Giorginetto

My 1988 924S has a very good battery , connected to the Porsche battery charger, stored in a dry garage and serviced every 12 months.... For the past 6 years of ownership the car always started first time without any problems or whatsoever... Two weeks ago I bought this new Porsche classic fuel additive and I followed the instructions i.e put it first in near empty fuel tank and then fill up completely which I did. Since then the car is having major difficulties starting up. it turns every time , battery is fine, I can hear the fuel pump but wont start , after 5-6 attempts and by depressing accelerator will start , puffing and vibrating a lot . on both last occasion once it started the car drives without any issues or whatsoever , idles as it should etc. I have also noticed that the longer it stays without starting the worse this start up issue is , afew hours after a drive is not too bad but a couple of days later need a few attempts !!!

My best guess is that this new additive removed debris /rust and things as such and have clogged the fuel filter. I will replace the fuel filter and flush out all the petrol and clean the fuel pump and injectors and then put new fuel in . Any further advice/ tips are more than welcomed

I have replaced the DME with a new unit but the problem stayed on. If it was DMW related the car wouldn't start at all I presume or drive properly ?

T&T Racing

The cleaner probably removed fuel varnish in the supply line downstream of the fuel filter.

Giorginetto

That wil lnot clear off unless I take all the steps above I would imagine....

Shouldn't happen with OE products... My fuel lines are all original btw and in good condition.....

Swenny

There's a lot in play that has to be in agreement to start that beast up. Go back to basics and check for a spark, (plugs wet or are they burning correctly?)no restrictions in airflow,vacuum and that the fuel is getting to the injectors. I had just drained my tank and the fuel was a rootbeer color.

Dan Martinic

Jfrahm

I'm not sure I'd blame the additive right away. It sounds like watered gas to me, you might try adding some Heet and/or some E85 (or denatured alcohol) to try to absorb any water in the tank.
From my experience if you add a product like this and it clears up quite quickly, it is watered gas. The problem may come back again and again though as more water falls out of suspension. It's kind of a pain to get it all out of there.

Swenny

On other diagrams it's shown as an IAC- controls idle.

Giorginetto

Interestingly , a coupel of days ago the car had a lot of problems starting but about after 1min of running really badly it all run smoothly . I drove the 924S for a good hours driving at high revs most of the times without any issues or whatsoever. Yesterday the car started quicker ( the longer times between drive the worse this symptom is...) and drove it again for a good hours , spirited drive as i pushed the car in the high 4-5k revs for a lot of the time, no issues . I am not 100% sure that this problem is related to the additive but it cant be a total coincidence that all this problem started once i put the additive in. I was adviced to run the existing tank of petrol and then refule with a small amount and if the problem persists then replace the fuel fitler, flush the tank and pipelines, clean the fuel pump and injectors....

Giorginetto

Thanks for the info, surely if i drain/ flush the tank, pipes, replace filter and clean injectors this will fix this problem ...?

Swenny

You want guarantees? Buy a toaster. You have a 30 year old Porsche that's getting older by the minute. Make an attempt to isolate what is actually going on. If the fuel system needs to be serviced, so be it. Testing each component that makes it go boom is the cost effective way of repairing. It's called "troubleshooting" it's painstaking but necessary. I'm going through it right now. Tossing parts at it is tempting....

Jfrahm

Massive overkill for watered gas, some additives would address it or worst case having to drain half the fuel, replace with fresh, more Heet, etc. Then burn the removed gas 2 gallons at a time (added to fresh fuel) in the truck.

gwistrup

Jfrahm

A bad check valve would only make for long crank times but it could be low fuel pressure or a leaking or "hosing" injector causing the difficult starting and idling problems. Good thought.

IMO if attempting to clear water from the gas does not help, when it's having trouble starting, stop trying to start the car and pull the spark plugs, checking each one to see if it is wet with fuel (or possibly coolant) and if any of them are suspiciously dirty or clean. You could have an injector dumping as into a cylinder, or maybe a blown head gasket leaking coolant into one jug.

Giorginetto

Very interesting info . I drove the 924S both on Saturday and Sunday , on Saturday too a couple of attempts to start and then the car was running poorly , clearly a poor supply of fuel as excess engine vibration and puffing at exchasut but once I pressed the gas pedal for a few secpond everything cleared and the 924S drove very smoothly. I drove the car for a good hour on Saturday at high revs ( trying to use up all the fuel tank which was full when I put the additive in ) and didn't have any issues or whatsoever. If anything, at hard acceleration from stop it felt better I couldn't say faster but a smoother acceleration ( bear in mind I did a thorough wheel alignment which was much needed as well ) . On Sunday the car started no problems there and enjoyed a good 2 hours drive at high revs a lot in the 4-5k region...no issues detected ..

Idle is perfect as always before at circa 900rpm

I will wait till I burn all this fuel with the additive in thec at and then troubleshoot I reckon.....

Giorginetto

Car wont start at all now. I pulled one of the voltage supply to the injectors and the car started but run very poorly and once i put the voltage supply to the injector back it started again but running very rough. That suggest a high fuel pressure which probably suggests to replace the fuel pressure regulator . I was lucky to find and buy one suitable for the 88 model ( different part number than the 86-97 924S) so when it arrive i will put it on and see what happens . I hope tha this solves the problem, at least the car started on injectors which suggests a fuel pressure problem. I was thinking as well if the problem can be attributed to a faulty DMW temperature sensor as these are prone to failure as well, this would not allow the car to start cold i would imagine but not sure if pulling one of the injectors as I did would allow the car to start which it did if the sensor was indeed the problem. i also got a set of new sparks which i will put in the car along with the regulator

If the regulator doesnt solve the start up issue I will start checking everything else ... drain fuel, check/replace in tank fuel filter, fuel filter , clean injectors etc etc