Over pressure on fuel blow off pipes

Stevie · Post Sat Jul 10, 2021 10:50 am

Hi all, help needed please and thanks for looking. Noticed a diesel pool under car & after taking off air box noticed fuel around injectors. Changed the blow off pipes as one had a little tear and also did injector test which seemed ok. So I now have no leak, but upon start up the blow off pipe that fits to injector on battery side of car almost doubles in size & then blows off, obviously got some over pressure going off somewhere? Anyone out there had same sort of problem, Don't really know where to start from here, any help much appreciated, thank you..

Arfur Dent · Post Sat Jul 10, 2021 11:08 am

Stevie wrote: ↑Sat Jul 10, 2021 10:50 am Hi all, help needed please and thanks for looking. Noticed a diesel pool under car & after taking off air box noticed fuel around injectors. Changed the blow off pipes as one had a little tear and also did injector test which seemed ok. So I now have no leak, but upon start up the blow off pipe that fits to injector on battery side of car almost doubles in size & then blows off, obviously got some over pressure going off somewhere? Anyone out there had same sort of problem, Don't really know where to start from here, any help much appreciated, thank you..

Hello Stevie

Typically the blowing off of the leakoff connectors are due to worn out injectors.

How did you do the injector test?

Stevie · Post Sat Jul 10, 2021 11:25 am

Thanks for the quick reply, did the test with injector kit, not a DIY one. All seemed pretty close to one another.

: Test

Arfur Dent · Post Sat Jul 10, 2021 11:47 am

Stevie wrote: ↑Sat Jul 10, 2021 11:25 am Thanks for the quick reply, did the test with injector kit, not a DIY one. All seemed pretty close to one another.
IMG_20210709_135326795.jpg

Yes, they all do look similar. Not the usual one that towers above the others.

Stevie · Post Sat Jul 10, 2021 12:01 pm

The car drives fine, even when it was leaking fuel, plenty of power, to be fair it pulls even harder with air box off, so this doesn't draw me to a bad injector. Would a failed fuel pressure regulator cause the pipe to blow off? Thanks

C3driver52 · Post Sat Jul 10, 2021 3:31 pm

Stevie wrote: ↑Sat Jul 10, 2021 12:01 pm The car drives fine, even when it was leaking fuel, plenty of power, to be fair it pulls even harder with air box off, so this doesn't draw me to a bad injector. Would a failed fuel pressure regulator cause the pipe to blow off? Thanks

Is there a pressure difference in the fuel tank? Can you remove the fuel filler cap and listen for a sound. Also does the leakoff pipe still blow off after or with the fuel filler cap removed?

Your leakoff test shows either 4 bad injectors or 4 good ones. There isn't one that stands out as bad.

Did you time the test and measure the RPM so we could work out if the leakoff is excessive or to be expected?

You should get fault codes stored if the fuel pressure regulation isn't working correctly, are there any codes stored?

Stevie · Post Sat Jul 10, 2021 6:40 pm

Hi c3drive, yesterday i did take filler cap off while running & made no difference or sound, no hiss of pressure when unscrewed either. I didn't time the pressure test, just did it on idle for couple minutes. However, it's thrown a couple of codes up today, Po238 boost sensor circuit high & Po203 injection circuit open cylinder 3. Very much doubt all four injectors gone at same time & it's not lost any power & actually runs fine. Very strange it runs fine while leaking, but stem the leak & seems to build to much pressure somewhere. Thanks

C3driver52 · Post Sat Jul 10, 2021 6:52 pm

Can you get pressure into the leak off pipe to the fuel tank and will it hold? I'm expecting it should leak away, back into the tank.

I think the leak off fuel will go through the fuel cooler and back to the tank.

If the return pipe is damaged by crush or crimp, or just blocked, the engine would run OK, the leak off pressure would build up quickly and blow a connector.

Stevie · Post Sat Jul 10, 2021 7:41 pm

Thanks buddy, will have a look at this tomorrow, wanted an easy day, not pissing about with that again.. A mate said there's a game on tomorrow or something??

Stevie · Post Mon Jul 12, 2021 4:51 pm

Update on problem. It's the little black non return valve that's given me the grief, seized up a little, very hard to push open. Was obviously putting pressure on fuel harness which led to my leaks. Done my head in, but grateful it's a couple of quid part and not an injector or other expensive bit. Hope this may help someone in the future. Thanks for the replies, no doubt I'll be back soon, it's a Citroen....

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Over pressure on fuel blow off pipes

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