Hi Dave K, what you mentioned is interesting but has nothing to do with the OP’s problems. What happened to the OP anyway? I usually refrain from these discussion because they devolve into d%ck swinging contests, but I’ll play a little longer. 73.5, 74 and ROW 75 had the “holy trinity” of CIS. That being FD, Throttle Position Regulator (TPR), and a true WUR which had one purpose…cold start, that’s it. These years had no safety on fuel pump activation. Consequently, when the key was turned on, the fuel pump activated. Makes things easy when checking pressures, no relays to jump, no sensors to pull, just turn the key one click. For these years a check valve is irrelevant, period. For all others, it is very important. The OP states he has a74 with the above components either new or remaned. Losing residual on this car in 20 sec is interesting but giving the pressures listed, is not the problem. The fuel pumps on these cars can empty an Olympic size pool in 5min. A bit of an exaggeration, but at 5.2 bars and return volumes well over 1600cc/min what do you need a check valve for on these 911’s? At full throttle you have 5 times the volume needed. As a result, a possible small blow by in the WUR or TPR diaphragm is inconsequential, the fuel pump is delivering tons of volume. Also the OP said these components were new or remaned. As for the accumulator, this provides protection from spikes on pump start-up and smooths out any harmonics created by the pump. Again, OP said NEW Accumulator. As for vapor lock, well theoretically possible, but nearly impossible. One of the benefits of CIS over Carbs, no vapor lock. Given the physical location, geometry of components and 5.2bars (75psi) along with air being a very compressible liquid, not to mention the boiling point of fuel…..vapor lock, not happening on CIS. Never seen it, never heard of it only read about it…..like unicorns.

So what do we have here? Alex said rebuilt 2.7 with new or remaned CIS components. The car starts fine, runs well but after warmed up and heat sinks for 20 min. won’t start. Alex said if he lifts the sensor plate manually, car will start, but rough for a bit (just dumped a bunch of fuel, not a surprise). Was directed by a post to increase warm idle pressure or get new WUR. Poor Alex, adjusts WUR which has nothing to do with warm control pressures on this car. Same problem but now hard starting when cold. Reset WUR to cold ambient air spec. Disconnect power lead, pump on, and dial it in.

What have we assume? Spark, timing set. No vacuum leaks, because just had rebuild on motor. No major fuel leaks, etc.

What didn’t Alex tell us? Did he clean or clear existing fuel lines? How did he set up all these new CIS components? Unfortunately, none are plug and play. As I eluded to in my first post, the first thing Alex needs to do is set the Zero position of the sensor plate. This plate should also be able to move freely when depressurized. Any binding should be looked into. See previous post. Next, I mentioned the baseline mixture control screw needs to be set. Place your injectors in baby bottles, bleed system and you can check flow volumes at same time. Next, get your 3mm allen mixture tool and turn clockwise till the injectors just start to weep, then back off 1 turn. Turn pump off, move sensor plate multiple times to depressurize. Turn pump on and check to see injectors DO NOT weep. If so, go ¼ counterclockwise. Repeat if necessary. The slightest moment in the sensor plate due to intake vacuum should deliver fuel. You may be getting movement but no fuel when hot because this is set incorrectly. Next, set cold pressure as described above. Plug in WUR, make sure it peaks out at 2.85bar or higher after 15 min. Next you need to set your warm control pressures at idle. This is done at the TPR. You need to loosen the TPR ( 2 Allen head ) so you can rotate it, similar to ign dist. Set the idle pressure at 2.85bar tighten screws. Now move throttle to ½ note pressure, should be 3.4 – 3.8. Now move throttle to full, note pressure, should be 2.6 -2.9bar, the lower the better!

Start it up, at warm temp set timing, then idle. Go for a spirited drive. Do hot starts at different times. 5 min, 10min, 15 min, 20min. Right foot ½ throttle may be needed when heat sink. CO sniffer would be nice to have as well.

This is where I would start. This is what I would do, have done. Don’t buy any parts till you have an answer.

If you want to find the leak down culprit for grins, just isolate each component one at a time. Pinch off the return line on the TPR and take note. Close the valve on WUR on your pressure kit and take note. Etc. 5 min you will have the answer, but if all your pressures above are good, it’s just academic.

Or buy me ticket to your little island, I could use a vacation! Have fun.

Wrench / Drive what could be better?

Thanks jsottile!! Very informative pic.

Alex,

Engine Fails to Start

The attached link is page 20 -21 of the CIS troubleshooting guide booklet.

You had actually diagnosed your problem when you lifted the sensor plate and you got it started. (its states that on the right side of page 20.)

Yep, it talks about vapor bubbles and a flow chart how to find and fix the fuel pressure leaks and how to set the sensor plate.

Good luck and keep us posted.

Dave K

:)

Good info Dave... I cant tell you how many times your postings have helped me (Lambda side).

Hope all is well..

Hi Dave, Just you and me, the OP is apparently MIA. Seems we have some common ground. The primer put together by Jim and the RarelyL8 guys is a great resource. Should be required reading for anybody rocking a CIS 911. You also seem to agree with my original post that setting the sensor plate and base line is the next logical step and very easy to do. Hand in glove, me and you. I am still a bit puzzled about the obsession with vapor bubbles? The trouble shooting guide you referenced is great, but it covers multiple years. The OP has a fairly rare U.S. 1 year only set-up. The good news is vapor bubbles, as I have explain, disrupting start-up, is a near impossibility. The bad news, in the event of an accident, the pump will continue to run, which could be very bad and is why Porsche changed this rather quickly. Unless these are magic bubbles or the laws of physics are somehow different on small islands off the coast of Morocco, bubbles are not the issue.

The OP basically stated he has new everything but has little experience setting up anything and this is where he needs helps. I provided detail instructions with pictures on how I would proceed. Without any more input, I need to tap out.

Dave thank you, it’s been fun. Next year at Hersey Swap, beers and brats are on me. Or better yet, come out to the vintage Hawk races at Road America in July and I’ll buy diner.

This Memorial weekend, I’m humbled and honored by those who gave their all so I would have the freedom to talk about minutia on an open forum. We truly live in the greatest county.

Wrench / Drive what could be better?

J

Thank you all for the great help!
Sensor plate is done - zero set.
Fuel pump started to make a strange noise.
I will order a new one.
Soon will let you know the results.

Hope some good news are coming.
Thanks once again for your precious help.

My lack of patience will probably lead me to a solution like that! 😀👍