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uvachief
 
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Question Changing the fuel pump and check valve on a Late 944

I am running into both a hard cold and warm start issue now. From what I've read, the most likely culprits are a bad fuel pump, check valve or my DME box needs to be rebuilt. Hoping it is the first 2 and not the last one. I want to replace my fuel pump and fuel pump check valve. Anyone got a nice step by step guide in doing this? It is for a 86 944 na.
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1986 944 NA Red 5SPD
Old 07-10-2013, 10:12 AM
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If it's a check valve, the car will take longer to start, regardless of the temp because the fuel has to run all the way from the tank to the injectors vs fuel remaining in the lines and ready to be used at start-up. Autozone has fuel pressure gauge kits that they will loan you to diagnose the fuel pressures for the fuel pump and the fuel pressure regulators (see Clarks garage for the test procedures). Replacing the fuel pump is a protracted procedure that involves removing a large cover that hides the fuel pump. When you are replacing the lines from the pump to the filter and from the filter on to the main feed line, I recommend installing everything but not tightened until all the lines are oriented properly and then tighten everything down. While the pump is out, this is a good time to check to see if there's adequate fuel flow from the tank, through the strainer that's in the tank. It unscrews from the tank.
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Old 07-10-2013, 03:30 PM
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might be worth looking at the pressure first, could also be related to the pressure regualtor / damper
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Old 07-11-2013, 12:44 AM
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Quote:
Originally Posted by strath44 View Post
might be worth looking at the pressure first, could also be related to the pressure regualtor / damper
Already replaced both the regulator and the damper.
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1986 944 NA Red 5SPD
Old 07-11-2013, 02:04 AM
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thats interesting as I had initial poor running then total no start. I also replaced those and finally tracked the prob to the fuel pump. Reckon the faulty damper or regulator put a strain on the pump. Have you tried a fuel pressure test at the rail? Also if you haven't already try replacing the fuel filter. The prob with my nr valve was it had seized against the fuel pipe / collar made it a real pita!
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Old 07-11-2013, 05:45 AM
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Did the filter 2 years ago. I'll test the pressure but I am 80% sure it is the check valve and the fuel pump.
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Last edited by uvachief; 07-11-2013 at 05:43 PM..
Old 07-11-2013, 11:41 AM
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So much for my theory. Changed out the fuel pump and the fuel pump check valve. Still fuel starved and struggling to start. What is causing this?
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Old 07-15-2013, 12:32 PM
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Quote:
Originally Posted by uvachief View Post
So much for my theory. Changed out the fuel pump and the fuel pump check valve. Still fuel starved and struggling to start. What is causing this?
Sorry to hear Chief..
I'd gladly drive down and swap DME for diagnosis but I believe my chipped '88 DME is not compatible..
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Old 07-15-2013, 01:52 PM
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Think I hooked up something wrong. Tough starting and when I give it gas it nearly chokes out and the car will only creep forward. What did I do wrong? Did the suction line blow off after I reassembled?
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Old 07-15-2013, 08:00 PM
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Problem solved (I think). The hose from the pump to the tank was old and internally collapsing. Came apart in my hands when I rechecked it. Repalced it with a new hose. Starting and runnng fine now. We'll see if it holds up. Otherwise, it is the dang AFM or the DME box. OBTW, the new Bosch fuel pump comes with the fuel pump check valve already installed. Didn't realize that.
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Old 07-16-2013, 11:18 AM
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Well, fixed the immediate problem of not moving other than a snails crawl. Driving fine but no change with the hard start problem. Popped the hood and tapped the DME box and voila - it started. Dying DME in need of resoldering?
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Old 07-16-2013, 12:21 PM
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Those dang dme fuel pump relays! I replaced my original one in may of 2010 with a uro part. I replaced it again about 6 months ago. Both were junk. Switched out for a new uro one this evening and voila....fires and catches. Need to order a porsche original oem one whatever brand that was. These uro ones are not very good.
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1986 944 NA Red 5SPD
Old 10-08-2013, 04:59 PM
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