put it all back together and now it won’t even fire up.

I used a little starter fluid and it kicked on for a second, so it’s getting spark.

Is it possible that the smoke test exacerbated a problem with the fuel regulators and they’re now completely choking off fuel?

[et cetera]

Sorry I fell off the map. I went on vacation then immediately on a work trip and didn’t have a chance to get back to the car.

I found a loose wire at the fuse panel which got the fuel pump going again. I must have knocked it loose when checking the fuses.

I’ve replaced the fuel regulator because I had a new one. Tested the fuel pressures and they were in the expected range.

I still can’t get the car to cold start without keeping my foot on the gas.

It will start and idle fine when I unplug the Cylinder Head Temp sensor and jump the female connector going back to the ECU. What I haven’t been able to find an answer on is what type of a condition this puts the ECU into, does it make it run more rich or lean with that connector jumped?

[yelcab1]

I think somewhere up above I suggested that you get a Air Fuel Ratio meter. That suggestion still stands.

[et cetera]

Originally Posted by yelcab1

I think somewhere up above I suggested that you get a Air Fuel Ratio meter. That suggestion still stands.

Not trying to be rude, but in Air Fuel Ratio meter isn’t useful when the car won’t start without forcing it into a different condition.

I did find this video on YouTube. https://youtu.be/kcTkFjOt8Kc?si=eIeHL_O3k1vrgwzP

He has the surging idle, and after he “repairs” the ICV he ends up with the same start issue I’m facing. In the end replacing the ICV seems to fix the issue.

I did the common tests for the ICV, but I suspect something is different when it’s actually running in the car. I’m just gonna order an aftermarket one to rule it out.

[wazzz]

Originally Posted by et cetera

Sorry I fell off the map. I went on vacation then immediately on a work trip and didn’t have a chance to get back to the car.

I found a loose wire at the fuse panel which got the fuel pump going again. I must have knocked it loose when checking the fuses.

I’ve replaced the fuel regulator because I had a new one. Tested the fuel pressures and they were in the expected range.

I still can’t get the car to cold start without keeping my foot on the gas.

It will start and idle fine when I unplug the Cylinder Head Temp sensor and jump the female connector going back to the ECU. What I haven’t been able to find an answer on is what type of a condition this puts the ECU into, does it make it run more rich or lean with that connector jumped?

Leaner. It tricks the ECU into "thinking" the engine is dead warm, so it leans the mixture.
Open circuit is the opposite, tricks the ECU into thinking the engine is dead cold, so it makes it run richer.

[et cetera]

Replaced the ICV, no impact.

I feel like I’m beating my head against a wall now. Not sure what direction to go next.

I think I’m gonna do another smoke test.

[et cetera]

I was curious to see where the bypass screw on the AFM was set to, and it seems to be tightened all the way down. I believe this will cause it to run on the rich side.

I turned it out a full 5 turns, but it doesn’t seem to have any impact. The car still fires and dies immediately.

I know I need some other tools to properly set the AFR, but how far can I back that screw out to try and lean out the mixture?

[mysocal911]

Originally Posted by et cetera

I was curious to see where the bypass screw on the AFM was set to, and it seems to be tightened all the way down. I believe this will cause it to run on the rich side.

I turned it out a full 5 turns, but it doesn’t seem to have any impact. The car still fires and dies immediately.

I know I need some other tools to properly set the AFR, but how far can I back that screw out to try and lean out the mixture?

The mixture screw ONLY affects the idle mixture, i.e. once the throttle opens it has no effect.

[et cetera]

I just unplugged the AFM and started the car. Fired up and idled perfectly. There’s gotta be something off with the settings on the AFM, right?

[mysocal911]

Originally Posted by et cetera

I just unplugged the AFM and started the car. Fired up and idled perfectly. There’s gotta be something off with the settings on the AFM, right?

Sounds like it. The AFM rarely fails, though. Hopefully the flap doesn't stick or the spring setting isn't wrong. Have you check the temp sensor cold resistance?
That's more likely the problem.

[et cetera]

Originally Posted by mysocal911

Sounds like it. The AFM rarely fails, though. Hopefully the flap doesn't stick or the spring setting isn't wrong. Have you check the temp sensor cold resistance?
That's more likely the problem.

I did check the temp sensor. The original one was in range, but I bought a new one anyway.

Tested the new one to ensure it was in range and it checked out as well.

I’m starting to worry the AFM was really messed with before.

[mysocal911]

Originally Posted by et cetera

I did check the temp sensor. The original one was in range, but I bought a new one anyway.

Tested the new one to ensure it was in range and it checked out as well.

I’m starting to worry the AFM was really messed with before.

Jump the temp sensor with a paperclip without disconnecting the AFM.

[et cetera]

Originally Posted by mysocal911

Jump the temp sensor with a paperclip without disconnecting the AFM.

I have, starts right up and idles. Anything I do that leans out the mix at start seems to have a positive impact.