Cold Start issues...

[huck369]

THe fuel pump is using the SVX ECU...sort of...It's using the positive feed from the ECU to the original XT6 Fuel pump relay, and then the fuel pump is grounded to the body which deleates the SVX "negitive pulses" to the ground side of things...

As for wiring up the CEL, I also don't have the conectors to "check the codes" anymore...

[Trevor]

(1) Starting from cold is directly dependant on the Auxiliary Air Control valve and it is strange that this item has not been mentioned .

The valve supplies extra air at cold start up and is electrically operated by means of an electrically heated bimetal element. Has connection been missed in the engine transplants, or is the valve faulty?

(2) The ECU normally depends on a signal from the inhibitor switch, registering neutral and park. This signal will surely be associated with the starting programme. Has this been missed in the engine transplants?

[huck369]

Originally Posted by Trevor

(1) Starting from cold is directly dependant on the Auxiliary Air Control valve and it is strange that this item has not been mentioned .

The valve supplies extra air at cold start up and is electrically operated by means of an electrically heated bimetal element. Has connection been missed in the engine transplants, or is the valve faulty?

(2) The ECU normally depends on a signal from the inhibitor switch, registering neutral and park. This signal will surely be associated with the starting programme. Has this been missed in the engine transplants?

Trevor,
I can only speak for mine, but I know that I wired up the Clutch position switch to give a "Nuetral" signal to the ECU when I push in the clutch, this alows it to start, they it assumes it is in "Drive" once the clutch is let out.

As for wiring to the AAC I just took a whole SVX harness and cut off anything that wasn't directly wired into the engine baasically, so the AAC wiring should still be intact, thought I have not honestly varified that, but the engine harness is completely stock, the SVX body harnes is what I butchered up to get it into the XT6...

But the ACC is something I should look a little closer at for sure.

[Crazy_pilot]

I think someone else mentioned this, but anywho...

Could it be that the fuel pressure is bleeding off overnight? Try cycling the key on-off slowly a few times before trying to start it.

[kcpaz]

The first thing that came to mind for me was the AAC valve, but I haven't been able to test it. I know the wiring is there in the harness, but I'm not sure that the valve itself is good. I think I may have read somewhere that these valves are problematic in these cars (I may be wrong though)

As far as my fuel system goes, I'm using a Pierburg turbo capable fuel pump and the stock Porsche fuel pump wiring (pump runs when key is on). I don't know if that could be the problem, but it would seem that the problem would still exist even after the engine is warm if that was the case.

I have rigged up a check engine light temporarly to check for stored codes, but I haven't driven the car with this hooked up yet. Maybe I should?

[huck369]

Originally Posted by Crazy_pilot

I think someone else mentioned this, but anywho...

Could it be that the fuel pressure is bleeding off overnight? Try cycling the key on-off slowly a few times before trying to start it.

I've tryed that....it doesn't help...but it was agood suggestion...

And Hocrest, it was the ECU temp sensor I swapped out, not the gauge one...


It's raining and cold here now, so it won't get looked at for a while....but will try to respond if I ever get it worked out.

[Trevor]

Originally Posted by huck369

Trevor,
I can only speak for mine, but I know that I wired up the Clutch position switch to give a "Nuetral" signal to the ECU when I push in the clutch, this alows it to start, they it assumes it is in "Drive" once the clutch is let out.

As for wiring to the AAC I just took a whole SVX harness and cut off anything that wasn't directly wired into the engine baasically, so the AAC wiring should still be intact, thought I have not honestly varified that, but the engine harness is completely stock, the SVX body harnes is what I butchered up to get it into the XT6...

But the ACC is something I should look a little closer at for sure.

The basis of my logic places the AACV as the prime suspect:-

The issue is starting from cold. The engine runs OK when at operating temperature. There is no reason to suspect fuel pressure as being at fault.

Opening the throttle provides the extra air required for starting, but at the same time an important confusing signal is supplied to the ECU, so that this is not a satisfactory alternative and the result is excess fuel injection and flooding.

Extracts copied from the thread which exactly support my logic:-


it will NOT start at all if I don't play with the throttle while tring to start it when it's cold, but no throttle is required once it's been warmed up to start it...

it is nearly IMPOSSIABLE to start when it's cold....during the summer months it starts pretty good, but once it gets cooler, it will hardly start, I have to crank on it forever, and play with the gas pedal to ever get it to start...once it's running it starts up fine.

Basically I have to nearly flood it to get it to fire up when it's cold, but like Kcpaz said, it runs perfect once it's started up, including the "Fast Idel" untill it's warmed up....and since both his and mine are "transplanted" EG33's,

I'm leaning toward something in the wiring that we both missed..

