nyounce Posted March 29, 2007 Report Share Posted March 29, 2007 My '93 is difficult to start on the first start of the day. After that, it starts on the first or second turn. On initial start, it frequently requires three, or more, 10 second attempts before it finally stumbles into an idle, races up to 2000+ rpm and then smooths out. Just bought a fuel pressure gage, but haven't yet taken any readings. Is there a check valve to hold the fuel rail pressure over long, overnight, periods, or is that a function of the in-tank pump? Later.... Just finished checking the fuel pressure with the following results: Turned key on Fuel pressure went up to 10-12 psi Turned key off, and then on again Fuel pressure advanced to 20-21 psi Turned key off and on again Fuel pressure advanced to 30 psi Key off and on again Fuel advanced to 41 psi and would advance no higher. Key off Pressure remained at 41 psi After 20 minutes, fuel pressure indicates 28 psi Engine was still warm when above tests were run. Problem won't occur until I attempt to start cold. Will post new readings after attempting to start the car in the morning. Link to comment Share on other sites More sharing options...
jackc Posted March 30, 2007 Report Share Posted March 30, 2007 Looks like its having a hard time building fuel pressure. You should be getting 40 after the first key on. Could be a plugged filter, but a failing pump sounds more likely. Link to comment Share on other sites More sharing options...
Ranger Posted March 30, 2007 Report Share Posted March 30, 2007 I agree. Pump is very suspicious. Link to comment Share on other sites More sharing options...
nyounce Posted March 30, 2007 Author Report Share Posted March 30, 2007 Looks like its having a hard time building fuel pressure. You should be getting 40 after the first key on. Could be a plugged filter, but a failing pump sounds more likely. Is there a definitive test for the fuel pump. I'd hate to pull the tank again. I replaced the fuel pump, with a third party unit, about a year ago. Looks like I should have sprung for the real thing after all! What codes would indicate a marginal fuel pump? Link to comment Share on other sites More sharing options...
PAUL T Posted March 30, 2007 Report Share Posted March 30, 2007 Before you replace the fuel pump, replace the Fuel Pressure Regulator (FPR). It is located under the top cover. There is alot of info on this in the archives. I would also change the fuel filter. Link to comment Share on other sites More sharing options...
jackc Posted March 30, 2007 Report Share Posted March 30, 2007 To my knowledge, fuel pressure is not a monitored condition, so there won't be a code. Your hard start is consistent with low pressure. That its starting ok when warm tells me that once the pressure is built its holding ok and your numbers support that. So that leaves you with a leak (which could be the FPR or an o-ring, but unlikely since it holds once it builds), an obstruction (filter?), or a pressure input problem (pump). You could try to find a point upstream to test, but you'll have to figure out a way to connect the gauge. Maybe you could cobble one on at the filter connection. Link to comment Share on other sites More sharing options...
nyounce Posted March 30, 2007 Author Report Share Posted March 30, 2007 To my knowledge, fuel pressure is not a monitored condition, so there won't be a code. Your hard start is consistent with low pressure. That its starting ok when warm tells me that once the pressure is built its holding ok and your numbers support that. So that leaves you with a leak (which could be the FPR or an o-ring, but unlikely since it holds once it builds), an obstruction (filter?), or a pressure input problem (pump). You could try to find a point upstream to test, but you'll have to figure out a way to connect the gauge. Maybe you could cobble one on at the filter connection. Good suggestion. I will try to test the pressure upstream of the filter. This morning I connected the gauge and found when I simply turned the key it reported 4 psi. Subsequent tries resulted in a maximum pressure of 22 psi. It took 10 tries to reach that pressure. Once I had the 22 psi, I attempted a start and it was successful on about the second turn. The pressure then went to 37 psi and remained there after shutdown. I really hate to go through the process of replacing the fuel pump, but it's beginning to look inevitable. Link to comment Share on other sites More sharing options...
Ranger Posted March 31, 2007 Report Share Posted March 31, 2007 Sounds like that pump is somewhat intermittent. Link to comment Share on other sites More sharing options...
95SevilleSLS Posted March 31, 2007 Report Share Posted March 31, 2007 Yeah, because wouldn't a plugged filter make it low pressure all the time? -Dusty- - 02 Seville STS, white diamond - 93 Sixty Special, Tan with vinyl top - 79 Coupe DeVille, Tan with Tan top - 06 GMC Sierra Z71, Black - 92 Silverado C1500, black and grey - 83 Chevy K10 Silverado, Black and Grey Link to comment Share on other sites More sharing options...
Ranger Posted March 31, 2007 Report Share Posted March 31, 2007 Yes it would. Plus if the filter was plugged enough to affect starting it would barely run at all at higher fuel demands and probably fall flat on its face at WOT. Link to comment Share on other sites More sharing options...
nyounce Posted April 2, 2007 Author Report Share Posted April 2, 2007 Yes it would. Plus if the filter was plugged enough to affect starting it would barely run at all at higher fuel demands and probably fall flat on its face at WOT. Thanks for the input! In the morning, I'm going to put a gauge upstream of the filter, just for grins, and then start pulling the pump. Link to comment Share on other sites More sharing options...
tco43 Posted April 2, 2007 Report Share Posted April 2, 2007 I have a similar problem with my 96 SLS. Is there any reason to suspect defective grounds as a cause for this? Link to comment Share on other sites More sharing options...
billybob Posted April 2, 2007 Report Share Posted April 2, 2007 I have the same tro uble also with my 96 sts its headed to the repair shop today for this problem. ill let you know what they find on mine im hopeing for only a cheap FPR for about $100.00 or something simple but with my luck it will be a $400.00 fuel pump. Link to comment Share on other sites More sharing options...
nyounce Posted April 3, 2007 Author Report Share Posted April 3, 2007 I guess this closes the thread. Finally bit the bullet and put in another fuel pump. Pressure is up and it starts on the first spin. Thanks for all your support. Going over to the Porsche group to see if I can tweak my 928 a bit. Thanks again! Link to comment Share on other sites More sharing options...
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