Hi all,

Weird AMM issue with my '89 740 sedan, N/A.

It has recently died and failed to start twice, once while shifting into park, once after a normal shut down.

Previously this car had died while running several times on returning from the shop (transmission replacement), unplugging the AMM got me home. I purchased a replacement at a junkyard, everything seemed fine. I bought a replacement AMM with a lifetime warranty, figuring I'd keep the junkyard AMM in the trunk for backup.

The first time I had recently replaced the AMM and gone on a test drive to let the computer learn the new sensor. All seemed well (after about 10 min the car ran smooth and idled properly). On pulling into a gas station, I shifted it into park and it died. Failed to re-start. I pulled the new AMM and replaced it with the old AMM I pulled from a junkyard. Car started and drove fine.

The next day the wife drove it, parked it, and was unable to start it back up. I tried it, no-start. I unplugged/replugged the AMM and it started right up. I replaced it with the new AMM, as before it ran rough and improved with a few minutes of driving around the neighborhood.

Naturally, the OBD threw a 1-2-1 (faulty signal to/from Air Mass Meter). I have reset the computer. The connector looks great, I was going to clean it but it's spotless. The wire going back into the harness and the harness looks fine.

Anybody have any insight on this? Bad ground somewhere? I'm baffled.


edit/update: Went here https://www.brickboard.com/FAQ/700-9...AMMCalibration

Checked resistance on both contacts on the ends on the AMM plug (FAQ does not specify which contact is #1... ), reading on the pin closest to the engine was 0.0, reading on pin furthest from the engine was 0.09. I cleaned up the two ground connections on the intake manifold (two wires running to each). Also cleaned the braided connection from the valve cover to the firewall.

Car ran rough with new AMM, took it for a drive around the block, died 3x, unplugging allowed a re-start. On the 3rd time, I shut it down, unplugged the AMM, car started and ran w/o it. Replaced new AMM with junkyard AMM, failed to start. Unplugged/replugged junkyard AMM, started up, purred like a kitten.

Halp.

 

I had a similar situation happen a couple of years ago where my car would stall when it was damp out. Unplugging the AMM would allow me to restart and drive leading me to suspect the AMM was faulty. However, when I replaced the AMM the problems didn't go away. Since it would start and drive fine I kept on thinking it was the AMM. Long story short, my problem was pinpointed to a bad distributer cap & rotor.

What I suspect happened in my case is that unplugging the AMM causes the computer to go into "limp home" mode - which changes the parameters (timing, fuel mixture, etc) used to run the engine.

When it stalls and won't start, go through the normal procedures of diagnosis for fuel, spark, etc. My bet is it's unrelated to the AMM.

 

Thanks Act. I drove the car 40+ miles today with the old AMM and it worked flawlessly. Going to try resetting the computer and driving with the new on Tuesday and see if I can get it to exhibit the same behavior. The only thing worse than a no-start is an intermittent no-start!

 

BTW, does anybody know what the pin numbering is on the AMM plug for this brick? Thanks.

 

this is a bosch lh2.4 car?

pin 1 - brown - ground
pin 2 - blue-green - to ECU pin 6 (signal ground)
pin 3 - blue-red - to ECU pin 7 (AMM output to ECU)
pin 4 - blue-white - from ECU pin 8 (used to signal 'burn off' for 1 second when the engine is shut off)
pin 5 - blue-yellow - power
pin 6 - yellow-white, only used on B230G engines (non-US).

 

Peirce, thou art a mench.

I'm pretty sure (but not positive) it's an lh2.4, so I'll RTFF (Read The Friggen' FAQ) and find out.

 

an LH 2.4 car has a MAF/AMM with a Bosch PN ending in 016. 007 is a LH2.2, and 001 is LH 3.1

 

I have the same car and every year during hot humid day we run into start problems. I carry a spare Suppression relay and FP relay. usually I just replace the suppression relay and it goes. Only have 345K miles on it so it's still pretty new.

 

one of those relays should last 20 years. but using cheap off brand (or old) relays, well, all bets are off.

 

OK, I'm going to search the forums to try and get a clue, but it's not the fuel pump relay. I replaced it with a spare, but during a 10min test drive the brick cut out once while driving for about a second and then re-started. Both FP relays engage when the ignition is on (held a finger on the relay, felt it click).

The only code it is throwing is 212, O2 sensor signal. It's been doing that since I owned it (which hasn't affected driving or fuel economy). No crank position sensor, fuel injection code, etc.

I replaced both fuel pumps within the last six months. I did the exterior one, the only thing I can think to do now is verify that the connections to that pump are secure.

Edit: I also had the transmission replaced before this, and had them put a new engine position sensor in. They mentioned the wire to the EPS was dodgy, so they inspected and taped it up to secure it. I suspected they might not have been as careful as I would have liked, so I un-taped, secured it, and re-taped it. Have not had an engine position sensor code.

I'm looking here http://www.swedishbricks.net/700900F...hile%20Driving and starting to think I need to wire some lights up to the coil and to the fuel pump to see if they are losing power...

