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Old 11-06-2020, 01:08 AM   #1
heavenschosen
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Default For the wiring gods

Have a maf issue, car runs lean as hell, hard to keep running but i unplug the maf and start it as it runs perfect good afrs and good vacuum. Only issue is I've replaced the maf with a good one and it ran the same, unplugged it and ran great, the connector doesn't look bad besides one place the coating is gone and exposed wire, i sprayed crc electrical cleaner in the connector no fix, how would one go about replacing or repairing the maf plug itself? from what I've read on here the wires to the maf are very finicky and have to be an exact length and stuff, any info on this?
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Old 11-06-2020, 07:30 AM   #2
snow_bound26
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iWire can help you with replacing the MAZf connector.

What brand MAF did you use? Do you have a tune done to the car? Anything other than an OEM MAF may not work properly and if you have a time on top of that then you're dealing with scaling issues.
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Old 11-06-2020, 10:20 AM   #3
heavenschosen
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Originally Posted by snow_bound26 View Post
iWire can help you with replacing the MAZf connector.

What brand MAF did you use? Do you have a tune done to the car? Anything other than an OEM MAF may not work properly and if you have a time on top of that then you're dealing with scaling issues.
Have a good protune on it, once it begins to warm up it pulls vacuum sounds like a miss and runs extremely lean, I unplug the maf and it immediately runs normal, goes from undriveable to driveable. Replaced DENSO maf with DENSO maf and it was the exact same thing.
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Old 11-06-2020, 05:48 PM   #4
snow_bound26
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I'd start by contacting your tuner. The calibration should be fine (have changed MAF without retuning myself), but your tuner may ask you to log and make sure everything is reading properly
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Old 11-06-2020, 06:43 PM   #5
heavenschosen
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Originally Posted by snow_bound26 View Post
I'd start by contacting your tuner. The calibration should be fine (have changed MAF without retuning myself), but your tuner may ask you to log and make sure everything is reading properly
He said it looked like a vacuum leak because if the lean condition and it was pulling vacuum, but as soon as i unplug the maf it drives perfect, great afr and normal vacuum. (it was pretty well undriveable before)
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Old 11-06-2020, 10:10 PM   #6
Elbert Bass
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The problem is probably not your MAF. When you unplug the MAF the ECM goes to limp-home mode - using a calculated base map instead of adding fuel based on on measured air volume.

Odds are you have another issue that does not trigger limp mode - from your minimal description perhaps a vacuum leak since you mention a lean condition. A vacuum leak allows air in that is not measured by the MAF so you get a lean condition. In limp mode the fuel is added based on a calculation of how much air the engine will use to keep the engine running at a specific throttle position/RPM.
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Old 11-08-2020, 10:28 AM   #7
heavenschosen
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Originally Posted by Elbert Bass View Post
The problem is probably not your MAF. When you unplug the MAF the ECM goes to limp-home mode - using a calculated base map instead of adding fuel based on on measured air volume.

Odds are you have another issue that does not trigger limp mode - from your minimal description perhaps a vacuum leak since you mention a lean condition. A vacuum leak allows air in that is not measured by the MAF so you get a lean condition. In limp mode the fuel is added based on a calculation of how much air the engine will use to keep the engine running at a specific throttle position/RPM.
I just have no clue where this leak could be, I've double checked the inlet, the turbo elbow, throttle body to IC. and that is all I touched when doing my vf39 sti injectors upgrades which is when this started happening. the thing is it must be a giant leak to make the car impossible to drive but then when i unplug the maf it drives with great power, could it be in limp mode with a massive vacuum leak and still drive totally normal with the maf unplugged? Given my plug for my maf has an exposed wire and is pretty crusty i ordered the iwire replacement kit and am going to try that. but after that i suppose i'll try a smoke test to officially rule out vacuum leak.
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Old 11-08-2020, 08:43 PM   #8
Elbert Bass
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Originally Posted by heavenschosen View Post
I just have no clue where this leak could be, I've double checked the inlet, the turbo elbow, throttle body to IC. and that is all I touched when doing my vf39 sti injectors upgrades which is when this started happening. the thing is it must be a giant leak to make the car impossible to drive but then when i unplug the maf it drives with great power, could it be in limp mode with a massive vacuum leak and still drive totally normal with the maf unplugged? Given my plug for my maf has an exposed wire and is pretty crusty i ordered the iwire replacement kit and am going to try that. but after that i suppose i'll try a smoke test to officially rule out vacuum leak.
It could run - as I said limp mode adds fuel based on a set table not measured air volume or lambda readings. This happened when you replaced injectors? Did you lose an injector seal - reuse old hard seals, not get a seal seated properly?
Then it could be that MAF connector - but you would need to know what the MAF and IAT sensors were reading to determine that. Smoke test? That's for Evap or boost leaks. Just squirt a little brake clean in short squirts at different places - engine will respond to the chemical if you spray at a vacuum leak.
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Old 11-12-2020, 12:07 AM   #9
heavenschosen
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Originally Posted by Elbert Bass View Post
It could run - as I said limp mode adds fuel based on a set table not measured air volume or lambda readings. This happened when you replaced injectors? Did you lose an injector seal - reuse old hard seals, not get a seal seated properly?
Then it could be that MAF connector - but you would need to know what the MAF and IAT sensors were reading to determine that. Smoke test? That's for Evap or boost leaks. Just squirt a little brake clean in short squirts at different places - engine will respond to the chemical if you spray at a vacuum leak.
Ordered a smoke tester to verify whether it's vac leak. New connector on the maf and same issue, have replace every maf component. runs awesome with the maf unplugged hoping it's just a real simple leak
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Old 11-12-2020, 02:11 AM   #10
SlammedSix
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From the sounds of your issues you have a leak between the MAF sensor and the throttle body. So this sounds to fit the last things you touched.

When the MAF is unplugged the car runs on the Volumetric tables that are installed in the ECU from the factory. The car solely uses the MAP sensor to generalize the amount of air the car should have. It still will use the Air/Fuel sensor to adjust fueling to fine tune it. Just because the car runs and drives OK with MAF unplugged does not mean this is a fix. If you have a scan tool or Accessport you need to look at the Short Term and Long Term fuel trims to see what the car is doing to make the motor run correctly. You'd be suprised how well cars run only to find out the ECU has been adding 30% fuel to get it to run like that.

If the leak was between the throttle body and the valves 1) you will not have 20" of vacuum and 2) your idle will be higher than normal. So if you unplug the MAF and idle is good and vacuum is good then there is no manifold vacuum leak.

You said you installed a VF39 and injectors, are the injectors a different size then when the car was tuned?
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Old 11-28-2020, 12:39 PM   #11
BoostFreeak
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Have you tried replacing the MAF again? I have ran myself in circles after replacing a part with a new one just to find out the new one is bad. I would find a MAF you know is good (like from a buddies car) and check that out. If you say the car drives great and is able to build normal boost when the MAF is unplugged I am doubtful you have a major boost leak.
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Old 01-10-2021, 10:00 PM   #12
Spendawg
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Could be the MAF wiring. On my car someone had spliced in a new plug using crimp connections and crimped part of the shielding to the wire which caused the MAF to read a constant air flow.
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