1996 Lumina - chasing intermittant starting issue

[dplantz]

I seen a similar post here and am thinking this is my deal
http://www.automotiveforums.com/vbul...uel+pump+issue

Here is my oissue, car has been doing this for 3 months off and on....
1996 Chevy Lumina 3.4 L DOHC V6 Fuel injected ( right?) 161k miles
The car runs fine for a while and then occasioanally just wont start

So, she drives it for a while say 30 minutes and then shuts it off. She then goes to start it. It starts, sputters, then dies Sometimes it keeps running, but it
chugs for a bit, then dies

AND KEEP IN MIND THIS DOES NOT ALWAYS HAPPEN. !

For example she drove it to Dallas ( over 400 miles) and back a couple weeks ago, with NO issues. And then a couple days later she drove it to South Austin and it left her stranded for an hour and a half, and then it started. Until it started, it would try to run and then die So, I am thinking electric fuel pump in the tank. But

it is so random when it does this.
Here is what I have done so far

Changed fuel filter ( the one in front of the tank)

I rented a fuel pressure guage. When I cycle the key on and off a few times to build pressure the most I get is 18-20 PSI Then when running the most I
get is 24-26 It has no drop when accelarating ( I had read if it does it may be the pressure relief valve) What should the pressures be? On the key?

When running? I read another post that when running it should be 41-47

I pulled the harness plug that goes up to the fuel pump in rear Grounded to frame and the purple wire ( assume that is the hot one) only registers 9v
with key on.... So may be a ground wire somewhere?

Next I went to look for bad wiring. I found the wiring harness in the driver side kickpanel. All looks to be in good shape there, Also went up to Fuel relay
fuse and it tested at 12v there Went back to back harness again and this time it tested 8v with key on.......

So is it possible the pump can run but not at maximum strength due to only 9 volts getting to it, this the lower pressure readings?

This morning I laid underneath it while my wife cycled the key. One time I "thought" heard nothing, then the next time I can hear the pump running, but it is a very "faint" noise. I am used to my 98 Chevy truck, you can hear that thing fire up from the cab.....

I dont wanna throw parts at this until I have a good hunch. I think it is the fuel pump, but I thought those things either worked or they did'nt.

[Tech II]

That is low pressure......

But you are also right, that is low voltage to the pump....either a bad ground, connection somewhere, could even be bad contacts in the fuel pump relay(try swapping a relay)......

Have seen many times where a pump fails and won't start right away....20-30 minutes later, it starts right up.....definitely get the voltage straightened out first.......could also run a direct feed to the pump(use a jumper box), to see if pressure increases....

[dplantz]

Regarding the relay.... You are talking the one on the pass side wheel well right? Do they make any kind of noise? Seems I remember hearing it "clicking" when cycling the key sometimes

[Schurkey]

For what it's worth...the wiring from auxilliary battery post to fuel pump fuse, to relay, to fuel pump, and back to ground is ALL undersized and inadequate based on industry standards for 3% voltage drop. (as inspected on my '92 and '93 Lumina Euro 3.4)

GM used 16 gauge wire where 12 gauge was required to carry the amperage load.

Translation: My vehicles lost over 1 volt on the supply side, and over 1 volt on the ground side of the fuel pump, and that was AFTER cleaning some connections. If the alternator provides 14.2 volts, the fuel pump gets 12.2 or less on my vehicle.

Fuel pump voltage is marginal in the BEST of cases; at least in the '92--'93 model years. There is NO "safety margin" for corrosion or other power-sapping wiring problems. The wires IN THE TANK are a known trouble-spot for corrosion and/or burnt connections on GM vehicles, so much so that some fuel pumps come with a replacement in-tank wire harness. I had to buy the wire harness separately for my '92 Lumina; about $20 at NAPA. I have photos of the original wires and nasty corrosion, but I don't think I've uploaded them or written the text describing that fuel pump replacement.

Using a low-amperage probe, and a digital oscilloscope, the current/voltage provided to the pump is easy to see; along with many potential fuel pump electrical problems. I did a write-up of fuel pump testing with an oscilloscope and amperage probe, using my '88 K1500. You can get the basic idea in this thread, Post 2:

http://www.thirdgen.org/techboard/tb...p-upgrade.html

Remember that amperage can be tested at a convenient location most anywhere in the circuit, but voltage must be tested AT THE PUMP, or as close to the pump as you can get, and the pump must be RUNNING for the test to be valid.

[dplantz]

So I guess here is what I will try next
Pull the fuel pump relay and clean the terminals and re-seat it
Check the voltage at the connecter in the trunk in the back ( the one that goes down to the pump) again
( I already checked the connecter in the drivers side kick panel, it looks all good)

As I said before though, folks keep telling me the grey wire is the hot one. I dont have a grey wire. I have a beige wire, a black and white wire, a black wire and a purple wire ( which is the only one I am getting a reading from of 9 volts. They must have changed the wire color from 96-97 to grey?

[Tech II]

You should have a purple(level sender to I/P), grey(power to pump), and two blacks(one may have a white stripe).....on the connector to the fuel tank, the power to pump(grey) is "A", the ground for the pump, should be "C"....

