Fuel Issue - need guidance

Need some help guys.

A few weeks ago my 94' 9C1 wouldn't start. Investigation revealed a sporadic fuel pump. A pressure test indicated low pressure and fast leak down to zero. Replaced the fuel pump and sending unit. Initial 3-5 second prime indicated 43-44 lbs, however there was leak down after the initial prime. Took about 10-15 seconds to reach zero but the car started and ran fine. Fuel pressure at idle was 37-38 lbs. This lasted about 3-4 days and the whine suddenly cut out again. It would crank, just wouldn't start. It sat for a couple of days and started just fine. Still had the same fuel pressure readings which are correct according to the FSM specs but rapid leak down after initial prime still occurred.

Stage two: We replaced the intake manifold with a cleaned one, fuel rails, and injectors (and all new seals) from a motor that ran fine. Also added an F-body EGR. Did not test injectors. Also checked fuel pump relay, fuse, regulator, and lines. All ok. Car ran great for about four days then died suddenly AGAIN. After sitting for a couple of days it started up first try. We moved it to the driveway and let it dle for 15 minutes and then it shut down again. Engine cranks but won't start.

Stage 3: Dropped the tank again, looked for holes and cracks in brand new sending unit supply tube. None found. All connections are tight and wires are good. Replaced the fuel pump with another new one (Airtex) from Autozone. Had to replace the NAPA oil pressure switch since it broke. Replaced with Auto Zone unit because it was the only one immedietly available. This is the second Auto Zone switch. Had one before the NAPA part but it was junk. Now the car won't start. Still have 43-44lbs fuel pressure at initial prime and still have leak down. Optispark, wires, plugs and coil are all new and check ok.

Note: Noticed that when the wires coming from the oil pressure switch connector are wiggled that the fuel pump kicks on. This did not happen with the NAPA switch. Replaced the connector, but this still happens. Picked up a new Standard (made in USA) switch today.

Anyone recognize these symptoms?

1. What would cause such a quick fuel pressure leak down?
2. What would cause the car not to start this last time even though it has good initial prime pressure?
3. Why does it start after sitting for a couple of days?

Any help is greatly appreciated.

Thanks,
Rich

I'm no expert but, here's a few things to consider


These could have leaks
Fuel pump check valve
Fuel pump feed hose
Valve or valve seat in the regulator
Or
Bad injectors

Also

Check the MAF and EGR operation
I realize you did a leak down test, but you could have multiple probs at once

Make sure PCM connections are good and tight

There could still be an intermittent short in the pump feed circuit

Could still be a crap fuel pump, it's hit or miss like optisparks

Use a test light on the power/ ground for the pump relay

You can jump a wire from the batt feed circuit to the pump circuit in the relay harness conn. pump should run

There's a bunch of other tests you can do. Get a dealer manual. Plenty on eBay. A BIG cost effective help!

You could have a bad PCM too. Any DTC's?

Hey Brian,

Thanks for your reply.

I did drop the tank and looked for cracks, holes in the sending unit supply tube. Also did the fuel pump test using the red lead wire on the passenger wheelhouse. Pulled the PCM and checked the connections. The regulator holds correct pressure during the 3-5 second prime and while the car idles, so my understanding is that it is working. I have a very cheap code reader that is basically of no use so don't know what DTC's are present.

I don't know where or how to check the fuel pump check valve. My guess was that there might be a bad injector or two, but the drop in fuel pressure after prime seems far too quick. I'm researching the best way to check the injectors and plan on sending some out to be cleaned and tested. There does seem to be an electrical issue somewhere and I suspected the oil pressure switch circuit. The confusing part is that it runs fine then suddenly dies and starts up just fine after sitting for a couple of days.

Does anyone have a scan tool that shows the codes by number I can borrow? I went to Auto Zone while the car was running and they couldn't plug into/test OBD1.

