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  1. #1
    Saab Fan
    Join Date
    05 Mar 2014
    Location
    California USA
    Posts
    5
    Saab(s)
    1991 900

    New Fuel Pump Didn't Fix It

    New Fuel Pump Didn't Fix It

    I've been wrestling with fuel delivery problems for more than a month and need a clue on what to try next.

    Back story: My 91 900 was having hard cold start problems which appeared to be a bad fuel line return check valve in the elbowfitting on top of the fuel pump. Then, for no reason the check valve started working and it would fire right up when cold. It worked OK for about 3 weeks and then the car died downtown and I had to have it towed home. The towtruck driver said "Let's try this first" and got under the car with a hammer, pounding on the bottom of the tank. The Saab started right up and ran for half a minute then quit again. I got the tow home, but now felt certain that the problem was with the fuel pump.

    I ordered a new pump, made a screw ring tool, took out the old pump and replaced the pump body only, using the old fuel pump cannister. Fired right up, but the pump was really loud, I could hear it with the rear seats in place. But the car ran, so I drove it for about a week when one morning it started missing on accelleration. I limped back home and figured the pump body was defective, being loud and not pumping gas. I ordered a full pump + cannister and installed that, but it didn't fix what looks to be a new problem.

    The only clue I have as to what might be causing the problem is that the car will start when cold, rev up OK for a few moments, and then, as the engine warms up, it gets prgressively worse, missing and stuttering until the engine dies. What ever is broken, it seems to have gone bad after putting in the new pump body and it seems to depend on how warmed up the engine is. I don't know how this Saab engine handles its warmup and choke settings, probably some sensor. But whatever it is, it's cutting fuel off to the injectors worse and worse as the motor heats up until the engine dies.

    Nothing more frustrating than fixing one problem and having a new one pop up elsewhere in the same system. Makes me wonder what's going to go next, sigh. I'm hoping there might be a few clues offered here that will give me some idea of what to replace next.

  2. #2
    Saab Fan spydergear's Avatar
    Join Date
    14 Dec 2012
    Location
    West Coast
    Posts
    33
    Saab(s)
    1985 900 Turbo EAG, 1990 SPG Talladega Red
    "Nothing more frustrating than fixing one problem and having a new one pop up elsewhere in the same system. Makes me wonder what's going to go next, sigh. I'm hoping there might be a few clues offered here that will give me some idea of what to replace next."


    There are probably many others that are more experienced than me with this model. So you can take what I say with that in mind.

    First, I would not replace any part unless you have done all the diagnostic work in the factory or Bentley manuals. Throwing parts at it will become a very expensive and frustrating process. And, you must understand how the system(s) works before you can diagnose it.

    What I would start with, and perhaps those that are more experienced can correct me if I'm wrong, is to make sure all the basic stuff is OK, including:

    Correct all vacuum leaks.
    Clean the throttle body, and AIC valve.
    Test to make sure the O2 sensor is working properly.
    Set up the idle as per the Townsend site.
    Check the ignition components and plugs, timing, component condition, etc.
    If necessary, check the fuel pressure settings.
    Have clean fuel and air filters.
    Most of my experience is with the LH 2.2, so I personally haven't done this yet, but you might also pull the codes.

    You will need a digital muti-meter, get at least the better one at HF.
    A Mighty Vac
    If you need a fuel pressure tester, they can be made. I can tell you what fittings you will need if you want to build one.

    Once all that is accomplished, then start going through the procedures in the manual and on the Townsend site.

    If you are not successful in the diagnostic process, then it may be time to take the car to a SAAB pro.

  3. #3
    Saab Fan spydergear's Avatar
    Join Date
    14 Dec 2012
    Location
    West Coast
    Posts
    33
    Saab(s)
    1985 900 Turbo EAG, 1990 SPG Talladega Red
    Question: Was the car sitting for any length of time, longer than three months?

