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Old 09-05-2012, 10:24 PM   #1
Bad Noodle
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Default Stumbling/Hesitation Problem - MAF Grounding Error & Bad MAF Symptoms

I've been battling a hesitation problem for about 7 months now and finally think I found what's causing it and it's nothing like I've ever seen before.

I'm not sure if it's physical, electrical, or tuning so not even sure where to post. But let me describe it:

My intake setup looks like:



So I found if I let the car idle, then take the intake pipe and pushing it down 1/4" or so until it rests on the brake booster line coming off the manifold (or the ac compressor line, not sure which it touches first) the engine stumbles and dumps fuel. I go form hovering at ~-1% correction to 17% correction in about 10 lines of the log.

Then I let go and it settles. If I pull up on the pipe, it doesn't do anything.

So my first thought is that it was related to the maf scaling, but there is very little change in the g/s:



So I have no idea what could be causing the problem.
Mechanical - resonance at that particulate angle?
Electrical - having the intake touch the Al ac line grounds something?
Tuning - To much change in that area?


I don't think it's tuning as I get crazy corrections in all parts of the maf curve.


So any ideas? I guess I can throw a bracket on it to keep it from moving, but I'd really like to find the real reason this is going on. So any thoughts?
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Old 09-06-2012, 01:48 AM   #2
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You can try putting a ground wire from the Maf housing pipe to the intake manifold. Then try replicating your problem. See if it changes anything.

DK
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Old 09-06-2012, 02:29 AM   #3
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Does the maf physically hit the manifold? Almost sounds like a slight maf leak. If it hits it and lifts the oring slightly that would cause the corrections you are experiencing.
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Old 09-06-2012, 03:07 AM   #4
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good grief, you pinch the lines closed and then wonder why it's grumpy?

when do the lines ever pinch closed normally?
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Old 09-06-2012, 07:33 AM   #5
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Thanks for the suggestions guys.

What lines? If you're talking about fuel, i got a perrin parallel setup and the lines have plenty of clearance. Nothing is getting pinched. I'll double ckeck but I don't feel it pinching anything. Ever things is moving freely with no resistance when this happens. Just the couplers flexing.

I also don't think it's an oring issue as I have a 0.5mm thicker oring than stock. Also pressure tested just to be sure. But will double check today. And the maf doesn't hit. I ground the brackets on the mani to make sure there is clearance.

Will also try a ground on it and see what happens.

Last edited by Bad Noodle; 09-06-2012 at 07:38 AM.
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Old 09-06-2012, 10:04 AM   #6
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Could be turbulence caused by the couplers as they change in shape when you push on the pipe. I would change the coupler closest to the TB on the blow-through setup just between the MAF sensor and the elbow pipe. It looks like those "Balloon" style couplers and since there is a cavity it could well cause turbulence. Try to replace it with a flat type of coupler like the one on the other side of your blow through setup.

Have you extended the MAF wiring to get the MAF sensor in that position? If yes, did you properly solder the wires? I've seen issues on cars where the wiring was extended in a real quick and dirty way and it was OK at the beginning but when the copper wires started oxidizing it started to have random problems like the ones you describe. Make sure wiring is soldered to ensure good contact and heatshrink each soldered joint individually.

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Old 09-06-2012, 11:52 AM   #7
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Quote:
Originally Posted by jkopinga View Post
Could be turbulence caused by the couplers as they change in shape when you push on the pipe. I would change the coupler closest to the TB on the blow-through setup just between the MAF sensor and the elbow pipe. It looks like those "Balloon" style couplers and since there is a cavity it could well cause turbulence. Try to replace it with a flat type of coupler like the one on the other side of your blow through setup.

Have you extended the MAF wiring to get the MAF sensor in that position? If yes, did you properly solder the wires? I've seen issues on cars where the wiring was extended in a real quick and dirty way and it was OK at the beginning but when the copper wires started oxidizing it started to have random problems like the ones you describe. Make sure wiring is soldered to ensure good contact and heatshrink each soldered joint individually.

