'70 D-jet runs terrible cold, great when warm,, Please share your wisdom Options

[Porsche Rescue]

Car starts when cold (not quickly, but it does start, air temp. 80 degrees), then it is a bitch to keep it going. Once on the road and warmed up it performs beautifully.

I have checked the Aux. Air Valve and it is sucking when cold, plugged when hot.
I replaced the head temp sensor even though the old one tested OK. The new one helped a little, but not near enough.

I have studied Brad Anders' site and can't come up with any other ideas of what to check. I have to believe the ignition system is fine because it runs so well when warm. I have checked timing and dwell and they are on spec.

Any suggestions out there?

[Bartlett 914]

Make sure you have the correct CHT and the Correct ECU. If you have a mis match you will have that exact problem.

[r_towle]

you could add the 270 Ohm resistor to your CHT line.

Rich

[Porsche Rescue]

Thanks Mark and Rich. Anders mentions the resistor and I think I'll try that. He suggests somehow wiring it to a switch in the cabin because it will cause rich running when warm. Think I'll wire one in and worry about the switch if it solves the problem.

I got an extra Porsche rebuilt ECU with the car. In checking Anders' numbers, it appears to be for a '73 2.0. I know my new temp sensor is correct for the car, but have no idea what ECU I have in the car. Guess I will pull it out and see. PO was the original owner of the car and is very knowledgeable. Wonder why his spare ECU is for a 2.0?

[r_towle]

the spare ECU is a 2.0 liter ecu, but from what I have read its just a renumbered 1.7 ECU that needs the 270 ohm resistor.

How do your plugs look?

Rich

[orange914]

the spare ECU is a 2.0 liter ecu, but from what I have read its just a renumbered 1.7 ECU that needs the 270 ohm resistor.

How do your plugs look?

Rich

rich is right. 73 2.0 used the same ecu as 1.7. they just added a 270 ohm resister to the cht inline. i thought about adapting my 73 ecu when i went to the 2056 (from 1.7), but located a 75-76 2.0 ecu (052 i believe). it has some great advantages like a fuel shut down at decel that not only helps mileage but saves fuel. not suposed to effect power either. i haven't had a chance to confirm any of that yet on the new motor due to just breaking a c.v. (IMG:style_emoticons/default/barf.gif) . i do know it's an amazing power difference but that could be attributed to most everything else (IMG:style_emoticons/default/confused24.gif)

mike

[Porsche Rescue]

I will do some ECU checking on Thursday. No time to play tomorrow.

[Porsche Rescue]

Took a week, but finally made time to do some more checking.
Removed the ECU plug and did all the Brad Anders resistance checks and everything meets his specs. My ECU is the correct 015 unit for a '70. I replaced the head temp sensor (probably unnecessary). Both old and new are the correct Bosch 012 unit. I have a back-up ECU (037) but I think it requires a different temp sensor and the '73 resistor.
My next step is to try a resistor as suggested above. Here's where my ignorance of things electronic really shows. Asked the guy at Radio Shack for a 1/4 or 1/2 watt 270 ohm ballast resistor. All he had was 220 ohms or 330 ohms. Opted for the 220. Word "ballast" is nowhere to be seen. After investing all of 99 cents for 5, I am thinking I don't have the right component. Before wiring one into the sensor line, thought I should check. So, do I have a resistor that might help? And is 220 too far away from 270 ohms?

[Rand]

Tweaking with resistors is cool and all, but it's off topic. This thing should start and purr flawlessly without having to modify the system. Something else is wrong.

But if the temp sensor and AAR are good, this is quite a puzzle. So is it just low idle on cold start? Anything else specific?

[Porsche Rescue]

My instinct is the same as yours, something else must be wrong, but what?
A bit hard to start, then have to play with the throttle a lot to keep it going. Once on the road it runs poorly until warm. Once warm it runs as well as any 914 I have driven (and that's a large number), idles fine, accelerates smoothly, plenty of power.
I have checked the aux. air valve. It is open when cold. At a loss as to what to check next.

[Rav914]

CSV?

[Porsche Rescue]

As I understand, CSV only injects at low temp (50 or less) and then only while starting. My car clearly needs more fuel while starting and while warming up.

[mattillac]

bad MPS? sticky decel. valve? the AAR might work ok but are hoses ok?

all simple things to check at least. check plugs as mentioned and also the gap.

[Rand]

CSV isn't kicking in at his ambient temps. Decel valve isn't related to cold idle.

Bad MPS would cause it to run rich.... Maybe something to that. But it would run rich across the board. Does it hold a vacuum? Maybe opening the idle air bypass screw a bit would help, but then it would just idle fast when warm.

Good luck Jim, I'm still stumped.

[toon1]

Does the car back fire on accel before it's warmed up.

I would still suspect the AAR IF it needs MORE fuel before it's warmed up.

Does the idle rise at start up?
Does it lower after a few seconds?

If the wire has diconnected( which they are prone to do ) they will still function, I.E. open when cold and close when warm, BUT it will only close with the heat from the engine bay which takes awhile to happen, usually about 10 min. or more.

Try taking the AAR out and putting it in the the freezer to open it.

Then hook the wire to 12v+ and an aligator clip from the batt. - to the AAR case (where it mounts to the air box is a good place) and see if it closes.

If not, the wire has come loose inside.

[mattillac]

could this be a bad TPS or need TPS adustment? another fairly simple component to test.

[Rav914]

Didn't know that about the CSV. Subscribed. Hope it gets solved.

[toon1]

could this be a bad TPS or need TPS adustment? another fairly simple component to test.

If it was the TPS it would do it all the time

[Porsche Rescue]

All who offered help last fall, please see my post of today, "Could this be my problem"?
Especially if you know something about old CD ignition boxes like this:

[orange914]

All who offered help last fall, please see my post of today, "Could this be my problem"?
Especially if you know something about old CD ignition boxes like this:

i had a jacobs unit that had savere intermittant chugging, then just fine. i confirmed the unit by installing it on another car w/ same results. can you throw in another dist. for temp.?