  4. #4
    Saab Fan
    Join Date
    05 Mar 2014
    Location
    California USA
    Posts
    5
    Saab(s)
    1991 900
    Quote Originally Posted by spydergear View Post
    Question: Was the car sitting for any length of time, longer than three months?
    No, I was driving it regularly. Thanks for your reply. I think there is a strong relationship between engine temp and the problem. What is the mechanism on the motor that works as a choke during cold starts? Is the air intake area reduced by a butterfly valve, is there a sensor that determines the leanness or richness of the mixture, are the injectors controlled mechanically at all times?

  5. #5
    Saab Nut 9-3 Aero's Avatar
    Join Date
    22 Apr 2013
    Location
    Tromsø, 69° 41' N
    Posts
    464
    Saab(s)
    2009 9-3 2.0T SC Aero XWD\eLSD. eSID2
    Not being familiar with the 900s, do I not know if there's a crankshaft position sensor (CPS) installed. In Saabs this sensor is known for its notorious failing, symptom being warm start failure, whereas it may start when the engine gets cold. At ignition "ON" the fuel pump primes and when cranking starts the CPS will close the fuel pump relay, only when a minimum revs. are detected.

  6. #6
    Saab Fan spydergear's Avatar
    Join Date
    14 Dec 2012
    Location
    West Coast
    Posts
    33
    Saab(s)
    1985 900 Turbo EAG, 1990 SPG Talladega Red
    Quote Originally Posted by WalterAlter View Post
    No, I was driving it regularly. Thanks for your reply. I think there is a strong relationship between engine temp and the problem. What is the mechanism on the motor that works as a choke during cold starts? Is the air intake area reduced by a butterfly valve, is there a sensor that determines the leanness or richness of the mixture, are the injectors controlled mechanically at all times?
    I was just wondering if it had old gasoline.

    Unlike cars with carburetors, there is no choke as none is needed. The computer knows how to control the mixture based on information it gathers from the coolant sensor, throttle position sensor, air mass meter and later when the car goes into closed loop, the oxygen sensor. The computer can react to idle changes using the automatic idle control valve.

    The injectors are electro-mechanically controlled. They are pulsed - that is the clicking you can hear under the hood.

    I will say one thing: I tend not to blame Robert (Bosch). Look everywhere else first, as it is some of the highest quality stuff on the car. Not that Bosch components can't be damaged or wear out. Recently, I had a fuel pressure regulator fail on me (on a very busy freeway) and since I replaced that, I've had stalling during cold running. You seem to have the opposite problem. Before that, it had run very well for fourteen years. I have no other solution for my problem or yours, other than to say that I would do what I listed above and then start testing using the Bentley manual.

    Unlike my '85, you do have the luxury of trouble codes that can be pulled on the LH 2.4, again that procedure is in the book.

  7. #7
    Robert Lee Clark
    Saab Fan 1986SPG's Avatar
    Join Date
    05 Dec 2014
    Location
    Sulphur, Oklahoma
    Posts
    14
    Saab(s)
    1986 SPG
    My '86 SPG began starting intermittently. I have replaced the pumps and fuel filter, AND replaced the distributor wiring harness, and may have solved the problem. Only time will tell.

  8. #8
    Rob Fox

    Join Date
    06 Aug 2016
    Location
    Sunshine Coast.Australia.
    Posts
    1
    Saab(s)
    91 T Coupe. 88Tconv.(White)88Tconv(Red)88Tconv(Black)2 x 93N/A conv(Green) 89N/A Sedan,85 N/A Sedan
    I had a similar problem on one of my '88turbo's,much googling of the problem seemed to point to fuel pump/relays,replacing pump relay appeared to fix and took it for a long drive,car died in a very inconvenient spot.Problem turned out to be the internal wiring on the distributor,as the engine heated up the wiring appeared to lift under the sensor and started hitting it causing a short.Replaced distributor. Runs fine now.Might be worth a look.

 

 

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