Volvo 940 B200FT Auto - Dies on Full Throttle

[grahamf940]

Hi Folks

Hoping you can help me out here.

On 'flooring' my B200FT auto estate (i.e. going into kickdown) the revs get up to about 4,000 and then the engine dies away as if not getting enough fuel. When I lift my foot off the accelerator everything is fine and there's no misfire or hesitation under normal driving. If I floor the pedal again and hold it to the floor, the same thing happens at around 4,000 rpm, it dies back to around 3,500 rpm and then picks up and revs to around 4,500rpm. If I keep the pedal pressed down, it dies back to around 4,000 rpm for a second or two and then picks up and revs to around 5,000 rpm and so on. I've replaced the fuel pressure regulator with a good spare I have as I suspected this could be the problem, but it's made no difference. I've also tested and adjusted the throttle position switch and this is working as it should.

About a year ago or so, I replaced the lift pump in the tank and also for good measure, the under floor fuel filter (about 1,000 miles ago) to fix what I thought was perhaps a problem with the lift pump, but I actually think I'd ran out of fuel at the time with the fuel gauge still showing quarter full :-/.

I'm now wondering whether the under floor fuel pump is supplying enough fuel with the engine at full throttle. I've ran a pressure test on it idle and it's showing approx. 41 PSI and I'm guessing that's about right. Other than the symptoms I've described above, there's no misfire or hesitation both when idling and under normal driving conditions. The car always starts first time too.

Any help or suggestions as to what the problem might be would be very helpful.

Cheers

Graham

[RollingThunder]

My initial thoughts would be fuel pump, fuel filter, coil or ignition amplifier breaking down at high rpm???

[classicswede]

That sounds like fuel pump not flowing enough fuel. Pressure is ok but lacking volume hence why when you lift off and re apply the throttle the revs will build higher as the loading by that point is reduced

Could also be a clogged filter causing the issue but my money would be on pump.

i would do both

[grahamf940]

Thanks for the help so far, but no luck at the moment I'm afraid.

I changed the underfloor fuel pump and filter this afternoon and I still have the same symptoms, so I don't think its fuel pressure.

I have also separately replaced the ignition amplifier and coil from my spares stock and neither had any effect.

Could it be the MAF perhaps? I think I have a spare somewhere but currently unable to lay may hands on it!

Any further suggestions greatly appreciated.

Cheers

Graham

[grahamf940]

OK. I found my spare Bosch MAF and this has fixed the problem. The one I replaced looked like an aftermarket MAF that had been fitted at some point. I'm guessing the MAF was misreading the level of airflow on full throttle and causing the fuel supply to be either shut off or reduced.

Thanks for your help and suggestions. Hopefully this might be helpful to others if experiencing a similar problem