Subject: Hot starting problems with 928 From: Michael Gerard Date: Tue, 28 Sep 1999 01:21:41 -0400 X-Message-Number: 3 Several folks have reported hot starting problems over the past few months... and the cries for help have been met mostly with the explanation of "vapor lock" or something similar. I just stumbled across the following in an Australian review * of the 1983 928 and thought others might find it interesting: "...they collected the Porsche 928S and in 36 degree heat drove out ... Pulling up at a set of traffic lights the engine cut out and then picked up of its own accord. They stopped for sandwiches and the car wouldn't start, or even fire. Fifteen minutes of trying and they phoned Porsche. The service manager, fresh back from Stuttgart suggests they take off the petrol cap, turn the engine over for up to eight seconds, pause and repeat the performance. It worked, the engine fired into life..." * excerpt lifted from a review sidebar in the new book titled: PORSCHE 928 HEAD TO HEAD "Porsche 928 Takes On The Competition" compiled by RM Clarke ISBN 1 85520 4118 (available through http://www.amazon.co.uk) - michael 1988 928 S4 A/T RMB -> Daily Driver see at... Cassisrot Metallic/Burg.-> http://members.rennlist.org/michael 928 OC Charter Member -> http://www.928oc.com PCA NOR From: Fred Rourke [rourkefg@omantel.net.om] Sent: Thursday, July 20, 2000 1:32 PM To: Pirtle John Subject: Re: intake removal John, If you lose fuel pressure cold starts not affected but hot starts are. If the owner replaced the fuel pump then there ought tobe new check valve with it. Of course the ball could be stuck with a little piece of crud in the valve seat. The acid test is to simply measure the fuel pressure [hot condition] if you have the rig and watch it for an hour or so. The pressure should not drop to any noticeable extent. Your symptoms show this sign but of course it may be something else the question is what? Do not forget, a leaky injector could cause pressure loss as well. Until you are certain you are retaining fuel pressure you have not eliminated the most likely source of the problem. As regards the fuel filter I would write that out of the hunt. The manual lists temp sensor 2 as a possible cause of hot start problems. I presume that is the one on top of the water manifold toward the front of the engine. You can check this by removing the sensor cover with the engine cold. You measure the resistance from either pin to ground [not pin to pin as there are two outputs- one for each computer and they both need to work]. At summer ambient [20C] the reading should be around 1500 to 3000 ohms. Warm up the engine and at 80C the reading should drop to around 300 ohms. At 100C it should be around 100 to 200 ohms. If this is OK you can also test the connections on the LH computer plug lead terminals 13 and 5 [just in case there is signal discontinuity]. Assuming your HT kit is good this really only leaves vacuum leaks [false air]. If have the inlet manifold off you can eliminate these. Did you put a vac gauge on to test the vacuum being pulled? There are other less likely possibilities such as fuel pump voltage, faulty ground connections and fuel tank venting. Knackered anti knock sensors do not affect the starting behaviour, just the oomph, although they need to be spot on to get your money's worth out of the fuel you re using. Not sure if you can use a timing light on our 928's. Take advice from those that know [Rennlist?] before you try. The ignition system is mighty powerful and those [expensive] computers are sensitive to rogue voltages. You can use kypton type kit but I would make sure those using it really know what they are doing. That should show the advance curve but you would need to know what the mapping point was to start with- I don't. Everything aside your 928 should start up first time everytime and if it does not then for sure something is less than perfect. Did you manage to check the idle speed contact setting? This should not affect hot starts. Justout of interest, how much did the fuel regulator set cost you and did you smell fuel on the old ones? That's me cleaned out of ideas. There are others who know plenty more but most problems usually boil down to these few basics. My 928 has been repaired and she looks great. She now sports a gts type rear valence with red reflector and a red spoiler same as the body paint. Send you a pics when I get one in ther meantime attached is photo as she was after last prang was repaired [a full factory spec respray] Regards Fred From: Wally Plumley [mailto:wplumley@bellsouth.net] Sent: Tuesday, August 06, 2002 10:12 AM To: 928 Subject: [928] Re: Vapor Lock At 02:40 PM 8/5/02, Abe Reinhartz wrote: >This might be a stupid question....but....sometimes the 928 GTS has a lot of >problem starting when hot. Anybody have any ideas what this is? Once it >lights, it's fine. There are several possibilities. Starting with the most likely - If an injector, pressure regulator, or pressure dampener leaks into the intake system, the added fuel will cause the fuel/air ratio to be too rich, causing hot-starting problems. If the hot engine starts more easily with the throttle half-way down, this is the primary suspect. You can pull the vacuum line from the pressure regulator and see if there is any trace of fuel in the regulator port or the line, and then do the same for both pressure dampeners. Any trace of fuel in the line is cause for replacement. If the problem is a leaking injector, Techron or another good fuel system cleaner might help. Remember that cleaners do more good on daily, short-trip driving than they do on a road trip. If the injector doesn't clear up in a month or two, you might want to pull all of the injectors and have them cleaned. There is another fuel-related possibility - there is a check valve in the end of the fuel pump that is supposed to hold system pressure to prevent fuel boiling in the lines while the engine is hot, and to make cold starting more positive. If this valve leaks, the pressure loss will allow hot fuel to boil in the injection lines, causing a hard-start condition similar to vapor lock. Only cure is replacement - not too expensive (we sell the check valve for $15.87 plus shipping) and not too difficult a task (except that the fuel pump/filter fittings are usually really tight). Some folks have installed a fuel pressure gauge in the end of the fuel rail to check on such things. The gauge (VDO, either 0-60 psi or 0-100 psi) is $29.95 plus shipping. Call Jeannie at (828) 766-9280 if you need anything. Wally Plumley 928 Specialists www.928gt.com