924Board.org

[numbers]

Marco, you have the typical hot start problem. Go to the tech section and read the write-up I posted there a couple of years ago. The switch will solve your problem if you install it properly. I don't know what kind of mechanics you have in Sweden, but there is no way that using the switch will cause your engine to blow-up. I do not usually disagree with Vaughn, but the cold start valve does operate when the engine is hot. It just operates for a reduced time period. This period is controled by the thermo-time switch suppling ground to the valve. When the engine is full hot, this switch still supplies ground to the valve for about three seconds. However, this time is not adequate for an old engine. That is where your problem lies. You can verify that your switch is not suppling the ground to you valve by splicing into the ground wire and just holding the spliced wire to chassis ground while someone else cranks the car. If it starts hot that way, but not with the switch, check out your switch loop.

Just a note on the leak down issue, if it were a leak down problem, the problem would be worse at cold start, since the pressure has had longer to leak down that for a hot start. Ditto for check valves and relays. It takes more fuel for cold starts than for hot starts. If any of these items were the problem, you would not get a cold start. Also, I doubt very much that it is getting hot enough for a vapor lock problem in Scandinavia in the winter. Check out your ground switch or even considerf installing a resistor in series with the thermo-time switch as I described in the article.

[dpw928]

Marko,

It appears you have one or two leaking injectors. Before replacing them you may want to try a good fuel system cleaner. The reason a leak down will normally show up on warm starts is due to the extra fuel the cold start injector supplies when the engine is cold. The leaking injectors could also explain the poor performance you are experiencing.

Dennis

[Marko Modiano]

Have done the check on the injectors and sure enough, number 4 did not spray at all!! while the others give the cone spray as described in Haynes. I thought that I would start by replacing that injector (any suggestions as to how to get it off and the new one on?) and see if that solves my problem. There is no place around that cleans them, and the new one was not so expensive. The replacement number was 0437 502 013, while on the net the number is listed as 0437 502 015. We are talking about a standard European 924 no turbo from 1980. I ordered the 013 as that is the number on the actual part I want to replace. Anyone know why the numbers are different on the site? Otherwise, I assume that replacing this part is part of my problem, at least with the missing at low rpm's in second gear. Is it possible that one faulty injector would make the care impossible to start when it is warm? Thanks beforehand

Marko

[-nick]

Hi Marko,

i'm a little suspicous here, these injectors fire when the pressure built up behind them is high enough. if it's not, it won't spray, unlike modern electrically fired injectors.

usually these injectors will leak if anything. i'm worried that you're not getting the proper fuel pressure in that line.

part of the warm start problem is that you get vapor lock which means you've got a mix of air and fuel in the lines. air compresses alot and the injector won't fire because it can't build up the pressure. once the air is purged out the injector will fire just fine.

i'm worried that your problem may have its roots before the injector. and that the injectors are fine.

what did you do to determine you had a bad injector? -lift up the air metering plate with the ignition on i guess? how long did you do it for? try swapping the bad injector onto another fuel line to see if it still doesn't fire. at least before you buy a new one, it's an easy check.

just some info to put out there...
good luck,
-nick

[Roger Hall]

correct dont assume the injector is bad move it to another fuel line and see if you get the same resultsyou can spend a fortune replacing parts because you think they are bad test twice buy once

[Joes924]

Mark if you suspect a injector get a big glass jar I use a commercial size pickle jar.
I put a small hole in it just enough to stick the injector tip in.. pull an injector
stick it in the jar. Start the car and observe the pattern it should be a conical shaped mist shut off the car observe the injector for leaks if it leaks out of the tip
or the pattern is bad its time for injectors
you can have them cleaned or get new ones
You still can get them for 24.00 some places charge as high as 34.00 .Good luck on your 80 924 dont just play in the snow either

[ This Message was edited by: Joes924 on 2002-03-06 14:29 ]

[dpw928]

Marko,

Please heed the advise of Nick and Roger. Blockages of the injectors are rare. Did you check the injectors with the engine warm or cold? Did you have the fuel pump #30 and 87 connectors bridged? Could pressure bleed down have caused this injector not to spray? Have you checked the electrical portion of the control pressure regulator (WUR)? Obviously there are a lot of tests that need to be performed prior to replacing parts.

Dennis

[Marko Modiano]

Well, things just seem to get worse. I have now rechecked the injectors by putting them in a jar, and have swapped the injector I thought was bad and sure enough it works on another line. There is a spark on all four sparkplugs, and gas gets into the chamber which will not fire because the plug is wet when I pull it. I have taken the car out for a spin and am now sure that it is only firing on three cylinders. As it is has been winter here it was difficult for me to know earlier because the problem started a few weeks back when it was very cold, and began with the engine missing a lot (which was when I tried to start fixing it). So, at the moment I have an engine which runs very well on three cylinders, but cylinder number 4 is not firing although there is a spark at the sparkplug and the sparkplug is wet when I pull it while the others are dry. It would seem that there is a presure problem in that particular line leading to the injector. Any advice as to what I should do now?

Marko

[-nick]

now i'm getting stumped. is the plug just wet, or is the cylinder getting flooded? i had a bad fuel distributor once but it would flood all the cylinders from what i remember and the car wouldn't start at all. i'm not sure if it's possible to just flood one.

other than that... you could switch ignition wires with that cylinder and spark plugs with it. just in case you're getting a spark but not a strong enough one.

it couldn't be really bad compression, i've had a motor that ran pretty well even with about 60psi per cylinder (hard to believe). also rule out any valve problems since this seems to be a progressive problem.

keep us updated, this is getting interesting.
-nick

[dpw928]

There are o rings in the fuel distributor for each injector line. If one of them go bad it allows system pressure (high) to enter the injector. Appears one of yours has deteriorated. Do you know anyone who has a good fuel distributor that you could try on yours? BTW the fuel distributor is considered "factory rebuild" only by Porsche but they have been rebuilt by home mechanics.

Dennis

[D Hook]

There's one on ebay right now, brand new.

[dpw928]

Beware of buying new or used ones. Make sure the part number matches yours and that the plunger is included, as they aren't interchangeable. The plunger and cylinder are machined as a pair.

Dennis

[JvGinPDX]

I had similar problems, turned out to be bad plug wires. I suggest trading wires, if the problem migrates to another spot, and if the bad cylinder does fire, you have solved your problem

[Roger Hall]

test the spark with a gap meter