[Nate]

I have been working on a 740 Turbo that seems to cut out at mild throttle. We are nowhere near boost and it does not always do it. It will sputter at idle until it warms up.
Fuel pressure at idle 36 psi even while it is sputtering. Remove the vacuum line from the regulator and fuel pressure goes to 48 psi.
Temperature sender in block changes resistance with temperature and is close to a working 2.3 in a 1990 760 wagon. Disconnecting this does not make car run better or worse.
Hot-wire Air Mass Meter was checked with an ohmmeter. It took me a while to figure out which pins went to the platinum wire but it is pins 5 and 6. I replaced it with one from the 90 wagon and no change. Part numbers were the same.
O2 sensor was unplugged and no change in running. The resistance of this sensor also changes with temperature.
Throttle switch was not making the "idle" setting so I adjusted it and it idles a little better but still runs bad.
Air filter is clean
When the car looses power the tach jumps erratically so tomorrow I tackle the ignition system.

 

[Nate]

Well the ignition rotor is definitely bad. I broke it into quite a few pieces trying to remove it. I thought they came off like a typical rotor until it broke twice so I tried twisting it and it broke further. I reassembled the pieces and discovered I was right; they do pop off like typical rotors. This one was so brittle and stuck it just kept breaking.

Any recommendations on brand of cap and rotor?

 

[Nate]

The list of what is NOT the problem is getting larger.
New cap and rotor, new Bosch platinum plugs, new Bosch plug wires set. Car still bucks. Tach still jumps so I continue to think it is ignition related. It does take more throttle before bucking so that is an improvement.

 

[Nate]

80 miles and no bucking with great acceleration! Turns out the wires on the primary side of the coil were corroded. I never have seen this before but then I have never seen the coil mounted right next to the AC accumulator. I cleaned the primary coil wires and it seems to be working excellent! Wish I figured this one out before spending all that time and money on the fuel and ignition!

 

[Black 850]

We're glad you got it straightened out Nate,
David.

 

[Nate]

Another 200 miles on top of the 80 and no issues. Something so simple and no cost other than labor but trying to figure this kind of problem can really be irritating!

 

[Black 850]

Just part of the learning curve Nate...congrats - David.

 

[Nate]

Nearly two weeks and the problem has not come back.

This is the first Volvo I have really driven on a regular basis; I have to say I am quite impressed with this car. It has 196,000 miles on it, is 20 years old and runs excellent! I would have never guessed Volvos were such good cars! They are very comfortable, have lots of neat features and fun to drive. Everything works, all electric windows, door locks, sunroof, seat heaters, cruise control and AC. Is this common or am I just lucky with this one?

Even my friends are now looking at Volvos differently and being impressed.
A 20-year-old Volvo, I guess it doesn't take much to impress us.

 

[Black 850]

Sounds crazy, but I am now driving my ten year old 850 everyday; it has 122k on the clock, and some people wonder how I can afford such an expensive car. I never heard that when I drove my Corvette everyday and it cost a lot more. Everything works on my car including the ice cold AC. I can't say the same for some of my other cars with fewer miles. All my other four wheel vehicles have only two doors, so my wife suggested getting the Volvo and it was a good choice. A little pricey for the year and mileage, but worth it,
David.