Jfrahm

Yes the DME temp sensor can skew cold and make the car run very rich, even fail to start. It's easy to test:
http://www.clarks-garage.com/shop-ma...9.htm#dme-temp

You could have one stuck/hosing injector, that should show as a wet plug when checked after an attempt to start the car.

Giorginetto

Fuel pump replaced, In tank fuel filter replaced, fuel fitler replaced, two fuel hoses replaced, fuel pressure regulator replaced, injectors cleaned, 4 new sparks and air filter, fuel drained and replaced. Still having start problem ... Porsche specialist is investigating and I will update when I have some news .... apparently the car started after all these works were carried out and was taken for a drive and all ticked but a few hours later it just wouldn't start again - turning but no go....

T&T Racing

IMO the fuel injectors are probably the culprit

Giorginetto

Putting reconditioned ones on. will update when I have news. Must be electric with them as they were all cleaned and stuff ...

perhaps one of these kits would help ?
https://www.ebay.co.uk/itm/Plug-Repa...53.m1438.l2649

and/or

https://www.ebay.co.uk/itm/Porsche-9...53.m1438.l2649

T&T Racing

Definitely purchase new seal and pintle cap kit. Call Jason at Paragon Porsche Products

Jfrahm

It's easy to tell if it's fuel or ignition with a puff of starting fluid when it won't start. Does the tach bounce when you try to start it? Maybe it's a coil or a crank sensor or the DME or DME relay. I do not think it'd run for a while and then stop dead and the injectors be at fault.

Giorginetto

All 4 injectors replaced , i was told the car is working fine, fingers crossed it wil be ok picking it up tomorrow and hopefully it will start in a few days ....... I am as mentioned above very suspicious on the crank sensor .....

T&T Racing

I spent hours ruminating over sensors when the no-start, then start, then no-start was malfunctioning fuel injectors.

jej3

Related situation to this one I think (that's why I'm posting my issue here, too)....

My full thread is here but essentially, I have a car which is a no-start after engine-out, new head, all new sensors, new fuel injectors, new fuel lines, new FPR and Damper and re-seal.

I've tested Fuel Pressure and the bleed down is as follows:

32-34 pressure with Fuel Pump running and engine off
20 pressure at 10 minutes after fuel pump off
15 pressure at 20 minutes after fuel pump off
0 pressure after 1 hour

Is there an issue with these results?

I do think I have wet plugs as I think I observed this previously but the pressure drop isn't consistent with leaking injectors (I wouldn't think)

Anyhow, my old injectors are functioning off of 12 volts and I have new pintle caps plus o-rings from a 928 project that didn't need them. Should I put the old ones in as the new ones are AC Delco?

Thoughts appreciated!!!!

jej3

Bump

Jfrahm

Probably best to stick in your own thread although maybe not you've moved off the sensors and onto a vacuum leak or something. So maybe a new thread?

Giorginetto

As far as my 924S is concerned , picked her from the garage yesterday , started effortlessly and took it for refueling and started again afterwards. Drove the car for a good hour in urban traffic and motorway , no issues there , I noticed an ' improved' behavior when taking my foot off the gads pedal , previously this deacceleation would be more abrupt ,feels much smoother now and normal . 924S in my garage , hooked to Porsche battery charger ( voltage display before start up was a notch below 14V) and will start the car again probably tomorrow morning. I hope and trust that this start up issue has been resolved .

Summary :

My 1988 924S was having some problems starting and got much worse after I added a fuel Porsche additive with a full tank - first time I filled the fuel tank so debris/rust and this additive made a nice mix . Car would have troubles starting and not very smooth driving at start . Removed all fuel , replaced in tank fuel filter, fuel filter, 2 fuel lines, new fuel pump and new fuel pressure regulator,. also replaced 4 sparks and air filter and new charcoal canister ( last is irrelevant to this issue ). also replaced all 4 injectors as well .

mrgreenjeans

After such an exhaustive attempt with addressing the fuel portion of the equation, if you are still experiencing starting issues, if it was me ( and from prior experience with a similar no or stubborn start ) I would seriously look at the reference sensors. In one situation, these were the culprit on a two year old 944 with around 7,000 miles.

It is entirely a possibility the fuel additive was coincidentally a part of, but not necessarily a total cause of the problem. Best wishes with your sleuthing and end resolve of the matter.

peanut

my inclination is the same as T&Ts . You probably clogged up the injector filters when you flushed the system.
I'm pretty sure that the general consensus is that you should never flush the fuel system with additives with the fuel rail connected otherwise everything that you flush out of the fuel lines ends up in the injectors.

In the past I have had the same difficulties starting my S2 due to infrequent use. The additives that we have in UK fuels leave a very sticky varnish in a very short space of time which prevents the injector solenoids operating properly.

I usually remove the injector pulse connectors and use a PP3 9v battery to flash each injector 10-20 times until I can hear the solenoids clicking freely . Once the car starts any residue injector stickiness usually disappears once the engine warms up.

I'm sorry to say it but this is a classic case of throwing money at new parts until the problem goes away instead of applying a methodical troubleshooting sequence to the issue to establish the cause.
If a simple fuel pressure , Fuel flow rate and leak down tests had been applied you would probably have realised that you didn't need the 2x filters or the fuel pump or the new injectors .
Anyway glad to hear that its running again these old cars can be very frustrating at times