The craziest problem with 96 Volvo 850 T5 Topic is solved

[misha]

You will need a special Volvo scanner....at least Vol-Fcr.
It can clear service light and you will have access to every module in the car except ECU since it produce flash codes being a M4.3 on a T5.
I have old version for old desktop or laptop with serial DB9 to OBDII cable bought 10+ years ago.
There are newer versions which can display live data too with usb to obdII cable.

[850oldschool]

I recently picked up a used iCarsoft i906 for $70 on ebay. It claims it will do engine, transmission, airbags, and ABS. My car is a manual and I've only used the engine diagnostics so far.

[esl_97_850_T5]

Similarly, xiaotec "850 OBD-II" Android app, in conjunction with an appropriate ELM327 tool, can read/clear the special Volvo codes.

[redbeak1]

After a whole year of intermittent stalling and crank but no-starts, the problem was finally found. In July of last year I changed the fuel injection relay (the grey KAE that goes on top of the radiator) thinking that after 23 years it may be causing a no start issue at times. Well, after thousands of miles and over a year of following all the great advice on this forum the car finally died where I couldn't start it all. The P0120 code still came up,but I could not clear it as before. Luckily my Volvo had the decency to die in my garage. So after a week at Kundert Volvo they found out that the FI relay was cutting out intermittently. I put in this brand new KAE from FCP but it was defective from the factory. Not blaming FCP. They are great!!! Nobody really thought to check this since I wrote on the relay "New 7-18"
My question is: Why does it come up as a TPS sensor CEL? Thanks to all very much for all your help. Nice to have my confidence back in my Old great Volvo!!!

[abscate]

Classic! Well done! The only thing worse than parts swapping is bad parts Swapping!

The fuel injection relay probably supplies voltage to the fuel injectors and ignition circuits, the low voltage to the TPS was getting generated by that

The only way you could have caught this is

On stalling, ether test would confirm a no fuel condition

Fuel pressure test would confirm fuel delivery is ok

That would point you to injector circuit , an oscilloscope trace in the fuel injectors would shine the light.

Hmmm, where do you find an oscilloscope on lane 7, upper deck of the GW?

[redbeak1]

Classic! Well done! The only thing worse than parts swapping is bad parts Swapping!

The fuel injection relay probably supplies voltage to the fuel injectors and ignition circuits, the low voltage to the TPS was getting generated by that

The only way you could have caught this is

On stalling, ether test would confirm a no fuel condition

Fuel pressure test would confirm fuel delivery is ok

That would point you to injector circuit , an oscilloscope trace in the fuel injectors would shine the light.

Hmmm, where do you find an oscilloscope on lane 7, upper deck of the GW?

This sure was a tricky one. So far so good a month later!!! After the stall I did test the relay and it was working fine. Not with an oscilloscope. Would an oscilloscope pinpoint the issue...if after the stall the fuel injection relay reverts back to normal function again?
I had a similar issue working on my 1977 VW Bus with a crank but no start issue. I don't like swapping parts to find a problem, so I tested everything and it showed that the airflow meter was faulty. I sent it to Fuel Injection Corp in California. It came back as repaired and working. Same symptoms again!! Drove me nuts. I went through the entire system again. Wiring, connections etc. Back to airflow meter. I returned it to FIC and they saw that the repair didn't hold. So the big lesson here is that never assume anything. Maybe my Volvo FI relay was returned as defective by a previous customer and was just sent out again.

The good thing about stalling out on the GW is that everyone is only going 2 mph. The horrible experience was being on the NJ Turnpike pulling a motorcycle on a trailer in the fast lane and just dying with no warning. God was looking over us a few times!!

Well anyway, Thank you again for everyone's input. It was a great learning experience.

[abscate]

A scope won’t be too useful on an intermittent relay. I wonder what the failure mechanisms are?

Coil overheating and opening circuit

Dirty points or chattering , voltage drop over the contact points ?

Might be good to measure parameters on a known to be good relay