BHCfarkas

open loop vs closed loop... I'd say it's likely related to one of the metering sensors for the engine temp, or the O2.

jadh

Hi Jorijori,

To answer to your question about my progress about my engine reactions, here are some points:

First of all, I took the decision to not touch to any thing till I am certain that my engine clearly differs from an other stock engine. I know that jevvy will post his engine videos soon. This will help me on this point. There are to many bad experiences of getting things worse while trying to solve them when you do not have the expertice. As I do not have any expertise, I will progress step by step on this subject.

If my engine realy has something to be improved, the next step will be KTS testing. But the difficult thing will be to find someone that has the equipment (and know how to use it) not to far away from home.

At present, all my suspitions are around O2 and temp sensors, as BHCfarkas said.

As the loop is closing after 90 seconds, I will do a new video to see if engine reaction is changing around this 90 sec time. If so, O2 sensor will need a deeper analyse.

I don't think that gas pressure is an issue. Because if so, I think that I would have some problems at high revs. It is not the case. Except the "strange" warm réaction when I give a kick of acceleration from idle, my engine is performing very hard.

jadh

Update information:

The garages around me (not Porsche specialist) have KTS 540, last evolution of Bosch diag tools (and no longer the 300 or 301...). This KTS 540 can help or not? According to the fact that the diag will not be done for free, is it worth to pay the money?

ras62

Ask them if they have the adapter to connect to OBD 1 as used on the 964.

jevvy964

Uploaded the first cold vid - still haven't had a chance to get a hot one yet:

jadh

Hi Jev!

Thanks for this first vid. Seems it is the same reaction as mine for the cold engine.

I can't wait to see how it is in the warm mode.

Except the exhaust pipe, all the engine is stock, isn't it?

Many thanks!

Navaros911

Another easy check is the fuel pressure regulator.

It sits under the intake and there is a small vacuum line that runs to it from the intake (just under the ISV) straight down. It's not that easy to get to, but I managed to test by pulling off the vacuum line. If there is fuel dripping out, you have a faulty FPR.

Let the fuel pump run a few seconds before this test to make sure there is pressure.

Don't think it's the FPR, but easy to check. I didn't even need any tools besides a light and two skinny hands.

jevvy964

Just did a hot video for you, seems your car is similar to mine in that it struggles with a deep quick throttle opening from idle.


Haway guys lets see some other hot videos!

jadh

First, Many thanks to Jev for his 2 vids Cold & Hot...

Considering all vids we have seen up to now, all engines have the same recation when quicking throttle to open from idle.

All 964 Rennlist-ers have the same reactions on stock engine?
I bet all engines have the same!

Post your hot vids to compare! Thanks

Cheers!

jevvy964

No worries dude - sorry it took so long for vid #2.

I think the other point to note is when it seems to fail to pickup when hot we have both also already been closing the throttle ie a blip rather than a hold which is rarely used day to day.

Maybe its the closing after the blip that is the issue?

For what its worth I couldn't really recreate this from the drivers seat which I suspect is due to the change in input v's output of the pedal v's throttle body - again probably another reason why no-one really notices it.

jadh

Here is an update about this thread.

I went to my Porsche specialist.

- We have made a KTS faultcode reading : no fault code
- We have made a road drive : ok
- My specialist has a stock 91 C4 for sale. We made a comparison test with this car : again, it has exactly the same engine reactions as mine and Jev's.

To conclude this thread : Engine reaction cold and warm shown in first post are NORMAL for a stock engine.

If someone has a different reaction on his stock engine, I still interested in receiving the vids.

Thanks to all of you for your inputs during all this thread.

Cheers

jlmartin94

nice news ...
that's what i thought ..

I think the only way to get a better "blip" response is the Leightweight flywheel ...
I guess the motors engineers who design the motronic don't care to give the 964 a "motorbike'like motor response" ....
it's just an unnecessary stress for the mecanic ....just to "show off" on red light

JasonAndreas

The fact that the engine response at zero load is temperature dependent (in the videos) would point to a sensor issue (it could even be the transition from partial throttle to WOT?) or a problem with the motronic fuel and/or ignition mapping?

Now I'm really curious, I will give it a shot and see if I can't figure out why!

hepkat63

sorry to dig this old thread up... but Jason, did you ever take a look into this? My car does exactly the same thing as these videos. My engine is not entirely stock though - with Cat bypass and maxflo muffler along with Steve Wong Chip. It has been adapted, but still does what these other videos show. Maybe the AFM ?

PhatPhlatSix

In this thread,
https://rennlist.com/forums/964-foru...t-low-rpm.html
I found that there is an cylinder-head-temperature-dependent throttle-accel injection-correction. In layman's terms, there is an extra bit of fuel when you blip the throttle, as a function of CHT. Anyway, this correction goes to zero when the CHT is up to normal running temperature.

Most people do not believe that from stock, the 964 behaves like this (hesitation when warm) however nobody has come forward to say that they have no hesitation with stock mapping and all the relevant sensors working correctly.

I know that all my sensors are working. I modified the CHT correction map and I now get perfect response at all rpm and all temperatures.

It is possible that Porsche did this for emission reasons or to reduce fuel consumption. Suppose there are minor oscillations in the AFM at low engine-speed with constant throttle - this would trigger throttle-accel fuelling increase with consequences on emissions and consumption. Not saying this is the case, just hypothesizing a reason why it is like this in stock form. We may never know....