I need help trying to figure out what's wrong with my daughter's 940. See is away at school and called to tell me that the car has started to lose power all of a sudden while driving on the interstate (although it has happened once in the city). Her description is this: while driving, it will suddenly lose power with the tach dropping back to idle level and her speed falling. She pedals the accerlerator to the floor and the car will again start accelerating. Talking to local mechanics,(not Volvo specialists), I've heard everything from the catalytic converter to relays to the transmission as possible suspects. I will be going down tomorrow to see for myself and see if there is anything I can do. Would like to know if anyone can point me in the right direction as to where to start looking. Thanks

Well I am going to give a different option. I have experienced this same problem on my 940SE wagon. It would only happen when the fuel tank was low generally near the red zone. Fill the tank up and never had it happen again until the fuel level got low again. Now I just keep the fuel level up and haven't had the problem for several months.

Note: A previous post referred to the positive terminal being oxidized. This existed on mine but this never interfered with the car starting or running. I never concerned myself that this could possible cause a problem and don't think it ever did at least IMO.

Dear pmiller7,

Good p.m. and hope this finds you well. Do cheap/easy things first.
(a) The crank/RPM sensor, atop the tranny bell housing (10 o'clock position, as you face the engine) just aft of the firewall. When the wire insulation deteriorates with age, an intermittent signal cuts power to the fuel pumps. to test for this, while the engine is running, reach behind the engine and wiggle the sensor's wires, that run straight up to a connector, on the firewall, just below a harness enclosed in corrugated black plastic tubing. If moving the sensor's wires causes the engine to "hiccough", you've found the problem, or at least a major contributor to it.

(b) intermittent failure of fuel pump relay (on block behind the ashtry) or fuel injection relay (in the engine bay, forward of the ABS unit,on non-turbo models) can produce erratic engine output. These are not costly (see www.fcpgroton.com). You should carry spares on board.

(c) Corroded battery terminals and grounds can disrupt engine operation. Trace the blue cable from the batter, and clean all connectors with fine steel wool or aerosol anti-corrosion treatment.

The transmission is almost certainly innocent of wrong-doing. Leave it alone, unless it has behaved strangely. The AW-71 trannies are super-reliable, unless water gets into the fluid. Few transmissions do well with an oil/water mix.

Hope some of this helps. Post back on your findings.

Yours faithfully,

spook

Spook,

I sort of have the opposite problem occassionally. After the car ('93 940 Regina, NA) has idled for a long time, or after it has sat after driving, and then you get in it again, when you do full foot-to-the-floor acceleration, the car will seem to lose fuel flow. However, easing off the accelerator, even slightly, will bring everything back to normal. I don't think it's the fuel pump, but some suspect that it is. Perhaps FP Regulator? FP Relay inside console was replaced 2 years ago.

Also, occassionally, I'll notice the tach fluctuate a few hundred rpm for no apparent reason. Could this be related to your wire insulation grounding theory (crank/rpm sensor)? I'll take a look later.

Tom

Your description does sound like the Fuel Pressure Regulator may not be providing the increased accelleration pressure that it should, when the vacuum sensing hose "sees" something more like atmospheric pressure with throttle wide open.

Or it may not raise the pressure enough to match the throttle opening. Try a few runs with the FPR Vac hose removed and plugged, so it runs at higher pressure all the time. If it seems better, the FPR may not be up to the job for sudden accelleration.

Also, if it's really fully Wide Open, the Wide Open Throttle (WOT) signal from the Throttle Position Switch to ECU may be missing or erratic for some reason.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Dear Tom,

Good p.m. and hope you're well. This sounds like a faulty/dirty throttle position switch. It seems that when the accelerator is fully depressed, the signal from throttle position switch to the fuel pump is lost, but is restored when you ease up, and re-apply the pressure. It is as if the contacts work fine, if moved gradually. However, when they're moved fast, contact is lost, and the engine stumbles.

How many miles on your car? Ever changed the RPM/Crank sensor?

Let me know how the test goes.

Yours faithfully,

spook

It is as if the _contacts_ work fine, if moved gradually. However, when they're moved fast, contact is lost, and the engine stumbles.

Spook,
I think you have the Throttle Position Switch confused with a TP "sensor". The only contacts it has are Idle and Wide Open Throttle. Nothing in between.

But I agree that the Crank Position Sensor is a good suspect.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Dear Bruce,

Good p.m. and may this find you well. You're correct: mea culpa!

Yours faithfully,

spook

Spook....you're 2 for 2 with your analysis. Have talked with a couple and you hit on what each of them said. One, the sensor on the tranny and 2, the fuel pump relay. Will go down there tomorrow and replace the fuel pump relay and check the wiring on the tranny. Will let you know how it turns out. thanks for the advice.

That sounds fishy to me. What year is the 940? I would look at the relays in General. A friends newer XC70 had a problem similar and it was a relay that costs $45.

--
92 240 2.3 L with a Borla! 103,000 Miles and More!!Go Team Grimace!!