Turbo cold start

[r lane]

I have a 92 Turbo converted to EFI programmable engine management. Lately on cold mornings a pain to get started. Have the same two fuel pumps now that fueled it when it was CIS. Before I start reconfigureing the cold start parameters, I wanted to install fuel pump check valves. I am assuming both pumps have them, but looking at the pump in the engine compartment and at diagrams, it doensn't appear to have one. Have not crawled under the car to check the second pump. Do we think the car just has one, and that being the one underneath. With CIS, there had to be one. I am trying to do as little research on my own as possible. Thanks, Bob

[pkabush]

930s have two fuel pumps. At least through 89. I’m not sure about later. One up front in the normal place and one in front of the rear drivers wheel.

[pkabush]

Disregard. I misread your post

[bkreigsr]

Silly question - but are you sure the front pump (suction) is working ?

Mine used to start with only the rear pump (pressure) working .
Did not find out the front was kaput until the rear finally gave up during a pit-stop 189 miles from Columbia, SC.

And yes, it is harder to start with only the rear pump.

Bill K

[Schulisco]

I've only seen a 911 Turbo on the street, but personally neither from underneath nor the engine compartment.

But I used to have also heavy cold start issues on my CIS SC US model and learned a lot on this.

Does yours start right away and stalls immediately or does it crank only without any combustion?

The engine needs additional fuel on start as well additional air while starting and warming up. I do not have any particular values on that for a Turbo, but I guess you can adjust the amount of fuel for every single cylinder in the ECU. If I understand you correct, you got some good values for idle... right? I would start with the idle setting with a warmed up engine and then add 15% more fuel for the cold start. Do you have sth. like an auxiliary air valve like the CIS engines? If not, I guess the throttle is fully controlled by the ECU - so also 10% more air in the beginning could be a good starting point. This would not be optimal for sure, but playing with the values is common on such ECUs until it fits perfect.

Concerning check valves: If one of those check valves is missing I guess the cold start is less easy because fuel will get air bubbles while engine sitting, and those make a quick cold start even harder, because both fuel pumps need a bit time to pressurize the fuel line to remove the bubbles. CIS cars have that fuel accumulator to keep the fuel lines pressurized as long as the engine is hot. But this won't work properly without check valves.

Thomas

[s5uewf]

Hopefully you have a fuel pressure gauge installed somewhere in your supply to your injectors (EFI). If so, it should be easy to verify you have adequate pressure when key switches to 'on' position. EFI should have a setting for the time the pumps will run with key set to on without engine running. For example, mine is 8 seconds. This lets me hear the pumps and also builds pressure that can be viewed on the gauge.

Cold start is relative, and the colder the atmospheric conditions are, the more your cold mapping is going to have to be tuned up in terms of timing, start, just after start, and then as the engine warms up the map should taper off. Not sure what type of EFI you have, but in my case I have a lot of enrichment at colder temps and also timing is also adjusted to add some advance once the engine starts and is idling. I also have a 'choke' setting on my Air Idle Control Valve setting that defaults my Control Valve to a higher level at cold start.

You may want to cross post this to the turbo forum and if you can let us know what type EFI you are using, someone may have that exact type and can help you very easily. Best of luck.

[prschmn]

Might be helpful if we knew what ECU you are using.
Regardless most all should have a "fuel prime" parameter
which kinda negates the check valve issue.

[r lane]

Originally Posted by prschmn

Might be helpful if we knew what ECU you are using.
Regardless most all should have a "fuel prime" parameter
which kinda negates the check valve issue.

Electromotive. I have confirmed that both pumps run and they prime for 8 sec, just haven;t checked delivery nor pressure. I have a fuel pressure sensor in the system. Will get around to data logging the pressure and checking delivery at some point. My primary query was about the car having check valves. As well as I can tell at this point, the rear pump does not, and the front one appears to. I guess one check valve on the forward pump makes sense as that would hold the fuel from there to the rear pump and fuel rails. Need to confirm on the front pump. EFI should not be as sensitive to fuel pressure bleed off as CIS but still could see it as a potential issue. The factory felt a need to install them on the 3.2 Motronic cars. Bob

[s5uewf]

I think CIS was a very different design and the fuel pressure accumulator and etc. was necessary.

With the EFI system you have I think the fuel more or less is pumped into the injector circuit under pressure and there is a return loop so all the unused fuel recirculates back, and the pressure gauge/valve will allow you to adjust your pressure to 43 lbs or whatever you need it to be for your system parameters.

Here is a link that may help (P112 talks fuel pressure, etc.) - not sure what system you are using, however;
https://electromotive.com/wp-content/uploads/2015/05/Tec-gt-Manual-2.3.pdf

Cold start tuning is going to involve more parameter adjustment after you verify your fuel supply is good.