No problem. Unfortunately all I have is an OBD II plug for the DLC. I got mine at Walmart in so cal 4 years ago for $100. Works great. I will keep researching on my end. I'll get back to you on the check valve test. It's getting late ha!

Leakdown does suck but shouldnt cause it to stop after its been running.
My old 95 had that same leakdown with no issues (on running that is)

Did you check your grounds on the front of the drivers side head
and ground for your fuel pump (trunk?)
Coil & ICM wiring? (Also both known good)
Let me know if this isnt the case, I have a known good pair sitting at the shop (not pretty but known good)

When you said you wiggled the oil pressure switch & it responded that sounded like your culprit. Maybe jump those wires out to test? As long as you have oil pressure.

Hey Steve,
How's everything? Thanks for your reply. I'll be doing a voltage check and replacing the Auto Zone oil pressure switch today. Also want to check voltage at the rear of the car, to the fuel pump. I replaced a passenger side head ground strap a while ago but don't recall seeing one on the drivers side head. Should both heads be grounded? The trunk has a ground strap on the passenger side hinge, is that what you are referring to? I did check the coil and ICM wires and they're good to go. Will report what I find later this AM.

Thanks,
Rich

Replying from phone, so shortt and sweet.
Bad oil pressure connection will tell the pcm there is no oil pressure. Pcm will shut down fuel pump for safety. Fix connection at oil pressure sender.

Hey guys...help me out here.

Do 94 9C1s have the same ground stud next to the coil on the drivers side head?

Rich, thats ^^ what I was talking about, its not a ground strap its 3 or 4 ground connections from the harness.
Pretty sure the outboard mounting bolt of the coil is a stud instead of a bolt & THAT's where the grounds are.
If I'm remembering wrong...its a stud RIGHT NEXT TO the coil.
If you dont solve this pronto, let me know & I'll bring you some known good parts to play with

I do believe you are correct. My 96 9C1 does, the 95 L99 did, and I remember replacing the coil on the 94 L99 and it had that stud with the ground wires. It was the cause of the 95 not to start, cold/wet out and cut out while driving. Couple broken ground terminals.

9C1s have all the grounds that the civi cars got and them some.

9C1s have a ground strap from one of the passenger side exhaust manifold bolts to the frame. None on the back of the head from what I remember.

Photos for your viewing pleasure:

Hey guys, thank you all for the feedback.

Steve, I am familiar with the ground stud by the coil. I rebuilt that whole assembly a few months ago but checked it after reading your reply. All three grounds appear intact. I also checked and there is a ground strap from the rear of the drivers side head to firewall. It's good. I am new at using a multimeter so didn't check them with that tool yet.
I did however install a new oil pressure switch (Standard Motor Parts brand) and the car fired right up. Only problem is that the oil guage in the dash is pegged to the right (high) side. Oil pressure is still good though according to the aftermarket guage.
Some research on the pegged guage indicates there is a ground short as everyone has mentioned here. I double checked the white, orange and tan wires from the replacement connector I installed and resoldered them. I get a 12 volt reading from the orange and white wires. The guage is still pegged. I took out the sensor and cleaned off the red thread lock/sealer from the threads (came out of the box with the stuff already applied) and reinstalled. No change. I am now stumped even more. Haven't bothered following up on the leak down issue as that has become secondary at this point. Going to look for a wiring diagram to try and troubleshoot.

So it fired right up & CONTINUED to run? problem solved?

Multimeters are pretty easy to use once you've got the concept.

To check grounds you can either read resistance or most meters have a bell symbol (continuity) that when set there will beep.

If you set it to resistance, clip or attach 1 lead to ground (anywhere easy) then any other GOOD ground you touch with the other lead will change the display to 0.00.

Same thing with the beep...any other GOOD ground will beep. Simple as that.

