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Hey guys, any help here is appreciated. ‘04 C5 A4, just under 150k. LT catless headers, axle back, ECS mail order tune.
I’m a couple hours from home, car was running & driving great on the way to visit family. Hit a bump in the road going about 50mph (nothing huge - I’ve definitely hit worse, but it was a decent bump in the road). Car started losing power, I pulled off to the shoulder and it quickly died. Would start up but wouldn’t hold idle and would eventually die again after a few seconds. Ended up finding the fuel pump fuse was blown (#13 I believe).
Swapped in a spare, fired up right away and held idle. Drove 20ft down the road and it lost power and died again. Same fuse blew again. Ended up having AAA tow it to my cousins house.
Any thoughts or suggestions on what may be causing this? I’m here with limited tools and no jack or stands so I can’t get under the car at the moment, but if anyone has pointers on what to check when I am able to it would be greatly appreciated!
Thanks for the help guys. Borrowed a car to get home last night, heading back out with all my tools today to get it in the air and check things out.
Could a bad/loose/corroded ground cause this? Spent the better part of last night searching the forums and found guys with similar issues also had bad grounds but I’m not sure if that would continuously pop a fuse.
I installed the longtubes a couple months ago so I wonder if they maybe cooked one of the harnesses which is now shorting somewhere.
Also, I’d like to rule out that it’s the pump itself but I’m not sure how to do so if I can’t unplug it. On an 04 is the fuel pump harness connector even accessible from under the car?
A bad / loose corroded ground would not allow the fuel pump to run at the correct RPM and amperage. I checked my fuel pump at idle a few months ago and it was running at 5300 rpm at about 6 amps !!...I’d start looking for frayed wires !!
A bad ground connection would not allow current to flow from ground to the pump, you have a shorted wire which is causing excessive current and that is causing the fuse to blow. I hope that you will not have to remove gas tanks that sounds like a lot of work. Good luck
So I spent the last few hours checking over the wiring and harnesses as best as I could. Everything around the engine & headers looks okay, nothing melted or cracked and no bare wires showing. Checked a bunch of different ground locations and nothing was loose or appeared bad.
I bought a 25 pack of fuses and tossed a new one in, and it started up fine and drove around the neighborhood with no issues. Let it idle for a bit, took it for another drive and it got to operating temp, still no issues. The fuse did not blow.
Is is there a possibility this could be heat related and maybe it only happened because I was 2 hours into a 100+ mile drive?
I did notice after my quick test drives just now that the fuel pump relay got hot. Not boiling hot but a bit hotter than “warm” if that makes sense. The fuse was not hot at all. Could this be a relay issue by any chance? Not sure if a failing relay could cause the fuse to pop.
Contemplating trying to make the drive home as a 120 mile tow would be quite pricey..
I would try a replacement relay. Or at least have one in my pocket before starting the ride home. The relay is what delivers the power to the fuel pump. A bad contact surface on the relay contacts would increase resistance (and generate heat) at the contacts and result in a voltage drop across the contact surfaces. The resistance at the relay contact surfaces should be VERY near Zero as it is just a switch. Replacement relay should run about $15 at most parts stores.
Understood. I picked up a new relay and tested it out this evening. Fuse still didn’t blow but the relay got just as hot as the original.
Oh well, at least I have a spare now. Instead of making the drive tonight I’ll be leaving tomorrow morning. Figure if the same thing happens it’s better to be stuck during the day than at night.
I could not comfortably get the rear of the car high enough due to the driveway being at an incline so I wasn’t able to check the lower connector for the fuel pump. However, I did notice that the HVAC drain was dripping right onto the main wiring harness just underneath it. The harness looked in tact, but maybe from a 2 hour drive in the 100° FL heat with the AC on the whole way it got saturated enough to cause a short?
I will definitely check that harness out when I am able to. It's a bit low on the firewall so I'll likely need to pull the passenger side header to get a good look at it.
Anyway, I left at 7am this morning and made the drive home successfully. I took back roads in order to avoid possibly getting stuck on the interstate and made it in a straight shot without a hitch, about 2.5 hours of driving. Did not blow a single fuse. I hit several bumps as well, one pretty decent one through a construction zone but still all good. I did not turn the AC on at all during the drive, so I may be onto something here, or it could be nothing. Checked the relays after the drive and most of them were just warm from the drive and heatsink, however the fuel pump relay and one of the cooling fan relays were very hot.
