S60 2.0T - stalling and LTFT majorly out [weak fuel pump] Topic is solved

[TroyMcClure]

So, to conclude the thread and hopefully provide some help to those with a similar issue in future... a new fuel pump seems to have solved it! STFT still bounces around a little but no more than my partner's Corolla of a similar age and mileage (always a great litmus test) plus it's not going to extremes under load any more. LTFT over the short distance I've tested hasn't moved from 0 yet, whereas previously it would get to 5+ quite quickly. I think it'll need some time to adjust as all adaptions have been reset.

This particular model didn't have a fuel pressure sensor on the rail - or elsewhere it transpires. This also meant it didn't have a pump module. As above, my understanding is that the pump supplies constant pressure which I assume is controlled solely by injector pulse length, so if fuel pressure is low it'll run lean - as mine did. With the lack of pressure sensors/PEM it could never have thrown a fuel pressure related code as nothing was monitoring it (backed up by both mine and the garages code reader) so it made the fateful assumption that lean running = misreading air flow = P0101. Some models of the same era do have such sensors, from what I've read these will throw a p0089 instead which is far more helpful.

It was also super tricky to identify as it only did it under load. Fuel pressure was fine at idle, but as above, when tested on a rolling road it dropped from around 3 bar to 1.8 bar. The subsequent explanation was that the pump was weak, but could build pressure in time at most rev ranges. When flat out, it couldn't build pressure quick enough or maintain what it had already built and thus ran lean.

I've been fortunate enough to do a lot of the work myself, or for mates rates with my mechanic friend which has kept costs down, but diagnostics and parts still added up (I don't want to calculate exactly how much!). For anyone else chasing similar, my recommendation to hopefully cut to the chase with least cost would be:

1) Get the intake and vacuum hoses smoke tested - this was part of my problem (the stalling at idle went away after sealing the leaks). Hose from crank case to PCV was the first, and another from breather to turbo. There seems to be a multitude of places these leak, so rather than replacing parts blind a smoke test saves a lot of grief.

2) Get fuel pressure readings taken at the rail - even with sensors there's no guarantee what the car reports is accurate. I'm not sure the issue would ever have been identified without a rolling road... so either go somewhere that has one, or find a gauge that can be hooked up to the fuel rail and read from inside the car on the move.

If I'd started with those steps, I'd have saved a lot of time and money. I think in hindsight I'd still have put a front O2 sensor on it, as odd as it sounds that exacerbated the issue and helped isolate it. I suspect the old one was so used to reading lean it had fallen out of tolerance. A MAF sensor won't hurt but despite the code pointing towards it, that would never be my starting point again.

The PCV system was due to be replaced, so no harm done there, but it might've waited a bit had I not been chasing this issue down.

Thanks to all who pitched in with ideas, those who suggested it was fuel supply related were on the money. Again, after 8 months (half-heartedly at times admittedly) of chasing the problem, I hope someone else can make use of this and save on some of the cost and frustration.

tl;dr - combination of vacuum leaks and tired fuel pump were the issue .

[jonesg]

I thought vida could show fuel pressure or pump efficiency if monitored whilst driving.

[abscate]

‘Mates rates’




Glad you solved it, Troy

What were the age and miles on the fuel pump, please?

[DavidE7]

Hello Troy - I just saw your reply. I haven't logged in for a long time! Replacing the fuel delivery module is the easiest solution. There are good videos on YouTube. The fuel module is accessible from the top of the tank under the back seat for both plastic and metal fuel tanks. I did it to a 2004 XC70 that had a cracked and leaking plastic flange.

You can also remove the core from the Schrader valve on the fuel rail, attach a hose, turn on the engine with the end of the hose in a bucket, and verify that there is big fuel flow from the pump. It will also push out any large contaminants from the fuel system into the bucket. The fuel pump only runs for a few seconds each time the car is turned on to position 2. If the bucket isn;t getting a big swig of fuel every time the pump is activated, replace it.