2.5 M51 poor starting hot or cold

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landyboots

Active Member
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330
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Republic of Austerity
Hi all. Have a difficult one to ask you all. I have been trying to work out what would cause this problem, for quite a while now. My classic Rangie has the BMW M51 engine fitted and it is a pig to start hot or cold. I have to put heat (new glowplugs) on for almost a minute to have any chance to start it. It has a mechanical FIP so my issue is nothing to do with sensors or ECU's. The fuel stop solenoid is working as it should and delivering fuel to the pump internals. When it fires it runs well with no clattering or banging with black smoke under load. I know that black smoke is a sign of overfueling but I'm presuming that it's also a sign that the FIP is working well because it has the capacity to overfuel?.....I know that the M51 is timed by chains and was thinking that chain stretch and the inevitable retarded timing could be the problem. I have also considered low compression but believe that if this were my problem, it should show itself as white exhaust smoke and a drop in power, which it doesn't. Where would you guys be looking for answers. I plan to get it re-timed and have the chains renewed at some point but, for now, I want to try and eliminate all other possibilities.

Any help very welcome.

Thanks guys.
 
Have static timing done, be aware that static on the none EDC pump is set with around 1.54 mm lift at TDC not the .90 of the EDC pump. Check that all the glow plugs actually work.
 
Thanks Guys. I will always listen to Wammers. ;)...... Another thing I forgot to mention in the OP was that I can see no air in fuel on the delivery side. I put a clear hose between filter and FIP for this purpose. Would air on the spill/return side cause starting problems. Sorry guys. I just want to eliminate the obvious before I go through any great expense with FIP/ Injectors etc...
 
As Wammers says, check the plugs are working clean and quickly glowing
When you do that think about checking the compression ratio in glow hole with an adapter for your pressure gauge

Re do static time for stretched chain with special tools and dial gauge...basic engineering
Chains often go at 120,000 plus and dont put crap back on unless you want the timing practice

All the knowledge is here, workshop manual and tools online

YOU need fuel, compression and air............simple so I am told ((
 
landyboots said:
Thanks Guys. I will always listen to Wammers. ;)...... Another thing I forgot to mention in the OP was that I can see no air in fuel on the delivery side. I put a clear hose between filter and FIP for this purpose. Would air on the spill/return side cause starting problems. Sorry guys. I just want to eliminate the obvious before I go through any great expense with FIP/ Injectors etc...
Click to expand...

What are you using for a lift pump, is it working? Check the spill pipes are not leaking.
 
wammers said:
What are you using for a lift pump, is it working? Check the spill pipes are not leaking.
Click to expand...
I am using the standard electric pump from the original V8 setup on the inside of the nearside chassis rail. It is working but I always wondered if it has a sufficient operating flow rate to supply the FIP. Not sure if they are compatible. What delivery rate does a standard in tank pump as fitted to a P38 have?. While I was fitting the clear tube to watch for air bubbles, I fitted one of those rubber hand priming thingy's with an inbuilt non return valve between the filter and the FIP. The reason I fitted it was just to make sure I had good pressure at the FIP for starting while investigating the starting problem. I have been checking this hand pump every time I nip out to go through the system and It does eventually lose pressure. I had a leak at one of the spill pipes at injector 4 but I changed it and didn't make a difference. They are all probably old and well passed their use by date by now and I do plan to change them as they could be perished under the braiding but they are not leaking....

Thanks Wammers,
 
markemark said:
As Wammers says, check the plugs are working clean and quickly glowing
When you do that think about checking the compression ratio in glow hole with an adapter for your pressure gauge

Re do static time for stretched chain with special tools and dial gauge...basic engineering
Chains often go at 120,000 plus and dont put crap back on unless you want the timing practice

All the knowledge is here, workshop manual and tools online

YOU need fuel, compression and air............simple so I am told ((
Click to expand...
and correct timing .)........ Thanks markemark.
 
landyboots said:
I am using the standard electric pump from the original V8 setup on the inside of the nearside chassis rail. It is working but I always wondered if it has a sufficient operating flow rate to supply the FIP. Not sure if they are compatible. What delivery rate does a standard in tank pump as fitted to a P38 have?. While I was fitting the clear tube to watch for air bubbles, I fitted one of those rubber hand priming thingy's with an inbuilt non return valve between the filter and the FIP. The reason I fitted it was just to make sure I had good pressure at the FIP for starting while investigating the starting problem. I have been checking this hand pump every time I nip out to go through the system and It does eventually lose pressure. I had a leak at one of the spill pipes at injector 4 but I changed it and didn't make a difference. They are all probably old and well passed their use by date by now and I do plan to change them as they could be perished under the braiding but they are not leaking....

Thanks Wammers,
Click to expand...

What year is your classic? Diesel lift pump as fitted to EDC engines should produce a minimum free flow rate of 180 millilitres of fuel in 10 seconds.
 
Black smoke is a no-no. NOT a good sign that the pump is working OK!
Tired injectors, poor timing or injection pump way out of calibration.
When you finally manage to start it do you have clouds of crap from the exhaust?
 
wammers said:
What year is your classic? Diesel lift pump as fitted to EDC engines should produce a minimum free flow rate of 180 millilitres of fuel in 10 seconds.
Click to expand...
My classic is 1982/83....one of the first 4 doors. I picked it up a while ago for a song and have only recently started to show interest in getting it back on the road. It has behaved like this since I got it so the problem didn't develop in my ownership. I am starting to suspect that the petrol lift pump might be causing a problem as it allows fuel to flow back to the tank. Am I correct in thinking that a diesel lift pump like the one's fitted in the tank on the P38's, maintain pressure at a minimum to aid the FIP in starting?.....
 
