312D veg oil and limp home

[Bill312D]

I fitted a smart veg 2 tank veg oil kit to my sprinter 312D a few weeks ago, it ran sweet for a few days then once at high revs in 4th goin up a hill the engine lost all power and wold only comfortably rev on the flat to about 2500rpm under load and wouldn't exceed about 60mph, would go faster down hill, the engine would also only rev to about 3600 ish rpm in neutral instead of going up to about 4200 then bouncing like normal, i have been tearingthe kit apart and re building it for days trying to eliminate any air leaks that could be causing a build up of air in the re circulating loop in the fuel system andthings and after taking it for a drive today to try and find the leak I reliased that after the power was lost, if i just stopped turned the ignition right off and on again the van worked perfectly, this lef me to thinkt hat the van was going into th elimp home mode i have read so much about, i couldn't actually get it to do it again tonight the thing would cruise along at 90mph instead of cutting off th epower at about 75-80 like 'normal'... . as it always seemed to happen in 4th or 5th gear at around 3500rpm. 1 thing that leads meto ebliev their could be a fuel problem is sometimes again at high revs doin about 80 it wouldhave a tiny tiny loss ofd pwer for like haf asecond then keep reving as normal, these would somitmes come ins sall bursts or singlarly thnthe van woudl continue as normal, or a few woudl then lead to complete power loss as mentioned earlier.

So is this limp home mode? and What coud be causing it? the veg oil is all heated and essentially like diesel when it goes through the pump and the engine so viscosity shouldn't be an issue. I am very confused any help would be much appreciated.

 

[Sprint'n'Go]

How does it run on Diesel? I would have thought that was the first test to make sure this is not just a coincidence. It may be nothing at all to do with the veg oil but it is quite odd that it has happened now. I am sure some of the forum members with veg oil experience will have an idea of what might be wrong.

 

[Bill312D]

It runs ok on diesel but i never use it on diesel for as long as veg as it costs twice as much.However once th eproblem occours, if i purge the system with diesel it doesn't rectify itself, was doingthis to flush out the air bubbles, which it seems were never there...

 

[Hibbo]

Sounds like fuel starvation or air ingress.

Have you changed the filter since running on veg? Veg cleans out all the crap from your tank and deposits it into your filters.

 

[Bill312D]

i am 99.9% sure there are no air leaks and due to the pruge valve any small amounts of air that could build up would eb flushed away when i do a diesel purge, it does nothing and the magical fixing of th eproblem when i turn it off and on again leads me to think its something to do with the engine managemebnt system, no liughts come on but revs are limited to 3600 or so even out of gear as i mentioned earlier. Smart veg reckon it could be because there is no pressure onthe outlet of the fuel pump as when the fuel is recirculating through the loop the intake onthe injection pump is basically suxking straight out of the return on the pump, so they are sending me a 1 way valve to go betweenthe valve manifold and the IP return to give bit of back pressure for the IP, and if pressure is the problem, which it should be (/I hope) this should give the sensors in the pump the redings they want. I'm gonna try this before i go to merc as they don;t seem very helpful onthe phone and want £40 at least just to diagnose the fault for me!! and i havn;t found alocal independant specialist yet who has the S.T.A.R software for commercials.

 

[Hibbo]

Does the return loop to before or after the lift pump?

 

[Bill312D]

the loop comes from the return ont he IP into the vale manifold, with a closed flush valve (i.e fuel is recirculating) then back out of the valve manifold into the heat exchanger out of the heat exhanger and back into the pump input.

 

[Hibbo]

So the fuel is returned AFTER the lift pump then? In this case the IP return will be at positive pressure (the pressure generated by the lift pump).

 

[Bill312D]

yeah, i am looking at gettingth epressure back to negative or nill...nearer to wghatever it would be when the pipe just returns to a tank.

 

[pcman_jh]

Veg oil conversion - my experiences, which I should sell!

I have a 2 tank system on my '99 E300. You're describing (experiencing?) classic fuel starvation due to -

1) If its the *first* cold start of the day, or had the engine off for more than 4 hours, AND you've only travelled less than 5 miles since starting, then it's fuel *gelling* in the fuel filter which leads to fuel starvation. The cure is to either buy a fuel heater or drive at less than 50 and *don't attempt* even moderate hills until the engine it fully heated (as per temp guage) *AND* then another 5 miles for the fuel filter element to fully heat up - no exagerration.

DieselVeg do a silicon based wrap for the fuel filter which helps alot, but doesn't cure fuel gelling.

or

2) If not the above and the engine AND fuel filter has fully heated up - after about 5 miles (yes 5 miles), then it's fuel starvation and you need to change the filter, but see tip below.

Just weeks (or was it a week, I can't remember) I had the same symptons - when cold and if you attempted to go up even *mild* uphill roads, or try to joint a main road which means getting to at least 60 mph as quickly as you can, you'd get a real flat spot with the engine feeling if it was missing and sometimes whitish smoke out the exhaust. After many sleepless nights thinking the pump had been blown etc, I've realised you need to drive on roads that allow a gently heat up - even if it means detours to avoid trunk roads and any moderate hills where you'll not hold hte traffic up.

Tip - My experience is you *cannot* run on 100% veg in the main tank without having to change drive characteristics. The reasons are - 1) I've found you need to add about 10% diesel to the veg to aid combustion - because otherwise you'll get noticeable flat spots and 2) Fuel gelling when cold although a fuel heater doesn't absolutely cure the fuel gelling, it only makes the effects last shorter.

