1977 CIS question - warm start

christojen · 09-28-2009, 11:11 PM

Hi Guys,

I have a problem which i know is really common, and i actually know how to get around now it but I am wondering if there is a simple fix...

BTW i have studied Jims CIS site and numerous posts here.

It goes like this....
As i have seen from previous posts, not being able to start a cis 2.7 when warm / hot is not new... (this is my problem)

As described in another post i have tried taking the air box off and pushing up the sensor plate and then try restarting, which doesn't really work.

However, if i leave the ignition (and fuel pump) on whilst doing this It is much harder to push up the sensor plate but then on starting it does seem to fire and catch (well it has worked two times in a row)

So obviously the fuel on and then going through the system seems to allow it to start. But what i am wondering is does this sequence of events make it clear to anyone what is the actual problem?

I know the most likely culprits are the accumulator and the WUR.

I would appreciate any help on this matter.

Chris in Aus.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by christojen

Hi Guys,

I have a problem which i know is really common, and i actually know how to get around now it but I am wondering if there is a simple fix...

BTW i have studied Jims CIS site and numerous posts here.

It goes like this....
As i have seen from previous posts, not being able to start a cis 2.7 when warm / hot is not new... (this is my problem)

As described in another post i have tried taking the air box off and pushing up the sensor plate and then try restarting, which doesn't really work.

However, if i leave the ignition (and fuel pump) on whilst doing this It is much harder to push up the sensor plate but then on starting it does seem to fire and catch (well it has worked two times in a row)

So obviously the fuel on and then going through the system seems to allow it to start. But what i am wondering is does this sequence of events make it clear to anyone what is the actual problem?

I know the most likely culprits are the accumulator and the WUR.

I would appreciate any help on this matter.

Chris in Aus.

Chris,

Your second procedure does help your car starts because you've been priming the system by running the FP. What you did was increased the residual fuel pressure before the 'start'. The two (2) most common culprits for warm start-ups are FP check valve and FA (fuel accumulator). A simple way to diagnose this problem is by checking your residual pressure. By using a fuel injection pressure gauge, check your control pressures (cold and warm) and it will tell you if your WUR is contributing to your warm start problem which I doubt at this point. Keep us posted.

Tony

T77911S · 09-29-2009, 05:37 AM

as said above.

lifting the plate with the key off is doing nothing for you.
with the key on, lifting the plate primes the system.

FA, and check valve are first order. check WUR if these dont help, a tune up never hurts.

vash · vash's Garage

you need to borrow some CIS gauges, and check your system pressures. if not, you can throw parts at it (in the order of T77911S's suggestion) and hope for the best...gets super costly this route.

the gauges helps you home in on the exact source of any pressure losses.

Paulporsche · 09-29-2009, 06:45 AM

If you check your WUR w/ a gauge, refer to these charts for fuel and control pressures
:

christojen · 09-29-2009, 06:16 PM

Thanks Guys,

So it sounds like the fuel pump on, lift the sensor plate - is a legitimate if not annoying solution to the problem. I presume i am not damaging anything by doing this? (e.g. sensor plate settings).

I will get some pressure guages and do some tests. Mind you i think it might be a while till i find a set. Even my mechanic, who is well regarded here, doesn't use them.

Maybe my best option is to buy some from our trusty host.

The important thing to me is that i have a way of starting the car when warm until i find a proper solution. Previous to this i was trying to time my driving habits to not stop when warm, unless for 1.5 hours or more.

That was hard.

Thanks again guys, fantastic.

Chris in Aus

Paulporsche · 09-29-2009, 07:13 PM

Make sure all your ignition components are up to spec. You may also want to verify that your mixture is correct.

As you said, your symptom is quite often associated w/ a bad fuel accumulator, but a too lean mixture and/or an out of spec WUR could be @ fault.

Many posts have quoted a JC Whitney CIS gauge as the one they use.

christojen · 09-29-2009, 07:17 PM

Thanks Paul - I will check it out.

Chris

Mia911 · Mia911's Garage

Wow reading this gave me bad flash back...I had the same issue at one time...the 1st thing I did was borrow a set of gauges to read the 2 sets of pressure ..which was real low...thought my FD was bad..bought a reman. Fd... I set everything up on a work bench and tested it again...Bam...everything work fine....on the two setting my guages told me the fd is working how it suppose to...plug up my wur on my battery and saw my pressure raise to what is should be....now that eliminated my fuel pump, wur,accum..and FD...put it back into the car...plug up the gauges...I got a low reading.....I was WTF is going on... Got the 5gal jug, put the pump to suck from it...same low reading....ok that eliminated the line coming from the tank....unplug the hose coming from the pump and going into the filter...cracks and holes like crazy, it was sucking air from it and not fuel, replace hoses...check both pressure...BAM good reading....car still don't want to start....check coil...no power going to coil....put tester on harness...no power...check fuses...they are all good...open up harness connector....wire was broken in it...solder it back into place and test for power...coil has power....car started right up...but it cost me while testing...1 fuel pump, 1 fd, 1 puma tune ignition cause I put on a msd, I could of save that money if I did test with gauges from the get go...and stop guessing...but I started eliminating problems one at a time...your problem might just be the cold start behind the engine not getting power, or wur malfunction ...I read the book and understand how the system work....I think every Porsche owner who's running cis should have a set of gauges....,and after all of that I swap it them out for webbers....

Paulporsche · 04:47 AM

Mia has a nice encapsulation of the test procedures. The last thing he (she?) did was the first thing recommended, which is to make sure the ignition system is operating correctly.

Let's see what Chris gets for fuel and control pressures.