Fergie46 said:
Black smoke is a no-no. NOT a good sign that the pump is working OK!
Tired injectors, poor timing or injection pump way out of calibration.
When you finally manage to start it do you have clouds of crap from the exhaust?
Click to expand...
Yes. I agree that black smoke is no good but it seems to me to show that at least the FIP is capable of overfuelling and must be good internally. There is a very large intercooler fitted so I suspect that the previous owner who did the conversion tweaked the pump, hence the black smoke....
 
landyboots said:
My classic is 1982/83....one of the first 4 doors. I picked it up a while ago for a song and have only recently started to show interest in getting it back on the road. It has behaved like this since I got it so the problem didn't develop in my ownership. I am starting to suspect that the petrol lift pump might be causing a problem as it allows fuel to flow back to the tank. Am I correct in thinking that a diesel lift pump like the one's fitted in the tank on the P38's, maintain pressure at a minimum to aid the FIP in starting?.....
Click to expand...

The diesel lift pump does pressurise the injection pump to some extent although not very much. It basically just supplies fuel to the internal high pressure pump. The injection pump has an high pressure pump within it to provide pre injection pressure and timing adjustments subject to RPM, controlled by a pressure relief valve. Any excess fuel flowing through the pressure relief valve is returned to the inlet side of the high pressure pump. Spill from the injectors and overflow from the injection pump returns to the tank via the overflow restrictor on top of the pump. Internal pressure will bleed away when the engine is stopped via the overflow restrictor, back to the tank. So without seeing what you have and not knowing how it is set up i would think your lift pump is the problem. Fuel at a minimum rate MUST be supplied to the inlet on the injection pump. And any spill off or return to the tank MUST be from the flow restrictor on top of the injection pump. Essentially giving a fuel circuit from the tank to the injection pump and back to the tank via the overflow on the injection pump. Any other set up will give problems.
 
The pump being tweaked sounds about right with the big intercooler, mind the m51 does not like to much tweeking especially the turbo boost which is a shame as in a range rover more power is always welcome
 
brianp38dse said:
The pump being tweaked sounds about right with the big intercooler, mind the m51 does not like to much tweeking especially the turbo boost which is a shame as in a range rover more power is always welcome
Click to expand...

No need to tweak anything if it's EDC just chip it, it will catch pigeons. The OPs car is slightly more of a problem being a fully mechanical pump. Who knows what has been done to it. People will play with things they don't understand and cock things up. OP seems to have inherited a problem.
 
Mines chipped would still like more, but will leave as is, but sounds like his non edc may have been played with to give more fueling, it's knowing what has been done that is the sixtyfour million dollar question, may be replacement standard pump and start again from scratch with the timing.
 
brianp38dse said:
Mines chipped would still like more, but will leave as is, but sounds like his non edc may have been played with to give more fueling, it's knowing what has been done that is the sixtyfour million dollar question, may be replacement standard pump and start again from scratch with the timing.
Click to expand...

Mine is chipped in the ECU, i cannot think of any reason anybody would want more power than it has. It gets away quickly and will do 30 + MPG on a good run. It will do for me.
 
wammers said:
The diesel lift pump does pressurise the injection pump to some extent although not very much. It basically just supplies fuel to the internal high pressure pump. The injection pump has an high pressure pump within it to provide pre injection pressure and timing adjustments subject to RPM, controlled by a pressure relief valve. Any excess fuel flowing through the pressure relief valve is returned to the inlet side of the high pressure pump. Spill from the injectors and overflow from the injection pump returns to the tank via the overflow restrictor on top of the pump. Internal pressure will bleed away when the engine is stopped via the overflow restrictor, back to the tank. So without seeing what you have and not knowing how it is set up i would think your lift pump is the problem. Fuel at a minimum rate MUST be supplied to the inlet on the injection pump. And any spill off or return to the tank MUST be from the flow restrictor on top of the injection pump. Essentially giving a fuel circuit from the tank to the injection pump and back to the tank via the overflow on the injection pump. Any other set up will give problems.
Click to expand...

Thanks Wammers.....Makes a lot of sense. I presume in my system that the NRV in the rubber hand primer tries to maintain pressure at the pump but, the overflow restrictor dumps it off into the spill circuit so my NRV is redundant. The flow rate of my petrol lift pump from new seems to match the figures that you gave earlier as a minimum but it may well be far below that with age and wear and tear. I may try an increased flow pump say, something around the 2 litres/min spec to see if it makes any difference and before I go messing with timing and Injectors etc...etc...
 
brianp38dse said:
Mines chipped would still like more, but will leave as is, but sounds like his non edc may have been played with to give more fueling, it's knowing what has been done that is the sixtyfour million dollar question, may be replacement standard pump and start again from scratch with the timing.
Click to expand...
I think with these types of pumps(same with the 200/300tdi's)the only real tweeking is a boost pin or turning the diaphragm under the top cover. I don't know if tweeking a pump would affect cold and hot starting though :(
 
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