Hot off the press - This week only I've been experimenting with adding 10% unleaded rather than diesel, and its not looking good. The general opinion is petrol is better than diesel as it has better combustion. I'm finding (hoping?) that after about 15 miles the engine had a definite characteristic where it's like someones putting the brakes on as the engine speed drops about 500 revs then return with this cycling like this every 30 seconds (it's still smooth unlike fuel starvation where the engine starts to hunt/lightly miss). If I switch to pure diesel (via my 2 tank switch) the sympton dissappears within seconds. Since it's never done this in 11k miles and only happened since I put petrol in, I'm putting it down to the petrol. If anyone's any opinion on this, let me know without highjacking this thread.

I converted mine back in Sept last year and have now done about 11000 miles and *many* days of lost sleep as I found out the hard way that the drive characteristics - giving it time to heat up AND adding about 10% diesel to veg was the best combination.

Hope this helps.

 

[Hibbo]

How on earth will an NRV help you achieve that? (Which is the opposite of what you said in post #5! v confusing!)

 

[Bill312D]

pcman JH, the problem occours even when the engine hs been warm for a good 20 minutes or more, as it only haoppens on the motorway or other fast roads, whenthrashing it a bit, like if i short hsift in 4th and go into 5th at 65mph it will not give me any trouble until have ben doing about 90mph for a bit. but i am running on pure veg and i didn't change the filter when i fitted the kit, but it was pretty new and only done about 1k. I am strugglign to see how the problem could be with the filter as the problem is cured form a simple switching off and then on of the engine, instantly. unless swithcing the engine off allows any debris in the filter to float back to the bottom of the filter very quickly which makes the problem disappear until another period of sustained high revs?

The possible problemw itht eh pump is there is no back pressure because the fuelis being sucked out the nrv which i can adjust the resistance on a bit will get the pressure at the pump outlet more like it is at stock when it is simply connected to the return pipe rather thanthe re circ loop.

 

[Hibbo]

pcman JH, the problem occours even when the engine hs been warm for a good 20 minutes or more, as it only haoppens on the motorway or other fast roads, whenthrashing it a bit, like if i short hsift in 4th and go into 5th at 65mph it will not give me any trouble until have ben doing about 90mph for a bit. but i am running on pure veg and i didn't change the filter when i fitted the kit, but it was pretty new and only done about 1k. I am strugglign to see how the problem could be with the filter as the problem is cured form a simple switching off and then on of the engine, instantly. unless swithcing the engine off allows any debris in the filter to float back to the bottom of the filter very quickly which makes the problem disappear until another period of sustained high revs?

The possible problemw itht eh pump is there is no back pressure because the fuelis being sucked out the nrv which i can adjust the resistance on a bit will get the pressure at the pump outlet more like it is at stock when it is simply connected to the return pipe rather thanthe re circ loop.

Hi again Bill, there WILL be pressure at the pump outlet, about one bar infact as this is at lift-pump outlet pressure. (As I understand it from your description)

I am nearly certain that your fuel filter is blocked.
The fact that it was nearly new is irrelevant; VEG OIL IS A BRILLIANT CLEANER. Your van is nearly 13 years old and I guess has quite a mileage on it, you will now have 13 years' worth of crud in your 'nearly new' fuel filter. (When I first ran my '83 300D with 190k on the clock on veg, it got through two canisters and two pre-filters)
Switching off the engine removes the forward pressure from the filter and allows some of the crap to fall away from the filter membrane (how I had to get home when my 190 had it's first dose of veg)

Always keep things simple Bill, don't try and look too deep till you've done the easy things.

Change your fuel filters and see how it goes then.

 

[Bill312D]

yeah, i am guilty of looking for a big problem...i'll graba filter and see what happens. I know ther eis meant to be some pressur eonth eoputlet, but with the re circ loop it is wrong apparently....get a filter the NRV is inthe post and was free and we'll see what happens, thanks for the help. Hopefully i wont have to bump this one back up.

 

[Hibbo]

Don't forget the prefilter!

Please do let us know how you get on, good or bad.

PS. your typing is getting harder and harder to understand!

PPS. there will only be suction at the IP outlet if the return is looped to BEFORE the lift-pump (ie into the suction line from the tank)

 

[Blobcat]

yeah, i am guilty of looking for a big problem...i'll graba filter and see what happens. I know ther eis meant to be some pressur eonth eoputlet, but with the re circ loop it is wrong apparently....get a filter the NRV is inthe post and was free and we'll see what happens, thanks for the help. Hopefully i wont have to bump this one back up.

I think you need a new spacebar as well as a filter

 

[Bill312D]

Anyone know what filter fits a '98 sprinter? havin a lok on diesel veg and all the numbers mean nothing to me.

 

[Bill312D]

sorry about the typing my coordination, or concentration sometimes goes, i thought the lift pump was part of the IP as I have a diesle tank with no lift pump and the ip gets diesel fine, I though tonly common rails used lift pumps.

 

[Hibbo]

The lift-pump is on the side of the IP, the normal flow is:
Tank > prefilter > lift-pump > main filter > IP

 

[Bill312D]

I havn't fitted a pre filter before the main filter and i don;t think there is a stock one there?