Problem: Car runs lean, or so say the E-check smog people / results (high NOx). It's not the EGR system as I replaced the solenoid and valve with new ACDelco units prior to taking the car to E-check. My E-check results were posted HERE if that would help. In that thread, I was told that the car is probably running lean and I should check the fuel pressure.
Test: I got a fuel pressure guage from harborfreight and ran some tests with key on engine off; idle, and at throttle. All tests were performed with the car stationary, in neutral in a parking lot.
Results: (psi) Engine on & Key off: 25ish, turn key off, wait a while, turn key back to on: 40ish Idle: 35ish As I give it throtle, the pressure goes up. I toyed with the accelerator and the pressure varied. It never got below 32ish and never quite got up to 45ish. I would say it ranged from about 33 to 43 psi, higher when the accelerator was depressed, and lower at idle. It dipped to the lowest after releasing the depressed accelerator then rose to 36ish at idle.
Questions:
Does the car need to be under load to test the fuel pump, or can I rule that out?
If the fuel system seems to be fine, what else could be the problem?
Could there be something wrong with the EGR that wasn't fixed with the new parts?
The GM spec for fuel pressure on the Fiero V6es is 40.5 to 47 psi with the fuel pump running but the engine stopped. Engine vacuum while running will cause the fuel pressure measured on your gauge to be as much as 10 psi lower than when the engine is stopped.
Incidentally, the best way to test fuel pressure with the engine stopped is by applying 12 volts to the fuel pump test pin on the ALDL connector located in the center console. This should give you a stable 40.5 to 47 psi pressure reading.
[This message has been edited by Marvin McInnis (edited 06-15-2006).]
TG oreiF 8891, Did you mean --engine off---key on 25 psi ? If so thats to low, should hit around 42psi & hold there for a good period of time , before dropping off slowly. Should idle at around 36-38 --then raise when blipped to around 42-44---but quickly drop off again --back to 36-38. If specified pressure is obtained ,but bleeds down, pinch the the return line and recheck pressure gauge, if pressure holds, replace/check your fuel pressure regulator.
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03:48 AM
TG oreiF 8891 Member
Posts: 776 From: Cleveland, Ohio; USA Registered: Aug 2004
TG oreiF 8891, Did you mean --engine off---key on 25 psi ? If so thats to low, should hit around 42psi & hold there for a good period of time , before dropping off slowly. Should idle at around 36-38 --then raise when blipped to around 42-44---but quickly drop off again --back to 36-38. If specified pressure is obtained ,but bleeds down, pinch the the return line and recheck pressure gauge, if pressure holds, replace/check your fuel pressure regulator.
Yes, engine off, key on it went to 25ish the first time. It did get up to 42ish, but it took two key turns. I suspect since the pump only runs for a few seconds it wasn't quite enough to put 42 psi in the entirety of the lines with only one run. I thought this was normal, are you saying my pump is bad even though while running I get the pressures you listed? Thanks to both of you for your help.
Your fuel pressure seems fine. To test, take a jumper wire and run it from the orange wire off the cigarette lighter to the Fuel Pump Test Terminal in the ALDL connector:
This provides power straight to the fuel pump itself and will cause it to run continuously. With the pump on continuously it should need the specs posted above.
JazzMan
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08:23 AM
TG oreiF 8891 Member
Posts: 776 From: Cleveland, Ohio; USA Registered: Aug 2004
Lean could be a 02 sensor, vac leak, ect, but you mentioned the pump is fine--did you do the leak down test to see if maybe the injectors are leaning out on you, A buddy that owns a auto repair shop down here in southern Ohio was saying --(before we got rid of e-check) that they where just looking for things to hold on to stay open -- & where going after things like cat, egr system, emmission things (grasping at a straw ) as long as they could .
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01:38 AM
TG oreiF 8891 Member
Posts: 776 From: Cleveland, Ohio; USA Registered: Aug 2004
Sure no problem , lets start with the one about 5 post above this one that I wrote about pinching your return line off, and taking the pressure again with that line pinched off, are you fimilar with which lines are which. Your return line is the one thats not going through the fuel filter, the other line that goes through the filter is your pressure line. The rubber part you need to pinch off is around/under your battery tray, the easiest way to pinch it off is through the pass-side wheel well. Try taking a reading with it pinched off and pressureized like jazzman said & shows in the pic, you can get a constant 12 volt with the orange cigg lighter wire, take a jumper from that to the line/connector marked in the pic for your fuel pump, this will keep the pump running constanty--so you can get a reading with the return pinched, after you do that write it down, then pinch the pressure line and write it down, this is going to rule out your pressure regulator , injectors, ect and let us know if anything in the fuel system is causing a problem, if not we`ll move on to the next step... Edit: Yes the test you did is saying that your fuel pump is ok.
[This message has been edited by 3800superfast (edited 06-16-2006).]
Can you explain how I do this leak-down test? I really don't know what I'm doing with this part of the car, but I'm willing to learn.
I remember that after I shut it off, it took only a few hours to drop from 40ish to upper 20's psi. Is that like a leak-down test?
If it takes hours to lose only that much pressure you've passed the leak-down test. If you had a leaking injector or faulty pressure regulator the pressure would drop significantly in only a few minutes and certainly be gone in an hour entirely.
Running lean can cause temps in the combustion chamber to hit the NOx formation temperature of around 2,500 degrees, but so can a faulty EGR system, overly-advanced timing, excessive carbon buildup in the combustion chamber (which raises the effective compression ratio), etc. Leanness can be caused by vacuum leaks that are big enough to force the ECM to the limit of its ability to adjust mixture ratios, or it can be caused by a faulty O2 sensor or wiring, or even a faulty circuit inside the ECM.
You can use a high-impedence multimeter to monitor the O2 sensor voltage directly by tapping into the wire at the ECM (don't break the insulation on any wires in the engine compartment) and if you use a meter like the Fluke 87-88 series you can take advantage of the rapid pointer and averaging features to study the readings in real-time.
JazzMan
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08:42 AM
Marvin McInnis Member
Posts: 11599 From: ~ Kansas City, USA Registered: Apr 2002
Running lean can cause temps in the combustion chamber to hit the NOx formation temperature ... but so can a faulty EGR system, overly-advanced timing, excessive carbon buildup in the combustion chamber (which raises the effective compression ratio), etc.
That's what I was thinking. You are assuming that your engine is running lean, because one or two people have suggested it as a possible cause of high NOx emissions, but that isn't necessarily the case. Diagnostic tools like WinALDL or an AutoXray scanner will provide hard data that will confirm or eliminate a lean condition. Start gathering hard data before you start throwing parts at the problem. You have a whole year before your next emissions check.
Just finished reading your other post on June 3rd, when you passed the test and noticed this time, that you mention , that you don`t know how to set the timing, you may want to start there, then move on to winaldl , this thread should help you understand the program & whats going on a little better. https://www.fiero.nl/forum/Forum2/HTML/069590.html
