Car won't start - Was running fine at idle, then just died

[Mikesinfiniti]

I have a 94 Q45 with 160,000 miles. This morning w/ temps in the low 30's I started the car and after about 5 minutes, the engine died and all of the idiot lights came on. There was a mesage that said "low battery", then went off. The car was running fine up until then and the only thing I noticed, like I have for the past 5 years or so is that in cold weather, the fuel pump makes a lot of noise. When temperature is cooler it seems to start making noise as soon as the key is turned on, but not started. After starting and idling for a few minutes the sound goes away, but it's definitely been like that for at least 5 years.

After the engine stalled, I turned the key and did not hear the pump. The car will turn over fine, and I don't notice any voltage weekness as the idiot light suggests. All of the fuses seem ok.

I don't have any sort of analytical meters or tools, but am pretty handy. Does it sound like the fuel pump? And if so, how expensive is it to replace it? Is an aftermarket brand the way to go and what brand would that be? I do have a service manual. I have read a number of past posts and it looks like I should see if it's a "corroded ground wire", but not even sure where to look.

Any help, past experience or guidance would be helpful. Thanks.

Mike

[96Qowner]

It could be your fuel pump controller (FPCU).

zerothread?id=196384

In the thread, there are instructions for grounding your fuel pump to see if it still works without the controller. If the FPCU is bad, you'll still need to replace the pump, because the bad pump is what fried the controller.

[Mikesinfiniti]

OK. I read through all the posts and my initial feeling was that the controller went bad due to a problem with the fuel pump. In tangalora's post it mentioned disconnecting the harness form the fpcu and inserting a aligator jumper wire in the #4 pin of the connector and grounding the other end. I guess this is suppose to bypass the fpcu and allow the fuel pump to work. I did that and I still get the same result - car turns over but won't start and I hear nothing out of the fuel pump.

Is there another fuse that controls the fuel pump other than the 15A fuse under the dash which looks fine? The fuse block under the hood looks ok too.

As I mentioned in my original post, the fuel pump has been buzzing for several years and especially in cooler weather so I'm sure it needs replacing. From what I can see in the fpcu, the connectors look fine and I don't see any soot or burned marks.

If the fpcu is still good, and the fuses are not the issue, then I guess I could conclude that the fuel pump failed. And from what I read that is very unusual to have a failure w/o the fpcu being affected.

Any additional insight would be appreciated.

Mike

[Q45tech]

Measure the fuel pressure before you assume anything.

Also if you measure the current that is flow thru the 15 amp fuse [remove and jump thru ammeter] you can gleen whether the pump is working.

The ecu will turn off [reduce speed mode] pump eventually if the engine doesn't crank so you have to recycle the key every 30 secs.

The waveform is smoothed [averaged] by passing thru the FPCU so harder to see current spikes.

[Mikesinfiniti]

I don't know how to measure the fuel pump pressure but did remove the 15a fuse under the dash and hooked up a tester to the fuse connectors. There was no measurement on my tester. The key was on and all connectors on the fcpu were plugged in.

Any idea what that means? Thank you.

[maxnix]

Check the Fuel pump circuit in the FSM for a relay.

With the fuel pump humming for several years, chances are a few things are amiss.

[Q45tech]

Never seen a FP relay fail* as the contact limits are higher than the fuse [by design] all we have ever changed in 10 years are fuel pumps [with new orings] and FPCU.

We always check by swapping but never the problem as opposed to the starter relay which always seems to be the problem.............significant difference in current flow thru the two.

[Mikesinfiniti]

I have a fule pump on order so I have some time to check the relay and fpcu as per the FSM. I guess it could be just the pump or do you think that the fpcu may also be bad?

Also, I'm assuming I can't start the vehicle with a bad pump even if I tried to bypass the fpcu? If not, I guess Ill be changung the fuel pump in the street when it comes.

Thanks for all of the valuable help.

Mike

[Q45tech]

The dealers change the pump and FPCU simultaneously to avoid within 12 month comebacks...............................a used junkyard FPCU may have already been stressed from a previous bad pump............or just stressed from running for years.............the electrolytic capacitors degrade from heat and age.

You can usually surge start most pumps by a direct ground.

[Mikesinfiniti]

Well I finally got a chance to pull it apart and the Pump Relay and the FPCU checked out ok. I then changed-out the fuel pump using the details on this forum and the car started right upand runs great. Boy that was a great feeling hearing the slight hum from the new pump when I turned the key.

It must have been an isolated case that the pump failed without affecting anything else.

Thanks for the help.

Mike