I posted this in the 4th gen forum, but got no response. I figure you guys would be more sensitive to running lean anyway.

Keep in mind i'm still not supercharged, but here is my story......

Guys I need some help. On Friday, I was teaching my girl to drive manual transmission, on my max.

After the "Lesson" my car started to hesistate in upper RPMS.

At first I thought i was paranoid when I said "My car feels slower". Then i looked at my air/fuel guage, and at about 4.5k RPM the car TOTALLY leans out (In all gears).

It's not getting the fuel it needs to keep going at high RPMS.

I hope this is a known issue and someone out there knows how to fix this.

I reset the ECU, and checked all my sensors and guages in the engine bay, no cigar.

P.S. I just changed my knock sensor 3 weeks ago, and I am getting NO codes from my ecu.

 

have you verified that your car is running lean by check your spark plugs?

 

No only by the air fuel ratio guage (which goes to 100% lean in the circumstances described above), and by the severe drop in power.....

 

what mods do you have?
When was last maintenance?
what have you tried(fuel system cleaner,adjust idle)?
Have you checked FPR? The connections of your Injectors?

 

DON'T base any major decisions/assumptions on an insignificant A/F gauge....unless its a wideband, its telling you next to nothing , useless. unless you can verufy the condition of the plugs as lean...I bet theres nothing wrong, just another a/f gauge inaccuracy causing a freak out

 

I recently purchased the car so I am not sure when the last full maintenance was performed.

Lots of mods

Supercharger... too many to list (Stock SC kit, but its not running right now)

Also has one step colder plugs installed.

I have tried a fuel injection cleaner, but no change.

Is it possible to adjust FPR without an adjustable regulator of some sort?

I inspected all vacuum hoses. Made sure all sensors were securely fastened. I reset the ecu, and no change.

The good thing about this problem is that it is VERY VERY consistent. Everytime I push the car it leans out up top. Before getting to 4 K + it runs stoich/rich.......... then you know what happens next.

If i were SCed right now I would probably be on the side of the street.

Any ideas guys? I am thinking of buying a fuel filter, but I don't want to waste time monkeying around with things that wont' solve the problem. I have had too many other problems with this car to begin another wild goose chase, and I haven't finish the 10 others i started!

 

CHECK THE PLUGS!!!!!!!!!!!! its the most accurate method...a/f gauges mean nothing at WOT

 

if your car was really running lean, you would have got a CEL that says: bank 1 lean or bank 2 lean. I have got those CELs before on boost spikes. I dont think your car is running lean and its NA. Those AFR gauges are a POS from what I been told by many. If you to go a dyno and they hook up a wideband, you will know for sure that you are running lean and you need fix that problem before even dropping a SCer in there.

 

jAY25 is right
If you use a scanner it would cost about double that of a dyno run. Try it and see. But if you don't dyno just shell out 100$ to get get it scanned.

Question for the S/C guys.
If you were running colder plugs without the S/C hooked up or running could it make it harder for your car to burn all the fuel?

 

OK well I can 100% sure without a doubt feel the power difference, and the only lead I have is the air/fuel ratio going to lean on the guage. Where do i go from here? I mean even if I pull the plugs and confirm that it is running lean, then where do I go from there?

 

Fuel filter?

 

I just got back from the Nissan Dealership. I tried to get the 300zx filter but they were out of stock. Anyway I picked up the maxima filter, and I will try to install it when I get a chance.

The thing is I don't want to go on another wild goose chase. The filter was cheap and I can absorb that cost, but its probably not the solution, and more than likely just the beginning....

 

You could always try some BG44K.

 

those two codes only appear in close loop, right? if he's talking about high end and power loss, his problem should lie in the open loop.

 

if you verified it and it is running lean, you will have a lot more to do...

-check MAF voltage
-check fuel pressure
-check injectors
-check intake air leak after MAF

 

Hmmm let us explore how an intake air leak after the maf could cause the car to run lean. When my girl was driving she did A LOT of BUCKING (came of the clutch too fast) may have rattled something loose. However, I don't understand how an AIR LEAK could cause more air, and less fuel into the system (Especially so much considering the system claimed I ran rich before)?

How can i check fuel pressure?

 

Did you do anything to your car while it was running rich?(to solve that prob. or where you running alittle rich as safety precaution?)

 

Well with all the fuel management stuff for use when the SC was running the car just ran naturally ran rich while NA. I did nothing to try and correct that.

 

MAF controls fuel injectors. when amount of air is incrased and it's measured by MAF, MAF will increase fuel injector duty cycle to allow more fuel enter thru the injectors. If there's intake air leak after the MAF, that means the air draw from this leak is not measured by the MAF. So more air enters to the engine, but MAF did not compensate by adding more fuel. Result = lean condition.

