MAF mod possible cause of knock?

[L0G1C]

When I got my car in february, I (like a dumb ass) let my brother in law take out the honeycombs in my MAF (it will let more air in and be less restrictive! You'll feel a difference, trust me! ) and the car started running like total crap. I put the larger of the two honeycombs back in, since it was the least damaged and the car started to run better. A few months later, I got my logger and noticed that I have hella bad knock when I'm putting any kind of load on the engine. I was wondering if the lack of the other honeycomb was letting in enough unmetered air to cause my car to freak out and run lean enough to cause knock. I have a new Denso O2 sensor, since the old one crapped out on me and caused me to get 14MPG. On the logger, my O2 sensor voltage seriously looks like a sine wave, fluctuating from a low to high reading about twice a second. I still get shitty gas mileage (about 250 miles between fill-ups), so I must not be running that lean. I would really like to track down the cause of this knock and get rid of it. Any help would be appreciated.

 

[DSM90AWD]

Have you logged your fuel trims low/med/high? If so what are they?

Knock can come from an over-rich condition, over-lean condition or be some misc electrical/mechanical noises your knock sensor/ECU interprets as knock.

Ensuring that you car is running well (fuel trims near 100%, no intake/boost leaks, correct plugs, plug wires in good condition, base timing set correctly..etc) will help narrow the search.

 

[L0G1C]

My fuel trims are:
High 137.5%
Med 119.5%
Low 137.5%
I probably won't be able to do anything about these without an AFC, right?

I've got new plugs and wires, I've got no boost or vacuum leaks etc. I haven't been able to check my base timing, though. I don't have a whole lot of daylight hours lately ...

 

[1fstSS]

my 1g is doing the same thing when i did the 3 inch gm maf conversion, i still havent figured it out!!

 

[DSM90AWD]

My fuel trims are:
High 137.5%
Med 119.5%
Low 137.5%
I probably won't be able to do anything about these without an AFC, right?

I've got new plugs and wires, I've got no boost or vacuum leaks etc. I haven't been able to check my base timing, though. I don't have a whole lot of daylight hours lately ...

You are definitely running lean as hell. 140% is the limit of the the fuel trim compensation.. though think you still may be past the limit (don't think the ECU will actually show up to 140%).

Something is majorly wrong. Maybe a clogged fuel filter, bad injectors, faulty FPR or a serious leak after the MAS (which you say you've checked already). Removing the lower screen will make yo urun leaner (less restriction = more air bypassing the air metering section).. but doubt it would be that much off.

I'd first try tracking down the real problem instead of masking it with a S-AFC.

 

[Talesin]

Yeah, hacking out both honeycombs will screw it over big-time. The LOWER one can be removed (relatively) safely, but the upper one is neccessary... you'll start running terribly badly if it's gone or damaged *at all*.

Sounds like it's time for a new stock MAS, or a MAFT and GM MAS.

 

[L0G1C]

hmm...

I've got a new fuel filter on there, I just forgot about it until you said something...

As far as the injectors go, I don't want to replace them with stock 380's (cuz it's an auto), so I would need to go to at least 450's and either a manual ECU or an AFC.

Would it be prudent to go aftermarket on the FPR? I haven't had to replace one ever so I'm not sure about that.

I'll run another boost leak test on the intake tract and double check everything the next chance I get.

Thanks a lot for all your help!

 

[L0G1C]

Sounds like it's time for a new stock MAS, or a MAFT and GM MAS.

Don't I wish...

 

[L0G1C]

I ran the intake test again today and I still can't find any leaks. I notice on my boost/vac gauge that I get around 24 in/hg when I let off the gas and decelerate, so I would figure that If I had an intake leak, my vaccum wouldn't get as high. So I guess it's down to injectors or FPR... damn...

 

[DSM90AWD]

I ran the intake test again today and I still can't find any leaks. I notice on my boost/vac gauge that I get around 24 in/hg when I let off the gas and decelerate, so I would figure that If I had an intake leak, my vaccum wouldn't get as high. So I guess it's down to injectors or FPR... damn...

Actually, a boost leak would make you run richer. Letting in unmetered air/ defective MAS or plugged/defective fuel system would cause you to run lean.

If you've exhausted all other avenues and think it the MAS/FPR/Injectors. PM me as have all those parts and could work a try-and-buy program if not sold already.

 

[zrk666]

make sure your running 93 octane or higher in your car that might be one factor. turbo cars are prone to run on high grade gas regardless. predetonation will cause it to knock remmeber that. your car will run like shit if you put crap gas in it.

 

[L0G1C]

It looks like I've got 2 450cc injectors on the 2 ends of my fuel rail and 2 380cc injectors in the middle. The 450's are blue and the 380's are black, right? That would make my fuel trims all out of whack too, right? Now... I have to track down some 380cc injectors... but just 2... YEAH RIGHT.

 

[L0G1C]

OK, so I borrowed a MAF sensor from a known good-running (read no-knock-having) 92 Talon TSi AWD and I still have really bad knock. I've replaced the timing belt/BS belt, water pump and all accessory belts (except the AC belt.. the system is discharged and I don't use it anyway, so I left it off). I'm running Chevron Supreme premium grade gas... my fuel trims haven't changed, and I still get really high amounts of knock... So I'm thinking something fuel related now. Where do I start? I'm on a fixed income/no budget and I really can't take any shots in the dark trying to figure this out. Any suggestions?

 

[mhuffman]

i used to get really high % fuel trims and very high knock using a hacked MAS. you might want to get a stock unmodified MAS, or get a 3" GM MAS and MAF-T. I am using drawthru setup, so i only had to pay $165 for the maft and $27 for the MAS. not only is it a nice upgrade, but it will let you tune your fuel trims and help alleviate the knock.