Help '87 Volvo 740 Turbo terrible gas mileage only on highway or freeway ?

james, did you ever replace that wiring harness that was giving you so much trouble? perhaps something electronic controlling your fuel mixture and/or ratio is shot. I hope someone else will chime in, but you posted in February all of the problems you had with your wiring harness.

Jamie

circuit slave wrote:

No, not yet. I know, I know. I really need to get that fixed. On a side note, it does idle like it's cold (kinda shaking) when I'm at a stop. I'll look into that harness wiring. I just haven't been able to come across it recently at a decent price. I'll look into that.

I will say this, though, It hasn't died one me once yet : ) like it used to. I isolated the shorts which were causing it to die, at least.

Jamie wrote:

Well replace or rebuild the wiring harness first, until you do that you're just chasing your tail.

Contact Dave Barton. I can't tell you his prices at this very moment, but I know that there are times when he has harnesses for around $100-$130. Sometimes he has some in decent order that require minor repairs and he can sell these cheaper.

You can always e-mail him and ask to be put on a "waiting list" for a $100 harness.

Good luck.

circuit slave wrote:

A malfunctioning turbo caused poor milage on my daughter's Saab.

Shaking at an idle could be from a lot of things, including a vacuum leak, bad valves, etc. You should really have the car looked at by someone with the proper diagnostic equipment rather than guessing and swapping out parts.

You need to carefully check all the hoses running from the MAF to the intake manifold. One of them has a split or blow out on the bottom. Any air leak at all between the MAF and the intake manifold will cause the fuel injection to be very rich. As a side note if the green wire from the O2 sensor is horted to ground the system will go full rich.

Bob

I'll check all hoses, thanks everyone. As far as having it looked at a Volvo mechanic or someone with experience and the equipment---I'll first invest in that wiring harness first---I know that is something that does NEED replacing. Thanks for all the replies, and suggestion, people ! : )

User wrote:

I rebuilt my existing harness by splicing new wires into the old connectors and putting heatshrink tubing over everything. Took a lot of patience and I was freezing my butt off in January doing it but I had to get the car back on the road and it worked.

Come on up to Northeast Texas - a cool 100 degrees. Thank goodness for low humidity and this drought. Dust held my old harness together for I think the last 6 months. I think in some places the wires rotted out and the electricity had to arc to make a connection.

Damn tough cars!

circuit slave wrote:

Yuck, we're pushing up into the high 70's here off and on, figure I'll have to start running the AC later this week.

High 70's? We call that a "cold front." LOL

We're about to go > Jamie wrote:

Once when I lived in Phoenix my wife and I were doing a Cub Scout thing outdoors the first weekend in Spring... the temperature hit 101 degrees. Only four months there have not recorded 100 degrees: November through February. My wife and I married in the middle of the longest unbroken run of temperatures above 110F recorded there: 21 days. Most of those days were

I'm so glad to be in Flagstaff now, where the summer temperatures are flirting with 90 degrees in the hottest part of the day.

Mike, the reformed desert rat