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Discussion in 'Technical Q&A' started by pnorman, Feb 12, 2004.
Can a Bosch FI fuel pump get weak or does it work or not? Patrick
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Yes they can get weak. They are suppose to put out so much fuel per minute but don't have the specs at the moment. I think the workshop manual has the flow rate. Anyhow I've changed quite a few on 911's that are very similar, mostly due to being noisey and a few due to total failure and or weak output. If you do end up changing it I would reccomend changing the check valve also. Would be good preventative maintenance. I was thinking on changing mine shortly on my 85 QV. These cars are approaching 20 yrs. old shortly. Good Luck.
Your profile doesn't say what car you have.
I'm guessing it's a fuel injected 308.
The BOSCH fuel pumps can get weak. It takes a flow & pressure test to diagnose which require special equipment.
the check valve is built into the pump & i understand it's not replaceable. (Search the old FChat tech Q&A archives for 'fuel pump' and 'check valve', there are several threads.)
It is a FI 308. I have all the test specs just need to buy the CIS test kit. Last time it started, it ran for a few minutes and died. It did that twice before but restarted and ran well for several days each time. It's not the relay, fuse or shut off switch(when it's disconnected the pump runs). The only thing I haven't tested was the fuel pressure...Patrick
It is built in on my QV but I replaced the union with a union that had a check valve in it. It was very hard to find. They make another external check valve that fits a mercedes but it would require a banjo fitting.
I chased a hot missing problem on my 85 QV for quite some time. I bought a CIS test kit and it almost passed all the pressure tests. The only test it didn't meet was the flow test where the pump is supposed to flow 1000ml/min. My fuel pump put out 900ml/min. I measured my voltage at the pump with it running and I was getting a bit over 11 volts so I suspected my fuse box. I cleaned it, made sure all the connections to the pump were good and considered running thicker gauge wire.
Luckily, my pump finally gave out when I ran the fuel flow test again. I bought a new pump and car ran perfect again.
Pnorman: '82 GTSi here. traced my sporadic dying to fuse box that was starting to go bad, causing the fuel pump fuse connection to fail now and then; New boxes, trouble free ever since.
as a proactive move I swapped out my fuel pump and accumulator last summer (got both from FofUK as they were cheaper than any shop in US, and they are common Bosch parts!). Also replace all fuel hoses down there and reverse blew air into tank to help clear in-tank filter (which I bought new but old one wasn't comming out).
I have a 86 TR that has recently started making a loud vibration noise at the passenger side accumulator while the engine is running and hot. The fuel lines and the acccumulator vibrate so hard that it drums the frame of the car and makes a pretty loud noise inside the cabin. I'm guessing that I have a fuel pump going out. It takes the car about 45 to 50 minutes of driving before the noise starts up. Is this a common indicator of needing to replace fuel pumps or something else?