Author Topic: Air leaks, diagnosing fuel system problems  (Read 11391 times)

Offline Tony

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Air leaks, diagnosing fuel system problems
« on: January 08, 2014, 11:26:39 AM »
Nick ha suggested a page on common problems with the fuel system (like air leaks, blocked breathers and tank vacuum etc) and how to go about checking/diagnosing these.  Sounds like a good idea to me.

So, what topics should we cover?


Offline greasemonkey

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Re: Air leaks, diagnosing fuel system problems
« Reply #1 on: January 08, 2014, 11:36:15 AM »
Ha ha ha. Thats it. I'm off to sniff some methanol.

I've been trying to cure an air leak since monday morning.
An injectors shot, the filter blocked, the lift pump packed in, and it started leaking air, all at the same time.
Now waiting on lift pump, hopefully friday.

I'll help write the page, after I come out of the psychiatric unit.
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Offline Twenty4Seven

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Re: Air leaks, diagnosing fuel system problems
« Reply #2 on: January 08, 2014, 01:25:11 PM »
Oh dear... that does not bode well for me GM as I'm very much an amateur mechanic.

With helpful guidance from Tony, I'm pretty sure I have an air leak on the Challenger.

So far, I've removed the intercooler and rear battery to get at the fuel filter and changed that. It wasn't bad at all to be honest. Had a hell of a job priming the system, but once I did manage it, it ran on tickover for about half an hour so I gave it a bit of a load by turning on everthing, lights, aircon etc at which point it stuttered and eventually stalled. It would not restart.

I don't think is is the pump front seal (Bosch VE on a 4M40 engine) based on the symptoms others have described.

I have some clear pipe and proper clips on order and my plan is to change the pipe between the filter and the pump to aid diagnosis. At Tony's suggestion, I'll also see if I can get to the tank strainer and check that the lines to/from the tank are clear.

It just occurred to me that this issue crops up pretty often and  a "how to" article for diagnosing and fixing this problem would make a usefull addition to the Wiki.

I'll be documenting my progress for the Wiki and if anyone has any other tips, I'd be really grateful.

cheers

Nick
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Offline greasemonkey

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Re: Air leaks, diagnosing fuel system problems
« Reply #3 on: January 08, 2014, 05:19:28 PM »
Right. A couple of E fags cut with methanol, and I feel a whole lot better.........

Air ingress makes me feel like an total novice, and I'm supposed to be trained.......

Some things that could be added to the wiki.
First thing about mechanicing,  never presume anything.

Classic example, I had loss of power.
I have a normal filter, followed by a good quality inline filter, which I use to bypass the normal filter on the side of the road, makes life easy. I find a crack in the glass tube of the inline filter, so obviously, that's where the air is coming from. Pull it out, still got problems, so obviously, the normal filter is blocked.
Change that, do a 70 mile run, goes fine. Turn round to come back, loosing power again.
Next morning, starts up and runs, no problem for 10 miles, return trip, goes like a dog, Plus an injector starts rattling. Pretending that isn't happening at the moment.

Into dry dock, clear pipe before IP, air coming in.
I've previously fitted a 8mm pipe from tank to lift pump, so obviously that has air getting in. Check unions, take them apart, new jubilee clips, still getting in. Drop tank, check unions on tank, maybe one was leaking.
Still got air getting in.

Change lift pump for known good one, still got problem. Known good lift pump is duff. It won't pump hard enough to pull the veg through the 8mm pipe. There's a lot more air in it than the original 6mm.

Have the brilliant idea of fitting an electric lift pump from a (retches) Freelander. Wire it up, turn it on, it makes an alarming groaning noise, blows a pipe off and squirts veg oil at high pressure all over the engine bay.
Decide at that point it's probably better wait for the new lift pump.

Point being, I could have ordered the lift pump Monday morning, if I hadn't been blinded by presuming it was a pipe leaking. As it turns out, there were air leaks, but that was not the cause of the problem, the lift pump was.

More things I'd add to the Wiki.
Chuck inferior quality filter housing off, and fit quality replacement parts. Be careful what you buy. I wouldn't buy the replacement filter housing I have again. It's a good CAV unit, but the seals are poorly designed, and it's fiddly to change the filter.

The filter cartridges are cheap, but they don't handle veg very well, they have a paper element in them. There are ones with a  different element, but can I get anyone to tell me what is what? Not a chance......

Buy some good fuel pipe online, Motor factors want body parts for a short length. When you need it, you need it then, not in two days time.

Keep pipe clips by you.

Collect odd lengths of pipe.

Get an electric lift pump off a (retches again) Freelander. They suck the fuel through like a good 'un. Just don't try to stop it.

Don't be afraid to cut off badly designed or poor quality parts, and move poorly placed parts into better positions. Under normal circumstances, most fuel system parts will never be removed in the lifetime of the vehicle, and filters will only be removed a few times, probably less than once a year. This is all they are designed to do. We need better stuff than that.

Don't put methanol in E fags.
« Last Edit: January 08, 2014, 05:22:40 PM by greasemonkey »
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Offline greasemonkey

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Re: Air leaks, diagnosing fuel system problems
« Reply #4 on: January 08, 2014, 05:40:14 PM »
Oh dear... that does not bode well for me GM as I'm very much an amateur mechanic.

With helpful guidance from Tony, I'm pretty sure I have an air leak on the Challenger.



I expect Tony has told you most of this already, but I'll try and make a few suggestions.

Has it got a lift pump? In theory, anything after the lift pump should be under pressure, so any air will be getting in before the lift pump, or, as I've just discovered, through the lift pump itself. Lift pumps really don't like dirt. The tiniest spec of dirt can hold open one of the valves, and stop it dead.
Some IPs will suck enough so that even with an under performing lift pump, the vehicle will still run OK, until the slightest bit of air gets in, then it's too much for it. The same amount of air could be getting in with a perfect lift pump, and never cause a problem.

