Fuel system priming - '87 300GD
Hi - hoping for some technical assistance regarding the priming fuel pump mounted on the engine block - should there be some resistance when I pump this? Please let me explain further... I suspect that this thread is a continuation of two previous entries regarding problems I have encountered in the last couple of months; 1. getting fuel to the injectors and 2. poor starting.
I replaced both fuel filters recently as I suspected a fuel supply issue (this led to thread No.1) but have continued to have problems (thread 2). This observation may however offer further help in resolving these issues. During running the clear fuel pipe between priming pump and cartridge filter is full of air bubbles - and these show no sign of clearing when engine run plus no sign of fuel leak anywhere else in system. Pumping primer has no effect or 'resistance' (I tried one on similar engine and could feel 'pumping' effect). Could these issues be related? Is it possible a seal has perished in this unit causing air ingress (stood 10 years covered in shed until I purchased), is it easy to replace/repair, can I replace the whole unit, anyone have one (expensive?), easy to remove...red herring?
Very grateful for any assistance - just driven 750 miles round N. York moors on family New Year holiday so still working OK (sort of) - just about got used to crawler lanes up hills (god bless 88hp although suspect running on significantly less) - goes as fast as me solving these technical issues! However, throw in a caravan (the parents - annual drive in search of snow; failed this year) and I feel almost embarrased for Mercedes by having to use first gear to get up some hills. Plenty of cars certainly queueing up behind to see the raw power of a normally aspirated 300GD Mercedes G-wagen?!?
Wishing you all a happy New Year
Stewart
Hello Stewart,
You must feel a light resistance in the pump whilst priming. Check your engine oil dip stick and look at the oil viscosity, is too liquidy, runny and has a whiff of Diesel? If so, suspect the priming pump seals to be leaking.
Check the part number by your local dealer confirming with the vehicle's chassis number.
With a reference chassis number of W 460.322 - 300GD OM617.931/2
A 001 586 12 07 - repair kit of seal at £10.50, 2 days in ordering.
A 000 090 88 50 - Manual feed pump with seal ring at £21.30, 2 days in ordering. These prices have not included VAT. In my opinion the job is not difficult to do yourself.
Considering you have air bubbles in the clear tube is indicative of an air leak in the system. This can be the fuel filter seal(s). The seal could be the banjo nut seal or the fuel filter seal, make sure the old seal from the old filter is not still stuck in the filter housing groove, the fuel hoses to and from the fuel filter housing; filter housing to fuel pump or the priming pump seals. To test these out you need a vacuum pump attached with a fluid collecting vessel or at a suit point remove fuel hose from the filter housing block that end and detach the fuel hose from the pump side, apply vacuum and check your gauge to see if the vacuum is maintained, if not you want to narrow down to trace to the leak and cure that. If the section inbetween the fuel housing and pump are fine then the awarkward section to test is the fuel housing and back to the fuel sender unit.
Alternatively, using some form of thick gel or even chassis grease, smear this around the fuel hose ends withe the engine runing and see which hose end the bubbles clear, from that you can deduce which hose end is the cause of your problem. Clean the grease off after your diagnoses.
Cheers,
I had a very similar problem on a 300GD I had bought from a deceased estate here in Australia. I replaced everything under the bonnet trying to eliminate the air bubbles you are referring too all to no avail. After much thinking and forum searching I checked the Fuel Tank sender and found the filter in the bottom of this to be virtually sealed off with black gloop (technical term that!) which turned out to be the after affects of an anti fungicide treatment in the fuel.
I removed the tank altogether and pressure washed it clean then dried it thoroughly before reconnecting. Once this was done there were no further issues.
If you send me your Email Address via PM I will send you a copy of the article I wrote for the AGOA newsletter, G’ocentric, which also includes a few photos.
Of course before removing the tank just remove the sender via the plug in the rear floor and check if it is blocked. Make sure you mark the lines to ensure you get them in the right place on refitting and I would also suggest you buy a new "O" ring for the sender seal. Just cleaning the sender filter will get you going for a while but it will stop you again further down the track if you dont clean out the tank properly.
I hope that this will help.
John
JOIN THE GWOA
This website and forum are provided for the benefit of enthusiasts and owners of all Mercedes Benz off road vehicles, in particular the G Wagen. The costs of development, upkeep and provision of the site are met entirely by the annual subscriptions of club members. If you are using the site and are not a member of the G Wagen Owners Association please consider joining. You will have access to areas on the site that are not open to non members, to club trips and meetings and to technical assistance. In addition your contribution (only £25 annually) will help us maintain and develop our website for future users.
Who's new
- Jaffa_JIM_23
- Wrabstar
- GG
- KTMSCANIA22
- 280ge
John,
Did check the sender unit recently and found it very clean (no technical 'gloop' to be seen). However will investiagate again although how did this cause air intrusion? Would be grateful for article and thanks for reply. Another consideration is that some of the hoses may have perished sufficiently to allow air ingress but not fuel leak - hence it would be useful to follow Rakesh's advice to try and isolate problem zone. All I need is some sunshine here (huh, not likely at the moment) or a garage to work in. Hmmmmm.
Cheers,
Stewart