OK - There are so many variables on this one I'm not sure where to start: I have a full time Fuel pressure gauge - recently only on hot days, over 95 degrees, I kinda lose fuel pressure after driving 20 min in the heat. I don't completely lose it, it just starts going wacko (technical term) - normally I have 51PSI steady, but when this starts happening the pressure drops to between 15 and 40 PSI and the pressure swings wildly from the 15 to the 40, until after a very short time (45 seconds) the pressure finally drops to 5ish PSI and the car dies. Now I don't drive it at all when this happens cause it will be lean, I pull off the road and start cussing.

If you start it back up, it might start but I don’t get full pressure still. If I wait a couple of hours (like after being towed home), let it get cooled off, its like there was never anything wrong with it.

Now one might think this could be fuel pump - possible but I don't think so; I have a custom dual pump setup and they run in parallel (needed for volume issues) - I think the problem is most likely electrical.

So the reason for this post is that I have heard rumor that the 2001s have a harness issue that’s known to produce a bad ground to the fuel pump in the heat. First question is: does anybody know about this and if so where has that fault been happening.


But - more info - the engine was out a couple of months ago, and during that process I know we had some pinched wires up by the engine, it caused an oil pressure sensor/gauge short for sure, we had to dig in to the harness behind the engine to get that one fixed. It is very likely that we have another compromised wire in there. So that’s my first guess on this. But it’s a serious PITA to get to so I thought I’d post here first to see if there are any great suggestions or knowledge of a possible 01 harness issue.

Thanks in advance,

Eric

 

Eric, check the sticky at the top of the forum under " Important Electrical Information" Bill Curly seems to have done an excellent job outlining electrical issues on the C5's. Let me know what you find it to be as I am currently suffering some of the same symptoms as you on a 00' supercharged car that I just bought.

Scott

 

Wild-***-guess: Have you pulled the pickup in the tank to make
sure it isn't clogged up with gunk? I've seen the situation where
gunk gets picked up, starves the pickup, but then after time,
the junk settles to the bottom of the tank, and it runs fine for
a while until you drive it and stir up the gunk again...

 

Thanks for the replies....

Well, I may be changing my mind now….

Yesterday was a nice hot day here. So I spliced in to the wiring, added some leads and then drove the thing around for a while. BINGO - The car started doing the bad thing. 95 degrees outside, just like the times before. So I first checked voltage – 11.8 volts – I’d expect a little more but that should be adequate. As a reference, another circuit I tested on the car was at 12.8 volts. Given the load on the pumps I expect 11.8 is OK.

Now having said that, as I turn on the car I watch the meter vs. the fuel pressure gauge; as I said above, when you turn the car on, the pressure will start out about 40psi and then drop to 15 – well as that happens the voltage goes from 10.5 back up through 11.8, until the car then dies where the voltage runs up to 12.8, so it seems the load on the line from the pumps is inversely proportional. Now, somebody out there might be able to read into that and still tell me there’s a problem… ???

OK so then I hooked up power to the leads right from the battery – no change – the pumps act just the same. If there was ground problem I would have expected this to clear things up.

Then I check the reference voltage: there is 5 volt reference voltage line to/from the pumps. I’m not sure what this is used for exactly. Can anybody tell me? – The thing here is that this 5 volt reference is sitting at 1.8 volts consistently. Perhaps that’s normal? But I checked it again after the car was cool and running properly and it always at 1.8. (I’m not entirely sure I checked it right, I used chaise ground).

So now I’m back to thinking that something is wrong at the pumps (one or both somehow, I don’t know yet) so I think I’m gonna pull them…

While I’m in there I’ll check the pick-up too.

But after applying what should have been clean power to the pumps, I can’t see how it can be anything other than inside the tank. (unless somebody knows something about the 5.0 volt reference thing).

Any other thoughts?


Thanks in advance again.

Eric