Bad Fuel Pump?????? Or Other Electrical Issue?
 

Hello All --

I've been fighting the same intermittent problem with my 99 FRC for the last month. I've spent hours researching various threads and haven't been able to isolate the problem. General Background: 99 FRC with 110k miles; Mods - LG Pros w/ cats, Vararam, LS6 intake.

My problem is that the car will intermittently die under load (usually around 2000 rpm). It's as if the ignition switch were turned off (but the gauges don't sweep). Once I pull over to the side of the road - I've been able to get it restarted. It usually sputters several times - idling around 300 - 400 rpm, then idles fine.

I've done the following to try to troubleshoot this:
Checked the battery -- I have 12.7 volts across the terminals. I also load tested the battery and it tests good.
Pulled codes -- No codes are present and No other messages scroll across the cluster either
A CLB is not installed - however the security light doesn't light up and I'm able to go faster than 2 mph so I don't think this is the issue (the security light does work as it illuminates during the gauge sweep).
I've cleaned the pellet on both keys. It doesn't seem like this would be a VATS issue since I can start it fine with no warning messages.
I checked fuel pressure at the rail -- 58 psi after the 2 second initial fuel pump run and it remains steady at 58 psi while running.
I've cleaned the grounds - they weren't corroded. I also inspected each ground and found no damaged wiring.
I cleaned the ignition switch (according to Bill Curlee's very helpful post). 2 or 3 contacts in the switch were black, but the issue remains.
I swapped out the fuel pump relay under the hood -- no change.
I'm not experiencing any other electricall issues.

Earlier today - it died again while driving and I was able to coast to my house and put the fuel pressure gauge on it. This time the fuel pump didn't run for 2 seconds at the "On" position. I tried switching to "on" several times with no pressure. However - when I went ahead and turned it to "Start" - the fuel pressure came up and it started fine. After that - it now primes for 2 seconds at "on" like it should.

I don't think it's related - but the first time this happened was immediately after I replaced both rear wheel bearings. Thinking I may have inadvertently damaged the rear ground point - I checked it and found no issues.

At this point - I think it's most likely the fuel pump. However - I'd like to make sure prior to replacing the pump. Is it feasible that the pump is failing intermittently?:willy:

If it was mine, I think I'd be going back to that ignition switch. Are you seeing anything else happen such as all the guages shutdown or sweep suddenly at the same time?

No gauge sweeps or lights. I also tested the current flow through the switch in the "on" position and full battery voltage is flowing through.

UPDATE
It acted up again this afternoon. It would barely idle at 300 rpm and won't take any gas. It acts like it's starving for gas. Still no codes. It acted up for maybe 30 minutes and then was fine.

Any ideas?????????????

Did you locate the ground for the fuel pump, back near it on the frame?

My 99 did the same thing yesterday and once last summer. I assume its a pump pick-up problem. Mine does it at 1/4 of a tank. I put a couple gallons in it and its fine. My gauge says 118 miles left on the tank. But I put 2 gallons in, when I got to the gas station it only took 10 more. It has more than a 12 gallon tank. So to me it sounds like its a pick-up problem. When I was driving mine it would just sputter, take no throttle, and die. Pulled over, started back up but just die instantly. Put the 2 gallons in, and bam started, stumbled, cleared up and fine. I just can get it to 1/4 of a tank. Need to pull the tank and see whats going on.

There are two tanks...left and right. The left tank contains the main pump that feeds the engine. The right tank contains a jet siphon pump which transfers fuel to the left tank.

Dgrant -- I did locate and clean the rear drivers side ground. It was secure with no corrosion.

I just filled the tank (12+ gallons) earlier this week - so I know I'm not low on fuel. An obstruction in the fuel tank pickup makes sense - but the intermittent nature of the issue has me stumped.

Thanks

Well.............. Its time to break out to volt ohm meter and see where or whats causing the loss of fuel. Heres the Fuel Pump Schematic. Start by swapping the relay with one of the same part number. Pull and check the fuse and make sure the Fuse and fuse holder are burnt or corroded. Install a wire in the relay output and connect the meter to it. Monitor the meter while driving and see if you loose voltage to the pump when the issue happens.

Bill

http://img.photobucket.com/albums/v4...pSchematic.jpg

I would ALSO check and clean G105 (on the passengers side of the engine block) and that Splice Pack (on the wiring harness on the fire wall near the battery)

http://img.photobucket.com/albums/v4...7/splice_4.jpg

Cool, Bill saw this thread. He's the best!

