1996 850 T Nearly died while running, P0103 code [ New MAF] Topic is solved

[rocketman4321]

My daughter was driving along at 35 mph on a pretty hot day and the car started to run rough. She limped into a residential neighborhood and parked it (smart girl!). I retrieved it this morning--a cooler day--but only with a a lot of difficulty--had to rev it to keep up the idle, and no power at all--needed to drop it into gear from 1500 rpm. If I let off the throttle suddenly it'll stall--did that 5 times in the 3 miles home. This was after a bit of warm up--at first it was worse. Possibly a slight gas smell out the exhaust.

I got a P0103 (mass flow) CEL--no other codes, and it will recur if I clear it. I tried cleaning the MAF connectors, the sensor itself and also leaving the connector off to force limp mode--no change. If it's a failed MAF, why won't it go to limp mode when disconnected?

I have 45 psi of fuel pressure after the pump runs but before starting. I can't really sustain the car long enough to take a running pressure. I haven't checked the relay yet, but the pump reliably runs in the "ON" position.

I can't find any vacuum leaks. Cleaned the IAC (though it was OK before cleaning). Distributor cap seems OK--a little light carbon but nothing bad. The rotor's a little worn but OK, and it doesn't seem like it'd go from good to awful that quickly. Coil reads 0.7 ohms on the primary and xx kohms (I forget) on the secondary, with the wires to the transistor module disconnected. I haven't swapped the coil ignition wire yet. I also cleaned the connectors on the ignition, throttle position sensor, IAC, and probably a couple others.

There's one prior incident that might be related. Several weeks ago my daughter ran the blower for 15 min with the car off--another hot day. Car wouldn't start. But an hour or two later it did. I thought this was electrical, and have been chasing battery, etc. But could it be related?

Any ideas what to try next? Thanks!

[theWIFES_S70]

Is your MAF the original one?

[rocketman4321]

Yes, original MAF. I've now repeatedly confirmed the problem's the same whether it's plugged in or not.
Voltage and grounds on the MAF connector look normal. On the MAF itself, the pin resistances are:
1 to 2: 47.5 k
1-3: 825 ohms
1-4: 25.3 k
2-3: 48.4 k
2-4: 71.5 k
3-4: 26.1 k
These are as numbered on the body. I think 1 is ground, 2 is ECU ground/return, 3 is +12V, 4 is signal. Does all that seem reasonable?

I've both resoldered the fuel pump relay (which needed it, but didn't help) and jumpered pins 87 and 15 with no change.

It runs a little better if I can get it warmed up--sometimes will even idle by itself for a couple minutes. I've put a timing light on a couple of the wires, and they seem to be firing. The coil wire reads 2.3 kohms and frankly looked a lot healthier than the old one I had, so I left it in. But overall, the car runs rough, with what seem to be misfires, until it's rev'd to 2500 or 3000 rpm. I went a while between reading codes and I did have the P0300-305 misfire codes, but that's unsurprising given all the stumbles and choking off in between readiings/resets. Squeezing the vac line to the fuel pressure regulator had no effect at idle--is that normal?

Should I be chasing the ignition side? Timing?

[abscate]

On a turbo, follow the air induction path from air cleaner to throttle body - look for holes, tears, splits, loose clamps.

Poor idle that clears at revs is one symptom of a massive induction leak

[rocketman4321]

A few updates--help still very much needed. I've checked for vacuum leaks, including pumping down all the lines at the tree and manifold with a hand pump. All good, except the bypass valve--see other post. I don't think that's an external leak though. This includes the line to the FPR, which holds vac. I've cleaned every sensor connector I can find, and check a few specifically as follows:
Camshaft position sensor-- cable shows ground, 5v, and 12 V.
Crankshaft -- cable shows 1.8V across the pins; sensor reads 324 ohms, which I think is OK.
Throttle position sensor -- Saw ground, 5 V, and 5.75 volts on the harness connector. Sensor did show rising and falling resistance across two of the pins (I think 1 and 3) with throttle movement.

I have now gotten codes p1310 and P0120 as well as the P3xx misfires and the P0103. I also have the up-arrow shift light on the dash and the "mode" switch light on the console blinking. (This is after I messed with the throttle--might need to go back into that.)

I replaced the distributor cap and rotor, checked the wire resistances, and the plugs. All seems normal, but no change with the new parts. I also pulled and re-seated the ECM modules.

What's next? At this point I'm ready to check the timing, and then run a compression test--If I can keep it alive long enough to warm up at all. Any way this could be power or ground? I've checked several of the grounds, but there's a few more. They measure OK, though.

Thanks for any help!

[abscate]

You have to remove all the induction pipes, clean, look for splits with a light , check clamps, etc. you can't even see more than half of the path of most of these hoses while they are on the car

It's not sexy work, but until you inspect it for real you can chase a lot of dead ends.

[abscate]

Oh, and don't forget to heap praise on that young lady again from me for shutting it down and getting it safe!

[rocketman4321]

I certainly agree on my daughter--very cool head for a driver with just over a year's experience!
I spent a chunk of yesterday pulling all the induction lines, from air box to turbo and turbo to throttle body. A few rubs, but nothing serious. I really doubt the intake manifold gasket could just fail. I could not check the line that goes under the manifold, but the part outside was healthy (I've replaced it, would have to look up when.)
Ran a voltage check tonight at the MAF connector, when it was plugged in and car quasi-running. All pretty normal, except the signal line reads roughly 6.5 V, pretty much pure DC--almost no AC signal. That's the same as disconnected. If the MAF is supposed to pull that line (pin 4) down (I've seen somewhere 0.2-2.2V at idle) then I really do have a MAF problem. Borrowing a scan tool tomorrow, and have a MAF coming, so should know more tomorrow night.
ECT looks OK at > 2000 ohms after parked outside on a 90 deg day.
The spark plugs, though OK, were somewhat blackened. Possible FPR problem? That might not be THE problem, just the next one coming!

I'll post back when I solve it.

[rocketman4321]

It was the MAF sensor. The Genisys scan tool was no help--couldn't seem to connect to the ECU. But the clue was the high voltage on the signal line, independent of engine speed. Even with the rough running, it became clear the MAF signal on pin #4 was incorrect.

So why the goose chase? Well, at least on my car, there's no real "limp home" mode. It was equally awful with the MAF plugged in or not. That simple test led me to look at ignition and hoses instead of MAF. To summarize, the test (a combination of a couple others suggested in various places I read):
1)the harness connector for ground on pins 1 and 2 (12 V from battery + to pin, or continuity from those pins to ground)
2) B+ (~ 12V) on pin 3 relative to ground (negative battery terminal, chassis, engine block) with key in the on position
3) 9-11 kohms looking into pin 4, with the key off
4) Connected up to the MAF, the signal on pin 4 when running the engine, relative to ground. You have to back-probe the harness connector with a pin or small nail. It should change with engine speed (intake air flow).

Hope that helps someone else. Can't complain: 150k and 21 years on the original MAF. On to that bypass valve I found leaking while I was hunting vacuum leaks!

[jenkinskg]

what about spark, is coil ok?
do you see spark on each plug?