 

OK makes perfect sense. I checked all piping and it looks tight...... So here we go.

 

Well guys let the games begin.

I changed the fuel filter, and no dice. Car is still running like crap!



Is it possible my inline fuel pump has gone bad? If so how can I test if it is still working? Voltmeter or something?

Update:

I used a multimeter on the 2 bolts with wires coming from the inline pump. I don't know if thats a good place to test or not. I got no voltage from them, so I await your suggestions.

I really feel this problem is electrical (Due to the consistency of the problem).

 

you can test your inline pump by putting your hand onto it and feel the vibration.

then you can test it by disconnect your STOCK pump by pulling out the fuse and see if you can start the car. you should, even though your fuel pressure might read funny.

the most accurate way to test it is to use a fuel pressure gauge.

I doubt it is your inline pump because you dont have your SC hooked up. again, verified first that your car is running lean by checking the plugs. to get the most accurate reading on the plugs, you will need to push the car close the redline and shut off the engine, wait for it to cool, then check the plug.

 

Ahhhhhhhhhhhhh well I just changed my fuel filter on Monday, and the first step was to remove the fuel pump fuse. I did this, and the car started and stalled. This is normal, but you're saying that with the inline fuel pump it should have continued to run?

I also put my hand on the inline fuel pump to feel for vibration (Something I never tried before this problem), and it doesn't really feel like its vibrating. It seems more like the vibration is coming from the BLUE vortech disc above the fuel pump. Both units are mounted together on a small metal mount.

I tried using a multimeter on the 2 power cables coming to the pump, and got no voltage. I don't think I tested it correctly, but that’s what I got.

My logic is this..... If the inline pump has failed, even though I am not Sced it could be INHIBITING the flow of fuel at high RPM because it is malfunctioning.

I don't really know how the device works, but if I didn't have any thoughts then I would be truly lost.

 

Try to bypass it with a straight piece of fuel hose

 

vortech FMU shouldnt have too much vibration. I bet it's from your car.

your car should run fine without the inline pump. you can just take it off your list and focus on something else.


btw.....have you verified your lean condition?

 

I tried to disconnect the power from the inline pump, by removing the power lines. I accidentally dropped the bolt/nut in the engine bay, and can't find it. The engine starts but to my suprise that little bolt actually holds fuel in the pump. SO now the pump sprays fuel everywhere. Now I need to get some kind of inline fuel connector to bypass the pump all together or find a replacement bolt.

The nightmare never ENDS!

 

you still haven't checked your plugs have you?

as far as the pump goes...just remove it and return the fuel lines back to stock....maybe its time for you to take your car to a professional

 

hmmm...did you accidentally disconnect the fuel line? I dunno what little bolt can cause a bad fuel leak like yours

I dont think your inline pump is on. the fuel is from your in tank pump.

like I said, the problem is not the in line pump and again......you have to verify your lean condition before you look for solution. (check the plugs first, please...)

 

I shipped that package for you already. Just letting you know. I have not received the check but I know youll send it out.

 

Let me chime in (though I ONLY quickly scanned the threads above)...

Assumption: Still Supercharged?

Do you have the T-REX inline pump running FULLTIME? It will only turn on when in boost if you are still using the HOBBS switch.

If you ARE running the HOBBS switch... it could explain why you are running lean at the upper RPMS... (provided you aren't running a Walbro GSS342 pump).

If you are still on the HOBBS switch... BYPASS it by grounding the T-REX relay supplying the power so it is on all the time... it'll be very noisy when it's on and the "output" fuel line will be very "hard".

If you are not Supercharged... this will still help you diagnose a bad intank pump...

 

hi Chunger

I thought it was the hobb switch too. but since he's not SC'ed, (assuming the vacuum hose on the hobb swithc is not connected to anything) and the pump should be on all the time if connected. Maybe his in-tank pump is half-dead and his inline pump was working fine until recently. If it is true, this can be the cause of his lack of power at high end.

 

Well Guys, I was right....... I guess.

I bypassed the inline fuel pump using a fuel line coupler.

The lean condition is now gone. Car pulls straight through the power band (Probably better than it ever has before while NA. This is also confirmed by my air/fuel ratio guage which you guys hate so much. I just think if the thing is PEGGED on lean that maybe its telling you something, hehe.

I am happy about that. My problem now is that the coupler has a small fuel leak! I have to either find a better coupler or run a whole new fuel line.

I don't know what Hobbs switch you guys are talking about, but the system ran fine until Friday night.

I guess this is a sign to get a Walbro and just dump the inline all together?


Jay25 I mailed the check out. You should get it by the end of the week. Thank you for mailing the package in good faith.