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Thread: Gas mileage/a little knocking noise..Please help me

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Posts: 1-10 of 26
2010-11-06 03:44:15
Gas mileage/a little knocking noise..Please help me

Hey guys I've been having some gas mileage issues on my 99 P11. I literally get like between 22-25 miles per gallon on highway driving(driving normal) and about 15-18 city. This problem has been happening for a couple months now. When I first bought the car all stock, I was getting excellent gas mileage. Like almost 380-400 to the tank and that's just driving from to and from work which is 10miles round trip. about 5miles of that is city and under 40mph. Now, I did a 91 intake cam and noticed a little drop in gas mileage, but nothing to stress out about like what is going on now. Then I thought it was my header leak, but I fixed that and on top of that put a ssautochrome header and still the same. Well, the mods I have now are: JWT pop charger, BC 264 cams, 2.5 exhaust, safc2(no adjustments touched), and its lowered. I did a full blown tune up: Wires, cap and rotor, both o2 sensors, plugs, clean maf, clean throttle body, seafoam(twice already in 2 months), and every single thing you can think of for a tune up. Well, for the past 3 months after all that, I'm still getting bad bad mileage, like 300 to a tank mileage, normal driving, most of it mixed highway and city. I never went passed 5k rpm for those 2 months to test if its just my foot. I then -3% on the fuel adjustments on the safc. Still no improvement, as if the safc is not working.

I meet up a guy who I sold a part to last month, and he seemed very smart about SR20s since he did over 10 swaps within the past 6 years and rebuilds his own motors He even told me that even with my mods, he still experienced at least 370 to the tank. I told him everything I did to fix the problem. I cleaned everything what I been knowing. I'm have immediate to almost professional knowledge about the nissans, and I've never come across this. Fuel injectors are not leaking, no fuel leaks at ALL. I do notice a strong smell from the exhaust as if I was running rich when the car is idling and thats with the safc2 adjusted at -5% at 800-1200rpm. I did put it back and no matter what I adjust it to, it still has shitting gas mileage. Timing is perfect, mechanical and physical. I am currently buying parts for a DET swap and can't wait to do it, but for now, my car is killing me with gas. And I only use 92 octane(shell or chevron). Can someone chime in on this.

For the knocking noise. This has been happening since I open the valve cover to replace the valve cover gasket and install my exhaust cam. Well, the noise sounds like its coming from the bottom but also on the top. If you put you ear closer to the distributor, you can hear it. I feared this was a bent valve or rod knock. But my motor runs good. I did not notice a loss of power at all. The last time I left a thread about it, somepeople said it was normal due to my cams being bigger(I DID BREAK THEM IN BY THE WAY and LEFT A VIDEO OF IT), and another person said its the rocker arm, needs to be bleed cause when I installed the exhaust cam, It came of the valve spring by accident and I put it back, but that arm is the one near the distributor and where I hear the noise more. If I put a screw on top of the valve cover, I don't hear any loud knocking noise except when I put it on the oil catch can, thats where that knocking noise is so loud, it kinda hurts my ears. But can someone tell me what to do about that. When a guy told me about bleeding them, thats too much of a hassel, cause he was talking about changing the oil, opening the valve cover, ect. Thanks for your patients for reading this.
2010-11-06 04:57:26
I read through everything you've changed and didn't see the fuel filter. Did you replace that as well?

I'm not sure about the knocking noise. I would look in the valve cover and check that everything is fit properly and it all looks fresh
2010-11-06 05:04:00
What ECU are you using? A stock one?

In regards to the noises, the noises only came when work was done. Logic would tell me that I did something wrong. But if nothing is wrong, then you are only jinxing yourself or second guessing your own work. I am a bit of an autochondriac but I have started to control it much better.
2010-11-06 18:52:12
ive been through 3 fuel filters in the past year, cause thats what i thought as well. When I bought the car last year, I put an OEM z32 filter and still was getting great mileage , then went to stock oem filter like 6 months ago, and that didn't do anything to imrove mileage, and now back to z32 just 3 months ago cause for some odd reason it was cheaper than the stock OEM at the nissan dealership. I have a stock ecu by the way. i already killed about a quarter tank of gas driving to work, to home for lunch and back to work then back home. Its only 2-3miles from my house to work.so a total of about 12 miles and lost a quarter tank of gas already. I do warm up my car for at least 2-3 minutes, but that didn't do anything before. I always warm up my cars. I will make another video so you guys can determind if its not a good or its just me. I know nissans do have loud valve trains
2010-11-06 18:52:42
and yes, everything looks fresh under the valve cover. spotless. no chips, marks, signs of burns or rubbing.
2010-11-06 19:26:18
I'm willing to bet that if you throw a wideband on the car, you'll see horrible AFR's. Why did you install the SAFC to begin with? I would remove it from the equation first. You don't need an SAFC for the BC STG2's. Secondly, bleed your lifters to get rid of the "knocking" sound you're hearing. There's a few threads around here that show you how to do this. It's not a difficult task to complete. Will take maybe three hours if you do the cams one at a time.
2010-11-06 21:55:37
I've been expierencing the gas mileage problem before I installed the safc2. And I will be using it soon cause I will be doin a motor swap. I will use it to fine tune a jwt ecu I have for the motor. I am getting crazy and horrible AFRs. I borrowed a friends LM-1 wideband and the a/f ratios were all over the place. Even as rich reading 7.6. Sometimes at idle it will go to 14.1-14.2. and sometimes at crusing it goes to 10.4-11.8. This was before I installed the safc. I will probably end up borrowing it again to tune it. I don't want to pay for a dyno tune since I'm currently spending money on motor swap parts.
2010-11-06 22:14:17
The ECU will run super rich. It makes sense to me at least.

Get a new ECU or take out a lot more fuel. I had settings as high as negative -12 on my SAFC II with the stock ECU.
2010-11-06 22:21:04
Fuel injectors may not be leaking, but are they sticking open? Try swapping the injectors for another set. If that doesn't cure it I'd try a new ECU as well. Not sure if you mentioned it, but try regrounding some of your grounds if they look corroded.
2010-11-06 23:19:40
viperdude, is that -12 across the rpm points up to redline?
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