Fuel Distributor leak caused by clogged return line 1983 380sl

[rowdie]

If it were me I would remove the questionable pump and install the proper Bosch pump. Bosch 69609 Electric Fuel Pump | eBay

[meltedpanda]

that is why I was asking, seems like that pressure is too high from the pump. I fiddled with my Djet fuel pump specs for a long time only found one aftermarket pump that was even close to the range needed, and even that was hard to source

[Chris8]

Specs are seldom given for pumps (other than weight). Pelican Parts lists 3 Bosch and 1 "MB" (which looks like the first Bosch w/"zig-zag" sleeve at $100 more). All except the third Bosch have external check valves (my orig had internal) which moves the pump closer to the right wheel (works, but moved blue sleeve to get it under the clamp).

During search, only SpectraPremium and Airtex (from chain store) showed operating specs - max free flow, max press, min ff, min press are 3.8 LpM, 130.5 psi, 3.2 LpM, 101.5 psi; and 2.8, 100, 2.8, and 90 respectively (both of these weigh 1.5 lbs vs 2.2+ for Bosch/MB... 25% less metal). I've seen no spec for 380sl fuel pump pressure in manuals, inet search, or with Bosch pumps.

I read forums about Hayg pumps and saw no complaints - one guy with two failed Haygs also killed a Bosch (contaminated tank), but nothing on pressure. I wrote the Hayg seller to get pressure info.

With the Hayg, my system pressure was high (90 psi) and control pressure at upper limit (55 psi) which may be caused by high input pressure. As Rowdie suggested, I'll get the proper pump instead of shimming the regulator.

In meantime, the tank is gummed (new gas turned brown) so will keep this pump until it's clean. My old Chevy which always starts/sits next to MB, also has 7 yr old gas which is not brown/bad. I suspect the MB had tank problems before I got it because the top of trunk carpet was peeled back (the car came from someone's dead uncle in Nevada so it probably sat long/gummed up before I got it). There was no gum on end of hose scraping bottom of tank near filler, so I'm guessing it's concentrated in the sump/swirl pot area - little doubt the hole into swirl pot is clogged.

For now I've got to get the Taurus transmission pump/valve body parts off my kitchen table and back into the car so I can shuffle vehicles before the monsoon hits Wednesday.

[rowdie]

What year 380SL is this? Thought it was a 1984. Does not really matter as all 380SLs use the same. Bosch is OEM and the 69069 is the right one. Isolating sleeve, or whatever it is called, does not mean anything. If the one you removed did not have an external check valve it was not the original pump.

[Chris8]

Mine is an '83. I figured all 380SLs are the same.

The Hayg vendor said the pump I got has a range between 40 and 65 psi, which means it wouldn't meet the system pressure spec (5.0-5.6 bar, ~70-80 psi). Maybe he means this will be the pressure at the injectors. He said maybe my electrical system is causing the pump to overwork (too high voltage? which it's not). He sent a troubleshooting link and said they'd exchange it if defective. I don't see how a defective pump can put out too much pressure (unless there's an "overpressure bypass valve" inside).

I've no doubt the P/N you gave is correct. It could be the pump I pulled was replaced when previous tank work was done - it had a Bosch tag on it (and looks like the 2nd Bosch pump in the Pelican Part listing). The fuel system has been messed with - my fuel strainer doesn't look like an original - it's paper instead of fine screen.

I requested operating specs for Pelican's "5 thumb" Bosch pump (they use a different P/N notation [8-9? digits with a suffix], so I can't tell if it's a 69069).

Do you know the spec for 380SL fuel pressure (gauge hooked to output of pump/no return flow)? Maybe they don't spec this, but they should - somewhere said pressure is correlated with a certain flow rate (flow = zero when return line is blocked).

[Chris8]

Pelican answered quickly and said the manufacturer doesn't give them the specs. I'm not going to chase it down through Bosch, digging more on inet, etc, but assume the numbers I saw for the two pumps are typical (between 100 and 130 psi). I'm still curious if these numbers are pressure at a certain flow - a return line should never be blocked. I'll write back to the Hayg vendor about this (their troubleshooting info dealt with causes of early failure and low pressure)

My high system pressure could be caused by sticking components/more resistance in the system from gum deposits. After I clean the tank, run gas with cleaner through the injection system/engine, I'll recheck pressures. If SP (90 psi) and CP (55 psi) are still high, I'll replace the pump.

[meltedpanda]

lots of good info in this thread if you have not already read it.
THis was my journey on my Djet, but general info may help you

http://www.peachparts.com/shopforum/sl-forum/327148-djet-fuel-pump.html

[Chris8]

Thanks! I hadn't seen that. 40 years is a long time for a fuel pump.

Great info, esp this: "Those Airtex or other no-name pumps, and the pumps for the later model SLs do not have an integral relief valve. It is there for good reason. The Djets use hoses and clamps on the fuel system. Anyone know what pressure those would give way at? I don't know, but I suspect 50psig would be max. Therefore pump should relieve pressure below that. With a non-Djet pump, you could blow the hoses off and maybe collect insurance on the car when it catches fire " <--- [one should avoid this...]

So most (good) pumps DO have overpressure control. The return line shouldn't get clogged, but it happened on my car. The weak link on the SL is the short piece of clamped rubber hose between the main return line and that leading into the tank (crimped lines under hood look stronger).

Good to see those specs (sourced from a good discussion http://www.peachparts.com/shopforum/vintage-mercedes/298814-help-i-need-fuel-pump-300sel-109-056-3-5-bosch-0580-970-002-a.html). All are Bosches, so likely have relief valves - even the CIS pump at 6.5 bar/94 psi 300 LPH. They have to be tested with some kind of load/backpressure (there's really no pressure with free flow).

My pump has to be hitting >200 psi (est'd from pegged scale) - will try to remember to bring transmission pressure gauge fm MO next time (max = 400psi).

I'll ask the vendor if Haygs have a pressure relief valve.