B6304 Mass Air Flow Sensor wiring

double_platinum · Post by **double_platinum** » 29 Dec 2008, 06:53

Have been having a bear of a time figuring out an intermittent starting issue with my 94 960. Pulled the codes, and I have one for the 02 sensor tripped (has been running with this tripped for a good long time), and one for the MAF sensor signal missing. Had a spare MAF from a running car w/ no codes I put in, reset the codes, and still having the same issue. Sometimes it will start and run fine, but most of the time I have to crank it for 5+ minutes to get it to fire up. Any issues with the wiring between the MAF and the computer I should be aware of before I go ahead and rewire the whole thing? I did pull back the rubber sheathing on the plug to the MAf and I have a kinked brown wire (should be ground) but I played with it and still no start.

Post by **billofdurham** » 29 Dec 2008, 11:05

I don't know of any issues with this wiring. The brown is the ground (earth). Did you try running a new ground lead to definitely eliminate the kink?

Bill.

double_platinum · Post by **double_platinum** » 29 Dec 2008, 11:27

Hey Bill, I am looking into it tonight and will run a ground jumper from that over to see if that is the issue. It actually looks like the kink was tucked into the rubber from the factory, so I just strightened it out while trying to start it to see if it came back to life. Anyhow, will advise in a few hours once I see if this is the issue or not.

DanR · Post by **DanR** » 29 Dec 2008, 13:36

I am wondering if it might be something else. Does it start/or not start when warm, does it start/or not start when only cold, or does it not matter?

Next time it happens, try disconnecting the MAF, if it is that or any of the wiring, it should start right up with it unconnected. If it does start with it disconnected, try cleaning the big plug on the intake side under the hood, under the black plastic cover, front wheel hump.

A failing ignition switch, a bad fuel pump relay, intermittant rpm sensor signal, ignition relay or injector relay.

You might have to do some diagnostics while it is not starting, check fuel pressure, check for spark, check for injector clicking.

When you initially turn the key, there should be an audible split second sound of the main fuel pump activating, but as soon as pressure is built up it turns off until the engine is running.

You could also swap the relays for the ignition and injectors, intake side front wheel hump and see if that changes anything. They share the same part number.

Are there any stored codes? Not all codes will turn on the dash warning light.

How old are the spark plugs? Is the wire harness to the coils sound, a very common problem is the insulation on the wires to the coils crumbling and shorting out the power feed.

Last but most unlikely, the coolant sensor can cause a no start condition.

I had a problem for a while with the fuel pressure regulator, it was drawing fuel into the intake and cause extremely hard starts when warm or hot. A very rich fuel mixture was the result. It start fine when cold, but after that it was difficult to start.

How does it idle when it is running?

DanR '94 964 342,000 miles (108,000 on the new engine)

double_platinum · Post by **double_platinum** » 29 Dec 2008, 14:06

I am having a problem starting it cold, warm or hot.

Let me see what I have covered in your list so far

fuel pump is coming on just fine, no problems I can detect with fuel delivery

plugs are within 5K miles of new

plug/coil wires I went through recently due to an errant idle issue, wires look new, was having trouble with getting fire to #5 cylinder, traced the problem back to the plug that mounts to the bosch resistor or whatever that is that mounts to the front side under the intake (would really like to know what this is anyways, I just replaced it with a part from a parts engine I had around) cured idle and engine still idles smooth (when starting).

I dont have the code #'s here with me, but I did check them from the test box under the hood, and it came up 02 sensor and MAF signals missing.

I am headed over to the car in just a bit to try cleaning the big plug under the black cover and try to check the ground that was kinked. However I did not know the car would start with the MAF disconnected, I will give that a shot too to see if I can get it fired up.

DanR · Post by **DanR** » 29 Dec 2008, 16:20

You might just have a broken wire, seems it would be a long shot but it just might be the problem.

Those two parts on the intake are called power stages.

One thing I have learned with my vehicle, is the electrical connectors under the hood are weather resistant at best, not weatherproof.
Resistance due to corrosion is a constant problem, twice a year cleaning and tightening keeps problems to a minimum.

You might also exchange the relays located on the intake side, on the wheel hump, gray in color. Just swap them, I believe the injector side draws more amps so that is the one that fails sooner, sometimes just swapping them can get it running.

DanR

double_platinum · Post by **double_platinum** » 05 Jan 2009, 18:57

Ok so I got into it finally tonight, after I started it last night right away, then turned it off, and it wont start again (warm or dead cold). Was running as smooth as always while going last night. I am having a no spark condition right now. Grounded out the mass air flow sensor from the kinked wire, and I also tried starting without the MAF connected, still no start. Swapped the grey relays, no effect. Changed the RPM sensor within 1K miles of now, changed out the power stage. Going to give swapping out the coolant sensor tonight a shot. Will advise in the AM. Any other thoughts feel free to chime in. Have to have it running reliably by this thursday! Thanks!

danr960 · Post by **danr960** » 06 Jan 2009, 10:46

There is a ground wire, it attaches to the intake side, engine mount bracket. This wire grounds the MAF and the power stages and the o2 sensor heater. It will be real hard to get at it, the lower part of the intake, the round ball shape is in the way. Maybe this wire is making intermittant contact? RPM sensor also controls spark, could there be a loose connection. Later today I will look at my trouble shooting manual for further causes of no spark.

DanR

double_platinum · Post by **double_platinum** » 06 Jan 2009, 11:03

thanks Dan, I didnt get to replacing the coolant temp sensor last night, but I will tonight for sure, as well as check out the ground wire. I don't have any codes for the coolant sensor though, so I am thinking I might be chasing a bad ground. I also checked the RPM sensor connection and all looks tight in there

double_platinum · Post by **double_platinum** » 06 Jan 2009, 19:00

ok back again. Changed out the coolant temp sensor, still no go. I also hard grounded the MAF, power stage, and still nothing. Changed out the power stage with one that had the car running, but was not sparking in one cylinder, and checked all the wires from the rpm sensor. Codes are still the same, missing/faulty o2 sensor and MAF sensor. I haven't dug down far enough to find the ground wire yet on the intake side, but I would figure with a hard ground into the power stage I should be seeing some result (digging for this begins in a few minutes). Just figured I would give a status on it while I am still greasy and see if anyone had any other issues they may have run across. Thanks!