ECU ground circuit for MAF

[mrbrian200]

I somewhere a few weeks ago saw a spec for this, but didn't save it.

on ME 7.1 That ground wire should show continuity between the sensor plug and chassis ground (measured with battery disconnected and a DMM set to OHMS) not to exceed-- is it around 3 ohms? I didn't save/commit to memory that spec I saw. The only thing I can find again is a spec on the wire run itself (between the sensor and ECU) not to exceed 1.5Ω

Car is in the body shop this week and next-- I'm doing this bit of digging before I get it back. When I measured it (day before it went to the body shop) I got 8 ohms between the (terminal at MAF to chassis), and seemed to think this might be out of spec...but I can't seem to get the right search terms worked to again pull that page with the spec I came across several weeks back.

Are there any passives/filter devices in line with this circuit within the ECU or is it merely shunted directly to a terminal leading out (it's there merely to ensure the ground plane between maf and +5v VREF = 0)?

[jimmy57]

DO NOT check it for resistance. Run the car and read it for voltage. The ground is from ECM internally connected to the wire going to chassis. Stray voltages will mess with an ohm-meter and cause you to chase all sorts of things. The caps inside various CM's in the car will provide the currents that fool your meter. The other issue is your leads. Ohm-meter is best tool for checking a component that has an ohm spec. or for verifying a connection but not quality of connection. If you do voltage test with engine running, which would have that wire carrying current, and it is more than 0.2 volts then there is likely a issue. Then you use voltmeter at connection points wire to chassis, again with it running, and see if you can locate where the resistance is by seeing the voltage across those connections.

[mrbrian200]

Ah, so probe it for voltage drop engine running connected to sensor. Accomplishes same end in circuit, got it. +5 VREF good steady at 4.97. Fixed trouble with +B @JP 53/315, replaced a weak coil pack. Highway econ (that was stuck in the mid 20s 99% of the time now in the high 30s, occasional random drop accompanied with LTFT rich limit, anywhere from a few seconds to a few minutes, then returns to normal) Well, not totally random->Seems tied to atmospheric RH and cold engine bay. It really doesn't like the car wash. When I get the car back I continue. 1) solder wire crimps on coil pack ground terminals (coil pack I replaced may not have actually been bad), 2) verify clean connections between MAF and ECU pins A58, A22. 3) recheck for air leaks again, just to be certain.
If I do indeed determine an internal ground circuit problem I'll pull it. I reworked the PEM board and it worked like a charm (by hand, no cook!). With the ECU not being plug and play I would be more reserved and just worry about A58 to Chassis and leave everything else well alone unless something is visually blown or leaky with the exception being if I find a schottky in that ground path.

[mrbrian200]

Finally got around to digging deeper at this. Measured exactly 0.2v during a period while it was acting up so it doesn't appear that ground circuit has a problem. Week ago I unseated the terminals from the MAF sensor plug and soldered the wire crimps (lead free solder). Haven't seen the LOW MAF specific code since. Couple days later I soldered the wire crimps at the coil packs' ring terminal grounds. Idle quality improved to "new car" (except that 1 in 5 starts when it just doesn't want to run worth a sh-). Down to intermittent LTFT rich coincides with drivability. Doesn't cost anything, just time, so go over all the pigtails just to rule that out before I start in with stuff that costs money (I'm hoping just a bad injector or another CP). Have way too much into this car if I could do it over again I would have probably gone with the Lexus or Acura even though they aren't quite as nice. Pretty much every known issue in the book I've seen with this one, only 85k miles strikes me as pretty sad. Discovered the other day (looking for traffic radio heading into Chicago) no AM radio! Dead as a doornail/not even static-bad HU. For petes sake.

[mrbrian200]

Missing/omitted weather pack seals in terminal position #2 on coil pack connectors. I might mention quite a few years back I worked in a GM wiring harness plant (W-body models) QA. No! except *in cabin*, unused wire positions used a plug with solid plastic at unused terminals -or- a solid (no wire) WP seal there. That was all soaking in engine oil (leaky oil filler cap seal) when I first bought the car.

Edit: 5 and 6 had silicone barriers down in (missing on 1-2-3). Look inadequate/ easily fall out. I know a full length blank seal that would stay is available.