Hi Guys,

Has been awhile since my last post. Hope you can guide me a bit.

This problem just started suddenly. Engine was running smooth before this problem.

Engine starts well when cold until air pump kicks in. Then it begins to run rough. Engine can be accelerated normally until engine warms up a bit. The warmer it gets the worse it runs at idle and feels like stumbling while accelerating. If accelerated slowing it'll build up RPM's, but if done quickly it stumbles badly. Eventually engine stalls and will restart but reluctantly.

I checked:
-Sprayed starter fluid around intake boots with no changes.
-Fuel pump relays by swapping them and didn't make any difference.
-Fuel pressure. KEY ON pressure was btwn 42-43psi
-Fuel pressure Engine Running at idle 38psi, accelerating 38-40psi
-Pulled vacuum hose off regulator and it jumped to 48psi
-Disconnected connector at air pump and oddly it sounded like it ran when started cold. Did I disconnect the wrong connector?? (PICS at link)

http://s244.photobucket.com/albums/gg26/photonut2008/Volvo%20FPR/

Was thinking possible fuel filter, fuel pump issue as pressure seems low while at idle or accelerating.

Any feedback appreciated.

Thanks.

Sorry gfor the late post but I've been gone for the last 5 days and just saw this.

It doesn't sound like a fuel filter. If it's affected by engine temp, it's not going to be the fuel filter or the fuel pump. Your pressure sounds good.

It sounds like it runs fine when it's in open loop (cold start up) then it leans out too much once it's in closed loop (after the cat heats up and data from the O2 sensor is available to the ECM). In closed loop the ECM takes the info from all the sensors and adjusts the fuel mixture.

- Can you test your O2 sensor?
- Have you checked every single vacuum hose in the engine compartment? They seem to rot at the rubber elbows.
- Have you checked your flame trap?

Have you pulled any codes from DTC?
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1998 S90 083,228 and 1995 964 154,100

Hi dewfpo,

I haven't checked here the past couple of days and am glad to see your reply. You've always been very helpful in the past and am grateful for that. My 964 with 211k miles has been running great until now.

I found 2 codes which I believe to be unrelated from my research but could be wrong.
Socket B2- 122 cruise control???
Socket A1- 114 transmission???

So far I've replaced the fuel filter and fuel pump. Fuel pump was from the local pull-a-part but in good shape.

- I've looked for loose connectors, vacuum lines but will recheck them more thoroughly.
- The flametrap honeycomb insert was removed years ago so no blockage there.
- 02 sensor hasn't been checked. I found some info on how to do this at this link but am open to suggestions

http://www.volvoclub.org.uk/faq/EngineFuelinjection.html#Oxygen_Sensor_Diagnosis

Thanks

Agree, the O2 sensor could cause a number of these symptoms - would be good to check that before going too far. I'd also suggest running Seafoam through both the intake and fuel system.

http://forums.nicoclub.com/how-to-seafoam-your-engine-the-right-way-complete-diy-t126583.html#p5757630

I have some Seafoam and will run it through the engine once I solve this issue or at next oil change. The engine seems to run smoothly with the MAF disconnected.

Hi, I agree, the DTC codes don't sound like they have anything to do with the engine issue. Along with testing the O2 sensor, I recommend you test the MAF sensor as well. I'm not familiar with the unit on pre-1995 960's so I can't help much there but I do know some folks have disconnected the connector on the MAF sensor (causing the ECM to use a default value instead of actual data from the MAF sensor), and they were able to tell if the engine idled better with it connected or disconnected.

It really does sound as if the engine is getting too much air, hence my suggestion to check for all vacuum leaks, O2 & MAF Sensor operation.

Wishing you success, DEWFPO

--
1998 S90 083,228 and 1995 964 154,100

Hello,

I've got a bit more info. Rechecked for loose connectors and vacuum lines. Didn't notice anything out of the ordinary.

Connected voltmeter to black signal wire of the 02 sensor (4 wires)

Key ON- .52v

Engine ON- Begins at .52v and then gradually drops to .1 and starts to run rough if accelerated. May fluctuate slightly between .1-.2v

Engine ON- Disconnected MAF and jumped up to .97v with immediate surge in RPM. Engine could be accelerated and ran better.

Engine OFF and RESTARTED- Begins at .50v and gradually climbs up to .97v

Shut OFF engine and reconnected MAF. Very difficult to restart. Would have to crank engine over excessively and reluctantly it restarted, held a low idle and stalled. Had to lightly push down accelerator to get it to stay running and then would idle roughly. .1v

Disconnected MAF- Engine restarted and ran better .96v

Bad MAF?? or possibly another sensor.

Thanks

The O2 sensor needs to be hot (at operating temps) when checked for the voltages generated, otherwise they will give you incorrect readings, hence open loop operation until they come online. I'm don't know if you were able to do that with a finicky running engine. A properly operating O2 sensor typically oscillates around 0.5-.6 volts. The reason it oscillates is because the ECM is constantly adjusting the mixture.

If the engine was warmed up and you got better readings with the MAF disconnected than with it connected, you may indeed have a bad MAF sensor, but I am no expect on this subject. The cheapest place to get would be in a pick and pull or off a parts car.

I hope this helps.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

Installed a used MAF sensor and the engine is running back to normal. BTW-Prior to replacing the MAF I bought a can of MAF sensor cleaner from Autozone and it did no good.

So with the multimeter connected to the 02 sensor the mixture appears to be rich. With the engine warmed up the voltage fluctuates between .2v-.9v every 1 second. Prior to having these issues, at best I was averaging 20mpg hwy.

Perhaps another sensor is bad? ECT at rear of head? I have a new one I've been planning on installing for a while as preventative maintenance. Any thoughts appreciated.

Thanks.

I'm glad you were able to solve the problem with the MAF sensor.

Is your O2 sensor original? If it is, it is likely 'lazy' if it has 211K miles on it. O2 sensors do get old (after 100+K miles) and become less accurate and don't register/cycle 'as fast' as when new. It won't hurt you any to change the ECT sensor but with 211K on your 964 I'd consider changing out the O2 sensor to get you back some mpg.

DEWFPO
--
1998 S90 083,228 and 1995 964 154,100

The 02 sensor was replaced at least 5 years ago so it's not the original. I was thinking to replace the ect sensor and then check to see if the readings change at the 02 sensor. As luck would have it, I bought a new oem Volvo sensor on ebay not too long ago and just tested it with ohm meter before installing it. It appears to be defective. Connected tester to the two terminals and get O.L. (out of limit). Then tried to dip the sensor end into hot water and still no reading. Time to find buy another one.

Thanks for your inputs.

Being the first time testing an 02 sensor, it took longer than normal. The engine was started and shutdown multiple times and was definetely warmed up by the time I finished.

Funny thing about pick n pull is that every one I've gone to seems like the MAF is always yanked out. Must be a high priority item. Over the last 2 weeks I must have looked at 8-9 cars. Hopefully I can find one soon.

Thanks.

No one?

Sounds like fuel when was the last time the fuel filter was changed and if your car has an in tank pump get someone to turn the key on while you listen down the fuel filler pipe and you should here it running. Does it also do it with a full tank of fuel.

Maybe be the filter. Haven't changed it for at least 5 years. The pump runs approx 1-2 seconds and can be heard with key ON. Couldn't tell you if it happens with full tank as the car has been sitting for 2 weeks in my driveway with 1/4 tank since the issue began.

Was thinking I'd replace the filter first and see how it runs. Next think would be fuel pump.

Thanks for your input.

Replaced the filter and the problem persists. I'll be replacing the pump next.