The ground for your oil pressure gauge is in/on the passenger side kick panel
Dont know if you were messing around down there but
better make sure thats good while your checking grounds
Is your volts gauge reading correctly? (that uses the same ground as the oil pressure)

You dont have a sender in there do you?
I only know impalas & we just have the switch.
You can always do the MOD that puts a real sender in there & lets your gauge be more then a good/bad indicator of pressure. If you dont find your problem that may be an option.

Hi Steve,

The oil pressure switch is the one called out for 9C1's with the oil pressure guage,. As far as my using the multimeter, not sure if I was using it correctly. I suspect probably not. I am meeting up with one of our electricians at work tonight to see if I was using it correctly and if the tool was working correctly.
That's great info on the ground location in the kick panel area, thank you. I will check that out next time I get to work on the car. That area was accessed quite a while ago to fix the heater core and fix some floorboard rust. Is there a black wire leading to a grounding screw? What should I look for?

Thanks,
Rich

Steve,

Forgot to address your initial question. Yes, the car ran well. I drove it around for an hour or so without actually breaking down. However, I suspect the elusive grounding issue is what is killing all the parts on this car. That was the fifth oil pressure switch in less than 2000 miles and I wonder if it is responsible for killing the fuel pump. Problem isn't completely solved until I get the stock oil pressure guage working correctly. The towing costs are killing me too....

There are grounds in both the drivers & pass side kick panels
Both are at the bottom of the A pillar & are clearly visible when removing that trim.
You care about the pass side now (drivers has 2 or 3 (one is AIR bag unique))

That TAN wire is the culprit I think
That goes to the resistor (in the harness that you probably never dug into in the top glovebox)& is the path to ground that keeps the gauge from pegging
Go to the links section of the forum...look at 94 Instrument cluster

Other wiring diagram is power distribution 3 of 3

Have you checked your fuel pump relay (or swapped it with the one next to it)?
Doubt its related but I'd just pull it to take a look
If I remember right there are 2 of the same in the pass rear engine compartment black box
That relay ALSO grounds on the drivers side front head (but we already talked about that.

Note: Says Fuel pump grounds in drivers rear wheelhouse engine compartment
Cant say I remember THAT ground.

Maybe someone else can say where THAT is

Good morning Steve,
I did check the relay and even though it checked out, I purchased a new one. That appears to be working fine. Thanks for the link and ground info, I'll check them out. Since the car is a 9C1 I didn't need to cut out the fuseable link above the glove box since they didn't come with one. I too believe the culprit is the tan wire and will begin tracing that. It's a PITA to get to behind the drivers side head.

On my car(& I'm pretty sure yours) the resisitor (68ohm) is used only to put the gauge at mid point after the oil pressure goes over like 4psi.. that switch is a sender too I think
That area does suc% to work...so I'll send you to another area

As the main harness enters thru the pass side firewall it turns to this

Harness


Only 3 main runs
Your interested in the tan wire shown here (forgive the lousy pic)

Connector


If you have this connector in your hand with the locking tab up & the sockets facing you, the Tan wire is the bottom left
Use your multimeter to ring from the switch connector Tan wire to that socket Tan wire
If you have continuity (0.00 resistance or the beep) that run 1/2 way checks out
Now take the lead that you just touched the inside connector with & touch a known good ground...it shouldnt read 0.00 or beep
If this all happens the wiring between the switch/sender & THAT point in the harness is ok

Hope this part of the harness is accessible, I didnt go out & pull the pass side interior to find the location of these 3 main runs

Hey Steve,

Thanks for the OUTSTANDING information and photos, they were invaluable and saved a boatload of hours fixing this issue. With your guidance I was able to check the continuity of the tan wire and BINGO!!!!.....it was no good. I had a spare harness laying around and tore it down just to see how the wiring ran to the white connector you showed in the pic. I also had an old (simple) Radio Shack multimeter (for DUMMIES) that I purchased years ago and was able to find and put to good use. I purchased two pigtails with the correct connector from NAPA and soldered in the pigtail. Very convenient that the NAPA warehouse is just a short distance from Sheila's house in Reading. Also purchased the 60lb switch, but holding off on installing that. Need to get some other stuff ironed out. SHOUT OUT to Matt Tracker who drove past us in the old tan Impala during our test run.