You have quite a new vehicle, with common rail injection? So you won't be cracking off the injectors to bleed her.

Definitely, your first step is getting into the tank, and getting a clear pipe to the IP. See how it goes from there. You may have to rev the engine quite hard, to get it to pull the air in, then shut off to see the bubbles.
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Offline Rotary-Motion

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Re: Air leaks, diagnosing fuel system problems
« Reply #5 on: January 08, 2014, 06:49:04 PM »
if its the tranny your talking about my mate had the same issues changed everything and tank, after all its the shit standard filter and filter cart fitting system, change it stick a sausage init and never look back :)

Offline greasemonkey

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Re: Air leaks, diagnosing fuel system problems
« Reply #6 on: January 08, 2014, 07:10:26 PM »
The original filter has long gone. Also have a cleanable sausage in it.
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Offline Twenty4Seven

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Re: Air leaks, diagnosing fuel system problems
« Reply #7 on: January 08, 2014, 09:27:50 PM »
The first problem on the Challenger is locating the filter and just getting at it. Various suggestions include removing the rear battery and removing the intercooler. I found that, with a novice's toolkit like mine, you really need to remove them both....



Now the dog can see the rabbit......

I spotted that the end of the pipe on the input side of the filter was crazed - so I cut if off....



"That's it!!", thinks I.

So, I change the filter, put it all back together, prime the system (eventually) and it runs well until I give the engine some work to do, whereupon it dies again.

Episode 2 follows this weekend.
« Last Edit: January 08, 2014, 09:31:40 PM by Twenty4Seven »
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Offline greasemonkey

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Re: Air leaks, diagnosing fuel system problems
« Reply #8 on: January 08, 2014, 09:55:27 PM »
That filter housing does look like a disaster.
Is that a primer pump on top? Sooner or later, or maybe even right now, that is gong to cause you problems.

Imagine trying to change that filter at night, standing on the side of the road with sleet going down your neck.
And look at the shape of that pipe, pushed oval by the hose clip, so it lets air in. Probably not a serious problem, but proper hose clips don't do that.
And the bowl the filter sits in looks like pressed aluminium, never a good thing.

I'd be pulling it off and fitting a good one before starting anything else. Get a good primer bulb too.
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Offline Head Womble

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Re: Air leaks, diagnosing fuel system problems
« Reply #9 on: January 08, 2014, 10:07:00 PM »
Nick your problems sound like what I had on the old 406, it would tick over all day but died as soon as you put some load on it.

It turned out the IP shaft seal was gone, I found this by putting a clear pipe on the IP return (allready had one on the inlet),
by doing this I could see there was no air going into the pump but loads coming out, it was also a pig to bleed the system every time it died.

I had spent a month or so changing filters every week as it ran (but not quite right) with a squeaky clean filter, but as soon as the filter started to get restricted it pulled in loads of air.
« Last Edit: January 08, 2014, 10:12:09 PM by Head Womble »
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Offline Twenty4Seven

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Re: Air leaks, diagnosing fuel system problems
« Reply #10 on: January 08, 2014, 10:24:25 PM »
Thanks for the input guys....

GM - yes, that's the primer on top of the filter. I found that I could not prime the system using it after changing the filter. In the end, I filled the filter through the bleed hole using a lab type wash bottle.

Mark - thanks for the suggestion - I do hope it's not the shaft seal though - that would be way above my skill level to fix. I thought perhaps I could plumb a temporary reservoir of fuel alternately straight into the IP and then straight into the input side of the filter to eliminate the filter... or maybe just go straight for GM's suggestion and change the whole filter, housing an' all. Any suggestions of a suitable filter that would fit in there?

Cheers

Nick
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Offline Head Womble

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Re: Air leaks, diagnosing fuel system problems
« Reply #11 on: January 08, 2014, 10:31:25 PM »
Before you go swapping any hardware replace as much of the pipework with clear pipe, then you have a simple way of seeing where the air is getting in, ie. no air going into the filter but air coming out = filter / housing is the problem.
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Offline greasemonkey

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Re: Air leaks, diagnosing fuel system problems
« Reply #12 on: January 08, 2014, 10:32:52 PM »
Thanks for the input guys....

GM - yes, that's the primer on top of the filter. I found that I could not prime the system using it after changing the filter. In the end, I filled the filter through the bleed hole using a lab type wash bottle.



That might be because it is sucking in air..........
There is a great thread on here somewhere about fuel filter housings, with links to a supplier with some real good looking housings.
I'm drunk and disorderly at the mo, so I'll try and find it in the morning.

What womble said aswell, also. Cross posting.
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Offline Head Womble

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Re: Air leaks, diagnosing fuel system problems
« Reply #13 on: January 08, 2014, 10:36:07 PM »
Don't forget the very last resort is to add an electric in-line pump, this will pressurise the system in front of the IP and stop any air ingress problems.
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Offline Tony

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Re: Air leaks, diagnosing fuel system problems
« Reply #14 on: January 09, 2014, 08:27:41 AM »
Nick's system doesn't have a lift pump, it's a Bosch VE pump that sucks directly from the tank.  So any air leaks turn out badly.

I'm not a fan of Mitsubishi filter housings, especially with primers, they let air in too easily and have caused me grief before.

I think Nick's first step is the clear pipe between filter and pump, most likely this will show bubbles.  If it doesn't and the problem persists, then I'm with Mark - replace the return pipe (6mm ID on that car) and check for bubbles/creamy looking fuel in that as well.