Regardless, now that I'm back in a flat garage I can get the car in the air comfortably and check everything over again, including the harness at the tanks. Testing the harness at the firewall for water infiltration should be easy enough as well.
If everything checks out and nothing is out of the ordinary, does this sound like it could be a failing pump? I was always under the impression fuel pumps tend to hard fail, as opposed to sporadically/gradually over time. I can hear it prime just fine, and I can hear it faintly humming from the driver's seat most days (which seems normal from other posts I've read). Some days it's louder than others, and some days I can't really hear it - but it's always been like this in the 2+ years I've owned it.
Backed the car up onto ramps today to try to get a look at the harness for the tank. 8VETTE7, I'm not sure if I located the correct harness that you mentioned above that was dangling from the left tank in your picture. The only harness I could see on the driver's side of the car was a small (seemingly) two-prong grey connector that is attached to the frame rail. I'll include a photo of it below - this is looking between the exhaust (left side of the photo) and the gas tank heat shield (right side of photo). I couldn't reach up and examine it without removing the axle back, but this connector and its wiring that I could see seemed in-tact, however there was some electrical tape that had unraveled some from it. Not sure if the tape is from the factory or if that could be indicative of the pump being replaced before at some point (would a stock one last 150k?).
There is an identical connector as described above on the passenger side frame rail as well. Also on the passenger side (slightly more difficult to see past the exhaust) was a larger connector between the tank and transmission with maybe 6-8 wires going to it that I could see (black, white, black&white, green, red, grey). It looked kind of like the connector that is dangling from the passenger tank in your photo above.
From some searching last night, I came across a couple of your posts #10 and #11 in this thread, which seems like it could possibly be my issue as well. In layman's terms, what is the proper way to test the original relay for resistance or other voltage measurements to see if it is out of spec? And what range of values should I be seeing? My electrical knowledge is pretty low, so I'm not sure of the correct way to test it. While the actual issue from the last post of the linked thread ended up being a short on the top of the gas tank, I'd like to test and rule out the easy things first before getting in too deep. I could be completely wrong in this assumption, but I feel like if I had a short somewhere, I would have had another blown fuse at some point in the 2 and a half hour drive home yesterday.
Bumping as this just happened again today, but under slightly different circumstances.
Since I made the drive home successfully from Tampa when this last happened, I haven't had an issue since. Drove it to work and around town consistently with no issues. On Friday I drove to Jacksonville (another 2 hour drive from where I live) and made it with no issues.
I left to head home this afternoon, made it almost all the way home and lost power on the interstate, this time only about 3 miles from home. Managed to put it in neutral and roll down the next exit. Checked the fuse and sure enough it was blown. I let the car sit for about 10 minutes, put the original fuel pump relay back in as the new one I replaced when I was stuck in Tampa was very hot, put a new fuse in and made it about a half mile down the road before it happened again. Let it sit for about a half hour this time before putting the new relay back in (since it had cooled off), as well as a new fuse, and made the rest of the drive home fine. Let it idle in the driveway for another 10 minutes to see if it would pop once more but it never did.
NOTE: I did NOT hit a bump this time. The first time this happened I lost power after hitting a decent bump in the road, which now I'm thinking might just be coincidental. This time I was cruising at about 80mph on a smooth section of the interstate when it happened.
Since the fuel pump itself is very difficult to access on an '04, I'm trying to rule as much as I can out before tearing the rear end of the car apart. It's almost sounding like a heat + runtime related issue since both instances occurred after a long drive and blew another fuse after only a few minutes of cooling down. Any suggestions on anything else I can check/test in the meantime? Any help is appreciated, you've all been a huge help in suggesting what to check so far.
I would say it could be a short to ground in the harness when you said the car shut down when you hit a bump but now that it’s doing it not hitting a bump I’d maybe lean towards the pump...since your electrical expertise is limited I’d check the amperage draw between pins 87 and 30 (load side) of the relay to the pump. See what the amperage draw looks like when the engine is first started and at higher RPM’s. Don’t know how good you are with a DVOM but this would be a way to check. If you want to fire the parts cannon go and change the pump...like I said my pump was drawing around 6 amps at idle !!
