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tristessa
Samba Member
Joined: April 07, 2004
Posts: 3992
Location: Portland, OR
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 Posted: Sun Jan 26, 2020 8:34 pm Post subject: Engine swap folks, check your fuel pump & fuel pressure! |
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Just a heads up, sharing what I recently found in case it's useful to anyone...
I've had a persistent P1136 " Long Term Fuel Trim Add.Fuel,Bank1 System too Lean" code on my AEB on my 1.8T swap for a couple of years. I had the injectors cleaned and flow-tested at the local Dr. Injector franchise at one point, and at another point installed a new genuine Bosch 4.0bar fuel pressure regulator. Nothing seemed to help but since it wasn't really causing a problem for driving and using the camper, I hadn't really pursued it.
Then I did a harness/ECM swap on the AEB, updating it to the wide-band-O2 ME7.5 system from an '02 AWM 1.8T with different -- higher flow -- injectors, and have been struggling to get the fuel trims dialed in. It's been consistently lean, and no amount of futzing with the tune or swapping to even bigger injectors was getting me anywhere on that front. Chasing my tail is such fun...
Last week I finally broke down, put a gauge on the fuel system and did some driving around, and saw that I'm getting maybe 3bar of pressure at the highest. I've been using the Bosch 0 580 463 016 fuel pump, which is commonly listed (Bughaus, Amazon, AutohausAZ and others) as a stock pump for Vanagon, EFI Bus, EFI Beetle and 914. After seeing the gauge top out at a hair under 3bar, I went looking for specs. According to what I found at Bosch Motorsport Australia's website, that pump -- which I'm sure many of you are also using, being that it's sold as a stock Vanagon fuel pump -- is rated at 75l/min @ 2.5bar .. which is kinda not enough for some engines.
I've ordered up a Walbro GSL392 to replace it after getting sticker shock on the Bosch 044, but either one should take care of any fuel delivery problems anyone's having...
Last edited by tristessa on Sun Jan 26, 2020 10:54 pm; edited 1 time in total |
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nsmal
Samba Member
Joined: May 09, 2019
Posts: 56
Location: San Francisco, CA
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| Posted: Sun Jan 26, 2020 10:48 pm Post subject: Re: Engine swap folks, check your fuel pump & fuel pressure! |
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| Interesting, thanks for sharing. I’ve been suspicious about the stock fuel pump being able to keep up with a larger engine. I’ll have to test my fuel pressure while driving. |
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tencentlife
Samba Member
Joined: May 02, 2006
Posts: 10075
Location: Abiquiu, NM, USA
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| Posted: Mon Jan 27, 2020 11:26 am Post subject: Re: Engine swap folks, check your fuel pump & fuel pressure! |
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-- is rated at 75l/min @ 2.5bar ..
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That's not the pump rating, that's the in-system rating. For this type of system to work (and it's the same type of system used on pretty much every EFI car made for the last several decades) the pump and regulator must be able to exceed 1 l/min. at 2.5bar head by a lot. The stock Digijet/Digifant fuel pump will dead-head at over 65psi, or 4.5bar. If yours doesn't develop that much then it's a tired and worn-out pump, or it's not receiving sufficient steady feed voltage, or there are inlet restrictions, although if the latter you would probably hear cavitation. 4.5bar is plenty to feed a 2.5bar regulator, but not nearly enough flow volume at that pressure to maintain stable pressure behind a 4bar regulator, you would want a pump that dead-heads at 7 or 8 bar if it were proportional to the stock pump/regulator combo. There needs to be a large share of excess flow for this type of regulator to maintain the specified constant pressure up to and exceeding peak fuel consumption for the particular engine.
I've said so many times here testing the fuel delivery system must be done as one of your earliest steps to diagnose any suspected FI problems because it's the foundation of the system and every other fueling function runs on the assumption that fuel pressure is being correctly modulated and delivery volume is more than adequate for the engine's peak fuel usage. But most people resist doing the simple tests, so they waste untold time and money guessing at other causes. You just learned, you can't short-cut this stuff.
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tristessa
Samba Member
Joined: April 07, 2004
Posts: 3992
Location: Portland, OR
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| Posted: Mon Jan 27, 2020 12:47 pm Post subject: Re: Engine swap folks, check your fuel pump & fuel pressure! |
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I'm just reporting what my experience has been and what I've found chasing the problem.
I'd had that P1136 code since nearly day one with the 1.8T. The pump was new when it went it, and it went in at the same time as the engine. The tank is clean, and the only thing between the EFI late Bay fuel tank outlet and the pump is some 5/16" Gates Barricade fuel hose, the stock early Vanagon square cube fuel filter p/n 133133511 and a couple inches of 1/2" Barricade hose connecting the 12MM filter outlet to the 12MM pump inlet. Prior to the 1.8T and this pump, the engine was an ABA/JH hybrid VW I-4 running K-Jetronic with an OEM Bosch pump and there was never a fuel delivery problem on that engine with CIS.
If the Vanagon pump I was using was down on delivery pressure, it was down since day 1. I was assuming that since everything was new and OEM brands from reputable suppliers, that it was all functioning correctly.
It'd sure be nice if we could find accurate specifications on parts from the manufacturer in 2020 so that people could make informed decisions. Between this fuel pump and some fuel injector data I was trying to find last year, I'd swear Bosch was deliberately trying to hide information from everyone. |
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