Any thoughts are appreciated.

 

first, the FP relay has TWO relays in it, one half goes on with ignition and powers the ECU, the other half goes on when the ECU tells it to go on, and powers the fuel pumps... the fuel pumps are only powered when the engine is turning over.

second, a relay can 'click' and still not conduct properly. the only proper test is with a test light or volt meter, to verify that the fuel pumps actually get voltage.

 

(Thanks Pierce)

Previous no start showed no spark (stuck a screwdriver into the longest plug wire, held near a ground, cranked it with the other hand through the window. Couldn't see any spark).

Just got back from breaking down on the street, coasted it into a parking lot. Called wife, went home, retrieved spare ignition coil, replaced, no-start.

Dicked around checking to see if the coil had 12v, looking at various connectors. Didn't unplug/screw/bolt any grounds or connectors. Elapsed time was ~15 minutes.

It started.

I let it idle for ~10 minutes, revved it a few times, went and got the wife, she followed me home.

Not sure where to begin on this one.

 

Update: I did this (in bold):

So, got the 5W bulb wired up and plumbed into the cabin, workin' good.

And, despite idling the car for ~20 minutes, and driving it around our parking lot for another ~15... It drove perfectly. Nary a hiccup. Purrrred like a well-fed kitten.

Here's something you hardly ever hear from a DIY mechanic:

GAWDDAMNIT, WHY WON'T MY !@#$%^& CAR QUIT WORKING!!!

 

intermittent problems suck.

 

So... (Skip to the *** at the end if you want the resolution, otherwise I hope this little story is both educational and entertaining).

Last year, we bought this beyootiful black brick. A 1989 740GL with practically no rust or body damage. Only 144k miles on it. Can't wait to get to the cosmetic parts, it will be sweet.

During the beginning of winter, remembering from our other brick how electrical connections can get dodgy after 20 some odd years and need cleaning up, I spent an afternoon going around cleaning up all the grounds, disconnecting and reconnecting connectors, etc.

There were a few connectors that were buried and hard to get to, specifically those on the left side along the fender near the power steering reservoir. I didn't detach the harness from the plastic tie downs, but tried to dis/reconnect them where they were. I'm pretty sure I gave up on them after a fair bit of tugging, deciding if they were that secure they were probably fine (some of you know where this is going).

Anyway, started having intermittent stalling issues (read this post from the beginning for the timeline). Was reading the FAQ, and saw that the "ignition power stage" could be the trouble. "Hell, I don't even know where that is!" I says to myself, in my best Bubba voice. I proceed to locate it.

It lives on the inside of the front left fender next to the airbox. The airbox is in the way. I get it out of the way. I disconnect the ignition power stage thingy and reconnect it a few times. I crank it, it doesn't start. I replace the airbox. It starts. I fiddle with the the AMM plug, thinking maybe I screwed up something from before.

It hiccups.

I start lifting and flexing the wiring harness. It hiccups some more, then it dies. I'm freakin' thrilled that my car quit running.

I remove the harness from the tie-wrap thingies. Car won't start. I notice the grey connector boxes. Now that they are free from the tie-downs, they are relatively easy to dis/reconnect.

I notice that one of them has one of the silicone wire terminators (they hold them in the box) is pulled out about 2 or 3mm, and the plug is slightly open at the base (like some jerkwad-in-a-hurry yanked on the connector and pulled one of the ends slightly out of the grey block).

I push it back in, put the block back together, reconnect, car starts. Any further manipulation of the harness fails to make the car quit running.

***

When I went around cleaning up all the grounds and connections last year, I stupidly pulled one connector so hard it partially pulled a wire out of one of the plugs, just far enough that it didn't start to cause problems until months later when it caused an intermittent open short.

Moral of the story: If you have to use force on your wiring harness in a way that puts a lot of stress on connections, you're doin' it wrong. Be careful in trying to make things better that you don't make things worse.

Thanks for chiming in guys, I hope I was at least entertaining!

 

Go to the Ignition box, unplug the harness and inspect the connector. There are little prongs inside the little tubes that need to be making contact and when bent back cause this exact problem.

I literally just described this in another thread so I'll c/p verbatim:

 

Thanks jupolupo, my issue was caused by my being a hammer mechanic instead of a technician on one of those grey connector boxes on the harness, but I'll have a look at the ignition box connector when I'm under the hood again (assume that's the 'ignition power stage' module that sits on the inner fender next to the air box).

Anyway, drove it for ~80 miles today, it performed beautifully. Once I get the undercarriage cleaned and sealed to keep the rust at bay, and put in some electric mirrors, it will be on to cosmetics.

It's funny: At this point in history, it now looks so different from just about every other car on the road it gets checked out. I parked it next to a totally boss new model Charger (with a shaker hood!), and the dude actually gave the brick a semi-appreciative once over.

Volvos: They're boxy, but they're good.

 

I get more looks and comments with my 240 than pretty much any car I've ever driven. The Hella driving lights mounted up front make it stand out slightly, but people are constantly walking up to me and telling me how much they loved their Volvo, etc. I'm always amused.