Jasper.
Good point. I extended the wires using the shielded wire. I soldered the inner signal, shrink wrapped it, then soldered the shielding mesh. I tried to move the wire around to see if contact is breaking but that had no effect. I will double check thought.
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Old 09-06-2012, 08:33 PM   #8
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Quote:
Originally Posted by WrXtaCy2003 View Post
You can try putting a ground wire from the Maf housing pipe to the intake manifold. Then try replicating your problem. See if it changes anything.

DK
Quote:
Originally Posted by jkopinga View Post
Could be turbulence caused by the couplers as they change in shape when you push on the pipe. I would change the coupler closest to the TB on the blow-through setup just between the MAF sensor and the elbow pipe. It looks like those "Balloon" style couplers and since there is a cavity it could well cause turbulence. Try to replace it with a flat type of coupler like the one on the other side of your blow through setup.

Have you extended the MAF wiring to get the MAF sensor in that position? If yes, did you properly solder the wires? I've seen issues on cars where the wiring was extended in a real quick and dirty way and it was OK at the beginning but when the copper wires started oxidizing it started to have random problems like the ones you describe. Make sure wiring is soldered to ensure good contact and heatshrink each soldered joint individually.

Jasper.
Looks like you guys are right. When I put a ground wire between the intake pipe and the manifold, I see the same effects.

Thanks for the idea.

do you guys have any idea what the ground wire on the sensor is?
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Old 09-09-2012, 07:29 PM   #9
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Today I put in a new ground wire and verified that the resistance is good. Unfortunately I still see the symptoms - scattered corrections hesitation and stumbling.

So I tried:


This seems to fix the problem. Corrections are consistent so I can tune the intake. But I don't want to do that until there is a permanent fix.

Any suggestions on what to try next?
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Old 09-10-2012, 02:06 PM   #10
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info bump
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Old 09-11-2012, 09:25 AM   #11
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Morning bump
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Old 09-11-2012, 12:55 PM   #12
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well, you're asking what, exactly? if this is a permanent fix?

i think you're the one to answer that.

if you can drive around for hours/days/weeks and everything is kosher, then yes, it is.
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Old 09-11-2012, 02:16 PM   #13
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you said you're pushing down on the brake booster line, why don't you try messing around with stuff under the intake pipe and see if that changes how the car runs.
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Old 09-11-2012, 02:36 PM   #14
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Quote:
Originally Posted by ride5000 View Post
well, you're asking what, exactly? if this is a permanent fix?

i think you're the one to answer that.

if you can drive around for hours/days/weeks and everything is kosher, then yes, it is.
I was wondering if anyone's seen this before / is this common? If not, what could be causing this issue - bad wiring, bad maf, or something else? I haven't seen this happen anywhere else so it makes me think this is being caused by a bad electrical connection and or short. So how would I go about correcting the problem / what is the "right" way to fix this.


Quote:
Originally Posted by tebriel View Post
you said you're pushing down on the brake booster line, why don't you try messing around with stuff under the intake pipe and see if that changes how the car runs.
It's definitely an electrical issue. The maf is grounded to the pipe and when the pipe touches the aluminum ac line, it gets grounded to the chassis directly. This causes the maf readings to fluctuate.
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Old 09-11-2012, 03:00 PM   #15
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Quote:
Originally Posted by Bad Noodle View Post
It's definitely an electrical issue. The maf is grounded to the pipe and when the pipe touches the aluminum ac line, it gets grounded to the chassis directly. This causes the maf readings to fluctuate.
the problem is that pushing the pipe down until it touches the ac line isn't just grounding the pipe: it's also moving the pipe, which WILL cause fluctuations/turbulence in the airflow past the sensor.

there is a very long history of folks battling with blow through maf sensor rigs. no two are alike.

i find it fairly unlikely that the pipe needs to be grounded for the sensor to provide an accurate reading, since the oem maf tube is plastic.

is your maf sensor harness extended? if so, who did the electrical work? can you inspect the junctions? were they soldered, or crimped? are they weathertight?
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Old 09-11-2012, 03:16 PM   #16
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Why not just go speed density and not worry about the maf ever again?
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Old 09-11-2012, 03:24 PM   #17
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Quote:
Originally Posted by ride5000 View Post
the problem is that pushing the pipe down until it touches the ac line isn't just grounding the pipe: it's also moving the pipe, which WILL cause fluctuations/turbulence in the airflow past the sensor.

there is a very long history of folks battling with blow through maf sensor rigs. no two are alike.

i find it fairly unlikely that the pipe needs to be grounded for the sensor to provide an accurate reading, since the oem maf tube is plastic.

is your maf sensor harness extended? if so, who did the electrical work? can you inspect the junctions? were they soldered, or crimped? are they weathertight?