Thanks for the suggestion - I have a volt meter but yeah my electrical expertise is very minimal, and from what I understand checking amperage is a little different than checking voltage which is about as far as my volt meter knowledge goes. What is the correct way to check amperage draw between these pins, and what should the amperage be at idle? Is there anything else I can check at the same time?
Measuring voltage is reading a difference in potential between ground and a positive voltage point, to measure current you have to connect you DVM in series in the circuit meaning that you sometimes have to cut a wire and connect your meter leads to both ends of that wire. You also have to move your positive "red" lead to the current jack on the meter, there are usually two jacks on a meter one is for milliamp currents and one for amps, you want to use the amps jack of course and select the DC current position on the meter. It doses seem by your description of your problem that your fuel pump may have to be replaced. Hope this helps, good luck.
Thanks for the suggestion - I have a volt meter but yeah my electrical expertise is very minimal, and from what I understand checking amperage is a little different than checking voltage which is about as far as my volt meter knowledge goes. What is the correct way to check amperage draw between these pins, and what should the amperage be at idle? Is there anything else I can check at the same time?
Here is a video to show you how...I would make a short video for you but I’m on vacation...your tests leads WULL NOT fit in the relay terminals at the fuse box when you remove the relay...I made my own leads from 2mm male spade terminals. My 01 with 55,000 miles was putting out around 6 amps at idle but I was using my oscilloscope to check not only amps but RPM as well.
Since you're frequently blowing Fuse 13 (20A) and you've found out that the fuel pump relay (Relay 35) is consistently very hot, that means that there is a good probability that the current in that circuit is routinely high and probably in the neighborhood of 20A.
Therefore, to be able to read this current you would need an ammeter capable of reading at least 20A. Be careful because common multimeters usually only read up to 10A and are fuse protected, so anything above 10A will cause it's internal fuse to blow.
As explained in posts above, you would have to insert your meter (set to read current and with its leads plugged in the correct jacks) in series with the circuit. To avoid having to cut any wire you can remove Fuse 13 and connect the meter's leads to the fuse socket, effectively making the meter take the place of the fuse.
Another way of doing this would be with a clamp meter. You would need to identify the wire coming out of Relay 35 to the fuel pump, and opening the meter's clamp, put it inside the clamp to take a reading.
Take a look at the schematic to help you visualize both ways of doing this:
Since you're frequently blowing Fuse 13 (20A) and you've found out that the fuel pump relay (Relay 35) is consistently very hot, that means that there is a good probability that the current in that circuit is routinely high and probably in the neighborhood of 20A.
Therefore, to be able to read this current you would need an ammeter capable of reading at least 20A. Be careful because common multimeters usually only read up to 10A and are fuse protected, so anything above 10A will cause it's internal fuse to blow.
As explained in posts above, you would have to insert your meter (set to read current and with its leads plugged in the correct jacks) in series with the circuit. To avoid having to cut any wire you can remove Fuse 13 and connect the meter's leads to the fuse socket, effectively making the meter take the place of the fuse.
Another way of doing this would be with a clamp meter. You would need to identify the wire coming out of Relay 35 to the fuel pump, and opening the meter's clamp, put it inside the clamp to take a reading.
Take a look at the schematic to help you visualize both ways of doing this:
...
Lets see if the OP wants to spend money on an amp clamp...if not and the DVOM fuse blows case closed !!!...change the fuel pump...anything approaching 10 amps is defective !!
Lets see if the OP wants to spend money on an amp clamp...if not and the DVOM fuse blows case closed !!!...change the fuel pump...anything approaching 10 amps is defective !!
He is routinely blowing a 20A fuse and the fuel pump relay is reported as constantly very hot. It doesn't look good for the pump...
Thank you so much for the help guys, this is a huge help. With this info I just went out and pulled fuse #13, and with the DVOM set as described above I'm getting 6.82 amps. This was with the car completely cold (had not driven it since yesterday) and with just turning the key to prime the pumps - I didn't actually start the car. Anything else I should test or is this pretty indicative of a failing pump?
I'll keep the DVOM in the car and test it after the next time I take it for a drive to see if the reading increases at all.
07-14-2018, 06:18 PM
Hit bump, fuel pump fuse blew and keeps blowing
