Bucking under heavy throttle, small amount of air in fuel line

'04 TD5 in a Discovery 2 | 140,000km
Symptoms:
- Under heavy throttle, it will buck / kangaroo / fuel starve. This occurs if I force a highway downshift (not frequent) or when I'm attempting to pass - but not quite to a down-shift.
- Initial morning start, the fuel pumps whines as air purges - about 1-2 seconds. It's possible that this is residual from last night's pump change - but it sounds like my 'pre-pump' condition.
- Starts promptly, idles smoothly, pulls as it always has (slow and steady?). Generally runs well and fuel economy is as expected.
What I've done:
- Replaced fuel pump: I replaced the original fuel pump last night with a VDO unit. This immediately resolved a non-start condition that occurred after I was trying to diagnose the pre-existing bucking
- Replaced the fuel filter: The VDO packaging / Paddock told me to. NOTE the pump screen was not especially grungy - especially given this truck's history... She's spent some time in a couple less developed countries
- Exercised and lubricated the waste gate. I removed the vacuum actuator and checked the waste gate. It was not bound - but did have a tiny catch at the extreme of travel. A bit of WD-40 (yes, I realize this is not a lubricant) seemed to eliminate the catch.
- Checked the boost controller: Using a Nanocom, I can hear the controller actuating (rapid cycling / clicking) it sounds like others found on YouTube. The controller module was replaced, along with vacuum hoses about 3 years ago.

What I need to do:
- Check the turbo hoses - haven't done that in a while.
- Check the ECU harness - the injector harness was replaced a few years ago, and I check the harness annually. Need to re-check.
- Replace fuel pressure regulator - I previously replaced just the vacuum / pressure module, and should have replaced the whole thing. No evidence of significant leakage - last time there was an actual drip. I bought one earlier this year and haven't taken the time to install.

Questions for the group:
- What am I missing?
- Injector seals: I don't have rising oil levels - but I'm wondering is one of my seals is failing. Can an injector seal result in loss of performance under heavy load? It may be the source of air at initial start-up. I'm parking in a non-sloping location tonight to see if a different orientation helps the initial fuel pump whine / purge.
- Injector seals: I'm a bit intimidated to take on this task based on the videos I've seen. If I buy the spendy injector removal tool - is this within the grasp of a competent DIY'r?
- Non-return valve: Apparently there are a couple of inserts on the fuel filter housing. i don't have any starting issues (it turns over promptly and reliably), but could these cause heavy-load bucking?

My family really likes this truck - and it's been pretty faithful. The bucking is a pretty discrete problem that I'd like to solve - and I don't want to bodge-up my new fuel pump unnecessarily.

All input is appreciated. Thanks for reading.
Andrew

Sounds like you’re maf sensor is duff, unplug it and see it the problem comes back

Detroit Disco said:

Symptoms:
- Under heavy throttle, it will buck / kangaroo / fuel starve. This occurs if I force a highway downshift (not frequent) or when I'm attempting to pass - but not quite to a down-shift.

Click to expand...

As you have nanocom put it on inputs fuelling and record a live data log on SD .... watch the screen when the symptom occurs cos i have the feeling that you'll see the MAF going up to 680 then to 0 ... the ''classic "MAF cut out" symptom...if it doesnt occur with unplugged MAF and the MAF is a good genuine one it means there's a boost leak somewhere and the sucction grows too much while the boost doesnt build up as expected.

Resolution:
In the end, I replaced the fuel pump + filter, cleaned the MAF, cleaned / lubricated the wastegate, and all is well. Some observations on the fuel pump:
- Easier to replace than expected.
- Removing trim bits is unnecessary
- Special tool for removing the fuel pump retaining ring is unnecessary

Thanks to all for the input.

Detroit Disco said:

I replaced the fuel pump + filter, cleaned the MAF, cleaned / lubricated the wastegate, and all is well.

Click to expand...

nice one.... so let's guess what was the problem now ? pump, MAF or wastegate ... ???

Primary issue seems to have been fuel pump - resulting in fuel starvation under heavy load. The pump finally failed in my driveway (Murphy and his law were sick that day). After the pump was replaced, there was still some bucking / kangaroo under load that was cleared up with the MAF cleaning. It's possible that the MAF is due for replacement - the numbers I'm getting with a Nanocom seem a bit lower than those that I've found on the internet (IIRC - topping out around 530 or so on my truck). For the moment, I'm focused on getting the sunroofs re-sealed and the headliner replaced before winter. A 2CV took the truck's slot in the garage - and I was starting to get water in the Disco's cabin.