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-   Porsche 911 Technical Forum (http://forums.pelicanparts.com/porsche-911-technical-forum/)
-   -   Troubleshooting Poor Cold Start on a 3.2 (http://forums.pelicanparts.com/porsche-911-technical-forum/1159230-troubleshooting-poor-cold-start-3-2-a.html)

et cetera 03-22-2024 02:41 PM
Quote:
Originally Posted by yelcab1 (Post 12217990)
I had this problem once. The thing that saved me was Air Fuel Ratio meter. That told me the engine was running rich and the computer was trying to compensate but unable to.

The solution for me was to open up the Air Flow Meter, and found that the previous builder has changed the factory setting to compensate for a different injectors / computer. He then removed said modification to sell the car and never reversed the AFM changes. Put back the factory setting, and the car ran solid after that.

That maybe a problem for you, but you need to NOT guess and just get the Air Fuel Ratio meter.
Just pulled off the AFM and bench tested it with a 9v battery. Starting out I got a reading of .28v. As I opened the barn door the volts steadily increased until it was fully open and rear 5v.

From the articles I found I would expect this to read 9v at full open. I can see two groves on the connection track. Makes me think I should adjust the arm to get a better connection.

How else can I tell if the AFM had other adjustments made?

mysocal911 03-22-2024 03:21 PM
Quote:
Originally Posted by et cetera (Post 12218197)
Just pulled off the AFM and bench tested it with a 9v battery. Starting out I got a reading of .28v. As I opened the barn door the volts steadily increased until it was fully open and rear 5v.

From the articles I found I would expect this to read 9v at full open. I can see two groves on the connection track. Makes me think I should adjust the arm to get a better connection.

How else can I tell if the AFM had other adjustments made?
Yes, measuring voltage is used, but it's the spring tension which determines the fuel enrichment versus air flow.
To lean the mixture, one just increases the spring tension for smooth engine RPM acceleration.

proporsche 03-22-2024 03:32 PM
little help for youhttp://forums.pelicanparts.com/uploa...1711150352.jpg

pmax 03-22-2024 04:12 PM
Quote:
Originally Posted by et cetera (Post 12218193)
I took the throttle body off and inspected the lines. One had a clear tear in it.
You could try pumping air into one of the ports, see if it holds pressure and hunt for leaks with a spray bottle.

mysocal911 03-22-2024 04:31 PM
Quote:
Originally Posted by pmax (Post 12218268)
You could try pumping air into one of the ports, see if it holds pressure and hunt for leaks with a spray bottle.
Please explain why you suggest he needs to search for air leaks, when he has a rich mixture?
When air leaks are the problem, the mixture becomes lean!

The OP's 1st post states the mixture is TOO rich and has to bypass the temp sensor to allow improved starting.

pmax 03-22-2024 05:41 PM
Quote:
Originally Posted by mysocal911 (Post 12218284)
Please explain why you suggest he needs to search for air leaks, when he has a rich mixture?

When air leaks are the problem, the mixture becomes lean!

The OP's 1st post states the mixture is TOO rich and has to bypass the temp sensor to allow improved starting.
OP, have you measured the AFR as recommended prior ?

Quote:
Originally Posted by et cetera (Post 12218197)
Just pulled off the AFM and bench tested it with a 9v battery. Starting out I got a reading of .28v. As I opened the barn door the volts steadily increased until it was fully open and rear 5v.

From the articles I found I would expect this to read 9v at full open. I can see two groves on the connection track. Makes me think I should adjust the arm to get a better connection.

How else can I tell if the AFM had other adjustments made?
I think you are jumping the gun by skipping the measuring step and going straight to thinking about adjusting this precision instrument below.

Quote:
Originally Posted by mysocal911 (Post 12218240)
Yes, measuring voltage is used, but it's the spring tension which determines the fuel enrichment versus air flow.
To lean the mixture, one just increases the spring tension for smooth engine RPM acceleration.
Resist the "encouragement" to tinker. In any case, without a means of measuring the effects, you are flying blind.

Quote:
Originally Posted by proporsche (Post 12218250)
Hope the brain trusts are working on a modern replacement for this 40 yr old electromechanical marvel.

mysocal911 03-22-2024 07:18 PM
Quote:
Originally Posted by mysocal911 (Post 12218240)
Yes, measuring voltage is used, but it's the spring tension which determines the fuel enrichment versus air flow.
To lean the mixture, one just increases the spring tension for smooth engine RPM acceleration.
The nice part of having an AFM is that one can easily move the AFM wiper, without adjusting the spring, and determine whether the AFR is too rich/lean based on how the engine reacts.

RobFrost 03-23-2024 03:14 AM
Redo the vacuum check. It's quick, immediate results, no tools required, and highest frequency cause of problems on these cars.

Sent from my SM-G988B using Tapatalk

mysocal911 03-23-2024 07:22 AM
Quote:
Originally Posted by RobFrost (Post 12218423)
Redo the vacuum check. It's quick, immediate results, no tools required, and highest frequency cause of problems on these cars.

