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Car Forum / Volkswagen / Water Cooled Volkswagen Cars / January 2007fuel pump or injectors ?
Hi, I have a 1988 Jetta (non-GLI). After driving it a brief time, it gets rough and looses power. All the plugs are getting a spark, because I can see the spark if I pull off the plug wire. First, the cylinders on the passenger side quit working (no change in engine when the wires are pulled off) then they all quit firing. It eventually quits running at all. If left over night, it will work for a while when first started. When it has quit running, if I squirt ether into the intake manifold through a vacuum cap I pulled off, the car will briefly run fine. From this I decided that the fuel system must be at fault. (I wasted some money on new plugs and wires and cap/rotor first.) I can hear the fuel pump run when I turn the key. Is there a way I can figure out whether it is the fuel pump or the injectors ? The car is getting to the point that I might junk it if it is something as expensive as new injectors, but I would replace the fuel pump if that was it. Can I measure the resistence of the fuel pump electrical terminals or something ? --Rob P.S. My Haynes manual does not mention an in-tank fuel pump, just the one external to the fuel tank. However someone at Autozone told me that they sell an in-tank and an external pump. Is there an in-tank pump ?  Signaturehttp://rgr.freeshell.org/ There are two fuel pumps in your car. The first one, the one you hear running, is under the passenger-side rear-seat passenger's feet. It's inside of a plastic "box" (scavange tank) next to the fuel filter. That's the exensive one. The other one is inside of your fuel tank. Not only is it relatively cheap, it's very easy to get to and replace. You simply get to the top of your fuel tank, which is the bottom of your trunk (you might have to crawl into you trunk), and unscrew the top of your fuel tank like it was the "sealing ring" of grandma's mason jars. Seriously -- my Bonneville needed this repair, and it was over $300, and you'll probably do it for under $50 or so. Chances are that the tank pump, which is high-volume and low-pressure, is the culprit. However, the high-pressure, low-volume one in the little plastic box (don't have to remove the box to pull the pump) can seem to run and pump nothing as well. If you can do the things you talked about, you can do the troubleshooting to find out which pump is bad. Tim Wohlford '89 Golf '98 Jetta > Hi, > [quoted text clipped - 28 lines] > Autozone told me that they sell an in-tank and an external > pump. Is there an in-tank pump ? Can't it be the fuel filter? First measure the fuel pressure at the fuel injector rail. Then after the filter change...........check the pressure again. I have also seen a clogged inlet at the main fuel pump housing. And clogged strainers at the transfer pump along with a lot of debris in some fuel tanks. REMEMBER THAT FUEL IS FLAMMABLE!!!! later, dave (One out of many daves) > There are two fuel pumps in your car. > [quoted text clipped - 54 lines] >> Autozone told me that they sell an in-tank and an external >> pump. Is there an in-tank pump ? Given that I've not changed an external filter on either of my VW's (350,000 miles combined) I didn't consider that possibility. The filter at the end of the low-pressure pump requires removing the whole thing... guess I assume if you've done that much then you're replacing everything? Sorry. Tim Wohlford > Can't it be the fuel filter? First measure the fuel pressure at the fuel > injector rail. Then after the filter change...........check the pressure [quoted text clipped - 8 lines] > dave > (One out of many daves) Hmmm Never changed the fuel filter huh? :-) Yes to get to the filter/strainer of the transfer pump you need to remove the pump from the tank. The dealer used to sell the strainer separately but I think you can easily clean it. I vote you test things out, like fuel pressure, before replacing everything. later, dave > Given that I've not changed an external filter on either of my VW's > (350,000 miles combined) I didn't consider that possibility. [quoted text clipped - 19 lines] >> dave >> (One out of many daves) I had a similar problem with my 1986 GTi a couple of weeks ago. Got into the car in the morning, started it up, and noticed that the fuel pump beside the right rear wheel was noisier than usual. :-( Car was running fine, so I drove out to do my errands. After a couple of errand stops (the fuel pump noise was still louder than usual) the car was running rough at idle, and I needed to keep pedal down to keep it running. Engine had low power. I managed to limp home, though, and got car back into garage. Pulled out the Bentley manual, and learned about the two fuel pumps (as described below). After understanding how the two pumps worked together, I thought maybe the high pressure one by the wheel (which is usually full of gasoline) may have been starved for fuel, not getting enough from the tank pump, which would explain the louder-than-usual noise. I went to the hatch area, pulled up the carpet, to access the fuel tank pump. Pulled off the electrical connector. With voltmeter, saw that 12V was present on the required connector pins when ignition on. Checked resistance of tank pump motor, and it looked open circuit. Aha! Found it!. However, a bit more probing around determined that the connector contacts on the tank fuel pump were slightly dirty/corroded. Cleaned them off a bit, re-attached the harness connector, turned the key and presto! The noise of the high-pressure fuel pump was back to normal, and the car started and ran just fine, like an '86 GTi should. :-) So, as far as checking fuel pump electrical stuff: - Is the pump by the right rear wheel running? It has a distinctive sound. I would suspect the engine wouldn't run at all if this pump was off. It needs to pressurize the fuel injection system. - Then, check the connection for the tank pump. These two electrical checks might be easier than checking pressure in the fuel lines. If these don't pan out, I'd agree with the suggestion about the fuel filter. Good luck! > There are two fuel pumps in your car. > [quoted text clipped - 39 lines] >> the resistence of the fuel pump electrical terminals or >> something ? > There are two fuel pumps in your car. > [quoted text clipped - 3 lines] > > The other one is inside of your fuel tank. And covered under recall warranty for some models. Call the dealer and give them the VIN. Mike >> The other one is inside of your fuel tank. > > And covered under recall warranty for some models. Call the dealer and > give them the VIN. > > Mike Will VW do that for a car that is almost 19 years old (the OP mentioned that his vehicle is a 1988 model)? |
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