Yes, same poster (sean) I referred to about leaky injectors. His problem was solved by having two fuel injectors replaced by the dealer. He mentioned it in another thread but he never closed the thread you quoted.

 

Based on what you wrote the first thing that comes to mind is the coolant temperature sensor is supplying the wrong -- too hot -- temperature and the fueling is lean.

I couldn't tell from the audio but if you hear spit back in the intake that's a sign the engine is too lean. (Backfires in the exhaust is a sign the engine is too rich.)

If you want to confirm this -- or eliminate this -- you need to capture intake and coolant temperature at cold engine start.

I had a coolant temp sensor in my VW Golf TDi act up at cold start. I can't recall the symptoms now -- they would be a different due to the engine differences (compression ignition vs. spark ignition) -- but I used my trusty hand held Actron OBD2 code reader/data viewer to observe coolant temperate and a couple of other things -- only room for 4 items on the display -- at cold start and while the coolant temp reading wasn't that off it was clearly off. I took the car to the dealer and requested the sensor be replaced and it was and the symptoms were no more.

Oh, you might try an E-Gas calibration. The behavior from the engine seems a bit much for just this to be the problem, but the calibration is easy enough to do.

Keep your foot off the gas pedal during this procedure. Turn the key to the on position. Leave in this on position for 60 seconds. Turn the key off for 10 seconds. Done.

 

Engine temp looks flat line. My experience is at cold start and idle coolant temperature should increase 1 to 2 degs F. every second.

 

This seems to make the most sense considering the OP issue is time dependent and based on if he let's it sit for a couple days. FWIW, I had a similiar issue before with the same symptoms on another car.

 

In the thread i posted, he says that they replaced the two faulty injectors, and even though it seemed like it fixed the issue, it came right back, although not as bad.

I am assuming engine and coolant temperature are the same thing? Durametric, i only see the engine temperature. I will repeat the test again tonight and follow the temps a little further and see what happens. Thanks.

 

Check post #10 here posted on 9/2013 https://rennlist.com/forums/996-foru...l#post10732999

Do you see a later update from Sean?

 

There are "engine compartment temperature" and "engine temperature" available in Durametric. Engine temp = coolant temp.

How much time for the log shown above? I assume only a few seconds worth? was the ambient at around 30C?

 

Yeah at least quite plausible. Too bad it's a lot of work to remove the injectors for testing. Hope my crude test of releasing the fuel pressure till next start-up works.

 

Interesting, in his earlier post from 2011 this is what he wrote when he got the car back from the dealer. Post #65.




Swapped the injectors from 2 and 4 with 3 and 6. Misfires during stumble moved to 3 and 6. They replaced those injectors and emptied/cleaned the fuel rails. reset everything and the stumble as gone. Engine now runs smoothly.

(Awesome, so it was the injectors. Although the work order lists injector valves...not injectors themselves, so maybe he just repaired them? Although he did tell me he replaced them.)


Whatever, I got her back and she's fixed. I pay for my new sparkplugs (parts only) and my oil change and head out. I get in the car, which has been parked for two days, and guess what? It does the exact same stumble on start!

I took her home as I was late for a shoot already. This morning, she started better, but there was still a hesitation and an rpm dip. Also, as with before, I cannot simply drive away...if I try to drive right away, the engine bogs and I have to over-rev and run the clutch to get it moving. So I don't think it's fixed. Sadly.

She does idle more smoothly now (once warm)

So when I bring it back for them to fix the leaks, I'll let him have another kick at it I guess.

 

The log was longer, but i only cut and pasted the first few seconds, once i get home i will check the excel file again and post what is there.

 

I know. Maybe you can PM him and see what he says.

 

Just in case you haven't tried to calibrate the e-gas yet, it is probably worth a shot since it is simple to do.

I had a similar cold-start problem although not quite as severe. It would stumble and almost stall for a few seconds only when cold.
Macster recommended calibrating the e-gas (which I knew nothing about and couldn't find any reference to in my manual). But it worked and the problem has not shown up since.

https://rennlist.com/forums/996-foru...0-seconds.html

Although for some reason the problem would also only occur when the hvac system was on auto when starting cold. My theory is that the car turns on the A/C briefly on startup (about 7-8 seconds in) which turns on the front fans and pulls a lot of current that somehow makes this problem worse.

 

I did that, and last two startups have been ok, but i am gonna keep watching this. There might be more to it. Thanks.

 

Here is another cold start with data spanning two minutes from the start. Yelow row is 25 seconds into it which is the first time engine temperature has gone up about 0.7C. Can those RKAT/FRA values really be that dead on? Based on Macasters theory that engine temp should go up 1 deg every second this may indicate that that coolant temp. sensor may indeed be waving bye bye.






This chart i made after a long run with engine at temperature in my garage.




Any input appreciated, thanks!

 

The numbers still look fine to me assuming the measured temp was close to the ambient temp at start up. If the temp sensor was bad, it should be significantly off. At warm up it reports 96C, which is right also.