Ok -- I've been able to do some additional testing.

I cleaned the passenger side block ground. However, I couldn't locate the splice pack for that ground. On my car - the negative wire from the battery goes directly to the battery to the block. I took out the battery and couldn't locate any splice pack for the block ground. Am I missing something here?

I bypassed the fuel pump relay (jumping between 30 & 87) and ran a test wire into the cabin so I could monitor voltage. It stayed steady at 13-14 volts (consistent with the DIC voltage, btw).

I then put the relay back in and left a test lead in at the output so that I could monitor voltage. Within a few minutes the issue reappeared... Loss of power, loss of voltage to fuel pump, and low (or no) fuel pressure. I bypassed the relay again so that I could make it home.

I then swapped out the relay for another working relay with the same number and went out again with the test lead. Same issue -- drop in voltage and loss of fuel pressure.

Based on the symptoms and what I found -- it looks like I have a bad connection somewhere relating to the fuel pump relay.

Any ideas? I'm going to go out now and take a look at the connections again and see if I can find anything.

Guys -- I really appreciate the assistance. Without the help here - I would have already purchased a fuel pump that wouldn't have fixed the issue.

So if you are jumping past the relay with a wire, it runs ok?

Yep. No issues with the relay bypassed.

I tried swapping the relay with another and I have the same problem. Makes me think there is an issue with the trigger signal received by the relay from the PCM. I just haven't been able to isolate it yet.

You've done an outstanding job of narrowing it down. First thought would be that trigger signal, the crimps on sockets to the bottom of the fuse panel where the relay plugs in. You can sample that trigger with a meter to insure its staying at 12vdc. Refer to the schematic above in Bill's post.

G-105 is on the drivers side of the engine block. Check that and meter the PCM signal and see if its constant.

Make sure that you make sure that the female pins for the relay are tight on the relay.

The splice pack will be taped to a wiring harness something like this:

http://img.photobucket.com/albums/v4...plicePack1.jpg



BC

Ok....

Found the G105 splice pack under the battery tray. Pulled it apart and cleaned it. Didn't look corroded- but glad I found it.

Pulled the underhood fuse panel apart and bent the female pins to get better (more) contact.

Put it back together and tried to test again. Same intermittent problem with motor stalling and no fuel pressure. Worked fine with the fuel pump relay bypassed.

By accident - I found that the car will run and fuel pressure stays up with the key in the "start" position. I can watch the fuel pressure gauge recover as I turn the key to "start" and drop when I release it to "run". Tomorrow I will pull the ignition switch and clean it again.

Wouldn't hurt to check the blue connector at the pcm (especially pin 37). Maybe the connector is loose or corroded from a previous battery leak or improper re-installation. They seldom have issues and usually if they do there would be issues with other systems as well, but it's a fairly easy thing to check. At least worth a look.

The issue has now worsened to the point that the car won't run/idle with the key in the "on" position. If I hold the key to "start" fuel pressure stays up and the car will run.

I took the ignition switch apart and cleaned it (again). There were some burnt spots on a couple of the contacts. Cleaned the contacts and re-installed -- same issue.

The car will still start/idle/run fine with the fuel pump relay bypassed.

I've tested the fuel pump relay trigger signal (from the pcm) with the car running with the bypass and I'm getting full voltage to the trigger. I don't think the relay has good contact in the fuse panel. After all my various testing -- the relay almost falls out of the pins.

Can the internal fuse panel female pins be rebent? I couldn't figure out how to get the fuse panel apart to access the internal pins. I bent the bottom side pins already - but the ones that are loose are inside the fuse panel.

It's not clear to me based on the schematic above - but is the fuel pump relay bypassed when the key is in the "start" position? I'm not sure why it starts fine and then looses fuel pressure in the "on" position.

If you are getting a constant 12vdc on the relay's coil and you have a solid ground on the other side, when the ignition is in the run position, following the start position, that leaves the connections from the socket to the relay itself. If that 12vdc is dropping out after going from the start back to the run, then you have either bad ignition switch or a bad wire from the switch to the pcm.

G105 ground. Not the splice pack under the battery. The one on the driverside of the engine block. Below the spakplugs/exhaust manifolds/headers. I had the same problem. Should be two wires going to it. A steel braided and a small black wire. Make sure it is tight!

edit; Saw that you cleaned it. How tight was it? Wiggle it around. If it moves at all tighten it. It is a weird angle. it will feel tight because of the angle. Get in there and make sure it is tight.