Another way to distinguish the grounds is, the thicker ground wire goes to the pump, the thinner ground wire is in the level sender circuit.....over time, that grey wire may look more beige than grey.....but you should have BAT volts at the grey wire, to ground......jumping A to C with the voltmeter should be close to BAT volts......but remember, you will only get voltage on the grey wire while the car is cranking(car is not going to start because this is disconnected)......if you turn the key on, you will only get voltage for 2 seconds, then it shuts off.....but while cranking, it should be a constant BAT voltage.....

As for the relay, cleaning the external contacts really means nothing....they are rarely corroded.....where the problem is, is the internal contact.....I would just swap with another relay to check the voltage at A and C.....

[dplantz]

TechII this is great feedback This changes things. When my wife gets home this afternoon I Will run these tests and report back

[dplantz]

TechII

So I ran the test you descibed and when cranking I get 12.46volts at the connecter plug in the trunk. Looks like I will be dropping the tank Am planning on replacing with a Delphi pump and then also a new strainer and a wiring kit from O'Reillys I also read that those wires in the tank are a problem

[dplantz]

OK so on lunch hour today dropped the tank The wires all "look" good on the fuel pump but am gonna swap them anyway

[dplantz]

And what is this deal? whats it's function?

[dplantz]

last one, here is a shot of the pump. I hooked up power source to it it tuns, kinda squeals loud to me, but I am not sure what it is suppossed to sound like

[Tech II]

That's called a pulsator....it reduces pulsations from the pump, and reduces noise transference....it goes on loose, and you swear it will leak, but when pressurized by the fuel, it seals....

Doesn't make sense though, not to just replace it why you are in there?

Also, never energize a pump outside of a tank.....that motor gets hot.....it's suppose to be submerged in fuel(that's why you should never drive under 1/4 of a tank), to keep it cool....

I have no idea what kind of noise it would make outside of the the tank.....

I'm sure it may happen, but I have never seen a wiring problem inside the tank....

[dplantz]

Ok so replaced fuel pump with a Delphi unit, new strainer and precision works wiring kit. When I turn on key I can definitely "hear" the pump turning on now, it was very very faint sound before. So far car is running and performing OK. Will monitor for a while and drive in Texas heat this week

[Schurkey]

Originally Posted by Tech II

Also, never energize a pump outside of a tank.....that motor gets hot.....it's suppose to be submerged in fuel(that's why you should never drive under 1/4 of a tank), to keep it cool...

Not entirely accurate. The motor is cooled by fuel, but it is adequately cooled by the fuel it pumps. The pump does not need to be submerged in fuel to be cooled by fuel. The reason to not run the tank low is so the fuel doesn't slosh away from the pickup, causing the pump to run dry.

Originally Posted by Tech II

I'm sure it may happen, but I have never seen a wiring problem inside the tank....

Common as dirt. I bet they're pretty much ALL corroded. The really bad ones have so much resistance that they melt the molded plastic connector body. The pump for my '88 K1500 came with a wiring harness in the box because the original harnesses were so prone to failure/melting. The Lumina pump didn't, but the wire ends were ugly. I suggest you pop the wires out of the molded plastic connectors next time--that's where the corrosion seems to start.

New in-tank wiring harness for '93 Lumina, and probably a hundred other applications as well.


Replacement wires included in harness kit (wires do not come assembled into plastic connectors--"Some assembly required".)


New, versus typical corroded wire end, visible when removed from plastic connector body


For those who haven't done much wiring work, the fuel pump wires (and many other wires) pop out of the molded plastic connector when you slide in a tiny pick or "shoe horn" to retract the lock tab. Then the wire pulls out the back of the connector.

[Tech II]

You may be right.....but.....

Quote:
Originally Posted by Tech II View Post
Also, never energize a pump outside of a tank.....that motor gets hot.....it's suppose to be submerged in fuel(that's why you should never drive under 1/4 of a tank), to keep it cool...

Not entirely accurate. The motor is cooled by fuel, but it is adequately cooled by the fuel it pumps. The pump does not need to be submerged in fuel to be cooled by fuel. The reason to not run the tank low is so the fuel doesn't slosh away from the pickup, causing the pump to run dry.

Was told by a GM engineer, the reason they went to the "module" setup, was to save the fuel pump, because a lot of pumps go bad due to fuel level going low.......the module encases the pump in a reserve of fuel to keep it cool....

Quote:
Originally Posted by Tech II View Post
I'm sure it may happen, but I have never seen a wiring problem inside the tank....

Common as dirt. I bet they're pretty much ALL corroded. The really bad ones have so much resistance that they melt the molded plastic connector body. The pump for my '88 K1500 came with a wiring harness in the box because the original harnesses were so prone to failure/melting. The Lumina pump didn't, but the wire ends were ugly. I suggest you pop the wires out of the molded plastic connectors next time--that's where the corrosion seems to start.

I have never run into a bad harness in a tank.....it may happen, but I've never seen one.....only problem I have seen is the contact ribbon of the fuel sender going bad, causing erratic readings.....