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Fuel trim

Discuss your latest mods or ideas, and anything to do with the BMW X5 (E53).
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henrym3
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Fuel trim

Post by henrym3 » Wed Jul 22, 2026 6:28 pm

Multiplicative is of the scale as is LTFT so the suggestions are big vacuum leak, low fuel pressure with possible ccv diaphragm split, o2 pre cat sensors or MAF. Odd thing is that it is running well, no stalling, hesitation or any other issues. I was just playing about with the diagnostics cos I was bored. So started with a smoke test. Had to abandoned that as there was so much smoke pouring out from the inlet pipe where it is jubilee clipped to the throttle body, throttle body to inlet manifold and the bit the throttle body connects to has another seal. Ordered the bits from BMW. Got them fitted and the smoke machine back on and one of the pipes from the LPG injector to inlet manifold is leaking. Fixed that and got the fuel pressure tester out. 2 bar pressure. Changed the filter, what a bloody difficult job just getting to the filter. Run fuel pump from diagnostics and get 2 bar. So now got a fuel pump on order. Oh, the new heater valves I fitted in January are letting hot air bleed through when a/c is on, the bottom couple of vents allow the hot air in. Changed them, luckily they were 10 year warranty so should get my money back. Hopefully when the pump comes that will cure the pre cat o2 sensors permanently reading 1.04 and that will be all the problems fixed that I didn’t even know I had. It’s been a great week.

Leslie
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Fuel trim

Post by Leslie » Wed Jul 22, 2026 8:43 pm

Was the heater valve a cheap ebay special ? , I've ordered a bosch one for my e70 of Autodoc as I was wary of the cheap ones were just too cheap on ebay circ 25 quid.
2 bar isn't enough should be at least 3 id think for older petrol cars , at least you found a few leaks you didn't know you had :rofl:

on a different note I found the rear 30 cm of my passat sills was detachable by hand :rofl: aka rotten to hell , spend 3 days under it welding so far ,still a bit to go ,id swap your issues for mine as welding inner sills under a car with about 30cm headroom in 20c heat ain't no fun :headbang:

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henrym3
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Fuel trim

Post by henrym3 » Sat Jul 25, 2026 12:59 pm

Well I payed £39.99 and it had a 10 year guarantee. So at the time I thought they must be confident in the product. When removed I plugged it back in and operated the temperature controls and you could see that the brass cones weren’t fully seating and would allowing coolant to bleed through. They have finally agreed this morning to replace the item. I’ve taken another one rather than the money as I only payed £24 for the one now fitted. Which probably guarantees that the £24 one will work for ever.
I h’ave decided to replace just the fuel pump rather than the whole cradle as they now seem to sell them separately, obviously I didn’t think it through enough as I can’t fit it as I haven’t got a jubilee clip small enough to secure the pipe to the pump, I’ll go and get one after I’ve watched f1 qualifying. If this pump doesn’t get me 3.5 bar I’ll be stumped.
You’re welcome to your welding task, I’ve had to give it up as I’ve got a bit of hand shake these days, something for you to look forward to as you age. I suppose if you wanted something welded in a zig zag pattern then I’m your man.

Leslie
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Fuel trim

Post by Leslie » Sat Jul 25, 2026 5:50 pm

I seen a few things guaranteed on ebay and have had replacements sent out before of cheap bits and although replaced it lasted no time either and in the end had to buy a more expensive one. My welding ain't anything to write home about either but it gets the job done , it doesn't need grinding much as its only an mot quality repair and is hidden by the skirt and certainly isn't worth spending much time on as its probably only got 1 more mot left now.

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