Fuel Pump Issue

[PitmanMK3]

I have a '98 Jetta with California admissions that has been working on for a little while and was trying to pinpoint an issue that ended up being a bad tps sensor. That is fixed now (I know this because there is now throttle response when I used starting fluid to start the engine) but now I have an issue of the fuel pump not priming and I do not believe it is working at all.

All of the fuses are good and I believe the relay is fine too because I have one out of one of my parts cars and swapped that to try it. I also replaced the pump since the one that was in there was old and cheap. With my luck I guess it is possible they both are bad, but is there a sensor that could be bad that would actually prevent the fuel pump from working?

[Anony00GT]

So this car will crank but not start, right? Have you scanned for codes? The TPS sensor on an OBDII ABA is inside the throttle body unit and not serviceable separately, what exactly did you do with it? Did you do a throttle body adaptation with VCDS after messing with it? Please advise.

If you suspect a fuel supply problem, stop swapping parts and do the testing. Check for power and ground directly at the fuel pump. If you've got power there while cranking, use a mechanical gauge to check fuel pressure at the rail. Post up the results.

[PitmanMK3]

Correct, the car will crank but not start. I have been only been able to diagnose the throttle response by using a spurt of starting fluid. I replaced the entire throttle body since the TPS was not serviceable.

I was not able to check for voltage at the pump, however did not think to use it as an ammeter though so I will try that tonight when I get home. I did check that there was continuity within the wire however, connecting one wire on the harness and placing the other lead at the fuse block where the relay plugs in, and it read 0.2 ohms so I know the power wire is at least good. I will also check the negative wire when I get home. Do you know where it grounds out? I did not try using the body as ground to check continuity because I figured it would be too much resistance for the ohm meter to detect, but if you're not sure I will try it any way. I do not have a way of scanning the codes, but have a pressure tester that I will be borrowing from a friend that I will hook up tonight.

I should have the results of tonight's tests up by 8:30 pm eastern time.

[Anony00GT]

Do not attempt to diagnose throttle response until the vehicle is running as designed. Have you hooked up a mechanical pressure gauge and read fuel pressure at the rail?

As for the electrical diag, you're doing it the hard way.

Disconnect the fuel pump connector. Then take your voltmeter or test light, connect it to both power and ground right on the connector. If you've got battery voltage on the meter while cranking, both sides of the circuit are good, no need to further chase wires. If this is the case, the pump is faulty.

[PitmanMK3]

I did have a problem with the throttle response as the initial problem, the fuel pump is the new problem, but I did check for power at the pump and that is a negative. I did recheck the fuses as well and they were good.

[greyhare]

Check for power at connector "M" pin 2 on the back of the relay panel. How did you check the fuse?

[Anony00GT]

Then isolate both sides of the circuit. Connect your meter between power at the connector and a known good ground. If you've got power cranking, the problem is in the ground side. If you've got no power, chase the power side of the circuit.

Time to break out the wiring diagram.

[PitmanMK3]

Sorry it took a while to respond, I did check the power terminal 2 of the fuel pump relay on the fuse block and there was no power when you turned the key foward nor when you cranked the engine over.

As for the fuse, i checked it with a multi meter and there was perfect continuity. Looking at the manual for relay locations, I did find that there was a spot for an engine control module relay that is not on the fuse block. Was it only select models that had this by any chance or is this necessary for all models?

[PitmanMK3]

Anony00GT, I wa looking arround on line for a wiring diagram for the 2.0 engine and came up empty handed, do you know where to find a good wiring diagram?

[germancarnut51]

Buy a copy of the Bentley VW Factory MKIII Service Manual.

[Anony00GT]

Anony00GT, I wa looking arround on line for a wiring diagram for the 2.0 engine and came up empty handed, do you know where to find a good wiring diagram?

What Germancarnut said. You're not going to be able to just find one for free on the Google.

Get a Bentley manual, or a cheaper alternative is to sign up at www.alldatadiy.com

[OddJobb]

Have you tried bypassing the fuel pump relay by connecting a 20A fused wire with an in-line switch from relay terminal 87 to the + on the car battery?

[PitmanMK3]

No I have not. I will have to try that later tonight. Thanks for the suggestion I should have the results up by tomorrow.

[OddJobb]

No I have not. I will have to try that later tonight. Thanks for the suggestion I should have the results up by tomorrow.

Make sure you have good connections on the fused/switched wire you will use. Also make sure the connector that will plug into terminal # 87 on the fuse panel relay fits tightly. I used about 10 feet of braided 14 gauge wire (taken from half of a spare appliance cord) with terminal connectors to hook up the fuse and switch and to plug into the replay panel and sandwich into the battery terminal. I used an illuminated switch so I could verify I had power on the wire when turned on. If the fuel pump runs when connected like this and turned on, you have a problem with one of 4 things: the fuse, the relay, the wiring, the ECU, or the ignition switch. Connected like this you should be able to fire the car up and keep it running if the fuel pump circuit is the problem.

[dekoone505]

Sorry to hijack the thread but im running into the same issue...
I've already replaced the fuel pump and the car started working once again. Ran and drove it for a whole day and had no problems. Went out of town for about a week and a half, came back and the car wouldnt start.

[OddJobb]

What brand fuel pump? I replaced mine late last year with a cheaper version and I had fuel delivery problems when the car sat for a few days or when the tank was below 1/4 full.

Have you tried all the above to verify the pump runs?

[PitmanMK3]

No prob dekoone. I actually had the same issue with buying the cheapest off-brand fuel pump from ebay. After I bought my throttle body to fix my tps issue, my fuel pump crapped the bed after only about 18 months. I ended up buying a bosch off of amazon.com, however it did not come with the sending unit, but I was able to splice the old one on to the bosch.

As for my issue, I took the advice of hard-wiring the pump, and it turns out that the black wire on my original fuel pump unit was not the ground after all. Long story short, I switched the wires and now she's purrin like a kitten!

Thank you everyone for all your input!

dekoone, it's all yours, I would maybe do as oddjob suggested to see if your fuel pump is shot before you go pulling your hair out as I was doing. I had a similar issue where I had the car running for a little bit, but then out of the blue it would die, so I know the frustration.

Do you have spark? Do you have access to a fuel pressure tester?

[Anony00GT]

Dekoone, I'd treat your problem as a new issue. Check for spark, if you have spark, check fuel pressure at the rail.

N...and it turns out that the black wire on my original fuel pump unit was not the ground after all. Long story short, I switched the wires and now she's purrin like a kitten

You need a wiring diagram.

Generally, on German cars, BROWN is the ground, not black. They don't call it ground, they call it "earth". And the dirt in the earth is brown. Common confusion, especially if you're used to working on domestics. That's why you gotta read the diagram

[dekoone505]

its an OEM Bosch but what really frustrates me is that this is the 2nd fuel pump I buy and after I stop "driving" the car for a few days, the car just stops working.
Also I replaced the fuel pump relay yesterday hoping that would work and that didnt help. I will try to get a better diagnostic this weekend.
Thanks for the help. Im starting to like the mkIII related forums more than the mkV ones...