1972 911 with 1996 3.6 engine very hard to start.

[rudya]

hello all!! my first post after lurking around this forum for 9 years. I bought my 1972 911 9 years ago and i have been working on it ever since. I replaced the engine with a 1996 3.6 varioram engine. i finally got everything together but i have a problem when starting. At first start it takes about 30 seconds of cranking before the engine fires up. as soon as it fires up and has stabilize for a few seconds you shot it down crank it up and it will start right back, but after 45 min you have to do the 30 second of cranking before getting it to fire again. it idles at 900 rpm.
fuel pressure with direct reading gauge is 50 psi.
replaced check valve at fuel pump.
replaced pressure regulator it has a diaphragm a leak.
any advice on how to fix this is would be greatly appreciated.

[rattlsnak]

Hook up a fuel pressure gauge, start car, then let it sit overnight. The next morning, turn the key to the run position (not start) and read the gauge and let us know what it says. Then crank it over and record the reading when the car finally starts.

[Joe Bob]

Residual fuel pressure and good cold start circuit is a good thing.

[rudya]

Hook up a fuel pressure gauge, start car, then let it sit overnight. The next morning, turn the key to the run position (not start) and read the gauge and let us know what it says. Then crank it over and record the reading when the car finally starts.
I run this test a few moths back the result was: key to run position 0 psi pressure pressure builds up to 50 psi in a couple of seconds until it fires up 30+ seconds later. in between that 30 seconds of continous cranking engine tries to fire up but will not stabilize. after shutdown and up to 45 min engine can be started without problem. residual pressure dessipates to 10 psi after 45 min and to 0 after an hour.

[rudya]

Thanks for the advice Joe Bob/rattlsnak. I removed and have the fuel injectors cleaned and tested at a fuel injector shop. from our host I ordered and replaced "O" rings. The result was good. The pressure now holds good, overnight there still residual pressure left about 3psi and it took 2 (2 seconds) of cranking before the engine finally fires up and stabilize to idle. Again thanks.

[tobluforu]

Please post pic of engine stuffed in car and car itself.

[axl911]

Have you checked the cylinder head temp sensor? It should be a white connector from cylinder 3. A dead one or shorted one would not tell the engine it is cold and need cold start enrichment. Ambient temp should yield about 2K resistance.

[Dan J]

Check the gap on the crank sensor if it's too wide and it's cold it will generate a weak pulse.
Tighten it up to .8mm and try it

[rudya]

Originally Posted by tobluforu

Please post pic of engine stuffed in car and car itself.

[tobluforu]

Awesome, I bet that is a real hoot to drive. Looks like it was made to go right in there, well I guess it really was, so to speak. I wish I had the time and wife that would let/allow me to do this.

[rudya]

Originally Posted by axl911

Have you checked the cylinder head temp sensor? It should be a white connector from cylinder 3. A dead one or shorted one would not tell the engine it is cold and need cold start enrichment. Ambient temp should yield about 2K resistance.

This morning I checked the resistance at the #3 cylinder head temp sensor, using a calibrated fluke 73 lll multimeter the reading was 2868 ohms. Do you think the extra .868k of resistance will cause a problem? Thanks

[axl911]

Here are what they should be:

0C = 4.4 - 6.8 kOhms
15 - 30C = 1.4 - 3.6 kOhms
40C = 1 - 1.3 KOhms
80C = 250-390 Ohms
100C = 160 - 210 Ohms

[ALXinNZ]

Originally Posted by axl911

Have you checked the cylinder head temp sensor? It should be a white connector from cylinder 3. A dead one or shorted one would not tell the engine it is cold and need cold start enrichment. Ambient temp should yield about 2K resistance.

+1

and is it at 50 psi iwhile engine is running?????