It idels fine once it's started, idels up a bit till it's warmed up, then drops to normal idle, just like it's suppose too

.it will NOT start at all if I don't play with the throttle while tring to start it when it's cold, but no throttle is required once it's been warmed up to start it....hope that clears it up.

The engine cranks over fine.....but doen't seem to get fuel, unless I give it throttle.


N.B. The manuals appear to give no indication that the AACV is incorporated in the self diagnostic system, so that a code is unlikely to be shown even if the system is operative.

[huck369]

Originally Posted by Trevor

The basis of my logic places the AACV as the prime suspect:-

The issue is starting from cold. The engine runs OK when at operating temperature. There is no reason to suspect fuel pressure as being at fault.

Opening the throttle provides the extra air required for starting, but at the same time an important confusing signal is supplied to the ECU, so that this is not a satisfactory alternative and the result is excess fuel injection and flooding.

Extracts copied from the thread which exactly support my logic:-


it will NOT start at all if I don't play with the throttle while tring to start it when it's cold, but no throttle is required once it's been warmed up to start it...

it is nearly IMPOSSIABLE to start when it's cold....during the summer months it starts pretty good, but once it gets cooler, it will hardly start, I have to crank on it forever, and play with the gas pedal to ever get it to start...once it's running it starts up fine.

Basically I have to nearly flood it to get it to fire up when it's cold, but like Kcpaz said, it runs perfect once it's started up, including the "Fast Idel" untill it's warmed up....and since both his and mine are "transplanted" EG33's,

I'm leaning toward something in the wiring that we both missed..

It idels fine once it's started, idels up a bit till it's warmed up, then drops to normal idle, just like it's suppose too

.it will NOT start at all if I don't play with the throttle while tring to start it when it's cold, but no throttle is required once it's been warmed up to start it....hope that clears it up.

The engine cranks over fine.....but doen't seem to get fuel, unless I give it throttle.


N.B. The manuals appear to give no indication that the AACV is incorporated in the self diagnostic system, so that a code is unlikely to be shown even if the system is operative.

It does seem to lean toward the AAC doesn't it...

I might add that once it start the first time, I can shut it off as soon as it starts, thaen it starts up pretty good...even if it's not warmed up yet....just that "First Start" when it's cold is the killer...

I Feel like I'm killing my starter on those starts...

[Zandar]

Where is the AACV and how do I inspect it for malfunction?

[Trevor]

Originally Posted by Zandar

Where is the AACV and how do I inspect it for malfunction?

The AACV is located under the intake manifold.

In and out flexible tubes run from the valve and if the outer ends of one of these can be detached this could provide a means of testing using lung power. Someone who has been in there should be able to provide exact information.

Logically with the ignition energised/on and the engine cold, the valve should be in the open position and able to pass air to the manifold for starting. Although not exactly defined in the manuals it would appear that the valve is opened when electrically energised and this can easily be confirmed by directly providing battery voltage after removing the existing connection.

Obstruction from dirt, or an inherent mechanical or electrical fault must be considered, as well as the possible lack of an operating voltage at start up.

[huck369]

hhmmmm....makes me question my sorces for the power I tapped into for the SVX ECU.....maybe one of them isn't getting power while cranking....I thought I checked for that....but that's been about 2 years ago now...maybe I should check it again....

[Trevor]

Originally Posted by huck369

hhmmmm....makes me question my sorces for the power I tapped into for the SVX ECU.....maybe one of them isn't getting power while cranking....I thought I checked for that....but that's been about 2 years ago now...maybe I should check it again....

Don't stuff about, directly check the signal and operation of the AACV.

[kcpaz]

after reading up on the operation of the AAC valve, I'm almost 100% sure that is my problem. I get the same "flooding" becuase I'm having to give it some throttle. Is it really as simple as blowing through the valve with the key on to test it?

[Trevor]

Originally Posted by kcpaz

after reading up on the operation of the AAC valve, I'm almost 100% sure that is my problem. I get the same "flooding" becuase I'm having to give it some throttle. Is it really as simple as blowing through the valve with the key on to test it?

I do not see why not, provided you understand what you are doing and can interpret the results. Have you not syphoned petrol, sucked on a needle valve, spat on a tyre valve or whatever?

I was under the impression that shade tree mechanics in the US, rivaled our number eight wire guys. If you have not smelt it, tasted it, or felt it, how can you expect it to work for you. Bloody hell!

[kcpaz]

I'll Git-er-dun tomorrow and let you know what I find out