1996 850 turbo, MAF Sensor wiring

cn124 · Post by **cn124** » 03 Jul 2015, 19:50

Hello fellow Volvoists. I've learned so much already from sites like this that I thought this would be a good place to ask about a very specific issue. So here goes: I have been told by my mechanic that the wiring harness to the MAF sensor on my 96 850 turbo is bad - it keeps throwing off an error code (in addition, the car was running horribly, stalling, bucking, worst I've ever experienced, had to floor it the entire time just to keep it running). We swapped out the old sensor for a brand new one, still got an error code. So we swapped that out and put a second new sensor in. Same error code. His theory is that there is a problem in the wiring between the sensor and the ECU and asked if I would be interested in doing some of the grunt work to try and pinpoint which wire may be causing the fault code. Here's the question I have: the car has been running beautifully with the sensor unplugged, so what would happen in the long term if I just never plugged it back in? The display says that the car is getting great gas mileage, and there's plenty of acceleration, etc. He also warned me NOT to plug it back in because it might ruin the new sensor, but didn't know how long the car would run without it. So, what's everyone think?

1988 740 Turbo
1989 240 Sedan
1996 850 Turbo wagon
2001 V70 Turbo

Post by **polskamafia mjl** » 03 Jul 2015, 21:19

I know some people use a zip tie on the connector to make it work. Perhaps you're suffering from the same problem. I would plug it in and, with the engine running, move the wiring for the connector around a bit and see if anything improves.

Post by **abscate** » 04 Jul 2015, 02:42

cn124 wrote:Hello fellow Volvoists. I've learned so much already from sites like this that I thought this would be a good place to ask about a very specific issue. So here goes: I have been told by my mechanic that the wiring harness to the MAF sensor on my 96 850 turbo is bad - it keeps throwing off an error code (in addition, the car was running horribly, stalling, bucking, worst I've ever experienced, had to floor it the entire time just to keep it running). We swapped out the old sensor for a brand new one, still got an error code. So we swapped that out and put a second new sensor in. Same error code. His theory is that there is a problem in the wiring between the sensor and the ECU and asked if I would be interested in doing some of the grunt work to try and pinpoint which wire may be causing the fault code. Here's the question I have: the car has been running beautifully with the sensor unplugged, so what would happen in the long term if I just never plugged it back in? The display says that the car is getting great gas mileage, and there's plenty of acceleration, etc. He also warned me NOT to plug it back in because it might ruin the new sensor, but didn't know how long the car would run without it. So, what's everyone think?

1988 740 Turbo
1989 240 Sedan
1996 850 Turbo wagon
2001 V70 Turbo

I'm not too impressed with this reasoning, especially the bit about bad wiring "ruining a good sensor"

These are complex, fine tuned machines that work well but need a systems approach to fix, not guesswork. If a mechanic doesn't know how to back wire to check voltages and confirm operation with a diagnostic tool then s/he isn't in a position to fix these cars. That doesn't make them a bad person,just not helpful in this case.

Eventually a no-MAF car will run rich and that will lead to more problems...fouled plugs, cost, fuel in oil, ugly.

A MAF code does not mean the MAF is bad. It's indicative of an air metering it flow problem and usually that's a vacuum leak.

Post by **erikv11** » 04 Jul 2015, 07:59

I agree the mechanic probably identified the problem correctly but some of the other comments suggest he is out of his comfort zone.

The first thing to try is to go into the MAF connector with a fine point screwdriver and attempt to close up or tighten up the gap on each of the female connectors. Then plug it back in. You aren't going to kill the MAF by using it, see abscate's remarks.

You can run it for a long time with the MAF unplugged, in that state the engine is running rich (adding more fuel than needed) and this will eventually lead to things mentioned above, plus excess carbon deposits on the valves and a valve may burn, effectively killing the engine if you don't do engine work yourself. I don't know how long that might take, presumably on the order of months.

cn124 · Post by **cn124** » 04 Jul 2015, 15:48

Thanks for all the input. I think (but I'm not sure) that my mechanic was concerned with the expense of diagnosing bad wiring that connects to the main engine harness, and so offered to have me do some basic continuity testing. As for plugging in the MAF, he may have thought it a bad idea since it was clearly causing the engine to run so terribly. But I will try your suggestions and see if they make a difference. Again, thanks for all the useful advice, and in such a short time!

Post by **abscate** » 05 Jul 2015, 05:05

Just noticed you have a turbo. That probably means you have a fairly bad induction leak in the path between turbo and cylinder head.

When you unplug the MAF, the car goes to a default set of injector firings based on rpm and will run decently, with bad mileage and high emissions.

When you plug in good MAF sensors, the engine tries to match fuel to air flow reported by the MAF, but since there is a leak somewhere, the match is crappy and poor running results.

Loose clamp on induction pipes
Split or hole in induction pipes..sometimes these are closed until pressure builds.
Split in intercooler ( if equipped)