Sent from my SM-G988B using Tapatalk
It still won't explain why the engine is running TOO rich!

et cetera 03-23-2024 08:41 AM
Quote:
Originally Posted by mysocal911 (Post 12218284)
Please explain why you suggest he needs to search for air leaks, when he has a rich mixture?
When air leaks are the problem, the mixture becomes lean!

The OP's 1st post states the mixture is TOO rich and has to bypass the temp sensor to allow improved starting.
It only starts running rich when I jumped the CHT sensor. It’s a bit on the lean side when the sensor is plugged in.

yelcab1 03-23-2024 08:42 AM
Quote:
Originally Posted by et cetera (Post 12218571)
It only starts running rich when I jumped the CHT sensor. It’s a bit on the lean side when the sensor is plugged in.
Did you measure it with a AFR, or with your calibrated nose?

et cetera 03-23-2024 08:58 AM
Quote:
Originally Posted by yelcab1 (Post 12218572)
Did you measure it with a AFR, or with your calibrated nose?
Haha, just the sniff test for me. The mechanic at the shop that put the motor in said it is running lean. He also suggested is was just the idle control switch, or the need to clean the ICV. So who knows.

They had the whole intake manifold off to replace some leaking fuel lines. They said they inspected and replaced the gaskets. I’m sure they didn’t vacuum test it.

mysocal911 03-23-2024 09:05 AM
Quote:
Originally Posted by yelcab1 (Post 12218572)
Did you measure it with a AFR, or with your calibrated nose?
You, like some, failed to read/understand the OP's first post;

Quote:
Separately, I can jump the CHT at the female connector and it fires right up and idles at 800 RPMs.
This implies that the mixture was too rich with the temp sensor connected, and that by jumping it (leaning the mixture), it ran normally.
It doesn't get any easier than that! Tests like that are why the 911 3.2 is very easy to troubleshoot.

Hey guys, get with it, this isn't a CIS engine!!!!!!

wazzz 03-23-2024 09:10 AM
When you say you jumped the CHT sensor, you mean you shorted (with a paper clip or whatever) the sensor connector terminals on the harness side, right? Not on the sensor side (this wouldn't make sense).

In that case I wonder why this makes the engine run richer, since shorting the CHT sensor input to the ECU simulates a warm engine. The CHT sensor is a NTC. The lower the resistance, the higher the temp. Shouldn't it be the opposite?

mysocal911 03-23-2024 09:12 AM
Quote:
Originally Posted by wazzz (Post 12218595)
When you say you jumped the CHT sensor, you mean you shorted (with a paper clip or whatever) the sensor connector terminals on the harness side, right? Not on the sensor side (this wouldn't make sense).

In that case I wonder why this makes the engine run richer, since shorting the CHT sensor input to the ECU simulates a warm engine. The CHT sensor is a NTC. The lower the resistance, the higher the temp. Shouldn't it be the opposite?
He assumes this!

Quote:
Separately, I can jump the CHT at the female connector and it fires right up and idles at 800 RPMs. It does run a little rich in this situation as indicated by small amounts of white smoke.

wazzz 03-23-2024 09:16 AM
Date, post #30: "It only starts running rich when I jumped the CHT sensor. It’s a bit on the lean side when the sensor is plugged in."

mysocal911 03-23-2024 09:23 AM
Quote:
Originally Posted by wazzz (Post 12218600)
Date, post #30: "It only starts running rich when I jumped the CHT sensor. It’s a bit on the lean side when the sensor is plugged in."
Who knows what kind of DME ECM chip is installed? It's total confusion at this point. No more guessing.

As I said up-thread, time for another DME ECM!

mysocal911 03-23-2024 09:46 AM
There're too many unknowns at this point for any productive troubleshooting;

1. DME ECM chip type
2. Injectors being used
3. Fuel pressure
4. FP/Damper leaks into intake via vacuum lines
5. AFM incorrect spring tension
6. Throttle enrichment switch shorted to ground

et cetera 03-23-2024 09:47 AM
I took the ECU out to hopefully test it in a friends car soon. Figured I would open it up to see what chip is in it. Clearly it had been opened before. Chip has a sticker on it, PAE i8. I did a search and couldn’t find a reference for that.

I had also opened up the AFM and noticed the spring was moved one notch towards the lean side.

http://forums.pelicanparts.com/uploa...1711216010.jpg

et cetera 03-23-2024 09:52 AM
Quote:
Originally Posted by mysocal911 (Post 12218617)
There're too many unknowns at this point for any productive troubleshooting;

1. DME ECM chip type
2. Injectors being used
3. Fuel pressure
4. FP/Damper leaks into intake via vacuum lines
5. AFM incorrect spring tension
6. Throttle enrichment switch shorted to ground
I agree, this is much more complicated than I originally hoped, or had described to me.

I posted the chip and AMF spring settings.

To my understanding these are OEM injectors that had been cleaned and refreshed.

It does seem like it might be a fuel pressure issue. I took the vacuum lines going to the FP damper and regulator off, they weren’t wet, but they smelled of fuel.


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