Sideways7

iTrader: (7)

I noticed last month that my car was very lean under acceleration. This is based on a narrow-band a/f meter hooked up to the stock O2 sensor. Under cruise and light acceleration it is in the rich range. Once I get past 1/3-1/2 throttle, it immediately goes basically all the way lean on the gauge. The only exception is when the car is first started. When I first start the car and after the O2 sensor has warmed up, for a little while (maybe 30 seconds) it will dip slightly lean then go back to a little rich. As the car fully warms up it starts going all -the-way lean.
What is weird is that it still runs well. I would never have noticed there was a problem if I didn't have the a/f gauge. Nonetheless, I want to fix this.
First, I replaced ALL of the grounds, as I was having other electrical problems. Still had the problem. Next, I cleaned the air filter (K&N type cone filter) then replaced the main fuel filter and the in-tank fuel filter. Nothing. Then I pulled the codes, and saw that the pressure sensor wasn't working. I traced it down to a bad wire (the brown/red wire that goes from the sensor to the ECU) and replaced it with a new wire. That fixed that, but it still does the same thing.

The only thing left I can think of is that the fuel pressure is too low, but before I go invest in a fuel pressure gauge, I want to make sure that there isn't anything else that could cause this.
So, any ideas?

Sideways7

iTrader: (7)

Ok, so I broke down and bought a gauge to test the fuel pressure. It is actually an oil pressure gauge, but it should work the same.

I hooked the gauge up to what I think is the output of the fuel pump - the one in the middle of the cover, not the one towards the left rear of the cover. When I turned on the car, it was reading about 28 PSI. When I drove around, it got as low as 22 PSI when I was in the high RPMs.

This tells me that there is something seriously wrong with the pump, either voltage wise of with the pump itself. So now I get to troubleshoot that.

This leaves me with another questions for now - that is the correct place to hook up to measure the output pressure of the pump, right?

HAILERS

Just the pump ALL BY ITSELF? Just pull off the fuel line at the engine that is the pressure line i.e. the one coming off the filter. Plug in the gauge. Turn the key ON and jumper the yellow check connector. PSI should be up in the 70-80 range. See FSM.

Want the fuel RAIL pressure? Go to the same place and install a TEE. Put your gauge on the TEE and turn the key to ON and jumper the yellow connector. Should read approx 39psi with the engine off. IDle the engine fully hot. Reading should be 28-32 psi IF the vacuum line is connected to the FPR.

Pull the FPR vacuum line off while idling and plug the line. PSI should be approx 39PSI. See FSM for the perfect number.

arghx

iTrader: (3)

uh are you sure your O2 sensor is working right?

Sideways7

iTrader: (7)

Yeah, thats pretty much what I thought. Thats why I was double checking that it was the right line, but I'm almost certain it is. I had already gone through all of the FSM (I always check it before posting.) According to the FSM, I should be seeing 65-80 PSI coming out of the pump when I jumper the test connector and turn the ignition on. I got about 25 psi when I did this. I'll put the gauge on the output of the fuel filter when I get home to see what is happening there, but I think its safe to say there is a major fuel pressure problem. I'll do some more testing and post it later this afternoon.

Also, what does the 02 sensor have to do with the fuel pressure? FWIW, the O2 sensor is brand new with about 100 miles on it.

Sideways7

iTrader: (7)

Ok, so I got home and did some more testing. I don't want to switch the pressure gauge yet because I have somewhere to go tonight, but I did check the voltage.

First of all, it has apparently already been re-wired by the previous owner. He was quite good at wiring work, so I'm not worried about that. The voltage between the two sold wires (forget the color) that supply power to the pump was 11.95 V. Power directly on the battery terminals was 12.2 V. That seems like a very low voltage drop, and well within the voltage it should be getting. For the record, this was with ignition on and the test connector jumpered to turn on the fuel pump.

So it seems to me that the logical conclusion is that the fuel pump is shot. Does anyone else have any objections to this?


Finally, there are 4 wires on the plug for the fuel pump. There is the ground and power wire, but what are the other 2 for? The wiring diagram (page 50-34 of the FSM) makes no mention of them.

HAILERS

The BLUE and BLACK on the Harness plug that connects to the fuel pump plug, are ground and power respectively. The other two wires can be found on the diagram called COMBINATION METER (I think that's it). One is for low fuel and the other fuel gauge.

scrip7

iTrader: (6)

You said that it had been re-wired by the previous owner. Did he bypass the stock pump resistor/relay and wire it directly with a common relay? The reason I ask is I had a lean condition a couple summers ago that ended up being a bad resistor. I was running around 4 volts at the pump when instead it should be around 9v @ idle and close to battery voltage under accel.

Sideways7

iTrader: (7)

Of course, the fuel gauge. Now it makes sense.


To tell you the truth, now that I look at it harder, I'm not sure it its a true re-wire. I think its just for the fuel pump kill switch he installed. It looks like what he did was add in a relay in-line with the power wire, with the switch cutting the ground to the relay, and thus cutting power to the pump. This way you aren't taking away from either the power or the ground connection. Its actually a very good way of setting it up, its the exact same way I set up the lumbar air pumps for my aux ports and VDI.

That said, I am getting basically battery voltage at the pump, so thats not a problem - 11.95 V at the pump, 12.2 at the battery terminals.

I'm about to do one more test to make sure that I'm really seeing voltage that low, then I will just get a "new" pump. I guess running out of fuel really did kill my pump......

HAILERS

I'd still take that gauge and plug it into the line coming off the fuel filter. Key to ON and yellow connector jumpered. That measures just the output of the pump. No other parts in the fuel system are involved. Should be 70-80 psi if memory serves.

Maybe something is clogging the sock on the bottom of the pump.

Sideways7

iTrader: (7)

I just connected it up to the output of the filter, and its the same. 22 PSI with the test connector jumpered and the key at "ON". And it can't be the sock, because it is brand new. I replaced it last weekend and it didn't make any difference. The old one wasn't really clogged anyway, but I had one laying around. I have a new main fuel filter as well. I replaced all of the soft fuel lines not long ago as well, so the pump is pretty much all thats left. I'll just get one from the classifieds.

Thank you for all of the help, I'll keep you posted of the outcome once I get the new pump installed.

scrip7

iTrader: (6)

Hope the pump gets you back up and running.

On a side note, you mentioned using a toggle switch to activate your lumbar pump. I also used a lumbar pump on a customer's car to run his ports but instead of a toggle switch I used this:

http://autospeed.com/cms/A_2810/article.html

It's uber-simple to solder up and easy to adjust the trip point. I set his to trip around 4k rpms. Needless to say it works brilliantly. The kit is cheap too. Make sure you order a enclosure box to put it in.

Sideways7

iTrader: (7)

Sorry, I wasn't really clean on my explanation. What I meant was that I wired up the relay for the lumbar pump the same way. I actually use a Summit RPM switch (not a toggle switch), but it outputs a ground, thus the similarity.
I actually did a full writeup on how I did it right here: http://howto.globalvicinity.com/gv_w...i=48&co=1&vi=1