1G Low Fuel Pressure but Running Rich

[kcd]

Hey guys,

Just as the title of this thread states, I'm having an issue with having low fuel pressure yet I'm running rich. If I try to up the pressure, the car attempts to die. Right now, I'm idling with about 20psi of fuel pressure and my wideband is reading 12.0s.

So what could cause this?

Any input is greatly appreciated.

 

[ceedawg]

Check your fuel pump!should be at 38 to 40 psi at idle I believe.

 

[2gmitsueclipse]

Agreed. Check fuel pump relay and voltage. Leaking injectors could also be causing you to run rich.

 

[kcd]

Just replaced the relay. I'm guessing it's the pump then.

 

[97 eclenger]

weak pump, pinched fuel line, clogged filter and bad fpr. check all of those

 

[kcd]

Any chance a bad O2 sensor could have anything to do with this? Because if my pump was bad, wouldn't I be running lean and not rich?

 

[ceedawg]

Any chance a bad O2 sensor could have anything to do with this? Because if my pump was bad, wouldn't I be running lean and not rich?

Faulty o2 will have nothing to do with fuel pressure as you stated was low.
A bad pump would give you low fuel pressure and have your car run lean, hard start or not start,stuck or leaky injectors could have your car run rich.
Faulty fuel pressure reg could cause issus too but rear unless it's aftermarket. Check fuel filter as well. These are the only answers we can give you that would cause your symptoms.


Check the fuel filter first and then go to the pump. Do you have an upgraded pump or stock?

 

[kcd]

Faulty o2 will have nothing to do with fuel pressure as you stated was low.
A bad pump would give you low fuel pressure and have your car run lean, hard start or not start,stuck or leaky injectors could have your car run rich.
Faulty fuel pressure reg could cause issus too but rear unless it's aftermarket. Check fuel filter as well. These are the only answers we can give you that would cause your symptoms.


Check the fuel filter first and then go to the pump. Do you have an upgraded pump or stock?

Filter was just replaced. Currently running a Walbro 255. Also running a FuelLab AFPR.

 

[ceedawg]

Do you have a fuel pressure gauge? Under hood or in the car? Does the fuel pump sound strong? Have you checked the fuel pump relay and wiring? Important questions! I still say your fuel pump is suspect. If the regulator is adjusted properly the pump should be putting out 38 to 40 psi at idle.

 

[ceedawg]

weak pump, pinched fuel line, clogged filter and bad fpr. check all of those

Again this yep!

 

[97 eclenger]

another question would be if the fpr was adjusted with the vacuum line on or off because that will make a difference to

 

[kcd]

The car was running perfectly before I changed the valve cover gasket. While changing the gasket, I accidentally arched my intercooler piping to my battery. And yes, I know. I should have disconnected my battery but I just wasn't thinking. This has happened before, so I didn't think much of it. But when I went to start the car to check for leaks, it started running like garbage. That's why I'm thinking I shorted out the pump. Because the relay is fine and I even rewired the power wire just to make sure it wasn't damaged.

 

[gofer]

1. How are you checking fuel pressure to know that it's low?
2. How do you know the car's running rich?

 

[kcd]

1. How are you checking fuel pressure to know that it's low?
2. How do you know the car's running rich?

1. Fuel pressure gauge on the FuelLab AFPR.

2. AEM wideband.

And just a side note, it's running super rich during idle and cruise, but is super lean at WOT. Not sure if that information is helpful or not.

 

[luv2rallye]

I'm having an issue with having low fuel pressure yet I'm running rich.

I accidentally arched my intercooler piping to my battery.

If the ECU is running in open loop mode, it will be rich no matter what the fuel pressure is.
Two simple possibilities that cause open loop mode are bad Coolant Temp Sensor (2 wire one) or bad front O2 sensor. Worse case is you blew the ECU when you shorted the pipe to the battery.

 

[Cooper-97gst]

Are you seeing 12. At idle? Cuz that would be lean right?
Wait...

Sorry about that, I'm feeling stupid right now.

 

[gofer]

1. Fuel pressure gauge on the FuelLab AFPR.

2. AEM wideband.

And just a side note, it's running super rich during idle and cruise, but is super lean at WOT. Not sure if that information is helpful or not.

Are you capable of capturing a log of it idling?

 

[kcd]

Are you capable of capturing a log of it idling?

Unfortunately, no. It's tuned on ProEFI and I currently can't afford the communication cable that it requires to capture logs.

 

[gofer]

The first thing I'd do is verify the ECU is still functioning, rule that out first. Turn the key to ON and make sure the CEL comes on for 5 seconds and the stock boost gauge centers. If it does, then pull the keys, disconnect battery ground and pull the ECU. Open the case and check sensor ground isn't blown.

Blown Sensor Ground Check​

If that checks good start ohming out sensors, start with the ones Gary mentions (CTS and front o2). It's also possible the MAS intake temp sensor popped (it's integrated into the MAS).

I can't explain the drop in fuel pressure but if you start the car you can test voltage going to the pump with a multimeter, verify it's 13v.

Here's a basic sensor test page.

DSM Sensor Testing​

 

[kcd]

The first thing I'd do is verify the ECU is still functioning, rule that out first. Turn the key to ON and make sure the CEL comes on for 5 seconds and the stock boost gauge centers. If it does, then pull the keys, disconnect battery ground and pull the ECU. Open the case and check sensor ground isn't blown.

Blown Sensor Ground Check​

If that checks good start ohming out sensors, start with the ones Gary mentions (CTS and front o2). It's also possible the MAS intake temp sensor popped (it's integrated into the MAS).

I can't explain the drop in fuel pressure but if you start the car you can test voltage going to the pump with a multimeter, verify it's 13v.

Here's a basic sensor test page.

DSM Sensor Testing​

I don't have the stock ecu. I'm running off of a ProEFI ecu.

 

[gofer]

[email protected]

You still have the stock sensors, test them and see if you find anything. If not contact ProEFI, hopefully you didn't damage that expensive ECU you've got on there.

 

[kcd]

Wasn't the fuel pump. So my next thought was a leaky injector since it wasn't holding fuel pressure for more than a minute. I threw an extra set in and now it holds fuel pressure, but it still won't run. It's still running very rich and I can't keep it running unless I keep giving it gas.