The car initially started up first try, but then started acting funny after we drove it. When warm it was taking two to three tries to start. I put some gas in it and tightened the gas cap and it's been starting first try since. Drove up to the beach house in Maine and back, no issues. Oh, except that the engine light came on. Put the OBD1 reader to it and couldn't find any codes. WTH!!!

Now, going to address the fuel pressure leak down and wondering why the voltage guage is reading higher than it used to. Think its reading around 14 volts (about 3/4) on the guage. Have the Opti Red Top battery. Seems to never end.

Thanks again to you, Bill, and Brian and the other guys for the excellent feedback.

I'm going to stop acting like I know what I'm talking about now...

This did jump out at me (after reading your last post...forgive me quoting myself...)

sdstick wrote:

.....The ground for your oil pressure gauge is in/on the passenger side kick panel
Dont know if you were messing around down there but
better make sure thats good while your checking grounds
Is your volts gauge reading correctly? (that uses the same ground as the oil pressure)..............

PS: 14V seems about right when the cars running & charging

Ha, just read this thread and wanted to say how awesome it was seeing the problem at least mostly solved. Gives me hope worrying about what's up with the SS. I'm guessing the volts gauge is maybe reading correctly now at 14 (I think it's supposed to read 14.4?) and that was fixed when the oil pressure gauge was?

Hey Matt,

Mine was a laundry list of ground wires and connectors that were bad. I had to splice into the tan wire from the oil pressure sensor to guage in order to repair a broken wire and replaced ALL of the connectors at the front of the motor. I have also learned that the oil ppressure sensors from NAPA and Auto Zone are garbage. Went through five of them. Put in an AC Delco sensor and no problems since then. Upon Steve's recommendation I went through the ground wires above the coil for a second time just to make sure it was done right. I think if you're at 14v you should be fine. I don't have the FSM with me and I am far from being an expert, but I believe it says something about if you're above 13.6v, you shouldn't worry.

Rich

Mojombo65 wrote:

Hey Matt,

Mine was a laundry list of ground wires and connectors that were bad. I had to splice into the tan wire from the oil pressure sensor to guage in order to repair a broken wire and replaced ALL of the connectors at the front of the motor. I have also learned that the oil ppressure sensors from NAPA and Auto Zone are garbage. Went through five of them. Put in an AC Delco sensor and no problems since then. Upon Steve's recommendation I went through the ground wires above the coil for a second time just to make sure it was done right. I think if you're at 14v you should be fine. I don't have the FSM with me and I am far from being an expert, but I believe it says something about if you're above 13.6v, you shouldn't worry.

Rich

Heh, it really makes you wonder why all those connections would get compromised like that...

The problem with the SS is that it would not run the fuel pump with a jumper from the relay to the pump, but it would run the pump if it were jumpered from the fuse panel through a different circuit, eliminating the fuel pump relay and the wiring from the fuse panel going to it. So I'm thinking it could maybe be something to do with the oil pressure switch, although IIRC, it does seem to work.

Did you try the red test wire that sticks out of the harness by the A/C accumulator and power steering resevoir on the passenger side wheel well?

I actually haven't done ANYTHING yet with it! I'm just messing around cleaning it up a little bit, once I have it registered it's getting a body cavity search to get to the bottom of what's wrong. All I know right now is it's running with the circuit completely bypassed from the fuse panel to the fuel pump (it actually runs great that way), the car is hard to start if it sits (probably a related leakdown type of problem, you can smell a faint odor of fuel when the car is running, around the rear wheels, so maybe a sending unit issue or something on top of the tank?) and uh....I forget what else...


I think I've officially assed up your thread!