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Discussion Starter #1
Now then fella's. I'm new to this forum and could do with some help from you guys hopefully. I think the American chaps might be able to help me out here, as there as so few 760's e65 in the UK now, and everyone wants to dodge them. So long story short, I've had this car for just short of a year, and it's fantastic. However, I've been chasing a problem for around 6 months, and it's steadily getting worse. As it stands, on a cold start, it will misfire like mad for 30 seconds, engine management light will flash, then it clears itself. When you initially try to take off, it hiccups quite badly, but once it warms up, it's better, but never perfect. If you turn it off, and back on, after it's been used, it starts fine. It never threatens to stall. It's like it's just missing on the lower rev range. The low end city driving is quite poor now, as it will fluctuate its rpms when you press the accelerator. I started basic, all new plugs, smoke tested, new air filters, injector cleaner. No difference. It has 138000 miles by the way, full service history. Changed both air pump valves, replaced secondary air injection pump, had it to a specialist, who changed the viscous fan and fan clutch, engine temp stat and nearside air mass meter. Still not right. Apparently it had a high concentration of fuel in the oil, so they are now saying injectors. I'm about 4 grand into this, and I'd like some input from someone who has worked on these before. There is minimal carbon build up on the intake ports, as I have the intake in bits at the moment while the injectors are cleaned. Any direction would be greatly appreciated. Cheers robbie
 

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Discussion Starter #2
Forgot to add, only fault codes I get are misfires. That's it. One morning it will be misfire cylinder 1. I'll clear it. A few mornings later, misfire cylinder 8. Next morning misfire cylinder 11. Seem to be random, and not justified to one bank.
 

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I would first be sure the high pressure fuel pump inst leaking internally. I believe there is a vent hose on top of the fuel pump that has a hose clamp, take that line off and see if you find fuel. If you find fuel then you have a bad fuel pump. Check for fuel on both banks at each high pressure fuel pump.
 

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Discussion Starter #4
Hi matey, thanks for the advice. I'll have a look over the next few days. I've had a browse in the 2 vent tubes before, on the right hand side of the engine, to the purge valves, but can't say I've ever seen any fuel in them, however I've never removed the tube on top of the pump itself. Surely, if the hpfp was leaking, it would only affect that one bank of cylinders, and I wouldn't get misfires across both banks. What do you think. The issue does feel like its air/fuel related. I have the injectors out of it at the moment, and they are just being tested and cleaned.
 

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Hi matey, thanks for the advice. I'll have a look over the next few days. I've had a browse in the 2 vent tubes before, on the right hand side of the engine, to the purge valves, but can't say I've ever seen any fuel in them, however I've never removed the tube on top of the pump itself. Surely, if the hpfp was leaking, it would only affect that one bank of cylinders, and I wouldn't get misfires across both banks. What do you think. The issue does feel like its air/fuel related. I have the injectors out of it at the moment, and they are just being tested and cleaned.
The fuel pump leaking would bleed pressure from the supply lines at both high pressure fuel pumps back into the tank and when the vehicle is started it wouldn't have to refill the fuel lines and build fuel pressure back to the high pressure pumps. This would be true for both fuel pumps ie both banks. Generally it will also show signs of an extended crank time. I know I have seen idling issues due to carbon building up on the tip of the injector creating incorrect fuel spray, but the times I've seen this it was a constant misfire at idle and would not matter if the engine was hot or cold.
 

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Discussion Starter #6
Ahhhhh OK that deos make perfect sense. When do you think I should look in the pipes, should I take her for a run, and look as soon as I stop or leave it overnight. What sort of volume should I see, a pool of fuel, a drip, a damp end?? Forgot to mention, this makes no difference to the running of the car, but started around the same time, if I take my foot of the accelerator, the revs will drop to idle level, then slowly start to rise again. Its a lot more prominent at lower rev ranges ie between 1-1500 rpm. If you release the accelerator at around 2300 rpm you get a slight dip and then straight back
 

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Discussion Starter #7
Hi ABoismenu

So ive got the car back together, with the tested and cleaned injectors in. Started terrible again, sorted its self out after 30 seconds, drives slightly better. Gonna see how it starts in the morning, as it had to build up fuel pressure. I checked the 2 quick release vent valves, there wasnt any fuel in at all. The oil does smell a little petrolly though. Should I check on top of the hpfp themselves too.
 

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Hi ABoismenu

So ive got the car back together, with the tested and cleaned injectors in. Started terrible again, sorted its self out after 30 seconds, drives slightly better. Gonna see how it starts in the morning, as it had to build up fuel pressure. I checked the 2 quick release vent valves, there wasnt any fuel in at all. The oil does smell a little petrolly though. Should I check on top of the hpfp themselves too.
I'm not sure where you checked for fuel but I would check where I have the red circles. https://drive.google.com/open?id=1OrLFwk-wVwqFjJMseS9108uPaD9szvGa
 

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Discussion Starter #9
Okie cookie, thanks ever so much. So I've just been and, and removed the jubilee clip on the nipple on top of the hpfp as per your diagram, and each one had a droplet of fuel that dipped out when I removed them. The car has not been used for 24 hours. There wasn't a huge amount, it didn't flow out, but when I removed it, and turned it to face downwards, I did get a full droplet out of each one. I'd say the same on each side. Would this be a indication of 1 or 2 failing pumps. Would I get away with replacing the diagphrams. Or is the amount what you would expect to see in a healthy system. Thanks for your help by the way. Ive had this into a couple of indy garages now, and nobody has been able to identify the issue.
 

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I may be incorrect in saying this but i'm pretty sure there should be no signs of any fuel inside the vent. There is a sticky on the high pressure fuel pump diaphragm I would suggest you read, it should tell you everything you need to know.
 

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Discussion Starter #11
Thank you ever so much ABoismenu, I belive your right. I've been speaking with a chap from [email protected], and he sells a diaghram kit to repair both pumps, that's as near to oem spec as possible. He is in the cech Republic, and can have it too me in a few weeks. So I'll give it a go, its better than shelling out a few grand on pumps. With the fuel being in the vent line, that would indicate the diaghram wouldn't it. I'm going to try the vent solinoid on the firewall too, just to be on the safe side.
 

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If I was in your shoes I would definitely try the repair kit because I know those fuel pumps are extremely expensive. I'm glad I could be some help. Good luck with the repairs, I hope it takes care of your issue.
 

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What year is your 7? It would be great if you could let us know of any changes in your situation! Having similar problems on my 06' 750Li. Been trying to figure out the problem for a good year+ now.
 

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Discussion Starter #16
Hiya buddy, no I'm still non the wiser at the moment. I've ordered some new fuel pump diaghrams. But it still starts rough. When you try and move off it loses power, but once warmed up, it's better. Not 100%, but about 90%. To add insult to injury, I've now got a coolant leak somewhere. It's a 54 reg by the way
 

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Discussion Starter #17
And ABoismenu is right, the 750 doesn't have the hpfp's like the 760's. Once I've got the diaghrams changed over, I'll let you know how she runs.
 

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Discussion Starter #20
To be honest, I'm not quite sure what the next step will be. I've done plugs, maf sensor on o/s, engine coolant sensor, viscous fan and fan clutch, injectors out and tested, cleaned, secondary air pump, air check valve n/s, oil change, new air filters, and the only codes I get at misfires, which are different all the time, I do get a cat convertor code, but if its seeing a misfire every cold start, it's gonna upset the cats and lamda sensors. The back of the valves don't look to bad for carbon. I'm about 3500 into repairs now, and I will have to knock it on the head at some point, regrettably.
 
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