I'm pretty sure it's electrical as I see the same symptoms if I simply ground the pipe to the manifold not moving it at all. I just touch one end of a wire to the maf pipe and the other to the mani at the same time and the car stumbles.

I extended the wires. They were soldered using soldering paste and flux, then shrink wrapped. To extend the signal wire, I got some insulated wire from and online air crafts part supplier, soldered the inside signal wire, shrink wrapped it, then soldered the outside wire, and then shrink wrapped that. I can go through the wiring at the ecu plug to verify there is no connection between the inside and outside of the signal wire and that there is no resistance between the two ends of the cable as well. Is there anything else I should do?
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Old 09-12-2012, 07:18 AM   #18
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there is one other possibility: that the metal maf pipe is acting like an antenna and picking up the electrostatic fields under the hood, causing spurious readings.

it's a bit of a reach, but one of the only things i can think of that fit the symptoms. there is a lot of high frequency crap in that area, with the injectors and plug coils very proximate.

a single short ground strap to the block should keep the pipe grounded. we are not talking any appreciable current here, but any inductance should be minimized (hence keeping the strap as short as possible).
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Old 09-12-2012, 10:49 AM   #19
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I did put in a grounding kit that grounds the manifold. I have the wiring harness ground bolted to the tgvs and the tgvs bolted to the mani, then mani to chassis. Maybe it's something to do with that. But securing a short fat strap between the intake and manifold is probably the best solution
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Old 09-29-2012, 03:33 PM   #20
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Found something new: Pin 4 on the maf has continuity to the metal on the underside of the maf housing. This probably shouldn't be happening as there is no continuity on another sensor I tested. Gotta get a new sensor and retune
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Old 09-30-2012, 04:40 PM   #21
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the wiring looks good:

Code:
                          maf connector
                  1      2      3      4      5
shielding         -      -      -     -       -
ecu-B34           -      -     0.5    -       -
ecu-B18           -     0.4     -     -       -
ecu-B26           -      -      -    0.5      -
grnd             0.4     -      -     -       -
12V               -      -      -     -      0.5
the above shows the resistance between the ecu plug and maf connector

Last edited by Bad Noodle; 09-30-2012 at 10:06 PM.
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Old 10-02-2012, 09:39 AM   #22
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If this was electrical, you should see some kind of change on the MAFv. Instead, you've got a solid MAFv, a small change on the MAF, and a big change on the correction. I'm inclined to think mechanical, like turbulence or resonance, and possibly the tune reacting too soon, too much, or both. Just my .02.

Last edited by Special J; 10-02-2012 at 09:41 AM. Reason: punctuation
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Old 10-02-2012, 09:47 AM   #23
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^ Thanks for your input. I'm quite sure it's electrical because if you ground the intake pipe, you get a huge swing in the corrections. Nothing physically moves on the engine, so the flow past the sensor remains unchanged. The only difference is that pin 4 on the maf is now grounded through the manifold vs ecu pin b26.

I think this is the ground for the temp sensor but I'm not sure.


Since the wiring doesn't have any shorts in it, I ordered a new MAF sensor. I do have a secondary maf I bought off someone here, but comes up with P1030 - High MAF sensor input when plugged in. So I think that one is bad. But a brand new sensor is on it's way so we'll see what happens when that goes in.
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Old 10-02-2012, 10:17 AM   #24
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I read #17 wrong, derp. I thought nothing changed with the grounding, it only happened when you moved stuff. Good luck with it.
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Old 10-03-2012, 11:52 AM   #25
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I've seen this before on a maxima that was turbo'd. Try playing around with the MAF angle (rotate the tube). It fixed that persons problem

http://forums.maxima.org/supercharge...make-work.html

Shot in the dark...

Last edited by OC_Nooby; 10-03-2012 at 12:01 PM.
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